1
00:00:00,000 --> 00:00:02,410
The following content is
provided under a Creative

2
00:00:02,410 --> 00:00:03,830
Commons license.

3
00:00:03,830 --> 00:00:06,840
Your support will help MIT
OpenCourseWare continue to

4
00:00:06,840 --> 00:00:10,530
offer high-quality educational
resources for free.

5
00:00:10,530 --> 00:00:13,400
To make a donation, or view
additional materials from

6
00:00:13,400 --> 00:00:17,190
hundreds of MIT courses, visit
MIT OpenCourseWare at

7
00:00:17,190 --> 00:00:18,440
ocw.mit.edu.

8
00:00:21,090 --> 00:00:22,620
PROFESSOR: We had a staff
meeting yesterday, and we

9
00:00:22,620 --> 00:00:25,540
decided that what we're going
to do is, we'll start with

10
00:00:25,540 --> 00:00:27,080
defects and solids.

11
00:00:27,080 --> 00:00:31,620
We didn't examine you on it
with the last celebration.

12
00:00:31,620 --> 00:00:34,510
So we'll pick it up with
defects, and we'll go through

13
00:00:34,510 --> 00:00:38,210
to the end of solutions,
acid-bases.

14
00:00:38,210 --> 00:00:41,980
So the stuff that we covered on
Monday, the nomenclature of

15
00:00:41,980 --> 00:00:43,540
organics, we're going
to leave out.

16
00:00:43,540 --> 00:00:47,750
Because you don't have enough
time with the recitations to

17
00:00:47,750 --> 00:00:50,420
really dig into that,
and I think it's--

18
00:00:50,420 --> 00:00:53,770
with the test being on a Monday
this time, and not on a

19
00:00:53,770 --> 00:00:58,710
Wednesday, the schedule is
little bit of out of balance

20
00:00:58,710 --> 00:01:00,800
from the way I'd
like it to be.

21
00:01:00,800 --> 00:01:04,170
But I thought having the third
celebration the Wednesday

22
00:01:04,170 --> 00:01:08,700
before Thanksgiving
was not wise.

23
00:01:08,700 --> 00:01:12,580
I know that a number of you
are going to be in transit

24
00:01:12,580 --> 00:01:14,240
that on Wednesday.

25
00:01:14,240 --> 00:01:17,990
But let me remind you that
Wednesday, we will have a

26
00:01:17,990 --> 00:01:19,040
full-blown lecture.

27
00:01:19,040 --> 00:01:23,250
I'm going without
any slow down.

28
00:01:23,250 --> 00:01:26,660
So next Wednesday, we will
start biochemistry.

29
00:01:26,660 --> 00:01:29,770
So those of you who are not
here, please make sure that

30
00:01:29,770 --> 00:01:30,840
you have viewed the lecture.

31
00:01:30,840 --> 00:01:33,660
Because when you return on
Monday, you will have no idea

32
00:01:33,660 --> 00:01:34,900
what's going on.

33
00:01:34,900 --> 00:01:38,370
And it'd be a good idea not to
blow biochemistry, because on

34
00:01:38,370 --> 00:01:39,400
the final exam--

35
00:01:39,400 --> 00:01:42,590
if you fail the final,
it's not good.

36
00:01:42,590 --> 00:01:44,440
It's really not good.

37
00:01:44,440 --> 00:01:49,270
So just to be clear, we're going
to start with defects

38
00:01:49,270 --> 00:01:53,260
and solids, and go through, and
end with acids, bases, and

39
00:01:53,260 --> 00:01:55,060
solution chemistry.

40
00:01:55,060 --> 00:01:56,310
OK.

41
00:01:56,310 --> 00:02:00,380
So today I want to start to get
some mileage out of what

42
00:02:00,380 --> 00:02:02,460
we learned on Monday.

43
00:02:02,460 --> 00:02:06,890
I want to talk today about one
of the applications of organic

44
00:02:06,890 --> 00:02:09,530
chemistry, and that's
polymers.

45
00:02:09,530 --> 00:02:13,430
So we're going to take two
lectures on polymers, and then

46
00:02:13,430 --> 00:02:16,260
we'll feed into biochemistry,
and you'll see a very natural

47
00:02:16,260 --> 00:02:18,830
progression from what we're
doing now into the

48
00:02:18,830 --> 00:02:20,360
biochemistry.

49
00:02:20,360 --> 00:02:24,490
So let's begin with a little
bit of reflection on what

50
00:02:24,490 --> 00:02:25,910
we've done so far.

51
00:02:25,910 --> 00:02:30,330
Up until now, we've looked at
various solid structures.

52
00:02:30,330 --> 00:02:33,220
We've started with single atoms.
We looked at crystals,

53
00:02:33,220 --> 00:02:35,560
disordered crystals,
and so on.

54
00:02:35,560 --> 00:02:38,510
We've looked at compounds,
and we've even

55
00:02:38,510 --> 00:02:41,300
looked at small change.

56
00:02:41,300 --> 00:02:44,350
We looked at alkanes,
straight chain

57
00:02:44,350 --> 00:02:46,860
alkanes, branched alkanes.

58
00:02:46,860 --> 00:02:49,260
And we've looked at
network solids.

59
00:02:49,260 --> 00:02:50,540
Here is a regular network.

60
00:02:50,540 --> 00:02:54,140
This is the structure of
graphite, for example.

61
00:02:54,140 --> 00:02:55,760
Nice, ordered crystalline
structure.

62
00:02:55,760 --> 00:02:59,640
Diamond grows in three
dimensions without abatement.

63
00:02:59,640 --> 00:03:01,480
We've looked at disordered
networks,

64
00:03:01,480 --> 00:03:03,440
such as silicate glasses.

65
00:03:03,440 --> 00:03:05,450
So that's what we've looked
at up until now.

66
00:03:05,450 --> 00:03:07,700
What I want to talk about
today is polymers.

67
00:03:07,700 --> 00:03:10,440
Polymers are macromolecules.

68
00:03:10,440 --> 00:03:13,000
These are long chain
molecules.

69
00:03:13,000 --> 00:03:17,550
By long, we're talking about
thousands and thousands of

70
00:03:17,550 --> 00:03:18,860
repeat units.

71
00:03:18,860 --> 00:03:24,260
And this is the distinguishing
feature between macromolecules

72
00:03:24,260 --> 00:03:26,040
that are found in
the body, versus

73
00:03:26,040 --> 00:03:29,780
macromolecules that are man-made.

74
00:03:29,780 --> 00:03:31,990
Mother Nature is a
polymer engineer.

75
00:03:31,990 --> 00:03:35,510
We are a macromolecular
organism.

76
00:03:35,510 --> 00:03:37,140
This is all polymer.

77
00:03:37,140 --> 00:03:37,860
It's all polymer.

78
00:03:37,860 --> 00:03:40,755
The changes in shape is all
elasticity in a polymer.

79
00:03:40,755 --> 00:03:45,870
And inside, of course, I've got
a ceramic skeleton, which

80
00:03:45,870 --> 00:03:47,630
keeps the frame in place.

81
00:03:47,630 --> 00:03:49,660
But this is all polymers.

82
00:03:49,660 --> 00:03:54,520
But the difference here is,
this is not a repeat unit.

83
00:03:54,520 --> 00:03:56,960
Whereas when we have a man-made
structure, it's the

84
00:03:56,960 --> 00:04:01,320
same repeating chemical
structure.

85
00:04:01,320 --> 00:04:04,170
And the other thing I want to
say at the beginning is their

86
00:04:04,170 --> 00:04:05,160
importance in commerce.

87
00:04:05,160 --> 00:04:07,160
Polymers are found
everywhere today.

88
00:04:07,160 --> 00:04:09,900
Trash bags, auto parts.

89
00:04:09,900 --> 00:04:12,460
And in culture, they're
absolutely

90
00:04:12,460 --> 00:04:13,880
essential to culture.

91
00:04:13,880 --> 00:04:14,870
Let's think about it.

92
00:04:14,870 --> 00:04:20,250
When you play that DVD, that
DVD is information

93
00:04:20,250 --> 00:04:22,220
embedded in a polymer.

94
00:04:22,220 --> 00:04:24,010
The magnetic drags.

95
00:04:24,010 --> 00:04:25,180
What are magnetic drags?

96
00:04:25,180 --> 00:04:29,310
These are polymers that have
been coated with gammaferic

97
00:04:29,310 --> 00:04:31,690
oxide or some other
magnetic material.

98
00:04:31,690 --> 00:04:34,605
Without polymers we couldn't
have the modern era.

99
00:04:34,605 --> 00:04:38,310
And if you go back before the
DVD, with the CD, before that

100
00:04:38,310 --> 00:04:40,400
was magnetic tape and
cassette, and

101
00:04:40,400 --> 00:04:41,760
before that was this.

102
00:04:41,760 --> 00:04:43,270
You might see some
of these around.

103
00:04:43,270 --> 00:04:47,180
This is an old way of
presenting musical

104
00:04:47,180 --> 00:04:47,820
information.

105
00:04:47,820 --> 00:04:52,160
This is the phonograph record,
photograph recording.

106
00:04:52,160 --> 00:04:57,570
And this is information that is
scribed into a platter, and

107
00:04:57,570 --> 00:04:59,330
it's made of polyvinyl
chloride.

108
00:04:59,330 --> 00:05:02,210
That's why you hear
the term vinyl.

109
00:05:02,210 --> 00:05:07,440
Why is Virgin, the big Virgin
enterprise, called Virgin?

110
00:05:07,440 --> 00:05:10,670
Because Virgin Records, when
they made their platters, they

111
00:05:10,670 --> 00:05:14,460
started with virgin vinyl,
not recycled polymer.

112
00:05:14,460 --> 00:05:18,280
And so their platters would
lie flat on the turntable.

113
00:05:18,280 --> 00:05:20,150
Whereas some of them you
buy, you put them

114
00:05:20,150 --> 00:05:21,290
down, and they warp.

115
00:05:21,290 --> 00:05:23,900
It's OK, because the needle
would still track, but it

116
00:05:23,900 --> 00:05:25,570
looked kind of--

117
00:05:25,570 --> 00:05:27,120
playing like this.

118
00:05:27,120 --> 00:05:28,640
And it's too bad that
we've lost this.

119
00:05:28,640 --> 00:05:32,590
Because this gives rise to the
real estate possibility for

120
00:05:32,590 --> 00:05:35,310
artwork, and liner notes, and so
on, that you don't get when

121
00:05:35,310 --> 00:05:37,970
you download something
for $0.99.

