1 00:00:16,583 --> 00:00:19,052 It's our last Friday. 2 00:00:19,052 --> 00:00:19,886 Did I hear an, "Oh?" 3 00:00:19,886 --> 00:00:22,322 Thank you for that one "oh." 4 00:00:22,322 --> 00:00:22,856 It's OK. 5 00:00:22,856 --> 00:00:26,059 I'll take what I can get. 6 00:00:26,059 --> 00:00:32,432 It's our last Friday, and so next week is our last week. 7 00:00:32,432 --> 00:00:34,367 We have class on Monday, and Wednesday 8 00:00:34,367 --> 00:00:37,337 will be the last class. 9 00:00:37,337 --> 00:00:40,040 And we've got one more smallish topic 10 00:00:40,040 --> 00:00:43,309 to cover after this, which is diffusion, 11 00:00:43,309 --> 00:00:46,212 and we'll wrap up on Wednesday. 12 00:00:46,212 --> 00:00:49,082 But today, I want to keep talking about polymers. 13 00:00:49,082 --> 00:00:51,418 So this is our polymer week. 14 00:00:51,418 --> 00:00:53,653 And I want to go back to the properties 15 00:00:53,653 --> 00:00:57,257 I've put here, the properties we've talked about. 16 00:00:57,257 --> 00:00:57,757 Right? 17 00:00:57,757 --> 00:01:02,595 So on Monday, we focused on what a polymer is, 18 00:01:02,595 --> 00:01:05,698 and we focused on the ways you make it. 19 00:01:05,698 --> 00:01:06,232 All right? 20 00:01:06,232 --> 00:01:11,170 The radical initiation, chain, addition, and the condensation 21 00:01:11,170 --> 00:01:14,207 polymers that you know, the condensation where 22 00:01:14,207 --> 00:01:16,709 you have two different mers. 23 00:01:16,709 --> 00:01:20,947 And then on Wednesday, we talked about things that matter, kind 24 00:01:20,947 --> 00:01:22,582 of like engineering polymers. 25 00:01:22,582 --> 00:01:27,454 Like what are the properties of the polymers that you 26 00:01:27,454 --> 00:01:30,056 can change, that we can change? 27 00:01:30,056 --> 00:01:30,657 All right? 28 00:01:30,657 --> 00:01:32,092 And so we talked about, well, you 29 00:01:32,092 --> 00:01:33,660 could pick a different monomer. 30 00:01:33,660 --> 00:01:34,994 That will change the properties. 31 00:01:34,994 --> 00:01:35,527 Right? 32 00:01:35,527 --> 00:01:37,130 We've been through that. 33 00:01:37,130 --> 00:01:40,934 You could try to grow longer or shorter strands, 34 00:01:40,934 --> 00:01:43,402 so that's going to change properties. 35 00:01:43,402 --> 00:01:47,006 The interactions between the strands, 36 00:01:47,006 --> 00:01:50,577 which will, of course, depend on what you pick there. 37 00:01:50,577 --> 00:01:52,512 Right? 38 00:01:52,512 --> 00:01:56,583 And then we talked about the density and the crystallinity 39 00:01:56,583 --> 00:01:58,318 and how that could depend on things 40 00:01:58,318 --> 00:02:02,655 like cooling rate, or maybe the physical structure itself 41 00:02:02,655 --> 00:02:03,823 of the chain. 42 00:02:03,823 --> 00:02:04,891 So what do I mean by that? 43 00:02:04,891 --> 00:02:07,060 Well, when I say physical structure, 44 00:02:07,060 --> 00:02:08,728 of course I mean the chemistry that 45 00:02:08,728 --> 00:02:12,765 makes that physical structure, so I could branch the chain 46 00:02:12,765 --> 00:02:15,335 with the same monomers, but now instead 47 00:02:15,335 --> 00:02:18,571 of being one linear chain it's a bunch of branches. 48 00:02:18,571 --> 00:02:21,808 Or maybe you could have a functional group 49 00:02:21,808 --> 00:02:24,010 that you can control which side of the chain it's on. 50 00:02:24,010 --> 00:02:26,412 And all those things would lead to differences 51 00:02:26,412 --> 00:02:30,083 in density an crystallinity. 52 00:02:30,083 --> 00:02:32,852 And then the last thing we talked about is cross-linking. 53 00:02:32,852 --> 00:02:34,420 And what I'm going to do is I'm going 54 00:02:34,420 --> 00:02:37,991 to add one more thing to this list today, 55 00:02:37,991 --> 00:02:39,759 but before I do that I want to pick up 56 00:02:39,759 --> 00:02:43,228 on the last slide of Wednesday, which is this. 57 00:02:43,228 --> 00:02:46,666 So we tend-- so all this kind of goes in together 58 00:02:46,666 --> 00:02:49,802 to give you these solids called polymers. 59 00:02:49,802 --> 00:02:50,870 Right? 60 00:02:50,870 --> 00:02:54,174 But we talked about how sometimes they're 61 00:02:54,174 --> 00:02:56,509 not fully solid, and that's what's 62 00:02:56,509 --> 00:02:57,677 going to come in the middle. 63 00:02:57,677 --> 00:03:01,314 But you can make a solid thermoplastic, 64 00:03:01,314 --> 00:03:02,682 which is these strands. 65 00:03:02,682 --> 00:03:03,183 Right? 66 00:03:03,183 --> 00:03:04,250 So what is a thermal? 67 00:03:04,250 --> 00:03:06,419 Ah, what's the? 68 00:03:06,419 --> 00:03:09,756 Anyway, so with thermoplastic we'll look over here. 69 00:03:09,756 --> 00:03:13,960 There is no cross-linking, so you don't have any of this. 70 00:03:13,960 --> 00:03:14,961 But what do I have? 71 00:03:14,961 --> 00:03:17,564 Well, I have these really long strands 72 00:03:17,564 --> 00:03:20,900 that are bonded together with these IMFs, 73 00:03:20,900 --> 00:03:24,671 typically in a thermoplastic you would 74 00:03:24,671 --> 00:03:27,473 have something like maybe van der Waals, 75 00:03:27,473 --> 00:03:30,577 and maybe you have some H bonds. 76 00:03:30,577 --> 00:03:35,915 And these materials, because you didn't cross-link them, 77 00:03:35,915 --> 00:03:38,117 and you didn't cross-link them strongly 78 00:03:38,117 --> 00:03:40,420 with some kind of strong bond, because of that, 79 00:03:40,420 --> 00:03:42,322 you can reheat them and reprocess them. 80 00:03:42,322 --> 00:03:45,692 So these are actually often the plastics 81 00:03:45,692 --> 00:03:49,128 that we recycle that we can recycle. 82 00:03:49,128 --> 00:03:51,831 And like I said, they're mostly linear and maybe slightly 83 00:03:51,831 --> 00:03:54,801 branched polymers, and they're used 84 00:03:54,801 --> 00:03:59,005 in a whole lot of applications, so we call them thermoplastics. 85 00:03:59,005 --> 00:04:01,474 Thermal-- you can heat them. 86 00:04:01,474 --> 00:04:01,975 Right? 87 00:04:01,975 --> 00:04:03,977 You can heat them, and you can see 88 00:04:03,977 --> 00:04:07,480 what happens is if I heat these back up, 89 00:04:07,480 --> 00:04:09,115 these links can start moving. 90 00:04:09,115 --> 00:04:12,619 They wiggle, and they wiggle until they can just kind 91 00:04:12,619 --> 00:04:18,324 of slide past each other and become a vicious liquid 92 00:04:18,324 --> 00:04:19,625 and then a melt. 93 00:04:19,625 --> 00:04:24,230 On the other hand, if I've got a thermoset, 94 00:04:24,230 --> 00:04:28,801 I heated it up, and then as it set I crossed linked it. 95 00:04:28,801 --> 00:04:30,737 And there are lots of ways you can cross-link. 96 00:04:30,737 --> 00:04:32,205 We talked about some of those. 97 00:04:32,205 --> 00:04:34,207 Right? 98 00:04:34,207 --> 00:04:36,709 And now I've got a pretty high density of cross-links, 99 00:04:36,709 --> 00:04:38,411 so that's drawn here. 100 00:04:38,411 --> 00:04:40,179 So I've got these long strands. 101 00:04:40,179 --> 00:04:42,548 Remember, they're super, super long, right? 102 00:04:42,548 --> 00:04:47,186 But now, every so often I have something linking them 103 00:04:47,186 --> 00:04:48,321 together. 104 00:04:48,321 --> 00:04:50,089 And if I put a lot of cross-links in, 105 00:04:50,089 --> 00:04:51,524 and if they're strong cross-links, 106 00:04:51,524 --> 00:04:54,460 then you can get really hard plastics. 107 00:04:54,460 --> 00:04:55,094 Right? 