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.