122
00:05:37,970 --> 00:05:38,750
OK?

123
00:05:38,750 --> 00:05:43,570
So an electromechanical device
moves along here, and jiggles

124
00:05:43,570 --> 00:05:46,840
in the grooves, and those
mechanical wigglings get

125
00:05:46,840 --> 00:05:52,790
converted into energy that
ultimately gets fed through

126
00:05:52,790 --> 00:05:54,340
the loudspeakers.

127
00:05:54,340 --> 00:05:56,900
And now let's talk about
visual information.

128
00:05:56,900 --> 00:06:01,590
Daguerre invented halide
photography in the early

129
00:06:01,590 --> 00:06:04,890
1800s, but we didn't get
motion pictures.

130
00:06:04,890 --> 00:06:09,470
Cinematography had to wait for
the advent of polymers,

131
00:06:09,470 --> 00:06:13,020
because only when we could make
material that would come

132
00:06:13,020 --> 00:06:18,850
out miles long on which we
could coat with halide

133
00:06:18,850 --> 00:06:24,470
photosensitive emulsion, could
we imagine images flashing

134
00:06:24,470 --> 00:06:27,380
past us faster than the
persistence of vision.

135
00:06:27,380 --> 00:06:28,980
You need-- what's the
persistence of vision?

136
00:06:28,980 --> 00:06:30,970
Around a twentieth
of a second.

137
00:06:30,970 --> 00:06:33,690
Motion pictures are 24
frames a second.

138
00:06:33,690 --> 00:06:37,400
So you couldn't have glass
plates on which you've got

139
00:06:37,400 --> 00:06:41,170
halide film zipping past
at 24 frames a

140
00:06:41,170 --> 00:06:43,470
second for 90 minutes.

141
00:06:43,470 --> 00:06:47,110
So only with the advent of
polymers did we have the birth

142
00:06:47,110 --> 00:06:48,920
of cinematography.

143
00:06:48,920 --> 00:06:52,070
So what I'm talking about
here changed the world.

144
00:06:52,070 --> 00:06:56,610
It changed the world, and gives
birth to the fantastic

145
00:06:56,610 --> 00:06:58,740
access that we have
to information.

146
00:06:58,740 --> 00:07:01,870
And now, of course, as things
move digitally, and they

147
00:07:01,870 --> 00:07:04,050
dematerialize, you're going
to see a shift away.

148
00:07:04,050 --> 00:07:07,490
But all this stuff was
enabled by the

149
00:07:07,490 --> 00:07:10,700
advent of polymer chemistry.

150
00:07:10,700 --> 00:07:14,870
So with that as a motivator,
let's dive in.

151
00:07:14,870 --> 00:07:15,910
This is good stuff.

152
00:07:15,910 --> 00:07:17,010
It's really, really good.

153
00:07:17,010 --> 00:07:18,180
So now the payback comes.

154
00:07:18,180 --> 00:07:20,570
You know, all those little
lessons about, where's the

155
00:07:20,570 --> 00:07:23,580
electron, where's the orbital,
you know, who wants to learn

156
00:07:23,580 --> 00:07:24,070
that stuff.

157
00:07:24,070 --> 00:07:24,840
You have to learn it!

158
00:07:24,840 --> 00:07:26,900
If you're going to write the
great novel, you've got to

159
00:07:26,900 --> 00:07:30,870
learn how to spell.

160
00:07:30,870 --> 00:07:32,470
All right.

161
00:07:32,470 --> 00:07:33,830
So let's go.

162
00:07:33,830 --> 00:07:36,040
So the polymer, it comes
from the Greek poly,

163
00:07:36,040 --> 00:07:37,770
meaning may, right?

164
00:07:37,770 --> 00:07:42,990
Poly is many And the mer,
the mer is this repeat

165
00:07:42,990 --> 00:07:45,620
unit, if you like.

166
00:07:45,620 --> 00:07:47,700
Many units, many units.

167
00:07:47,700 --> 00:07:50,000
So let's take a simple
example.

168
00:07:50,000 --> 00:07:52,740
Last day we studied
polyethylene.

169
00:07:55,760 --> 00:07:58,300
So polyethylene looks
like this.

170
00:07:58,300 --> 00:08:01,090
Double bond, one, two, three,
four, four hydrogens.

171
00:08:01,090 --> 00:08:02,705
So this is just ethylene.

172
00:08:06,380 --> 00:08:09,560
And what I can do with ethylene,
is I can react it.

173
00:08:09,560 --> 00:08:11,650
Ethylene's a gas, room
temperature.

174
00:08:11,650 --> 00:08:17,230
Put it into a reactor and expose
it to an initiator.

175
00:08:17,230 --> 00:08:18,830
And the initiator
is a radical.

176
00:08:18,830 --> 00:08:19,700
You know what the radical.

177
00:08:19,700 --> 00:08:22,240
It's something that's got
this unpaired electron.

178
00:08:22,240 --> 00:08:23,710
It's very active.

179
00:08:23,710 --> 00:08:29,240
And the radical sees a unit of
ethylene, which I'm going to

180
00:08:29,240 --> 00:08:30,670
write like this.

181
00:08:30,670 --> 00:08:33,710
We don't need to put the
120 degrees now.

182
00:08:33,710 --> 00:08:38,020
And what the ethylene does, is
this radical attacks this

183
00:08:38,020 --> 00:08:40,830
double bond and figures, well,
it's better to have two single

184
00:08:40,830 --> 00:08:41,970
bonds than one double bond.

185
00:08:41,970 --> 00:08:44,030
Reacts the double bond,
breaks it, and

186
00:08:44,030 --> 00:08:46,250
then forms the following.

187
00:08:46,250 --> 00:08:52,920
The radical now bonds to the
ethylene, breaks that double

188
00:08:52,920 --> 00:08:57,690
bond, and transfers the unpaired
electron to the end.

189
00:08:57,690 --> 00:09:01,810
But now this thing is itself a
radical, and it's swimming in

190
00:09:01,810 --> 00:09:03,180
a gas of ethylene.

191
00:09:03,180 --> 00:09:10,150
So now a second C2H4 comes up
against this, and it's turned

192
00:09:10,150 --> 00:09:15,850
into the following, are now C
C C C C, one, two, three,

193
00:09:15,850 --> 00:09:17,580
four, one, two, three, four.

194
00:09:17,580 --> 00:09:18,480
And so on.

195
00:09:18,480 --> 00:09:21,740
And this can go without limit,
until we shut down the

196
00:09:21,740 --> 00:09:25,560
reactor, or we introduce
something that terminates,

197
00:09:25,560 --> 00:09:27,690
that will cap this.

198
00:09:27,690 --> 00:09:28,220
All right?

199
00:09:28,220 --> 00:09:30,090
So this is the beginning
of it.

200
00:09:30,090 --> 00:09:32,920
And what you see is attachment,
attachment,

201
00:09:32,920 --> 00:09:35,060
attachment, breaking
of double bonds.

202
00:09:35,060 --> 00:09:36,870
And so we have a repeat
unit here.

203
00:09:36,870 --> 00:09:40,920
This repeat unit, the mer unit,
is this ethylene unit,

204
00:09:40,920 --> 00:09:46,390
and it can go to a value of
n that is very, very high.

205
00:09:46,390 --> 00:09:49,490
What kind of numbers can
we expect to get?

206
00:09:49,490 --> 00:09:53,900
We can have numbers here
where n takes values--

207
00:09:53,900 --> 00:09:56,100
and these aren't hard and fast,
but just to give you

208
00:09:56,100 --> 00:09:57,020
some idea--

209
00:09:57,020 --> 00:10:01,640
you could have a, you know the
oxymoron jumbo shrimp.

210
00:10:01,640 --> 00:10:04,420
You could have a short
chain polymer.

211
00:10:04,420 --> 00:10:06,590
A short chain, long chain.

212
00:10:06,590 --> 00:10:07,980
You know?

213
00:10:07,980 --> 00:10:09,290
Boy, you're really dead today.

214
00:10:09,290 --> 00:10:10,010
What's the matter with you?

215
00:10:10,010 --> 00:10:10,960
Sleep deprived?

216
00:10:10,960 --> 00:10:12,240
You've--

217
00:10:12,240 --> 00:10:12,510
All right.

218
00:10:12,510 --> 00:10:15,890
So n can go up to
about 10,000.

219
00:10:15,890 --> 00:10:19,920
Now what's the atomic mass of
this, just as representative?

220
00:10:19,920 --> 00:10:24,140
This is 2 times 12 is 24,
25, or 26, 27, 28.

221
00:10:24,140 --> 00:10:30,060
28's roughly 30, so 30 times
10,000, you've got 300,000.

222
00:10:30,060 --> 00:10:34,670
That's 300,000 grams per mole.

223
00:10:34,670 --> 00:10:37,620
This means you can have
molecular weights on the order

224
00:10:37,620 --> 00:10:44,480
of a million grams per mole
for one molecule.

225
00:10:44,480 --> 00:10:46,760
And by the way, the polymer
people, they come from a

226
00:10:46,760 --> 00:10:49,150
different branch of science.

227
00:10:49,150 --> 00:10:50,820
So they don't use this
grams per mole.

228
00:10:50,820 --> 00:10:55,740
Instead of grams per mole, they
like to use the word, the

229
00:10:55,740 --> 00:10:58,030
dalton, as a unit of measure.

230
00:10:58,030 --> 00:11:00,650
So you might see in the pollymer
literature, you'll

231
00:11:00,650 --> 00:11:05,340
see the polymer with so many
kDa, kilodaltons, thousands of

232
00:11:05,340 --> 00:11:06,920
grams per mole.

233
00:11:06,920 --> 00:11:08,740
That's the nomenclature
you will see.

234
00:11:08,740 --> 00:11:11,060
OK.

235
00:11:11,060 --> 00:11:14,610
Now, what are the properties of
these things going to be?

236
00:11:14,610 --> 00:11:17,675
Oh wait, I'm going to
show you something.

237
00:11:17,675 --> 00:11:18,820
To give you a sense.

238
00:11:18,820 --> 00:11:20,570
You need to be awakened.

239
00:11:20,570 --> 00:11:23,550
So let me give you a sense
of just how long

240
00:11:23,550 --> 00:11:24,940
these molecules are.

241
00:11:24,940 --> 00:11:27,520
So I'm going to give you a
little mechanical model here.