108 00:04:55,094 --> 00:04:58,064 And so these are high-- the thermoset, they're set. 109 00:04:58,064 --> 00:04:59,365 They're set. 110 00:04:59,365 --> 00:05:01,601 Thermoset, good. 111 00:05:01,601 --> 00:05:04,570 It solidifies, and it can't be reheated. 112 00:05:04,570 --> 00:05:05,138 Why? 113 00:05:05,138 --> 00:05:05,772 Think about it. 114 00:05:05,772 --> 00:05:11,344 If I heat that up, then, OK, I might melt the polymers, 115 00:05:11,344 --> 00:05:13,212 so the chains are kind of wiggling around, 116 00:05:13,212 --> 00:05:16,816 but those cross-links aren't going anywhere. 117 00:05:16,816 --> 00:05:18,818 They're really strong. 118 00:05:18,818 --> 00:05:20,286 And so what happens with thermosets 119 00:05:20,286 --> 00:05:22,689 is they're very difficult to recycle. 120 00:05:22,689 --> 00:05:25,291 They're very difficult to recycle because what'll happen 121 00:05:25,291 --> 00:05:29,629 is before those things melt the whole thing catches fire. 122 00:05:29,629 --> 00:05:30,863 The whole thing catches fire. 123 00:05:30,863 --> 00:05:32,765 It burns often. 124 00:05:32,765 --> 00:05:35,368 Or maybe it doesn't burn, but when you melt it, 125 00:05:35,368 --> 00:05:37,337 you've got this weird chemistry now 126 00:05:37,337 --> 00:05:40,173 of the cross-linker mixed into the polymer, 127 00:05:40,173 --> 00:05:42,008 and it's not useful anymore. 128 00:05:42,008 --> 00:05:44,010 So these kinds of plastics-- 129 00:05:44,010 --> 00:05:45,511 the cross-link is really great. 130 00:05:45,511 --> 00:05:49,615 You make, you know, like I said, over 30% of all toys. 131 00:05:49,615 --> 00:05:51,551 It's used in many, many applications, 132 00:05:51,551 --> 00:05:55,855 these harder plastics, but they're not recyclable. 133 00:05:55,855 --> 00:05:59,392 And then, we talked about this intermediate region. 134 00:05:59,392 --> 00:06:00,526 And this is where we ended. 135 00:06:00,526 --> 00:06:05,798 We talked about elastomers, and elastomers are in between. 136 00:06:05,798 --> 00:06:11,170 And so in an elastomer, you've got light cross-linking. 137 00:06:11,170 --> 00:06:13,940 And the cross-linking, like in slime, 138 00:06:13,940 --> 00:06:18,911 that cross-linking has a weaker hydrogen bond. 139 00:06:18,911 --> 00:06:19,579 All right? 140 00:06:19,579 --> 00:06:20,980 And remember, we talked about how 141 00:06:20,980 --> 00:06:23,816 that could lead to viscoelasticity, really 142 00:06:23,816 --> 00:06:26,686 cool stuff. 143 00:06:26,686 --> 00:06:32,325 In other cases, like in the case of the vulcanized rubber-- 144 00:06:32,325 --> 00:06:33,659 remember that, Charles Goodyear? 145 00:06:33,659 --> 00:06:35,128 That story from Wednesday? 146 00:06:35,128 --> 00:06:37,130 In that case, you put a covalent bond 147 00:06:37,130 --> 00:06:42,235 of sulfur between the strands, and that gave you 148 00:06:42,235 --> 00:06:47,874 a much stronger rubber that still had some elasticity. 149 00:06:47,874 --> 00:06:51,377 But now, the best analogy here is still the spaghetti. 150 00:06:51,377 --> 00:06:53,146 I keep coming back to it. 151 00:06:53,146 --> 00:06:54,814 I'm not letting go. 152 00:06:54,814 --> 00:06:56,115 Think about it. 153 00:06:56,115 --> 00:07:01,687 If I've got a bowl of spaghetti, and I pull on it, 154 00:07:01,687 --> 00:07:04,190 that's my plastic bag on the left. 155 00:07:04,190 --> 00:07:04,690 All right? 156 00:07:04,690 --> 00:07:05,591 That's my plastic bag. 157 00:07:05,591 --> 00:07:07,360 I pull on it, and those chains are all 158 00:07:07,360 --> 00:07:10,563 crumpled up and tangled, and I'm untangling them, 159 00:07:10,563 --> 00:07:12,832 and then I'm sliding them past each other, 160 00:07:12,832 --> 00:07:15,101 and pulling them until the whole thing rips. 161 00:07:15,101 --> 00:07:16,202 That's the bowl spaghetti. 162 00:07:16,202 --> 00:07:20,807 But now I've got this spaghetti that attaches every so often, 163 00:07:20,807 --> 00:07:22,942 one strand to another. 164 00:07:22,942 --> 00:07:23,576 Think about it. 165 00:07:23,576 --> 00:07:27,113 I've got a bowl spaghetti, but in each strand of spaghetti, 166 00:07:27,113 --> 00:07:29,148 there's like five places where it's attached 167 00:07:29,148 --> 00:07:30,416 to another strand of spaghetti. 168 00:07:30,416 --> 00:07:31,751 Now what happens? 169 00:07:31,751 --> 00:07:34,954 I can pull that as well. 170 00:07:34,954 --> 00:07:36,522 I can pull it because those spaghetti 171 00:07:36,522 --> 00:07:39,459 these are all curled up, and so there's 172 00:07:39,459 --> 00:07:42,929 some amount of pulling that I can do while they 173 00:07:42,929 --> 00:07:47,133 uncurl until those links take over, 174 00:07:47,133 --> 00:07:49,302 and I can't pull past them. 175 00:07:49,302 --> 00:07:50,002 All right? 176 00:07:50,002 --> 00:07:54,273 That's what the light cross-linking will do. 177 00:07:54,273 --> 00:07:56,808 And you say, well, if I had heavy cross-linking 178 00:07:56,808 --> 00:07:58,978 in the spaghetti, then the whole bowl of spaghetti 179 00:07:58,978 --> 00:08:01,013 wouldn't be very easy to move because I'm 180 00:08:01,013 --> 00:08:04,083 always up against all the links between them. 181 00:08:04,083 --> 00:08:05,251 All right? 182 00:08:05,251 --> 00:08:08,054 And so that's why these elastomers are so interesting, 183 00:08:08,054 --> 00:08:10,456 because they fall-- it's all interesting. 184 00:08:10,456 --> 00:08:11,924 But the elastomers fall in between, 185 00:08:11,924 --> 00:08:15,194 where there's some of that uncurling of the polymers 186 00:08:15,194 --> 00:08:17,930 until you get to a point where, depending on how much you've 187 00:08:17,930 --> 00:08:20,299 cross-linked, and the bonding of the cross-link, 188 00:08:20,299 --> 00:08:22,902 you're going to go up against the cross-linking. 189 00:08:22,902 --> 00:08:23,970 All right? 190 00:08:23,970 --> 00:08:26,572 And so these are used, so they're free to move. 191 00:08:26,572 --> 00:08:29,275 Now, must be above its glass transition temperature. 192 00:08:29,275 --> 00:08:31,210 I want to talk about that for a second 193 00:08:31,210 --> 00:08:32,578 because I did mention this, and I 194 00:08:32,578 --> 00:08:34,780 want to be sure that we all have a good sense of what 195 00:08:34,780 --> 00:08:35,881 that means. 196 00:08:35,881 --> 00:08:40,520 And so I wanted to-- taking this elastomer, 197 00:08:40,520 --> 00:08:42,755 say, what happens when you melt it? 198 00:08:42,755 --> 00:08:43,256 All right? 199 00:08:43,256 --> 00:08:49,195 And we drew this curve, but I want to go very carefully. 200 00:08:49,195 --> 00:08:50,196 This is the temperature. 201 00:08:50,196 --> 00:08:55,067 Oh, we love this curve, the molar volume. 202 00:08:55,067 --> 00:08:55,635 Right? 203 00:08:55,635 --> 00:09:00,806 And now up here, you've got your liquid. 204 00:09:00,806 --> 00:09:01,707 Right? 205 00:09:01,707 --> 00:09:02,942 We know that. 206 00:09:02,942 --> 00:09:06,612 And then here is the place where it would crystallize. 207 00:09:10,249 --> 00:09:11,417 Can a polymer crystallize? 208 00:09:11,417 --> 00:09:12,318 Sure. 209 00:09:12,318 --> 00:09:12,818 Right. 210 00:09:12,818 --> 00:09:14,387 If a polymer crystallized, then it 211 00:09:14,387 --> 00:09:16,889 would just be these strands in a crystal. 212 00:09:16,889 --> 00:09:17,957 What is a crystal? 213 00:09:17,957 --> 00:09:21,460 We know it's a repeating ordered structure. 214 00:09:21,460 --> 00:09:23,663 Yes, polymers can crystallize. 215 00:09:23,663 --> 00:09:26,899 But as we've talked about so often, what 216 00:09:26,899 --> 00:09:33,406 happens is because, like we talked about with silica, 217 00:09:33,406 --> 00:09:35,908 you know, you've got this very viscous, amorphous, 218 00:09:35,908 --> 00:09:37,577 can't find the crystal sites-- 219 00:09:37,577 --> 00:09:38,811 same with polymers. 220 00:09:38,811 --> 00:09:41,814 And so you get a glass. 221 00:09:41,814 --> 00:09:44,383 And then this was the Tg. 222 00:09:44,383 --> 00:09:45,518 Now, why am I showing this? 223 00:09:45,518 --> 00:09:48,387 Because with these strands-- 224 00:09:48,387 --> 00:09:49,522 and I want to show you. 225 00:09:49,522 --> 00:09:53,225 You know, we've drawn this before where often what you 226 00:09:53,225 --> 00:09:55,461 get in polymers is some degree. 227 00:09:55,461 --> 00:09:58,965 It's right here, some degree of crystallinity. 228 00:09:58,965 --> 00:10:00,132 Right? 229 00:10:00,132 --> 00:10:01,801 So what do I do? 230 00:10:01,801 --> 00:10:03,769 How do I do this? 231 00:10:03,769 --> 00:10:07,039 Well, you literally have both. 232 00:10:07,039 --> 00:10:07,873 All right. 233 00:10:07,873 --> 00:10:09,075 So I've drawn this already. 234 00:10:09,075 --> 00:10:13,245 So if I'm here on my polymer, then it 235 00:10:13,245 --> 00:10:15,581 might look like what I've drawn already on the board. 236 00:10:15,581 --> 00:10:16,749 Oh, I love doing this. 237 00:10:16,749 --> 00:10:19,452 And then there's the crystal, and then there's more. 238 00:10:22,121 --> 00:10:23,122 I've drawn this already. 239 00:10:23,122 --> 00:10:23,155 Right? 240 00:10:23,155 --> 00:10:25,024 You've got this crystalline region, 241 00:10:25,024 --> 00:10:29,028 so you've got the crystal, and here, 242 00:10:29,028 --> 00:10:31,831 because I'm below the glass transition temperature, 243 00:10:31,831 --> 00:10:34,767 this part here is an amorphous-- 244 00:10:34,767 --> 00:10:39,338 oh boy, it's kind of small, but this word says "amorphous"-- 245 00:10:39,338 --> 00:10:39,839 solid. 246 00:10:42,375 --> 00:10:44,043 It's a solid. 247 00:10:44,043 --> 00:10:46,812 That part is a solid because it's below the glass transition 248 00:10:46,812 --> 00:10:47,613 temperature. 249 00:10:47,613 --> 00:10:48,514 All right? 250 00:10:48,514 --> 00:10:51,250 OK, but now let's start heating this up. 251 00:10:51,250 --> 00:10:52,785 And as I get to the-- 252 00:10:52,785 --> 00:10:56,022 so now I'm going to get here. 253 00:10:56,022 --> 00:10:58,790 And what happens is it doesn't actually 254 00:10:58,790 --> 00:11:04,096 go straight to the full liquid. 255 00:11:04,096 --> 00:11:07,667 I mean, it's got this crystalline stuff in there, 256 00:11:07,667 --> 00:11:08,234 right? 257 00:11:08,234 --> 00:11:09,869 It's got these regions. 258 00:11:09,869 --> 00:11:14,874 This crystal has one melting point. 259 00:11:14,874 --> 00:11:16,976 Remember, the melting point of the crystal 260 00:11:16,976 --> 00:11:19,412 is the melting point of the crystal. 261 00:11:19,412 --> 00:11:21,380 It doesn't change. 262 00:11:21,380 --> 00:11:24,684 Glass transition temperature can be tuned. 263 00:11:24,684 --> 00:11:25,651 But this is a melting-- 264 00:11:25,651 --> 00:11:27,153 Now, so what happens. 265 00:11:27,153 --> 00:11:30,756 Well, what happens is there's more of a curvyness to this, 266 00:11:30,756 --> 00:11:34,160 and you might kind of have the shape look more like this. 267 00:11:38,330 --> 00:11:39,598 So what's happening? 268 00:11:39,598 --> 00:11:42,101 This just gets a little bit more at the detail 269 00:11:42,101 --> 00:11:43,769 of how a polymer would melt if it's 270 00:11:43,769 --> 00:11:45,137 got any crystalline regions. 271 00:11:45,137 --> 00:11:47,440 And as I've told you, very often it does. 272 00:11:47,440 --> 00:11:50,376 Not always-- it could have no crystalline regions. 273 00:11:50,376 --> 00:11:53,479 It could be totally amorphous, but I've drawn this enough 274 00:11:53,479 --> 00:11:56,182 that I wanted to explain this curve with that 275 00:11:56,182 --> 00:11:58,017 as our starting point. 276 00:11:58,017 --> 00:11:59,452 All right? 277 00:11:59,452 --> 00:12:01,854 And I've also talked about how the degree of crystallinity 278 00:12:01,854 --> 00:12:04,890 is so important for properties, and it can be controlled. 279 00:12:04,890 --> 00:12:05,958 So what's happening? 280 00:12:05,958 --> 00:12:09,195 Well, in this region here-- let's draw that picture. 281 00:12:09,195 --> 00:12:10,496 So now I'm in here. 282 00:12:10,496 --> 00:12:15,067 And what happens is I'm below Tm, but I'm above Tg. 283 00:12:15,067 --> 00:12:19,238 So that means that, literally in the same strand-- 284 00:12:19,238 --> 00:12:21,774 this is so cool. 285 00:12:21,774 --> 00:12:24,243 That looks the same. 286 00:12:24,243 --> 00:12:29,882 It's not supposed to be the same because now this is a liquid. 287 00:12:29,882 --> 00:12:39,391 This is a viscous liquid, and this is still a crystal. 288 00:12:39,391 --> 00:12:42,228 That's an xtol. 289 00:12:42,228 --> 00:12:44,563 I'm below Tm. 290 00:12:44,563 --> 00:12:46,732 So the crystalline region has not melted, 291 00:12:46,732 --> 00:12:50,102 but the rest of the polymer is above its glass transition. 292 00:12:50,102 --> 00:12:51,103 This is so cool. 293 00:12:51,103 --> 00:12:55,908 This one strand is both a solid and a liquid, one strand. 294 00:12:55,908 --> 00:12:58,277 That's so cool. 295 00:12:58,277 --> 00:12:59,812 That's in here. 296 00:12:59,812 --> 00:13:00,312 All right? 297 00:13:00,312 --> 00:13:04,083 And then I get over here, and now here-- 298 00:13:04,083 --> 00:13:05,818 OK, well, let's see. 299 00:13:05,818 --> 00:13:08,854 So now this is all liquid, and the crystalline part 300 00:13:08,854 --> 00:13:10,589 is starting to come apart. 301 00:13:10,589 --> 00:13:16,929 So crystal melts, xtol melts. 302 00:13:16,929 --> 00:13:18,664 All right, well, that sort of was 303 00:13:18,664 --> 00:13:21,867 supposed to be the remnants of a crystal. 304 00:13:21,867 --> 00:13:25,404 And then above Tm, the whole thing's a liquid, right? 305 00:13:25,404 --> 00:13:26,739 So that's kind of zooming in. 306 00:13:26,739 --> 00:13:28,407 I wanted to make sure that we understood 307 00:13:28,407 --> 00:13:31,110 this plot in the context of these polymers. 308 00:13:31,110 --> 00:13:33,145 And that also gives you a sense-- 309 00:13:33,145 --> 00:13:36,682 OK, now, that's this one strand. 310 00:13:36,682 --> 00:13:38,083 Now, I've got a bunch of strands. 311 00:13:38,083 --> 00:13:40,419 Did I connect them or not? 312 00:13:40,419 --> 00:13:43,455 And that adds the layer of what an elastomer is. 313 00:13:43,455 --> 00:13:43,956 Right? 314 00:13:43,956 --> 00:13:47,660 Because now you can imagine, is the elastomer 315 00:13:47,660 --> 00:13:49,795 above or below Tg? 316 00:13:49,795 --> 00:13:50,596 Where's is Tg? 317 00:13:50,596 --> 00:13:55,134 Are we above or below Tg when we bounce a ball? 318 00:13:55,134 --> 00:13:56,402 Right? 319 00:13:56,402 --> 00:14:01,040 How does that influence the properties of the ball? 320 00:14:01,040 --> 00:14:05,077 A rubber ball is likely cross-linked. 321 00:14:05,077 --> 00:14:08,848 And you can imagine that if you're below Tg, 322 00:14:08,848 --> 00:14:14,620 then all that amorphous part of the ball is a solid, 323 00:14:14,620 --> 00:14:16,488 so there's an elastic response. 324 00:14:16,488 --> 00:14:19,291 Sure, it could still bounce. 325 00:14:19,291 --> 00:14:23,829 If you're in this region, then that part of the ball 326 00:14:23,829 --> 00:14:25,731 is a liquid, but it's likely cross-linked 327 00:14:25,731 --> 00:14:28,100 so the ball doesn't fall apart. 328 00:14:28,100 --> 00:14:29,301 Right? 