242
00:11:27,520 --> 00:11:29,230
I'm going to put up here
so we get some--

243
00:11:29,230 --> 00:11:31,655
So what I've got here is
just a pull chain.

244
00:11:31,655 --> 00:11:35,110
If you go in the basement, you
might see these pull chains.

245
00:11:35,110 --> 00:11:39,690
They're just made of brass,
little brass balls, and then

246
00:11:39,690 --> 00:11:41,920
they've got links
between them.

247
00:11:41,920 --> 00:11:44,850
And when you cut them-- you buy
them by the foot at the

248
00:11:44,850 --> 00:11:46,030
hardware store.

249
00:11:46,030 --> 00:11:51,230
You put it on a light, you can
turn the light on and off by

250
00:11:51,230 --> 00:11:52,820
toggling up and down.

251
00:11:52,820 --> 00:11:57,760
So I'm going to say, let's say
this distance here represents

252
00:11:57,760 --> 00:12:00,800
the distance between
mer units.

253
00:12:00,800 --> 00:12:03,280
This distance could be
between 2 mer units.

254
00:12:03,280 --> 00:12:06,670
And I figured, let's see,
I've got 40 feet here,

255
00:12:06,670 --> 00:12:07,610
and I did the math.

256
00:12:07,610 --> 00:12:11,220
So this thing here, with the
40 foot pull chain, has a

257
00:12:11,220 --> 00:12:13,510
polymerization index--

258
00:12:13,510 --> 00:12:15,700
let's call this the
polymerization index.

259
00:12:23,150 --> 00:12:26,330
So my polymerization index, I
calculated it for this thing.

260
00:12:26,330 --> 00:12:29,610
It's on the order
of about 3,000.

261
00:12:29,610 --> 00:12:30,920
So that's pretty good.

262
00:12:30,920 --> 00:12:33,020
It's right in the
middle of this.

263
00:12:33,020 --> 00:12:34,190
It's actually--

264
00:12:34,190 --> 00:12:38,250
this qualifies as a
bona fide polymer.

265
00:12:38,250 --> 00:12:41,880
So let's take a look at
what happens here.

266
00:12:55,260 --> 00:12:57,150
This is one molecule.

267
00:13:01,590 --> 00:13:04,420
So what do you know about

268
00:13:04,420 --> 00:13:06,070
interactions between molecules?

269
00:13:06,070 --> 00:13:09,180
Now, in the liquid state,
what's this going to be?

270
00:13:09,180 --> 00:13:12,640
Is it going to be fluid, or
is it going to be viscous?

271
00:13:12,640 --> 00:13:13,480
It's going to be viscous.

272
00:13:13,480 --> 00:13:17,580
Look, this is one molecule, and
it entangles with itself.

273
00:13:17,580 --> 00:13:21,450
Now, to make a liquid, I have
thousands of these things

274
00:13:21,450 --> 00:13:24,200
swimming around, above their
crystallization--

275
00:13:24,200 --> 00:13:26,410
oh, crystallization
temperature.

276
00:13:26,410 --> 00:13:27,420
Freudian slip.

277
00:13:27,420 --> 00:13:29,790
Above their solidification
temperature.

278
00:13:29,790 --> 00:13:32,180
When they solidify,
are they going to

279
00:13:32,180 --> 00:13:33,760
form an ordered solid?

280
00:13:33,760 --> 00:13:35,775
One of these at each
lattice site?

281
00:13:39,600 --> 00:13:41,040
Probably not.

282
00:13:41,040 --> 00:13:43,820
They're probably going to
form disordered solids.

283
00:13:43,820 --> 00:13:46,800
So most of the polymers that
we encounter are probably

284
00:13:46,800 --> 00:13:48,260
going to be disordered.

285
00:13:54,610 --> 00:13:59,920
How is this held together
when it forms a solid?

286
00:13:59,920 --> 00:14:01,290
It's polyethylene.

287
00:14:01,290 --> 00:14:03,100
Well, what's your menu?

288
00:14:03,100 --> 00:14:05,120
Is it ionic bonding?

289
00:14:05,120 --> 00:14:07,810
Is it metallic bonding?

290
00:14:07,810 --> 00:14:09,700
Is it hydrogen bonding?

291
00:14:09,700 --> 00:14:12,400
How is it held together?

292
00:14:12,400 --> 00:14:14,070
Weak van der Waals.

293
00:14:14,070 --> 00:14:15,380
Weak van der Waals bonds.

294
00:14:15,380 --> 00:14:16,705
But look at the surface area.

295
00:14:19,410 --> 00:14:23,560
So this is what it looks like.

296
00:14:23,560 --> 00:14:26,290
See, and it entangles, is even
entangles with my clothing.

297
00:14:26,290 --> 00:14:27,790
It just grabs onto everything.

298
00:14:27,790 --> 00:14:28,620
All right.

299
00:14:28,620 --> 00:14:30,820
Actually, why don't we--

300
00:14:30,820 --> 00:14:33,665
David, let's cut
to the screen.

301
00:14:37,646 --> 00:14:39,840
So here we are.

302
00:14:39,840 --> 00:14:41,420
This is it.

303
00:14:41,420 --> 00:14:42,950
This is the polymer.

304
00:14:42,950 --> 00:14:47,380
And every once in a while,
a polymer will do

305
00:14:47,380 --> 00:14:49,460
something like this.

306
00:14:49,460 --> 00:14:52,410
It'll say, you know, I still,
even though I'm in this big

307
00:14:52,410 --> 00:14:56,350
long chain molecule I still
want to try to order.

308
00:14:56,350 --> 00:15:00,470
Because I read in 3091 that
ordering lowers the free

309
00:15:00,470 --> 00:15:03,500
energy of the system...

310
00:15:03,500 --> 00:15:06,180
So what it does, it
starts doing this.

311
00:15:06,180 --> 00:15:08,970
And can you see when it starts
doing this, that it

312
00:15:08,970 --> 00:15:11,720
starts to take on--

313
00:15:11,720 --> 00:15:15,520
if you walked into the room
just now, and this were

314
00:15:15,520 --> 00:15:18,950
blowing up really high, you
might see just this little

315
00:15:18,950 --> 00:15:21,250
snippet and say, wow.

316
00:15:21,250 --> 00:15:24,920
This thing is starting to look
like a cubic array isn't it?

317
00:15:29,000 --> 00:15:31,040
This is a really good model.

318
00:15:31,040 --> 00:15:32,720
It's a really good model,
because this

319
00:15:32,720 --> 00:15:35,470
is what really happens.

320
00:15:35,470 --> 00:15:39,730
And so that decreases the
energy of the system.

321
00:15:39,730 --> 00:15:41,040
The bonds are greater there.

322
00:15:41,040 --> 00:15:44,540
So what's that going to do to
the mechanical properties?

323
00:15:44,540 --> 00:15:45,890
Going to strengthen it, yeah.

324
00:15:45,890 --> 00:15:47,690
It's going to make
things stiffer.

325
00:15:47,690 --> 00:15:51,050
Instead of being this soft,
squishy polymer, it's going to

326
00:15:51,050 --> 00:15:52,240
have some stiffness to it.

327
00:15:52,240 --> 00:15:53,730
And you've come up across
that stuff.

328
00:15:53,730 --> 00:15:58,250
The most notable one
being the CD case.

329
00:15:58,250 --> 00:16:00,400
The people that make those, I'd
like to bring them here

330
00:16:00,400 --> 00:16:03,570
and sit them down and teach
them some polymer science.

331
00:16:03,570 --> 00:16:04,790
Those things are so brittle.

332
00:16:04,790 --> 00:16:05,580
They crack, right?

333
00:16:05,580 --> 00:16:07,380
There's only two classes
of jewel cases.

334
00:16:07,380 --> 00:16:09,450
Those that are cracked, and
those that will crack.

335
00:16:12,330 --> 00:16:15,020
Because these people don't
know what they're doing.

336
00:16:15,020 --> 00:16:15,350
OK.

337
00:16:15,350 --> 00:16:20,370
So now let's have some
time here to codify

338
00:16:20,370 --> 00:16:21,980
what we've just see.

339
00:16:21,980 --> 00:16:25,050
So first of all, we suspect that
they're going to be solid

340
00:16:25,050 --> 00:16:28,210
at room temperature.

341
00:16:28,210 --> 00:16:29,080
Dominantly.

342
00:16:29,080 --> 00:16:32,200
We can engineer them to be
liquid, but dominantly solid

343
00:16:32,200 --> 00:16:33,430
at room temperature.

344
00:16:33,430 --> 00:16:38,305
And van der Waals
bonds abundant.

345
00:16:44,100 --> 00:16:44,430
OK.

346
00:16:44,430 --> 00:16:47,516
And the liquid, as a liquid,
we expect viscous liquid.

347
00:16:55,580 --> 00:16:56,550
Good.

348
00:16:56,550 --> 00:16:57,450
Got that down.

349
00:16:57,450 --> 00:17:00,430
What else to have to know?

350
00:17:00,430 --> 00:17:02,260
Let's do calculation here.

351
00:17:02,260 --> 00:17:05,800
So I did one here where I said,
what's this distance?

352
00:17:05,800 --> 00:17:08,300
We saw last day that this
distance, carbon-carbon,

353
00:17:08,300 --> 00:17:10,720
remember, we're looking at
single bond, double bond.

354
00:17:10,720 --> 00:17:14,000
A single bond carbon-carbon is
about 1.5 angstroms. So this

355
00:17:14,000 --> 00:17:18,480
is 1.5 angstroms. The distance
between successive mer units

356
00:17:18,480 --> 00:17:23,820
is about 3 angstroms. And so
if you take something 3

357
00:17:23,820 --> 00:17:28,940
angstroms, and you make it this
number of mer units, I

358
00:17:28,940 --> 00:17:35,940
came up with a polymerization
index of 3571 when this thing

359
00:17:35,940 --> 00:17:38,790
weighs 10,010 kilodaltons.

360
00:17:38,790 --> 00:17:45,040
And so then that means that
you'd end up with a length,

361
00:17:45,040 --> 00:17:56,690
molecular length is on the order
of 10,714 angstroms,

362
00:17:56,690 --> 00:18:00,800
which is on the order of 1
micrometer, which then makes

363
00:18:00,800 --> 00:18:05,410
it greater than the wavelength
of visible light.

364
00:18:05,410 --> 00:18:11,340
So this is really a different
type of matter.