329 00:14:29,301 --> 00:14:31,003 So it's going to bounce differently. 330 00:14:31,003 --> 00:14:32,371 Right? 331 00:14:32,371 --> 00:14:34,740 It's going to bounce differently. 332 00:14:34,740 --> 00:14:37,009 OK, so anyway, I wanted to just go 333 00:14:37,009 --> 00:14:40,613 into detail of that to make sure that we feel our oneness. 334 00:14:40,613 --> 00:14:43,115 And I mean, you could add here. 335 00:14:43,115 --> 00:14:47,219 This is, because it's so important in just-- 336 00:14:47,219 --> 00:14:50,522 like I was saying, just in terms of what this material, how 337 00:14:50,522 --> 00:14:52,925 this material behaves, you could add the glass transition 338 00:14:52,925 --> 00:14:57,563 temperature, which, as we've already talked about, 339 00:14:57,563 --> 00:15:00,966 has a number of ways that it can be tuned. 340 00:15:00,966 --> 00:15:02,768 On the other hand, it may also be 341 00:15:02,768 --> 00:15:05,070 tuned by some of these other things that you do, 342 00:15:05,070 --> 00:15:08,440 but it's a very important part of the polymer property 343 00:15:08,440 --> 00:15:10,142 ecosystem. 344 00:15:10,142 --> 00:15:11,243 OK. 345 00:15:11,243 --> 00:15:11,911 Good. 346 00:15:11,911 --> 00:15:14,146 So that's the elastomer. 347 00:15:14,146 --> 00:15:15,781 Now, there's one more thing that we can 348 00:15:15,781 --> 00:15:17,683 do that I wanted to talk about. 349 00:15:17,683 --> 00:15:18,918 Oh, that's the picture. 350 00:15:18,918 --> 00:15:20,853 Yeah, I thought I'd show you another picture. 351 00:15:20,853 --> 00:15:24,123 So I'm not the only one that draws things like this. 352 00:15:24,123 --> 00:15:24,757 All right? 353 00:15:24,757 --> 00:15:27,660 OK, there's a nice one from Encyclopedia Britannica, 354 00:15:27,660 --> 00:15:32,331 and you can imagine this region being a solid down here, 355 00:15:32,331 --> 00:15:33,132 then a liquid. 356 00:15:33,132 --> 00:15:35,467 But that's still solid, and then that region 357 00:15:35,467 --> 00:15:38,103 melts all at once at Tm. 358 00:15:38,103 --> 00:15:39,571 The last thing that I want to add 359 00:15:39,571 --> 00:15:44,843 is another way that we have to control polymer properties, 360 00:15:44,843 --> 00:15:50,049 and it's another bullet here, and it'll be our last one. 361 00:15:50,049 --> 00:15:53,385 And it's really the composition and sequence. 362 00:15:56,889 --> 00:15:58,924 So what do I mean by that? 363 00:15:58,924 --> 00:16:04,763 Well, it turns out that-- 364 00:16:04,763 --> 00:16:07,599 remember when we did condensation. 365 00:16:07,599 --> 00:16:08,100 Right? 366 00:16:08,100 --> 00:16:11,103 Polymerization, a poly condensation it's called. 367 00:16:11,103 --> 00:16:12,604 The condensation polymerization. 368 00:16:12,604 --> 00:16:15,374 We had two different mers. 369 00:16:15,374 --> 00:16:17,009 And we could have picked the box. 370 00:16:17,009 --> 00:16:20,713 Remember, the box inside the mer could be different things. 371 00:16:20,713 --> 00:16:23,515 And then when we've done the radical initiation, 372 00:16:23,515 --> 00:16:25,718 we've just had one mer with the double bond. 373 00:16:25,718 --> 00:16:26,618 Right? 374 00:16:26,618 --> 00:16:28,287 Now, if you have one mer, then that's 375 00:16:28,287 --> 00:16:33,425 called a homopolymer, Homopoly. 376 00:16:33,425 --> 00:16:35,861 And if you have two, it's called a copolymer. 377 00:16:39,631 --> 00:16:43,669 The thing is that we actually can even make copolymers 378 00:16:43,669 --> 00:16:46,171 with both approaches. 379 00:16:46,171 --> 00:16:48,607 And not only that, but we're learning more and more 380 00:16:48,607 --> 00:16:53,946 how to control the sequence, and that's what this shows here. 381 00:16:53,946 --> 00:16:57,349 So I could have a polymer A. 382 00:16:57,349 --> 00:17:00,986 Let's say I have a-- 383 00:17:00,986 --> 00:17:02,955 yeah, I'll put it below this. 384 00:17:02,955 --> 00:17:08,493 Let's say I have a, you know, polymer, polyethylene, PE, 385 00:17:08,493 --> 00:17:10,863 which is-- oh, we know now how to draw these-- 386 00:17:10,863 --> 00:17:17,770 C, C, N. And then I've got the other one, which 387 00:17:17,770 --> 00:17:21,607 is PVC polyvinyl chloride, and that looks like this-- 388 00:17:21,607 --> 00:17:26,111 C-- all I've done here is swap out a hydrogen for a chlorine, 389 00:17:26,111 --> 00:17:29,448 and I've got a totally different polymer. 390 00:17:29,448 --> 00:17:30,349 All right? 391 00:17:30,349 --> 00:17:32,651 Some other end, OK? 392 00:17:32,651 --> 00:17:35,187 And an N, whatever. 393 00:17:35,187 --> 00:17:37,356 I can now alternate these. 394 00:17:37,356 --> 00:17:39,558 I can alternate them, and I could alternate them 395 00:17:39,558 --> 00:17:40,059 in this way. 396 00:17:40,059 --> 00:17:44,196 So PE might be my A, and PVC might be my B. 397 00:17:44,196 --> 00:17:46,532 And if I alternate them, we might-- you know, 398 00:17:46,532 --> 00:17:48,000 if it's like regular alternating, 399 00:17:48,000 --> 00:17:49,468 we might write PE-- 400 00:17:49,468 --> 00:17:53,705 this is how we'd write the copolymer-- a, PVC. 401 00:17:53,705 --> 00:17:56,675 All right, but you could also have it be random, 402 00:17:56,675 --> 00:17:58,043 so then you'd write PE-- 403 00:17:58,043 --> 00:18:01,814 you can take a guess-- r, PVC. 404 00:18:01,814 --> 00:18:03,215 Right? 405 00:18:03,215 --> 00:18:06,318 You could write a grafted version-- 406 00:18:06,318 --> 00:18:09,488 PE, g-- well, you get the point-- 407 00:18:09,488 --> 00:18:11,490 PVC, and so forth. 408 00:18:11,490 --> 00:18:14,359 What I mean when I write this is that I've 409 00:18:14,359 --> 00:18:17,963 taken these two polymers, and I've copolymerized. 410 00:18:17,963 --> 00:18:19,231 I mean, sorry, these two. 411 00:18:19,231 --> 00:18:20,899 Well yeah, these are the polymers. 412 00:18:20,899 --> 00:18:23,268 I'm taking the monomers, and I've 413 00:18:23,268 --> 00:18:26,004 made one polymer out of the two of them, 414 00:18:26,004 --> 00:18:27,873 but I've controlled the sequence. 415 00:18:27,873 --> 00:18:28,407 It's not-- 416 00:18:28,407 --> 00:18:29,942 Now, maybe it's not controlled. 417 00:18:29,942 --> 00:18:33,245 Maybe it's random right there. 418 00:18:33,245 --> 00:18:36,448 Or maybe I've figured out how to do this in a way 419 00:18:36,448 --> 00:18:39,618 that I have the backbone all one type, 420 00:18:39,618 --> 00:18:41,153 but I can have these side chains, 421 00:18:41,153 --> 00:18:43,889 the branches, another type. 422 00:18:43,889 --> 00:18:46,692 That's really powerful, it turns out. 423 00:18:46,692 --> 00:18:50,429 Or maybe you can control that I have a certain number of them, 424 00:18:50,429 --> 00:18:52,064 and then a certain number of the other, 425 00:18:52,064 --> 00:18:55,834 and this is called a block copolymer. 426 00:18:55,834 --> 00:18:57,469 And some of you may have heard of block 427 00:18:57,469 --> 00:19:01,707 copolymer chemistry, which is growing, 428 00:19:01,707 --> 00:19:04,810 is a very growing, very powerful field. 429 00:19:04,810 --> 00:19:06,945 Because when you make these blocks 430 00:19:06,945 --> 00:19:09,381 and you control their properties, 431 00:19:09,381 --> 00:19:11,550 you can imagine that you control all sorts of things 432 00:19:11,550 --> 00:19:14,586 about how that polymer behaves. 433 00:19:14,586 --> 00:19:19,057 Imagine you make something that bonds to A but not B. 434 00:19:19,057 --> 00:19:21,193 Like dissolves like. 435 00:19:21,193 --> 00:19:22,761 All right, we've been there. 436 00:19:22,761 --> 00:19:26,765 B is something that bonds to B but not A. OK, 437 00:19:26,765 --> 00:19:27,733 what's going to happen? 438 00:19:27,733 --> 00:19:30,736 They're stuck, but they're going to try 439 00:19:30,736 --> 00:19:34,606 to come together and stay apart in the same strand. 440 00:19:34,606 --> 00:19:36,675 All sorts of interesting things can happen. 441 00:19:36,675 --> 00:19:40,412 It can be engineered when you can control 442 00:19:40,412 --> 00:19:43,749 these blocks or these graphs. 443 00:19:43,749 --> 00:19:45,350 All right? 444 00:19:45,350 --> 00:19:47,853 So that's the last thing that we-- 445 00:19:47,853 --> 00:19:49,121 Here's an example. 446 00:19:49,121 --> 00:19:51,356 This is-- I was trying to look for a good exam-- 447 00:19:51,356 --> 00:19:53,358 here's something called-- 448 00:19:53,358 --> 00:19:54,526 actually, what is it called? 449 00:19:54,526 --> 00:19:55,661 Surlyn. 450 00:19:55,661 --> 00:19:56,795 Who comes up with that? 451 00:19:56,795 --> 00:19:59,064 I don't know why that's the name, but that's the name. 452 00:19:59,064 --> 00:20:02,901 It's the Surlyn resin, which is the ingredient that 453 00:20:02,901 --> 00:20:06,672 goes into the polymer, OK? 454 00:20:06,672 --> 00:20:08,674 And look at what it does. 455 00:20:08,674 --> 00:20:13,045 Oh, it provides clarity, toughness, versatility. 456 00:20:13,045 --> 00:20:17,216 Surlyn is a leading choice for food, cosmetic, medical device, 457 00:20:17,216 --> 00:20:23,288 skin, stretch, packaging, as well as golf balls. 458 00:20:23,288 --> 00:20:24,556 The tunability is enor-- 459 00:20:24,556 --> 00:20:25,057 why? 460 00:20:25,057 --> 00:20:27,092 What is Surlyn? 461 00:20:27,092 --> 00:20:30,128 Well, we don't know exactly because they won't tell us, 462 00:20:30,128 --> 00:20:32,798 but Surlyn is actually really cool. 463 00:20:32,798 --> 00:20:36,235 It's using-- OK, it's using-- 464 00:20:36,235 --> 00:20:37,035 where? 465 00:20:37,035 --> 00:20:38,270 Dah! 466 00:20:38,270 --> 00:20:39,071 Where did I put it? 467 00:20:39,071 --> 00:20:42,374 Composition, sequence-- it's using sequence 468 00:20:42,374 --> 00:20:48,046 to make a graft polymer where one type is 469 00:20:48,046 --> 00:20:50,349 going along the chain and the other type is coming out. 470 00:20:50,349 --> 00:20:54,052 But really importantly, the other type 471 00:20:54,052 --> 00:20:58,257 is made specifically to form ionic bonds. 472 00:20:58,257 --> 00:21:01,159 So here B is made so that it can form 473 00:21:01,159 --> 00:21:04,329 ionic bonds with other parts. 474 00:21:04,329 --> 00:21:09,668 Ionic, remember, that's basically by grafting, 475 00:21:09,668 --> 00:21:13,071 by creating a copolymer, where one type wants 476 00:21:13,071 --> 00:21:14,439 a form ionic bonds. 477 00:21:14,439 --> 00:21:15,507 I've cross-linked. 478 00:21:15,507 --> 00:21:18,810 I've made a cross-link built into the polymer itself. 479 00:21:18,810 --> 00:21:23,315 The cross-link is going to be linking the strands together, 480 00:21:23,315 --> 00:21:25,717 maybe within itself, maybe with other strands 481 00:21:25,717 --> 00:21:28,754 but with an ionic bond. 482 00:21:28,754 --> 00:21:29,454 Right? 483 00:21:29,454 --> 00:21:33,191 But I've done it all just built into the polymer. 484 00:21:33,191 --> 00:21:34,860 And that's why you can see here. 485 00:21:34,860 --> 00:21:39,031 Look at this it's an ethylene copolymer. 486 00:21:39,031 --> 00:21:39,531 All right? 487 00:21:39,531 --> 00:21:41,099 So ethylene is the backbone. 488 00:21:41,099 --> 00:21:44,002 The co is what's coming out of the side, 489 00:21:44,002 --> 00:21:47,806 and that's an ionic bond, so it's also called an ionomer. 490 00:21:47,806 --> 00:21:48,674 What's an ionomer? 491 00:21:48,674 --> 00:21:52,077 A polymer that has ionic cross-links, ionic bonding 492 00:21:52,077 --> 00:21:52,611 cross-links. 493 00:21:52,611 --> 00:21:53,712 And what's cool about that? 494 00:21:53,712 --> 00:22:00,385 Well, you get the whole world of ionic bonding now in the mix. 495 00:22:00,385 --> 00:22:02,287 And so what does that mean? 496 00:22:02,287 --> 00:22:05,691 Well, you could have it be very strong, golf ball. 497 00:22:05,691 --> 00:22:08,160 You can have it be thermally responsive. 498 00:22:08,160 --> 00:22:08,660 Right? 499 00:22:08,660 --> 00:22:12,464 You can tune at what temperature these bonds break. 500 00:22:12,464 --> 00:22:13,865 There's all sorts of flexibility, 501 00:22:13,865 --> 00:22:16,635 and you can see it right here in how they're marketing it. 502 00:22:16,635 --> 00:22:19,404 It can do almost anything. 503 00:22:19,404 --> 00:22:23,675 Another example of the copolymer-- 504 00:22:23,675 --> 00:22:25,977 I'll give you a couple examples of copolymers. 505 00:22:25,977 --> 00:22:32,651 This is one that you may have seen, maybe many of you 506 00:22:32,651 --> 00:22:34,252 experienced, you just don't remember. 507 00:22:34,252 --> 00:22:36,054 This is the diaper. 508 00:22:36,054 --> 00:22:36,588 Right? 509 00:22:36,588 --> 00:22:41,593 And so what what a diaper is is it's 510 00:22:41,593 --> 00:22:46,164 got this copolymer made out of acrylic acid. 511 00:22:46,164 --> 00:22:48,900 These are the monomers. 512 00:22:48,900 --> 00:22:50,369 Notice the double bonds? 513 00:22:50,369 --> 00:22:53,905 Oh, we're going to take advantage of those, 514 00:22:53,905 --> 00:22:55,640 and we're going to make a polymer, 515 00:22:55,640 --> 00:22:58,377 but we're going to do it in a controllable way. 516 00:22:58,377 --> 00:22:59,978 So we're going to take these two mers, 517 00:22:59,978 --> 00:23:02,814 and we're going to control how they come together. 518 00:23:02,814 --> 00:23:06,651 And very importantly in these kinds of materials-- 519 00:23:06,651 --> 00:23:09,988 they're broadly called hydrogels. 520 00:23:09,988 --> 00:23:13,058 These are materials that can absorb hundreds of times 521 00:23:13,058 --> 00:23:17,262 by weight, hundreds of times water into them. 522 00:23:17,262 --> 00:23:18,063 Why? 523 00:23:18,063 --> 00:23:24,302 Because in one of the copolymers you've got this sodium atom, 524 00:23:24,302 --> 00:23:26,371 and what happens is there's the dry state. 525 00:23:26,371 --> 00:23:29,975 It's all curled up and the chains want to be all together, 526 00:23:29,975 --> 00:23:31,443 but as soon as you introduce water, 527 00:23:31,443 --> 00:23:35,647 those sodiums like going into the water. 528 00:23:35,647 --> 00:23:36,348 And what happens? 529 00:23:36,348 --> 00:23:41,720 They leave behind this oxygen that really wants the water 530 00:23:41,720 --> 00:23:43,922 because it's a negative charge. 531 00:23:43,922 --> 00:23:46,158 And so you get a sodium ion going in the solution. 532 00:23:46,158 --> 00:23:49,594 You get the solution coming to the anion . 533 00:23:49,594 --> 00:23:54,499 And even more than that, now if the sodium leaves, 534 00:23:54,499 --> 00:23:55,801 then what happens? 535 00:23:55,801 --> 00:23:58,837 Well, what happens is all those negative charges are left 536 00:23:58,837 --> 00:24:01,173 and they repel each other. 537 00:24:01,173 --> 00:24:04,109 That's going to help this whole thing want to expand. 538 00:24:04,109 --> 00:24:05,243 Right? 539 00:24:05,243 --> 00:24:12,918 So that's a diaper, 2% of all landfill by the way. 540 00:24:12,918 --> 00:24:17,255 Now, so that's another example of a copolymer 541 00:24:17,255 --> 00:24:20,091 and a really interesting way of tuning the properties. 