365
00:18:11,340 --> 00:18:12,190
And we can go there.

366
00:18:12,190 --> 00:18:17,470
We've talked about viscous, so
I'm going to remind you of two

367
00:18:17,470 --> 00:18:18,710
observations here.

368
00:18:18,710 --> 00:18:22,550
Viscous liquids, amorphous
solids.

369
00:18:22,550 --> 00:18:25,090
If you put those two ideas
together, what

370
00:18:25,090 --> 00:18:27,090
else can we call upon?

371
00:18:27,090 --> 00:18:28,410
We can go back to this.

372
00:18:35,180 --> 00:18:36,870
Yeah.

373
00:18:36,870 --> 00:18:38,120
Remember this?

374
00:18:40,470 --> 00:18:41,520
What's this?

375
00:18:41,520 --> 00:18:45,510
This is super-cool liquid,
super-cool viscous liquid.

376
00:18:45,510 --> 00:18:48,720
This is the solidification
temperature, which in the case

377
00:18:48,720 --> 00:18:53,030
of liquid to amorphous solid
is the glass transition

378
00:18:53,030 --> 00:18:54,320
temperature.

379
00:18:54,320 --> 00:18:58,180
And here we have the excess
volume, right?

380
00:18:58,180 --> 00:19:00,220
This is the volume, and then
there's some crystalline

381
00:19:00,220 --> 00:19:01,780
volume, and so on.

382
00:19:01,780 --> 00:19:02,240
Right?

383
00:19:02,240 --> 00:19:06,860
I can cool at a second
rate, and I get this.

384
00:19:06,860 --> 00:19:12,930
So this is slow cool,
this is fast cool.

385
00:19:12,930 --> 00:19:14,970
We have a Tg up here.

386
00:19:14,970 --> 00:19:20,030
Tgf I'll call Tg fast,
and Tgs, Tg slow.

387
00:19:20,030 --> 00:19:21,780
So that'll give me a
different volume.

388
00:19:21,780 --> 00:19:25,490
So this is volume fast
and volume slow.

389
00:19:25,490 --> 00:19:26,100
All right?

390
00:19:26,100 --> 00:19:30,650
And since I know that density is
equal to mass over volume,

391
00:19:30,650 --> 00:19:34,340
so therefore v fast
is greater than--

392
00:19:34,340 --> 00:19:38,540
I observe v fast is greater
than v slow, so therefore

393
00:19:38,540 --> 00:19:48,290
density of the fast cool must
be less than the density of

394
00:19:48,290 --> 00:19:51,030
the slow cool.

395
00:19:51,030 --> 00:19:52,460
Now I'm going to put
some names on here.

396
00:19:52,460 --> 00:19:54,850
I'm going to call this the
cooling curves for

397
00:19:54,850 --> 00:19:56,560
polyethylene.

398
00:19:56,560 --> 00:19:59,030
These are the cooling curves
for polyethylene.

399
00:19:59,030 --> 00:20:01,620
So this, down here, gives me--

400
00:20:01,620 --> 00:20:06,340
this is now high-density
polyethylene, and up here is

401
00:20:06,340 --> 00:20:08,620
low-density polyethylene.

402
00:20:08,620 --> 00:20:10,230
Same thing, just different
processing.

403
00:20:13,520 --> 00:20:16,740
So faster cooling quenches
in more free volume.

404
00:20:16,740 --> 00:20:24,250
And since volume is a measure
of disorder, right?

405
00:20:24,250 --> 00:20:28,040
What's the difference between
great disorder and

406
00:20:28,040 --> 00:20:30,720
not-so-great disorder?

407
00:20:30,720 --> 00:20:34,540
David, again cut to the
projector, please?

408
00:20:34,540 --> 00:20:37,520
Forgive me, the document
camera?

409
00:20:37,520 --> 00:20:40,680
So the difference between
high disorder and

410
00:20:40,680 --> 00:20:43,350
low disorder is this.

411
00:20:43,350 --> 00:20:46,100
This is the order, here.

412
00:20:46,100 --> 00:20:49,710
So what that tells me is that in
high-density polyethylene,

413
00:20:49,710 --> 00:20:54,190
there is a greater percentage
of zones like this.

414
00:20:54,190 --> 00:20:56,710
And we just reasoned that this
is going to give stiffness and

415
00:20:56,710 --> 00:21:00,950
so on, and sure enough, for the
low-density polyethylene,

416
00:21:00,950 --> 00:21:05,170
low-density polyethylene is used
in things like food wrap,

417
00:21:05,170 --> 00:21:08,460
things like stretch and seal,
where you can pull because you

418
00:21:08,460 --> 00:21:12,510
can move those macromolecules
relative to one another

419
00:21:12,510 --> 00:21:16,160
without fracturing the material
to stretch it over.

420
00:21:16,160 --> 00:21:21,420
Whereas the high-density
polyethylene is used in such

421
00:21:21,420 --> 00:21:25,140
things as milk jugs,
where you want a

422
00:21:25,140 --> 00:21:26,860
little bit of stiffness.

423
00:21:26,860 --> 00:21:31,490
Polyethylene milk jugs are
still kind of floppy, but

424
00:21:31,490 --> 00:21:33,380
there's a little bit
of stiffness to it.

425
00:21:33,380 --> 00:21:36,590
The other thing is, because the
low-density polyethylene

426
00:21:36,590 --> 00:21:42,310
is dominantly amorphous, with
almost none of this second

427
00:21:42,310 --> 00:21:46,190
zone here, it's transparent
to visible light.

428
00:21:46,190 --> 00:21:48,350
But now, let's think about
what's going on here.

429
00:21:48,350 --> 00:21:50,960
Where I've got this chain,
and then all of a

430
00:21:50,960 --> 00:21:53,712
sudden I get to this.

431
00:21:53,712 --> 00:21:55,240
All right?

432
00:21:55,240 --> 00:21:58,030
So this is clear
and colorless.

433
00:21:58,030 --> 00:21:58,320
Right?

434
00:21:58,320 --> 00:22:00,240
It's a high band gap material.

435
00:22:00,240 --> 00:22:02,190
There's no free electrons.

436
00:22:02,190 --> 00:22:04,730
It's going to be transparent
to invisible light.

437
00:22:04,730 --> 00:22:07,940
So this is transparent to
visible light all along.

438
00:22:07,940 --> 00:22:13,890
But can you see that because I
have this zone of ordering,

439
00:22:13,890 --> 00:22:18,280
the density of matter here is
different, and so therefore,

440
00:22:18,280 --> 00:22:25,960
when a photon comes in, the
index of refraction--

441
00:22:25,960 --> 00:22:27,610
now, you know, this is one
of those days where n is

442
00:22:27,610 --> 00:22:28,190
going to come up.

443
00:22:28,190 --> 00:22:31,120
So here n is the polymerization
index.

444
00:22:31,120 --> 00:22:33,010
Here it's index of refraction.

445
00:22:33,010 --> 00:22:34,630
So maybe we'll use a
different color.

446
00:22:34,630 --> 00:22:35,450
How about that.

447
00:22:35,450 --> 00:22:36,200
All right?

448
00:22:36,200 --> 00:22:39,880
So the green n is index
of refraction.

449
00:22:39,880 --> 00:22:46,630
So the index of refraction
in the amorphous zone, is

450
00:22:46,630 --> 00:22:50,330
different from the index of
refraction in the partially

451
00:22:50,330 --> 00:22:52,680
crystalline zone.

452
00:22:52,680 --> 00:22:57,410
So index of refraction varies
from zone to zone.

453
00:22:57,410 --> 00:23:00,880
Even though each zone is clear
and colorless, can you see

454
00:23:00,880 --> 00:23:04,640
that this boundary between the
ordered and in the disordered

455
00:23:04,640 --> 00:23:07,100
zone acts like an interface?

456
00:23:07,100 --> 00:23:09,120
And what happens when you have
an interface with a different

457
00:23:09,120 --> 00:23:10,350
index of refraction?

458
00:23:10,350 --> 00:23:11,450
It scatters light.

459
00:23:11,450 --> 00:23:15,220
And as a result, the milk
jugs, they appear white.

460
00:23:15,220 --> 00:23:16,940
You can't see through them,
even though they're

461
00:23:16,940 --> 00:23:21,170
constituted of the same
continuous material.

462
00:23:21,170 --> 00:23:24,770
But there's these density
fluctuations, because this is

463
00:23:24,770 --> 00:23:26,830
a higher density than this.

464
00:23:26,830 --> 00:23:30,210
So you can rationalize
all of this stuff.

465
00:23:32,790 --> 00:23:33,110
OK.

466
00:23:33,110 --> 00:23:35,370
So this is what we would
call partial

467
00:23:35,370 --> 00:23:37,750
crystallization in this zone.

468
00:23:45,080 --> 00:23:48,290
And that gives rise
to the changes.

469
00:23:48,290 --> 00:23:50,100
Now, how would we distinguish
these?

470
00:23:50,100 --> 00:23:53,890
What technique would I use to
see if I've got order in this

471
00:23:53,890 --> 00:23:56,860
polymer, that I don't
know anything about?

472
00:23:56,860 --> 00:23:59,530
How do I interrogate
atomic order?

473
00:23:59,530 --> 00:24:02,550
What technique would I use?

474
00:24:02,550 --> 00:24:03,740
X-ray defraction.

475
00:24:03,740 --> 00:24:05,260
Thank you.

476
00:24:05,260 --> 00:24:06,780
Back to the slides,
please, David.

477
00:24:11,900 --> 00:24:14,480
I'll find you the piece.

478
00:24:14,480 --> 00:24:18,940
This is called polyethylene,
but remember last day, the

479
00:24:18,940 --> 00:24:22,680
IUPAC notation for this
is ethyne, so

480
00:24:22,680 --> 00:24:24,140
this becomes polythene.

481
00:24:24,140 --> 00:24:28,100
And in the UK, it's known as
polythene, and there's a

482
00:24:28,100 --> 00:24:31,850
Beatles song, Polythene Pam.

483
00:24:31,850 --> 00:24:32,590
The only reason--

484
00:24:32,590 --> 00:24:33,950
I put up here for two reasons.

485
00:24:33,950 --> 00:24:36,840
One is, it has something
to do with polymers.

486
00:24:36,840 --> 00:24:39,400
At least they knew something
about polymers.

487
00:24:39,400 --> 00:24:42,560
It's apparently, they must have
been in a drug haze at

488
00:24:42,560 --> 00:24:44,460
this period in their careers.