542 00:24:20,091 --> 00:24:23,662 In here it has to do with, what did we do? 543 00:24:23,662 --> 00:24:27,833 We tuned the ionic character of the backbone. 544 00:24:27,833 --> 00:24:30,168 We tuned the charge. 545 00:24:30,168 --> 00:24:32,904 We made it responsive it in terms of its charge 546 00:24:32,904 --> 00:24:35,841 to something, in this case water, the presence of water. 547 00:24:35,841 --> 00:24:37,042 That's cool. 548 00:24:37,042 --> 00:24:38,176 OK. 549 00:24:38,176 --> 00:24:42,214 Last one, and here I want to talk about mechanical strength. 550 00:24:42,214 --> 00:24:47,419 So this is the tensile strength. 551 00:24:47,419 --> 00:24:50,555 So how far could you pull this thing, 552 00:24:50,555 --> 00:24:53,391 this material before it breaks? 553 00:24:53,391 --> 00:24:56,495 And then here's the elongation until it breaks, 554 00:24:56,495 --> 00:24:57,496 so it gives you a sense. 555 00:24:57,496 --> 00:24:59,631 Now the tensile strength, this is how far can you 556 00:24:59,631 --> 00:25:01,566 pull it in the elastic regime? 557 00:25:01,566 --> 00:25:05,070 You can see that for steel it's really high, 558 00:25:05,070 --> 00:25:07,339 but you can't pull it very far before it breaks. 559 00:25:07,339 --> 00:25:08,206 We know that, right? 560 00:25:08,206 --> 00:25:12,344 So steel is really strong, but it's not very flexible. 561 00:25:12,344 --> 00:25:13,278 There is nylon. 562 00:25:13,278 --> 00:25:16,381 We did nylon, so it's kind of not nearly as strong, 563 00:25:16,381 --> 00:25:19,217 but it has a lot of elongation. 564 00:25:19,217 --> 00:25:20,051 There's fiberglass. 565 00:25:20,051 --> 00:25:23,688 This is plastic reinforced glass, 566 00:25:23,688 --> 00:25:26,157 where you can get a lot of strength, 567 00:25:26,157 --> 00:25:28,627 very little flexibility, more than steel, a little bit more 568 00:25:28,627 --> 00:25:29,361 than steel. 569 00:25:29,361 --> 00:25:30,729 Well actually, it was a lot more, 570 00:25:30,729 --> 00:25:33,832 but still it's only 3% or 4% elongation, 571 00:25:33,832 --> 00:25:35,333 and here's cellophane. 572 00:25:35,333 --> 00:25:40,605 That can be a naturally occurring polymer. 573 00:25:40,605 --> 00:25:42,908 You can also make it synthetically in the mix. 574 00:25:42,908 --> 00:25:44,676 And I want to point out nitrile. 575 00:25:44,676 --> 00:25:48,446 Nitrile rubber is a really interesting copolymer, 576 00:25:48,446 --> 00:25:51,283 and many of you may have seen or used-- if you're in a lab, 577 00:25:51,283 --> 00:25:53,351 you might use nitrile rubber gloves. 578 00:25:53,351 --> 00:25:56,688 You might have them at home at the sink. 579 00:25:56,688 --> 00:25:58,557 And one of the advantages of nitrile rubber 580 00:25:58,557 --> 00:26:03,161 is, again, this enormous tunability by just picking 581 00:26:03,161 --> 00:26:04,563 how you copolymerized. 582 00:26:04,563 --> 00:26:07,699 How much of one did you put in the other? 583 00:26:07,699 --> 00:26:12,804 And this is-- maybe I'll use this board here 584 00:26:12,804 --> 00:26:15,941 because it's a really cool copolymer, where you're 585 00:26:15,941 --> 00:26:19,544 putting in acrylonitrile. 586 00:26:19,544 --> 00:26:20,912 So here's what this looks like. 587 00:26:20,912 --> 00:26:28,987 So you put your CH2, your CH, your double bond your CH, 588 00:26:28,987 --> 00:26:32,390 your CH2, and there it is. 589 00:26:32,390 --> 00:26:34,759 And that's going to repeat some number of units 590 00:26:34,759 --> 00:26:40,432 that you control because it's a block copolymer before you 591 00:26:40,432 --> 00:26:43,602 put this one in, and here's the kick. 592 00:26:43,602 --> 00:26:47,539 It's got a triple bond nitrogen on it. 593 00:26:47,539 --> 00:26:50,742 And that's going to go a certain m. 594 00:26:50,742 --> 00:26:51,242 All right? 595 00:26:51,242 --> 00:26:54,546 Now, that comes from acrylonitrile and butadiene, 596 00:26:54,546 --> 00:26:58,049 but again, it's the synthesis to make the copolymer. 597 00:26:58,049 --> 00:27:00,619 It's the sequence. 598 00:27:00,619 --> 00:27:01,853 I keep on forgetting where. 599 00:27:01,853 --> 00:27:02,687 It's up there. 600 00:27:02,687 --> 00:27:06,524 It's the composition, the architecture. 601 00:27:06,524 --> 00:27:08,026 How did I put those copoly-- 602 00:27:08,026 --> 00:27:09,728 if you do this in the right way, it's 603 00:27:09,728 --> 00:27:12,063 the amount of the acrylonitrile that you put 604 00:27:12,063 --> 00:27:15,467 in will control the strength. 605 00:27:15,467 --> 00:27:18,203 It'll make it stronger and stronger, 606 00:27:18,203 --> 00:27:21,072 because you've got this really nice, strong bond in here, 607 00:27:21,072 --> 00:27:23,141 and this will give the material a lot of strength. 608 00:27:23,141 --> 00:27:26,277 So that's why you can go up to, you know, fairly reasonable. 609 00:27:26,277 --> 00:27:29,748 But then, how much of this I put in 610 00:27:29,748 --> 00:27:31,883 is going to determine how far you can stretch it, 611 00:27:31,883 --> 00:27:33,652 and so you balance those. 612 00:27:33,652 --> 00:27:38,023 And you can make a whole bunch of kinds of nitrile rubber. 613 00:27:38,023 --> 00:27:40,925 OK, so I hope this has given you some examples 614 00:27:40,925 --> 00:27:44,696 of the tunability of polymers. 615 00:27:44,696 --> 00:27:47,499 And you know, if you take the bigger picture-- 616 00:27:47,499 --> 00:27:48,900 and this is a little hard to read. 617 00:27:48,900 --> 00:27:49,801 You know, it will be in the slides, 618 00:27:49,801 --> 00:27:51,536 so you can look up this paper here. 619 00:27:51,536 --> 00:27:53,838 It was published in Science a few years ago-- 620 00:27:53,838 --> 00:27:55,707 and you look at the fracture toughness 621 00:27:55,707 --> 00:27:57,876 with the yield strength. 622 00:27:57,876 --> 00:27:58,543 So what is that? 623 00:27:58,543 --> 00:27:59,577 Well yield strength is-- 624 00:27:59,577 --> 00:28:01,212 Remember, we know that because it's 625 00:28:01,212 --> 00:28:04,115 when you're in the elastic region, and you're pulling, 626 00:28:04,115 --> 00:28:06,618 and then you yield to plastic deformation. 627 00:28:06,618 --> 00:28:07,318 Right? 628 00:28:07,318 --> 00:28:08,553 That's the yield strength. 629 00:28:08,553 --> 00:28:10,689 Now what about fracture toughness? 630 00:28:10,689 --> 00:28:12,757 Well, that's if you start a crack, 631 00:28:12,757 --> 00:28:15,460 does the thing tend to crack more or not? 632 00:28:15,460 --> 00:28:17,829 That's the fracture toughness basically, right? 633 00:28:17,829 --> 00:28:19,864 And so you could put materials down on this plot. 634 00:28:19,864 --> 00:28:20,699 You've got ceramics. 635 00:28:20,699 --> 00:28:22,000 You've got concrete down here. 636 00:28:22,000 --> 00:28:24,769 You've got-- so you're not going to be. 637 00:28:24,769 --> 00:28:28,540 So the polymers sit here. 638 00:28:28,540 --> 00:28:29,040 All right? 639 00:28:29,040 --> 00:28:31,443 Here's metals, and alloys, metallic gases. 640 00:28:31,443 --> 00:28:32,977 You can look at this on your own, 641 00:28:32,977 --> 00:28:35,480 and look at each one of those, but I just want to point out, 642 00:28:35,480 --> 00:28:37,849 polymers have a fairly wide range, 643 00:28:37,849 --> 00:28:41,953 but there's so much interest in going beyond. 644 00:28:41,953 --> 00:28:44,556 There's a lot of interest in using polymers 645 00:28:44,556 --> 00:28:45,990 in many other applications. 646 00:28:45,990 --> 00:28:48,927 We can't get there yet because we can't push it 647 00:28:48,927 --> 00:28:52,197 out here or maybe out here. 648 00:28:52,197 --> 00:28:56,167 We still need to figure out how to tune it more. 649 00:28:56,167 --> 00:28:59,104 We've got all these ways to control the properties, 650 00:28:59,104 --> 00:29:02,340 and we're still only at the very beginning of understanding 651 00:29:02,340 --> 00:29:03,641 how to engineer polymers. 652 00:29:06,411 --> 00:29:09,848 Now, there is no better way to make that point clear 653 00:29:09,848 --> 00:29:11,549 than to look at nature. 654 00:29:11,549 --> 00:29:12,317 All right? 655 00:29:12,317 --> 00:29:14,319 And I already showed you the tree 656 00:29:14,319 --> 00:29:18,623 and you know, the examples of nature as a polymer engineer. 657 00:29:18,623 --> 00:29:23,328 I want to talk about that a little more because nature 658 00:29:23,328 --> 00:29:27,132 is not just a polymer engineer. 659 00:29:27,132 --> 00:29:29,234 Nature-- I'm going to write this down nature. 660 00:29:29,234 --> 00:29:34,472 Nature is a polymer engineer gone wild, 661 00:29:34,472 --> 00:29:35,540 and I'll show you why. 662 00:29:35,540 --> 00:29:36,307 Polymer engineer. 663 00:29:45,416 --> 00:29:49,154 Humans, what can humans do? 664 00:29:49,154 --> 00:29:53,458 Well, we are a natural polymer engineer material, but what can 665 00:29:53,458 --> 00:29:56,528 we make with all of what I've just shown you? 666 00:29:56,528 --> 00:29:58,596 What can we make? 667 00:29:58,596 --> 00:30:02,500 I can put like one, or maybe two, 668 00:30:02,500 --> 00:30:04,536 or if you really go into the research, 669 00:30:04,536 --> 00:30:08,640 you get three mers, trying to control 670 00:30:08,640 --> 00:30:10,441 where they are in the chain. 671 00:30:10,441 --> 00:30:10,942 All right? 672 00:30:10,942 --> 00:30:12,243 You've got three, maybe two. 673 00:30:12,243 --> 00:30:14,512 We have really two in most materials. 674 00:30:14,512 --> 00:30:17,081 Copolymer-- we're so proud of this nitrile. 675 00:30:17,081 --> 00:30:22,754 Two mers, and we control them, and we make rubber sheets. 676 00:30:22,754 --> 00:30:26,024 But nature-- but then they're everywhere. 677 00:30:26,024 --> 00:30:28,827 They're everywhere is just that. 678 00:30:28,827 --> 00:30:29,727 All right? 679 00:30:29,727 --> 00:30:31,296 So nature can have-- 680 00:30:31,296 --> 00:30:47,111 so humans have the same functional group every stop. 681 00:30:47,111 --> 00:30:47,912 All right? 682 00:30:47,912 --> 00:30:49,147 OK, that's one mer. 683 00:30:49,147 --> 00:30:53,551 Maybe I've got two, maybe two or three. 684 00:30:53,551 --> 00:31:06,731 Nature can have different groups, and here's the key. 685 00:31:06,731 --> 00:31:08,566 It can have them everywhere. 686 00:31:11,369 --> 00:31:13,171 OK? 687 00:31:13,171 --> 00:31:22,647 So what I have is I have many, many more possibilities. 688 00:31:22,647 --> 00:31:24,315 I mean, we have these possibilities too, 689 00:31:24,315 --> 00:31:27,018 we just can't control it. 690 00:31:27,018 --> 00:31:27,652 All right? 691 00:31:27,652 --> 00:31:30,154 So if I look at-- like let's go back 692 00:31:30,154 --> 00:31:32,223 to condensation polymerization because this 693 00:31:32,223 --> 00:31:34,659 is what nature does. 694 00:31:34,659 --> 00:31:38,129 So this was what I drew for you on Monday. 695 00:31:38,129 --> 00:31:40,198 There's a dicarboxylic acid. 696 00:31:40,198 --> 00:31:42,233 Here we're making nylon. 697 00:31:42,233 --> 00:31:44,002 And a diamine, and we're making polyamide. 698 00:31:44,002 --> 00:31:45,637 And remember, the box-- 699 00:31:45,637 --> 00:31:47,972 in nylon 66, the box is 6 carbon atoms. 700 00:31:47,972 --> 00:31:50,875 I call that boring. 701 00:31:50,875 --> 00:31:53,044 It's at six carbon atoms from hydrogen, 702 00:31:53,044 --> 00:31:54,312 but that's kind of boring. 703 00:31:54,312 --> 00:31:59,050 But in nature, this box is an amino acid. 704 00:31:59,050 --> 00:32:01,452 That's much more interesting. 705 00:32:01,452 --> 00:32:03,788 That's much more interesting because if you 706 00:32:03,788 --> 00:32:08,126 look at an amino acid, and this is an amino acid-- 707 00:32:08,126 --> 00:32:09,127 why is it an amino acid? 708 00:32:09,127 --> 00:32:12,130 Well, it's got an amine group here and a carboxylic acid 709 00:32:12,130 --> 00:32:15,333 there, so it's an amino acid. 710 00:32:15,333 --> 00:32:18,536 But see, here's the thing, R. 711 00:32:18,536 --> 00:32:22,941 This is nature's "the box." 712 00:32:22,941 --> 00:32:24,208 We can put six carbons in. 713 00:32:24,208 --> 00:32:25,543 We're really proud of ourselves. 714 00:32:25,543 --> 00:32:32,050 Nature can put almost anything it wants for R. All right? 715 00:32:32,050 --> 00:32:43,261 So R, just to spell this out, is nature's choice, 716 00:32:43,261 --> 00:32:44,662 and I'll show you what it chooses. 717 00:32:44,662 --> 00:32:52,737 Nature's choice-- because there are hundreds of amino acids, 718 00:32:52,737 --> 00:33:01,245 and this R group can do many things, but just 20 is all we 719 00:33:01,245 --> 00:33:02,914 need to make proteins. 720 00:33:02,914 --> 00:33:06,417 Most proteins are made out of just essentially 20. 721 00:33:06,417 --> 00:33:08,219 But if you do the math-- 722 00:33:08,219 --> 00:33:10,855 I think I have the math here-- 723 00:33:10,855 --> 00:33:13,291 and you take-- let's see. 724 00:33:13,291 --> 00:33:17,862 OK, if I take two amino acids. 725 00:33:17,862 --> 00:33:19,330 Let's say I take two amino acids, 726 00:33:19,330 --> 00:33:21,065 so I've got two different R's. 727 00:33:21,065 --> 00:33:30,475 Two amino acids, and I've got a length is 2, 728 00:33:30,475 --> 00:33:32,610 and this is called the dipeptide. 729 00:33:32,610 --> 00:33:34,145 I'll tell you why in a sec. 730 00:33:34,145 --> 00:33:36,581 OK, but let's compare this now. 731 00:33:36,581 --> 00:33:41,586 Now I've got 20 amino acids, and I just told you that 20 is what 732 00:33:41,586 --> 00:33:46,057 nature makes most proteins out of, 20 different R's. 733 00:33:46,057 --> 00:33:47,225 There's an amino acid. 734 00:33:47,225 --> 00:33:49,494 R is nature's choice. 735 00:33:49,494 --> 00:33:56,901 But see, if I've got 20, then I've got 20 squared 736 00:33:56,901 --> 00:33:59,904 equals 400 dipeptides. 737 00:33:59,904 --> 00:34:02,540 I've made a two-unit polymer. 738 00:34:02,540 --> 00:34:03,341 It's not a polymer. 739 00:34:03,341 --> 00:34:06,077 It's a peptide. 740 00:34:06,077 --> 00:34:09,347 But now, what if I take the 20, and I've got-- 741 00:34:09,347 --> 00:34:18,456 but now I've got, let's say, 1,000 units long, 742 00:34:18,456 --> 00:34:25,396 then I would have 20 to the 1,000 possibilities, which is 743 00:34:25,396 --> 00:34:32,170 10 to the 1,300 combinations. 744 00:34:32,170 --> 00:34:39,043 So 10 to the 1,300 possibilities-- 745 00:34:39,043 --> 00:34:41,579 that's because there's 1,000 units, 746 00:34:41,579 --> 00:34:43,547 and I've got 20 amino acids, right? 747 00:34:43,547 --> 00:34:46,684 But now you think, how do you possibly 748 00:34:46,684 --> 00:34:48,853 think about what to do? 749 00:34:48,853 --> 00:34:51,155 That is nature. 750 00:34:51,155 --> 00:34:54,324 It's had 1 billion years, and it's 751 00:34:54,324 --> 00:34:57,361 given us the world that we live in, that we know. 752 00:34:57,361 --> 00:35:01,866 It's messed with these combinations 753 00:35:01,866 --> 00:35:04,435 in a way that's impossible for us to even understand. 754 00:35:04,435 --> 00:35:07,905 That's why I say, nature is a polymer engineer gone wild. 755 00:35:07,905 --> 00:35:13,544 It's got almost limitless flexibility, and it's used it. 756 00:35:13,544 --> 00:35:14,512 Right? 