489
00:24:44,460 --> 00:24:47,440
This is absolutely terrible.

490
00:24:47,440 --> 00:24:49,970
Some of your parents probably
adore the Beatles.

491
00:24:49,970 --> 00:24:53,140
If you want to provoke a
conversation at Thanksgiving,

492
00:24:53,140 --> 00:24:56,000
pull out this one and ask them
to talk about the lyrics here.

493
00:24:56,000 --> 00:24:57,030
But this is just garbage.

494
00:24:57,030 --> 00:24:57,650
This is garbage!

495
00:24:57,650 --> 00:24:59,730
This should be trash bag,
is what it should be.

496
00:24:59,730 --> 00:25:02,470
But evidently, this woman used
to show up at parties dressed

497
00:25:02,470 --> 00:25:05,080
only in a polythene bag,
a see-through polythene

498
00:25:05,080 --> 00:25:06,260
bag, I might add.

499
00:25:06,260 --> 00:25:08,520
So this is a paean to her.

500
00:25:08,520 --> 00:25:10,650
Anyways, it's bad.

501
00:25:10,650 --> 00:25:12,580
Yeah, yeah, yeah.

502
00:25:12,580 --> 00:25:12,850
Anyway.

503
00:25:12,850 --> 00:25:13,930
So here we are.

504
00:25:13,930 --> 00:25:18,150
This indicates chrystalline
polyethylene.

505
00:25:18,150 --> 00:25:20,740
Here you can see
the C2H4 unit.

506
00:25:20,740 --> 00:25:26,530
And it's attempting to try to
occupy, as these beads line up

507
00:25:26,530 --> 00:25:31,280
here, they're trying to
set up a faux lattice.

508
00:25:31,280 --> 00:25:33,470
And this is what
you might see.

509
00:25:33,470 --> 00:25:36,060
And towards the end of the
lecture, I'll show you a

510
00:25:36,060 --> 00:25:38,830
transmission electron micrograph
where you can see

511
00:25:38,830 --> 00:25:43,530
this by dying it with
different colors.

512
00:25:43,530 --> 00:25:43,820
OK.

513
00:25:43,820 --> 00:25:45,360
So now here's some
x-ray defraction.

514
00:25:45,360 --> 00:25:49,000
So this is crystalline, where
they zoomed in on one of these

515
00:25:49,000 --> 00:25:52,160
zones, and they've just
gotten the defraction

516
00:25:52,160 --> 00:25:53,490
pattern from that zone.

517
00:25:53,490 --> 00:25:55,430
And you see Bragg peaks.

518
00:25:55,430 --> 00:25:57,400
And then this is in the
amorphous region.

519
00:25:57,400 --> 00:25:58,500
it's not featureless.

520
00:25:58,500 --> 00:25:59,810
There's one broad peak.

521
00:25:59,810 --> 00:26:02,100
Why one broad peak?

522
00:26:02,100 --> 00:26:04,500
Because even though there's no
long-range order, you have

523
00:26:04,500 --> 00:26:05,280
short-range order.

524
00:26:05,280 --> 00:26:07,570
You know that you've got a
carbon on either side, you've

525
00:26:07,570 --> 00:26:08,710
got hydrogens and so on.

526
00:26:08,710 --> 00:26:11,880
So that short range order gives
you the broad peak.

527
00:26:11,880 --> 00:26:13,410
But look at C here.

528
00:26:13,410 --> 00:26:15,130
Isn't this interesting?

529
00:26:15,130 --> 00:26:22,720
That if you have a polymer that
has both some order and a

530
00:26:22,720 --> 00:26:26,400
lot of disorder, if you take the
x-ray defraction pattern

531
00:26:26,400 --> 00:26:32,410
more broadly, more globally, you
get the additive spectrum.

532
00:26:32,410 --> 00:26:36,940
So you can see that this is
amorphous, but there are some

533
00:26:36,940 --> 00:26:39,950
zones of crystallinity.

534
00:26:39,950 --> 00:26:44,610
And that's the additivity power
of x-ray defraction that

535
00:26:44,610 --> 00:26:46,650
allows us to interrogate.

536
00:26:46,650 --> 00:26:51,130
So now let's talk in a little
more fine structure about

537
00:26:51,130 --> 00:26:52,820
molecular architecture.

538
00:26:52,820 --> 00:26:57,115
So tailoring molecular
architecture.

539
00:27:01,700 --> 00:27:02,590
And why are we doing this?

540
00:27:02,590 --> 00:27:05,050
Because we want to engineer
these materials for desirable

541
00:27:05,050 --> 00:27:05,660
properties.

542
00:27:05,660 --> 00:27:10,010
Like CD cases that break after
about one or two uses, OK?

543
00:27:10,010 --> 00:27:12,990
Of polymers.

544
00:27:12,990 --> 00:27:15,100
Actually, there's probably a
business opportunity there.

545
00:27:15,100 --> 00:27:16,870
You start a company where
you make jewel cases

546
00:27:16,870 --> 00:27:18,830
that actually work.

547
00:27:18,830 --> 00:27:20,890
People might be willing to pay,
you know, a penny more

548
00:27:20,890 --> 00:27:22,340
for something that works.

549
00:27:22,340 --> 00:27:22,740
All right.

550
00:27:22,740 --> 00:27:24,280
So how do we change this?

551
00:27:24,280 --> 00:27:28,060
What I'm going to show is a
whole bunch of cartoons of

552
00:27:28,060 --> 00:27:28,710
architecture.

553
00:27:28,710 --> 00:27:30,200
But how do we control this?

554
00:27:30,200 --> 00:27:31,970
It's processing.

555
00:27:31,970 --> 00:27:33,590
It's processing.

556
00:27:33,590 --> 00:27:37,100
Processing and in the
synthesis algorithm.

557
00:27:37,100 --> 00:27:39,310
I'm assuming I already have
polyethylene, so how am I

558
00:27:39,310 --> 00:27:40,460
going to tailor it?

559
00:27:40,460 --> 00:27:41,830
It's in the processing.

560
00:27:41,830 --> 00:27:45,300
And so what I can do, is
I've got a number of

561
00:27:45,300 --> 00:27:48,920
levers I can move.

562
00:27:48,920 --> 00:27:53,240
One is the composition of the
polymer, and the second one

563
00:27:53,240 --> 00:27:56,810
is, I can use catalysis.

564
00:27:56,810 --> 00:27:59,940
I already hinted at that last
day in talking about gasoline.

565
00:27:59,940 --> 00:28:03,500
How do you start with petroleum
and get octane and

566
00:28:03,500 --> 00:28:05,280
not heptane and so on?

567
00:28:05,280 --> 00:28:11,040
By playing with cataylsis, we
can direct certain forms. You

568
00:28:11,040 --> 00:28:15,220
can actually preferably
synthesize a certain

569
00:28:15,220 --> 00:28:17,920
architecture by using
catalysts.

570
00:28:17,920 --> 00:28:19,680
So let's look at these
variables.

571
00:28:19,680 --> 00:28:22,600
First one is composition,
obviously.

572
00:28:22,600 --> 00:28:25,640
If you change the composition
of something, you can very

573
00:28:25,640 --> 00:28:27,950
much expect to change
its properties.

574
00:28:27,950 --> 00:28:30,490
So what do we have here?

575
00:28:30,490 --> 00:28:32,080
We can--

576
00:28:32,080 --> 00:28:36,960
here's a simple example
I can start here with.

577
00:28:36,960 --> 00:28:38,210
This is ethylene.

578
00:28:40,490 --> 00:28:47,890
Or I can put a chlorine
here, so this now

579
00:28:47,890 --> 00:28:50,420
becomes chloride, right?

580
00:28:50,420 --> 00:28:53,020
This will become, what's the
radical, is vinyl, so this is

581
00:28:53,020 --> 00:28:56,800
vinyl chloride.

582
00:28:56,800 --> 00:28:59,810
So if I polymerize this, this
becomes polyethylene.

583
00:28:59,810 --> 00:29:01,470
If I polymerize this,
this becomes

584
00:29:01,470 --> 00:29:03,940
polyvinyl chloride, PVC.

585
00:29:03,940 --> 00:29:08,470
Which is why you heard the
fellows from Blue Man Group at

586
00:29:08,470 --> 00:29:13,130
the beginning banging on PVC
tubing to make their music.

587
00:29:13,130 --> 00:29:13,410
All right.

588
00:29:13,410 --> 00:29:18,270
So I use a pure, in other
words, only one mer.

589
00:29:18,270 --> 00:29:20,050
It's pure polyethylene.

590
00:29:20,050 --> 00:29:21,460
This it's called
a homopolymer.

591
00:29:26,210 --> 00:29:31,830
Only one mer type in use.

592
00:29:31,830 --> 00:29:35,950
If I want to make the polymer
analogy of an alloy--

593
00:29:35,950 --> 00:29:40,040
in ally metals, alloy has more
than one metal mixed in, or a

594
00:29:40,040 --> 00:29:42,340
metal can even have nonmetals
mixed in.

595
00:29:42,340 --> 00:29:46,085
Then the polymer term
is called copolymer.

596
00:29:46,085 --> 00:29:48,640
I'll call this a copolymer.

597
00:29:48,640 --> 00:29:55,730
And a copolymer has greater
than one mer type.

598
00:29:55,730 --> 00:29:59,700
So for example here, this could
just be polyethylene.

599
00:29:59,700 --> 00:30:04,800
Whereas here, an example would
be polyethylene, and then the

600
00:30:04,800 --> 00:30:10,100
notation is hyphen lowercase c
hyphen, which is an indication

601
00:30:10,100 --> 00:30:13,040
of the fact that you're
making a copolymer.

602
00:30:13,040 --> 00:30:17,420
And this copolymer has mer units
of ethylene, and mer

603
00:30:17,420 --> 00:30:19,430
units of vinyl chloride.

604
00:30:19,430 --> 00:30:22,630
So this is a copolymer
of polyethylene

605
00:30:22,630 --> 00:30:24,430
and polyvinyl chloride.

606
00:30:24,430 --> 00:30:27,960
And then we can start looking
at the various ways of

607
00:30:27,960 --> 00:30:29,380
arranging these.

608
00:30:29,380 --> 00:30:32,590
So we can start with, for
example, we can have a

609
00:30:32,590 --> 00:30:45,680
sequence of random mer types.

610
00:30:45,680 --> 00:30:48,960
So as you're going down the
chain, you get either an

611
00:30:48,960 --> 00:30:53,120
ethylene, or a vinyl chloride.

612
00:30:53,120 --> 00:30:58,050
So this is called a random
copolymer, and it's designated

613
00:30:58,050 --> 00:31:01,400
polyethylene-r-polyvinyl
chloride.

614
00:31:01,400 --> 00:31:05,560
And actually, I think I've got
a cartoon showing this.

615
00:31:05,560 --> 00:31:06,250
Yeah.

616
00:31:06,250 --> 00:31:10,600
So A and B are different
mer types.

617
00:31:10,600 --> 00:31:13,150
And so a random copolymer
just has A, B, B,

618
00:31:13,150 --> 00:31:15,330
A, A, A, B, A, whatever.

619
00:31:15,330 --> 00:31:18,770
And this is controlled in
the synthesis process.

620
00:31:18,770 --> 00:31:24,200
So I can take the same mix of
A and B, in other words, the

621
00:31:24,200 --> 00:31:26,980
same two mer types,
but mix them in

622
00:31:26,980 --> 00:31:28,390
an alternating sequence.

623
00:31:28,390 --> 00:31:29,730
So they're very regular.

624
00:31:29,730 --> 00:31:35,040
It's 1 mer of ethylene, and
then one mer of vinyl

625
00:31:35,040 --> 00:31:37,540
chloride, alternating all the
way down the backbone.

626
00:31:37,540 --> 00:31:40,760
So this gives you a regular
copolymer, and it's designated

627
00:31:40,760 --> 00:31:42,140
A for alternating,
because we've

628
00:31:42,140 --> 00:31:45,030
already used R for random.

629
00:31:45,030 --> 00:31:48,580
So instead of a sequence of
random, we have a sequence of

630
00:31:48,580 --> 00:31:54,210
alternating mer types.

631
00:31:54,210 --> 00:31:55,500
So that would be, in this case,

632
00:31:55,500 --> 00:31:59,165
polyethylene alternating PVC.

633
00:31:59,165 --> 00:32:00,940
So that's two of them.

634
00:32:00,940 --> 00:32:05,320
And then you see the block
copolymer shown.

635
00:32:05,320 --> 00:32:13,520
And in that case, the
mers grouped into--

636
00:32:13,520 --> 00:32:15,860
they call them blocks, even
though it's a line.

637
00:32:15,860 --> 00:32:17,790
You know, maybe it's like
walking down the street.

638
00:32:17,790 --> 00:32:19,480
I've walked down one block.

639
00:32:19,480 --> 00:32:23,950
So this is one block, and then
there's the next block.

640
00:32:23,950 --> 00:32:26,720
They're grouped into blocks.

641
00:32:26,720 --> 00:32:32,750
So in that case, we have the
block copolymer, lowercase b,

642
00:32:32,750 --> 00:32:35,030
and then PVC.

643
00:32:35,030 --> 00:32:38,470
And what you see
there is a run.

644
00:32:38,470 --> 00:32:39,720
A run of--

645
00:32:42,370 --> 00:32:45,260
So all of the A's are
grouped, and then we

646
00:32:45,260 --> 00:32:47,090
have all of the B's.

647
00:32:47,090 --> 00:32:50,310
And this is actually an artist's
misconception.

648
00:32:50,310 --> 00:32:54,060
In point of fact, most block
copolymers that you find, this

649
00:32:54,060 --> 00:32:56,180
is the stuff they use for
the soles of your

650
00:32:56,180 --> 00:32:57,110
sneakers and so on.

651
00:32:57,110 --> 00:32:58,650
They're block copolymers.

652
00:32:58,650 --> 00:33:00,730
They're usually just
a diblock.

653
00:33:00,730 --> 00:33:03,620
There's usually just two
different mer types.

654
00:33:03,620 --> 00:33:07,320
One half of the macromolecule
is one mer type, the other

655
00:33:07,320 --> 00:33:10,770
half of the macromolecule
is the other mer type.

656
00:33:10,770 --> 00:33:14,250
Sometimes you might find a
triblock, where you might find

657
00:33:14,250 --> 00:33:16,690
block A, block B, and then
another block A.

658
00:33:16,690 --> 00:33:20,210
But this is a pentablock and
he's even got ellipses here as

659
00:33:20,210 --> 00:33:21,350
though this thing keeps going.

660
00:33:21,350 --> 00:33:23,230
There's no commercial product
that looks like that.

661
00:33:23,230 --> 00:33:26,430
It's usually a diblock,
occasionally a triblock.

662
00:33:26,430 --> 00:33:27,060
OK?

663
00:33:27,060 --> 00:33:30,500
And then the last thing you can
do, as is shown up here,

664
00:33:30,500 --> 00:33:33,270
is what is known as the graft.

665
00:33:33,270 --> 00:33:37,280
And in the graft, the thing that
distinguishes the graft

666
00:33:37,280 --> 00:33:39,750
is mers grouped into blocks.

667
00:33:39,750 --> 00:33:50,310
In this case, a long side
chain of other mer.

668
00:33:50,310 --> 00:33:53,470
So that's different from side
group that we saw last day.

669
00:33:53,470 --> 00:33:55,570
These are long macromolecular
chains.

670
00:33:55,570 --> 00:33:59,130
So you see here the primary
backbone is A, and then you

671
00:33:59,130 --> 00:34:02,890
have this very, very long
macromolecular chain of B.

672
00:34:02,890 --> 00:34:07,625
And this is called the
graft copolymer.

673
00:34:07,625 --> 00:34:10,730
So that would be polyethylene,
could be the backbone, and

674
00:34:10,730 --> 00:34:14,180
then long side chains of
polyvinyl chloride.

675
00:34:14,180 --> 00:34:18,070
And all of these have their
different architectures.

676
00:34:18,070 --> 00:34:20,310
And I think I have an
example here of one.

677
00:34:20,310 --> 00:34:22,540
This one, I think I mentioned
last day, when we were looking

678
00:34:22,540 --> 00:34:25,920
at the butadiene.

679
00:34:25,920 --> 00:34:28,520
So this is hard-sided luggage.

680
00:34:28,520 --> 00:34:30,850
And if you go to grandma's
house, and she hasn't gotten

681
00:34:30,850 --> 00:34:34,390
into the digital age, and isn't
an old hipster with a

682
00:34:34,390 --> 00:34:38,800
cell phone, she's still got
the old hard plastic

683
00:34:38,800 --> 00:34:40,680
telephone, it's made
of this stuff.

684
00:34:40,680 --> 00:34:44,830
ABS, which is acrylonitrile
butadiene styrene.

685
00:34:44,830 --> 00:34:48,880
And the backbone is butadiene,
and then you have--

686
00:34:48,880 --> 00:34:50,400
OK, so here's the backbone.

687
00:34:50,400 --> 00:34:53,130
It's long butadiene, which
we saw last day.

688
00:34:53,130 --> 00:34:55,970
And then you've got side
chains of two types.

689
00:34:55,970 --> 00:34:58,740
And this is just indicating
A, A, but this is a

690
00:34:58,740 --> 00:34:59,750
macromolecule.

691
00:34:59,750 --> 00:35:03,210
This might be 3,000 units long,
whereas this is 10,000

692
00:35:03,210 --> 00:35:04,110
units long.

693
00:35:04,110 --> 00:35:06,390
And this might be 2,000
units long.

694
00:35:06,390 --> 00:35:09,590
So you have side chains of
acrylonitrile and side chains

695
00:35:09,590 --> 00:35:11,650
of polystyrene.

696
00:35:11,650 --> 00:35:14,650
And that's the hard plastic.

697
00:35:14,650 --> 00:35:18,300
It's coming back, because
people want luggage that

698
00:35:18,300 --> 00:35:21,980
doesn't destroy their
contents anymore.

699
00:35:21,980 --> 00:35:23,760
So that's coming back.

700
00:35:23,760 --> 00:35:24,040
OK.

701
00:35:24,040 --> 00:35:27,940
So this is what we can do
in terms of composition.

702
00:35:27,940 --> 00:35:31,570
Let's look at, also, the
side group arrangement.

703
00:35:31,570 --> 00:35:33,840
And this is called tacticity.

704
00:35:33,840 --> 00:35:38,290
Tacticity, which is the
equivalent of what we saw last

705
00:35:38,290 --> 00:35:39,600
day as stereo isomerism.

706
00:35:44,640 --> 00:35:50,730
Remember, I showed you the cis
and trans on the butadiene.

707
00:35:50,730 --> 00:35:56,230
On the cis, you've got, in one
case, you've got whatever the

708
00:35:56,230 --> 00:35:57,120
functional group is.

709
00:35:57,120 --> 00:36:01,370
I'm going to put A, A, B, B.

710
00:36:01,370 --> 00:36:05,660
And then so this is the cis
version, or I can do a trans

711
00:36:05,660 --> 00:36:09,630
version, which is instead,
I'll put in A up here

712
00:36:09,630 --> 00:36:10,900
and an A down here.

713
00:36:10,900 --> 00:36:13,450
I'll put a B up here
and a B down here.

714
00:36:13,450 --> 00:36:15,090
So this is a trans version.

715
00:36:15,090 --> 00:36:18,410
So imagine the analogy
for polymers.

716
00:36:18,410 --> 00:36:19,380
So let's look at that.

717
00:36:19,380 --> 00:36:22,160
It's easier to see it, and then
we can just document it.

718
00:36:22,160 --> 00:36:25,430
So here's three different
polymers, all right?

719
00:36:25,430 --> 00:36:28,780
So I'm going to start
with the lowest one.

720
00:36:28,780 --> 00:36:32,460
This is called isotactic,
because this is vinylchloride.

721
00:36:32,460 --> 00:36:35,890
There's vinyl chloride
by itself.

722
00:36:35,890 --> 00:36:38,160
There's the vinyl radical
from ethylene.

723
00:36:38,160 --> 00:36:39,930
And then we tack on chlorine.

724
00:36:39,930 --> 00:36:42,580
And now when we polymerize,
we're going to break this

725
00:36:42,580 --> 00:36:45,920
double bond in order to link
this carbon to the neighbor.

726
00:36:45,920 --> 00:36:48,350
So now the backbone only has
single bonds, right?

727
00:36:48,350 --> 00:36:50,830
You start with the double bonded
precursor, and now

728
00:36:50,830 --> 00:36:52,950
you've got this chain
of single bonds.

729
00:36:52,950 --> 00:36:53,220
Right?

730
00:36:53,220 --> 00:36:54,390
But look at the chlorine.

731
00:36:54,390 --> 00:36:57,460
The chlorine could either be
below, or it could be above.

732
00:36:57,460 --> 00:36:58,720
Well, in this case,
the chlorine is

733
00:36:58,720 --> 00:37:00,410
always below the chain.

734
00:37:00,410 --> 00:37:03,680
So this is called isotactic
polyvinyl chloride.

735
00:37:03,680 --> 00:37:06,830
Now this one, you know, they're
trying to mix two

736
00:37:06,830 --> 00:37:07,540
things at once.

737
00:37:07,540 --> 00:37:09,980
I would have shown this
with vinyl chloride in

738
00:37:09,980 --> 00:37:11,090
all three, but OK.

739
00:37:11,090 --> 00:37:13,830
So imagine now, in this case
it's syndiotactic.

740
00:37:13,830 --> 00:37:17,090
This happens to be polystyrene,
because this is

741
00:37:17,090 --> 00:37:21,840
vinyl benzine, or what's
the other way to

742
00:37:21,840 --> 00:37:25,360
call it, phenyl ethylene.

743
00:37:25,360 --> 00:37:26,410
You can have either way.

744
00:37:26,410 --> 00:37:26,680
All right?

745
00:37:26,680 --> 00:37:30,830
So you can say you're putting a
phenyl group onto vinyl, or

746
00:37:30,830 --> 00:37:33,850
you're putting onto the
ethylene, or vice versa.

747
00:37:33,850 --> 00:37:36,930
But the radical, this thing here
is called styrene, and

748
00:37:36,930 --> 00:37:39,040
we're going to break that double
bond and away we go.

749
00:37:39,040 --> 00:37:43,720
So this is the benzine ring, and
it alternates from above

750
00:37:43,720 --> 00:37:44,840
the chain to below the chain.

751
00:37:44,840 --> 00:37:46,610
Above the chain to
below the chain.

752
00:37:46,610 --> 00:37:49,010
So in this, this is called
syndiotactic.

753
00:37:49,010 --> 00:37:52,040
And the top one is a
polypropylene, so you start

754
00:37:52,040 --> 00:37:55,250
with propylene, that has
the double bond here.

755
00:37:55,250 --> 00:37:59,020
It's got three carbons and the
methyl group coming out, and

756
00:37:59,020 --> 00:38:02,940
so you break that double bond
and make the chain.

757
00:38:02,940 --> 00:38:05,600
And it seems to be on a random
basis where that

758
00:38:05,600 --> 00:38:06,540
methyl group appears.

759
00:38:06,540 --> 00:38:08,750
Sometimes above the chain,
sometimes below the chain.

760
00:38:08,750 --> 00:38:13,830
So those are three different
ways of arranging, so three

761
00:38:13,830 --> 00:38:15,060
different tacticities.

762
00:38:15,060 --> 00:38:25,710
So we've got isotactic, we've
got syndiotactic, and we've

763
00:38:25,710 --> 00:38:28,620
got atactic.

764
00:38:28,620 --> 00:38:31,370
So the way to remember them,
isotactic obviously means,

765
00:38:31,370 --> 00:38:33,590
everything's on the same side.

766
00:38:33,590 --> 00:38:35,500
And when I'm talking about the
same side, what is it?

767
00:38:35,500 --> 00:38:38,580
Same side of the backbone.

768
00:38:38,580 --> 00:38:41,390
And we're talking about
the position of

769
00:38:41,390 --> 00:38:43,380
functional groups, right?

770
00:38:43,380 --> 00:38:44,560
That's what this is all about.

771
00:38:44,560 --> 00:38:46,440
The positioning of functional
groups.

772
00:38:56,830 --> 00:38:59,450
In other words, a methyl, or a
benzine, or what have you.

773
00:38:59,450 --> 00:39:01,230
So same side of backbone.

774
00:39:01,230 --> 00:39:06,050
Atactic is random, and then by
elimination, this one must

775
00:39:06,050 --> 00:39:09,970
mean alternating,
above and below.

776
00:39:09,970 --> 00:39:11,870
On opposite sides
of the chain.

777
00:39:11,870 --> 00:39:14,580
And these have different
propensities for

778
00:39:14,580 --> 00:39:15,470
crystallization.

779
00:39:15,470 --> 00:39:16,960
Which of these three--

780
00:39:16,960 --> 00:39:20,650
imagine that all three of them
were polyvinyl chloride.

781
00:39:20,650 --> 00:39:24,770
Which of the three, atactic,
syndiotactic, isotactic, would

782
00:39:24,770 --> 00:39:29,010
be most favorable from the
standpoint of partial

783
00:39:29,010 --> 00:39:32,730
crystallization, to loop
back and forth?

784
00:39:32,730 --> 00:39:37,870
The one that's most regular,
so the isotactic one has.

785
00:39:37,870 --> 00:39:40,060
OK.

786
00:39:40,060 --> 00:39:41,220
Third one.

787
00:39:41,220 --> 00:39:44,930
Third one is the backbone
configuration.

788
00:39:53,280 --> 00:39:56,290
This is the configuration of
the main chain, all right?

789
00:39:56,290 --> 00:39:59,276
And this is called
conformality.

790
00:39:59,276 --> 00:40:03,510
You see, they have different
words for everything that came

791
00:40:03,510 --> 00:40:04,850
from a different heritage.

792
00:40:04,850 --> 00:40:09,040
So to me, it answers
the question, how

793
00:40:09,040 --> 00:40:10,503
distended is the chain?

794
00:40:14,850 --> 00:40:18,690
And we saw this last day, when
we looked at what happens when

795
00:40:18,690 --> 00:40:23,050
we start with something like
this, where we have staggered

796
00:40:23,050 --> 00:40:27,440
or eclipsed, remember,
orientation of

797
00:40:27,440 --> 00:40:29,480
the hydrogens here.

798
00:40:29,480 --> 00:40:32,860
In the case of staggered,
we get the lower.

799
00:40:32,860 --> 00:40:35,640
Both of these are straight
chains, because if you start

800
00:40:35,640 --> 00:40:38,180
at one end, you move
monotonically all the way down

801
00:40:38,180 --> 00:40:40,010
the chain to the other end.

802
00:40:40,010 --> 00:40:41,640
There's no branching here.

803
00:40:41,640 --> 00:40:47,250
But one of them, the lower one,
has staggering of that

804
00:40:47,250 --> 00:40:49,660
carbon-carbon bond, with
the result, things

805
00:40:49,660 --> 00:40:51,190
form this giant loop.

806
00:40:51,190 --> 00:40:54,550
So in polymers, imagine this,
instead of being 36 units

807
00:40:54,550 --> 00:40:57,490
long, imagine it being
3,600 units long.

808
00:40:57,490 --> 00:40:59,390
So now you can have
things to do this.

809
00:41:02,115 --> 00:41:04,540
You can even take a little
break here and

810
00:41:04,540 --> 00:41:06,500
crystallize and so on.

811
00:41:06,500 --> 00:41:13,980
So how do I distinguish that
from something that does this?

812
00:41:13,980 --> 00:41:15,600
So how distended is the chain?

813
00:41:15,600 --> 00:41:20,020
This one here is as distended
as it can be, and others can

814
00:41:20,020 --> 00:41:21,480
be much more coiled.

815
00:41:21,480 --> 00:41:23,430
So this one is called
linear chain.

816
00:41:29,300 --> 00:41:30,500
This is branch chain.

817
00:41:30,500 --> 00:41:32,460
Now, this is not graft.

818
00:41:32,460 --> 00:41:34,960
Don't confuse this with
the graft copolymer.

819
00:41:34,960 --> 00:41:38,920
Graft copolymer means, I have
one mer down the backbone, and

820
00:41:38,920 --> 00:41:41,300
a second mer off to the side.

821
00:41:41,300 --> 00:41:42,490
That's a graft copolymer.

822
00:41:42,490 --> 00:41:43,640
This is a homopolymer.

823
00:41:43,640 --> 00:41:46,630
A homopolymer that has
different branches.

824
00:41:46,630 --> 00:41:50,030
So all of these, let's put
this here to remind us.

825
00:41:50,030 --> 00:41:53,710
These are homopolymer
cartoons.

826
00:41:53,710 --> 00:41:55,520
Homopolymers that haven't
changed anything.

827
00:41:55,520 --> 00:41:56,890
So this is something
that actually

828
00:41:56,890 --> 00:41:58,500
has different branches.

829
00:41:58,500 --> 00:42:04,180
So this is branched chain,
branch chain architecture.

830
00:42:04,180 --> 00:42:06,170
Good.

831
00:42:06,170 --> 00:42:10,790
So which one of these is going
to be harder to crystallize.

832
00:42:10,790 --> 00:42:12,760
Which one is-- well, obviously,
I've given it away,

833
00:42:12,760 --> 00:42:15,470
I put that little piece of
crystallinity in there.

834
00:42:15,470 --> 00:42:19,130
Can you see that when these two
solidify, that the one on

835
00:42:19,130 --> 00:42:21,380
the right, because it's got
these branched chains with the

836
00:42:21,380 --> 00:42:22,980
covalent bonds sticking out.

837
00:42:22,980 --> 00:42:24,320
It's not going to
pack as well.

838
00:42:24,320 --> 00:42:27,120
And if it doesn't pack as well,
it's going to have a

839
00:42:27,120 --> 00:42:28,250
higher free volume.

840
00:42:28,250 --> 00:42:30,430
If it's got a higher free
volume, it's got a higher

841
00:42:30,430 --> 00:42:31,330
degree of disorder.

842
00:42:31,330 --> 00:42:33,970
So the branched chains
have a greater

843
00:42:33,970 --> 00:42:36,000
propensity for disorder.

844
00:42:36,000 --> 00:42:38,710
So let's put that down.

845
00:42:38,710 --> 00:42:42,020
Branched chain, harder
to crystallize.

846
00:42:46,490 --> 00:42:51,080
And crystallize, it's not a
giant crystal or polycrystal.

847
00:42:51,080 --> 00:42:54,030
We're talking about the degree
to which we can get that

848
00:42:54,030 --> 00:42:55,200
amount of ordering.

849
00:42:55,200 --> 00:42:59,330
And then the last one I want to
show you is, here's three

850
00:42:59,330 --> 00:43:00,820
different chains.

851
00:43:00,820 --> 00:43:04,042
1, 2, and 3.

852
00:43:04,042 --> 00:43:08,560
And what we're going to do is
we're going to cross-link.

853
00:43:08,560 --> 00:43:11,080
We're going to form bridges.

854
00:43:11,080 --> 00:43:12,660
These are covalent bridges.

855
00:43:15,770 --> 00:43:17,290
These are not hydrogen bonds.

856
00:43:17,290 --> 00:43:19,180
These are not weak van
der Walls bonds.

857
00:43:19,180 --> 00:43:22,830
These are strong covalent bonds,
all the way along here,

858
00:43:22,830 --> 00:43:26,100
linking backbone to backbone.

859
00:43:26,100 --> 00:43:27,420
So this is cross-linked.

860
00:43:34,750 --> 00:43:37,080
And what do you think the
mechanical properties of this

861
00:43:37,080 --> 00:43:38,270
are going to be?

862
00:43:38,270 --> 00:43:42,320
If I want extend this, like
stretch and seal, I can pull

863
00:43:42,320 --> 00:43:46,150
chain number three relative to
chain number one quite easily,

864
00:43:46,150 --> 00:43:52,630
until this covalent bond has
bent over as far as it can,

865
00:43:52,630 --> 00:43:54,070
and then what happens?

866
00:43:54,070 --> 00:43:56,160
I can't pull it anymore.

867
00:43:56,160 --> 00:43:58,660
And what happens when
I let it go?

868
00:43:58,660 --> 00:43:59,910
It springs back.

869
00:43:59,910 --> 00:44:02,570
So this imparts elasticity.

870
00:44:02,570 --> 00:44:05,850
This makes the polymer
rubbery.

871
00:44:05,850 --> 00:44:08,230
Cross-linked polymers
are rubbery.

872
00:44:08,230 --> 00:44:10,040
But you know, the polymer
people, they

873
00:44:10,040 --> 00:44:11,770
want elevated words.

874
00:44:11,770 --> 00:44:14,030
If you say to a polymer person,
oh, so you've made a

875
00:44:14,030 --> 00:44:15,430
rubber, they cringe.

876
00:44:15,430 --> 00:44:16,490
They want to have
a fancy word.

877
00:44:16,490 --> 00:44:19,040
They call this an elastimer.

878
00:44:19,040 --> 00:44:22,060
It's got the word mer in it,
so they're happy, and it's

879
00:44:22,060 --> 00:44:24,110
elastic, so it's an elastimer.

880
00:44:24,110 --> 00:44:25,450
Rubbery.

881
00:44:25,450 --> 00:44:27,600
So how are we going to make
these cross-links?

882
00:44:27,600 --> 00:44:30,080
What are we going to have to
look for as an architectural

883
00:44:30,080 --> 00:44:33,150
feature to make cross-links?

884
00:44:33,150 --> 00:44:34,662
We look at the backbone.

885
00:44:34,662 --> 00:44:38,680
If we've got a backbone going
like this, all these

886
00:44:38,680 --> 00:44:40,900
carbon-carbon bonds, and
down here I've got

887
00:44:40,900 --> 00:44:42,390
carbon-carbon bonds.

888
00:44:45,100 --> 00:44:49,210
If I break one of these bonds
in order to go up in this

889
00:44:49,210 --> 00:44:52,220
direction, I've broken
the chain.

890
00:44:52,220 --> 00:44:55,790
So how am I going to have the
bonding capability to form a

891
00:44:55,790 --> 00:44:59,420
covalent bridge between chains
without breaking the very

892
00:44:59,420 --> 00:45:01,400
chain I'm trying to link?

893
00:45:01,400 --> 00:45:05,810
What feature am I going to have
to have in the chain?

894
00:45:05,810 --> 00:45:08,820
I need, after polymerization,
to still

895
00:45:08,820 --> 00:45:11,090
have some double bonds.

896
00:45:11,090 --> 00:45:14,300
And if I've got still double
bonds in the backbone after

897
00:45:14,300 --> 00:45:15,760
polymerization--

898
00:45:15,760 --> 00:45:17,460
and now would I do that?

899
00:45:17,460 --> 00:45:20,510
I have to have a double bond to
break in the first place.

900
00:45:20,510 --> 00:45:24,050
So what would happen if I
started with a unit that had

901
00:45:24,050 --> 00:45:25,420
two double bonds in it?

902
00:45:25,420 --> 00:45:28,450
That way, I give up one double
bond in order to make the

903
00:45:28,450 --> 00:45:30,600
chain, and I still have
a second double bond.

904
00:45:30,600 --> 00:45:36,120
That's why the rubber
has butadiene.

905
00:45:36,120 --> 00:45:39,130
The diene has two double bonds,
after polymerization,

906
00:45:39,130 --> 00:45:42,410
still has one double bond, and
now what I can do is break

907
00:45:42,410 --> 00:45:46,210
this double bond and this double
bond, and link them.

908
00:45:46,210 --> 00:45:47,190
But if I link them,
they're going to

909
00:45:47,190 --> 00:45:48,930
be too close together.

910
00:45:48,930 --> 00:45:50,260
They're going to be
scrunched in.

911
00:45:50,260 --> 00:45:52,560
I want to have some
play, here.

912
00:45:52,560 --> 00:45:53,650
I want to make this rubbery.

913
00:45:53,650 --> 00:45:54,810
So what do I do?

914
00:45:54,810 --> 00:45:56,290
I put a spacer in here.

915
00:45:56,290 --> 00:45:57,760
What do I use as a spacer?

916
00:45:57,760 --> 00:45:58,655
An atom.

917
00:45:58,655 --> 00:46:00,670
And what kind of an
atom do I need?

918
00:46:00,670 --> 00:46:03,890
I need an atom that's capable
of making one,

919
00:46:03,890 --> 00:46:05,910
two covalent bonds.

920
00:46:05,910 --> 00:46:07,620
What am I going to choose?

921
00:46:07,620 --> 00:46:11,660
What atom do you know likes
to make linkages?

922
00:46:15,950 --> 00:46:19,140
How did we make silicate?

923
00:46:19,140 --> 00:46:21,390
What's the linker in silicate?

924
00:46:21,390 --> 00:46:22,280
Oxygen.

925
00:46:22,280 --> 00:46:25,280
You could use oxygen, but I want
to make this thing even

926
00:46:25,280 --> 00:46:28,105
farther apart, and a little bit,
you know, oxygen's small

927
00:46:28,105 --> 00:46:29,300
and it's got too
much strength.

928
00:46:29,300 --> 00:46:31,810
If I want to make it weaker,
but something that behaved

929
00:46:31,810 --> 00:46:35,080
like oxygen, sulfur, I'd
go down one row in

930
00:46:35,080 --> 00:46:36,270
the periodic table.

931
00:46:36,270 --> 00:46:37,460
So I'd put a sulfur in here.

932
00:46:37,460 --> 00:46:40,880
And if I wanted to do a really
good job, I'll put a sulfur

933
00:46:40,880 --> 00:46:43,620
here, since I got a double bond
from both sides, I'll put

934
00:46:43,620 --> 00:46:47,010
two sulfurs, and make a
disulfide linkage, and now

935
00:46:47,010 --> 00:46:49,810
I've got the making of rubber.

936
00:46:49,810 --> 00:46:51,060
Disulfide linkage.

937
00:46:55,080 --> 00:46:57,680
And again, the feature, I have
to start with the backbone

938
00:46:57,680 --> 00:47:00,800
that has a covalent
bond at the end.

939
00:47:00,800 --> 00:47:03,120
OK.

940
00:47:03,120 --> 00:47:08,170
Well, let me tell you a little
bit about the birth of rubber.

941
00:47:08,170 --> 00:47:09,325
It started here in
Massachusetts.

942
00:47:09,325 --> 00:47:13,500
It started just across the
river, in Roxbury.

943
00:47:13,500 --> 00:47:16,720
Nathaniel Hayward discovered
that rubber treated with

944
00:47:16,720 --> 00:47:19,090
sulfur was not sticky.

945
00:47:19,090 --> 00:47:20,570
If you take natural rubber--

946
00:47:20,570 --> 00:47:22,330
you ever work with
natural rubber?

947
00:47:22,330 --> 00:47:23,130
It's very sticky.

948
00:47:23,130 --> 00:47:24,790
You can't do anything with it.

949
00:47:24,790 --> 00:47:28,740
And Hayward reasoned that by
playing with the sulfur, he

950
00:47:28,740 --> 00:47:30,700
could-- he didn't understand
the molecular architecture.

951
00:47:30,700 --> 00:47:34,430
But he learned that by playing
with sulfur, and introducing

952
00:47:34,430 --> 00:47:38,090
sulfur to the rubber, he lost
the stickiness and he got an

953
00:47:38,090 --> 00:47:40,470
enhanced elasticity.

954
00:47:40,470 --> 00:47:46,530
So Charles Goodyear came to
Boston from Ohio to meet with

955
00:47:46,530 --> 00:47:52,150
Hayward, and he learned about
disulfide linkage and so on.

956
00:47:52,150 --> 00:47:54,490
Took the idea back to Ohio.

957
00:47:54,490 --> 00:47:57,580
And one day in the laboratory,
he was trying to prepare a

958
00:47:57,580 --> 00:48:00,690
batch of sulfonated rubber.

959
00:48:00,690 --> 00:48:03,240
And it was a laboratory
accident.

960
00:48:03,240 --> 00:48:06,610
He knocked over the vessel
containing this sulfonated

961
00:48:06,610 --> 00:48:09,810
rubber, and it landed
on a hot stove.

962
00:48:09,810 --> 00:48:12,640
Things were powered by fire.

963
00:48:12,640 --> 00:48:15,600
Landed on a hot stove, and then
by heating it, he gave

964
00:48:15,600 --> 00:48:18,510
birth to the process
of vulcanization.

965
00:48:18,510 --> 00:48:22,490
And hence was born the American
rubber tire industry,

966
00:48:22,490 --> 00:48:26,280
by that accident, starting with
the trip to Roxbury to

967
00:48:26,280 --> 00:48:27,580
learn about this.

968
00:48:27,580 --> 00:48:30,550
And you could have done it all
with what you learned today.

969
00:48:30,550 --> 00:48:33,280
You're just about 150
years too late.

970
00:48:33,280 --> 00:48:33,860
OK.

971
00:48:33,860 --> 00:48:35,960
I will see you on Friday.