757 00:35:14,512 --> 00:35:16,781 Now, how does nature make its polymer? 758 00:35:16,781 --> 00:35:18,516 Well, its condensation polymerization. 759 00:35:18,516 --> 00:35:21,953 This is just what we saw. 760 00:35:21,953 --> 00:35:23,621 Look at that. 761 00:35:23,621 --> 00:35:25,156 This is what an amino acid is. 762 00:35:25,156 --> 00:35:27,325 It's got this carboxylic, so there's 763 00:35:27,325 --> 00:35:30,228 the OH group that can condense with the H 764 00:35:30,228 --> 00:35:32,430 here and form the link. 765 00:35:32,430 --> 00:35:33,264 There it is. 766 00:35:33,264 --> 00:35:35,199 That's called a peptide bond. 767 00:35:35,199 --> 00:35:37,435 When two amino acids come together, that's a CN. 768 00:35:37,435 --> 00:35:39,003 That's a peptide bond. 769 00:35:39,003 --> 00:35:40,271 Right? 770 00:35:40,271 --> 00:35:41,806 But look, this had R1. 771 00:35:41,806 --> 00:35:49,814 That had R2, and I've got 20 different amino acids 772 00:35:49,814 --> 00:35:50,748 to choose from. 773 00:35:50,748 --> 00:35:53,751 The possibilities are endless. 774 00:35:53,751 --> 00:36:01,759 So the protein synthesis is condensation pol-- 775 00:36:01,759 --> 00:36:02,426 you knew that. 776 00:36:02,426 --> 00:36:04,562 You knew it couldn't be anything else because there 777 00:36:04,562 --> 00:36:06,063 is no double bond. 778 00:36:06,063 --> 00:36:09,467 Where would I have done a radical initiation 779 00:36:09,467 --> 00:36:11,536 with these amino acids? 780 00:36:11,536 --> 00:36:14,505 If I'm nature, I've got to make it with condensation 781 00:36:14,505 --> 00:36:15,706 polymerization. 782 00:36:15,706 --> 00:36:18,476 That's how we are made. 783 00:36:18,476 --> 00:36:22,180 OK, now, so just to give you a sense, so the R-- 784 00:36:22,180 --> 00:36:24,015 I'm not going to go through this, obviously. 785 00:36:24,015 --> 00:36:25,183 I'm just giving this to you as if you 786 00:36:25,183 --> 00:36:26,284 want to read more about it. 787 00:36:26,284 --> 00:36:29,687 There's some wonderful charts here, 20 amino acids, 788 00:36:29,687 --> 00:36:33,191 the 20 that are most common and that nature puts together. 789 00:36:33,191 --> 00:36:34,859 And what they've done that's really nice 790 00:36:34,859 --> 00:36:36,360 here is they've grouped them, right? 791 00:36:36,360 --> 00:36:39,897 Because what did nature choose to do? 792 00:36:39,897 --> 00:36:43,367 How is it most utilizing the properties, the tunability 793 00:36:43,367 --> 00:36:44,268 in these amino acids. 794 00:36:44,268 --> 00:36:45,903 I said there were 20, but most proteins are-- 795 00:36:45,903 --> 00:36:47,271 I'd say there are hundreds, but most proteins 796 00:36:47,271 --> 00:36:48,673 are made from these 20. 797 00:36:48,673 --> 00:36:54,679 It gives you the tunability in having maybe non-polar groups. 798 00:36:54,679 --> 00:36:55,313 Right? 799 00:36:55,313 --> 00:36:57,582 So it might be then hydrophobic. 800 00:36:57,582 --> 00:37:03,754 Polar groups, hydrophilic-- maybe you can put, 801 00:37:03,754 --> 00:37:08,159 nature can put, R groups in there that maybe have a charge, 802 00:37:08,159 --> 00:37:10,695 or that lose or take an ion. 803 00:37:10,695 --> 00:37:13,631 All right, so it can play with the charge, 804 00:37:13,631 --> 00:37:15,533 and it has done all of that. 805 00:37:15,533 --> 00:37:17,935 It can have groups that become acids, that make something 806 00:37:17,935 --> 00:37:20,204 acidic, and so forth. 807 00:37:20,204 --> 00:37:22,707 OK, so that's cool. 808 00:37:22,707 --> 00:37:24,942 What has nature done? 809 00:37:24,942 --> 00:37:28,913 Well, I got to show you this spider because-- 810 00:37:28,913 --> 00:37:30,748 and if you're interested, Professor Bueller 811 00:37:30,748 --> 00:37:33,184 does some wonderful work on spider silk-- 812 00:37:33,184 --> 00:37:37,655 because I think this is a great example of something 813 00:37:37,655 --> 00:37:43,794 that nature can do that gives us a sense of how far away we are. 814 00:37:43,794 --> 00:37:49,934 Like I said, we're very proud of this, and we want to do more. 815 00:37:49,934 --> 00:37:52,837 And so we take our two mers, and we mix them together, 816 00:37:52,837 --> 00:37:54,372 and we make branches, and maybe we're 817 00:37:54,372 --> 00:37:56,607 going to try to add a third. 818 00:37:56,607 --> 00:38:00,144 Meanwhile, nature has had a lot more flexibility and a lot more 819 00:38:00,144 --> 00:38:00,845 time. 820 00:38:00,845 --> 00:38:01,579 What can it do? 821 00:38:01,579 --> 00:38:03,581 Well, here's spider silk. 822 00:38:03,581 --> 00:38:05,349 Now, this is a spider. 823 00:38:05,349 --> 00:38:10,254 Spider is an incredible polymer synthesis machine. 824 00:38:10,254 --> 00:38:12,623 It's an incredible polymer synthesis machine. 825 00:38:12,623 --> 00:38:14,725 And here it is weaving a web, and I love this-- 826 00:38:14,725 --> 00:38:15,092 [MUSIC PLAYING] 827 00:38:15,092 --> 00:38:16,460 --because I think it's so cool. 828 00:38:16,460 --> 00:38:18,562 OK, there's music, I guess. 829 00:38:18,562 --> 00:38:20,765 I forgot about that, and there it is. 830 00:38:20,765 --> 00:38:21,599 Now watch. 831 00:38:21,599 --> 00:38:25,202 Out of here, this is the back of the spider. 832 00:38:25,202 --> 00:38:26,971 There it is right there. 833 00:38:26,971 --> 00:38:28,239 It's making protein. 834 00:38:28,239 --> 00:38:31,042 That's called spider silk, but these are proteins. 835 00:38:31,042 --> 00:38:32,209 These are polymers. 836 00:38:32,209 --> 00:38:35,513 It is doing condensation polymerization right there, 837 00:38:35,513 --> 00:38:38,015 and then there's all sorts of structural stuff that it does. 838 00:38:38,015 --> 00:38:38,482 Right? 839 00:38:38,482 --> 00:38:39,684 It's got a specialized hook. 840 00:38:39,684 --> 00:38:40,584 It knows how to step. 841 00:38:40,584 --> 00:38:41,686 It creates-- look at that. 842 00:38:41,686 --> 00:38:43,721 There's a branch place where it knows to put it. 843 00:38:43,721 --> 00:38:44,221 Right? 844 00:38:44,221 --> 00:38:47,558 It's already created the glue. 845 00:38:47,558 --> 00:38:50,995 So not only is it putting this spider silk out there, 846 00:38:50,995 --> 00:38:54,031 but it can put other types of polymer 847 00:38:54,031 --> 00:38:55,199 depending on what it needs. 848 00:38:55,199 --> 00:38:58,002 Does it need something really sticky, less sticky? 849 00:38:58,002 --> 00:38:58,536 Right? 850 00:38:58,536 --> 00:39:00,037 And so there it is weaving its web, 851 00:39:00,037 --> 00:39:02,873 and it's generating this polymer on the fly. 852 00:39:02,873 --> 00:39:04,975 It's doing condensation polymerization. 853 00:39:04,975 --> 00:39:07,311 Now a couple properties about spider silk. 854 00:39:07,311 --> 00:39:10,348 OK, so here we go. 855 00:39:10,348 --> 00:39:10,981 Let's see. 856 00:39:10,981 --> 00:39:19,590 So spider silk, this is just one example of what nature can do. 857 00:39:19,590 --> 00:39:21,592 It's five times stronger than steel. 858 00:39:27,198 --> 00:39:29,567 Remember the mechanical strength chart, 859 00:39:29,567 --> 00:39:31,502 nothing was stronger than steel. 860 00:39:31,502 --> 00:39:34,405 Spider silk is five times stronger. 861 00:39:34,405 --> 00:39:39,009 Just to give you sense, the example, I found that I like. 862 00:39:39,009 --> 00:39:42,012 If you had a spider silk that was a pencil width, 863 00:39:42,012 --> 00:39:45,383 and you made a strand, it would stop a Boeing 747 in midair. 864 00:39:45,383 --> 00:39:47,585 That's how strong it is. 865 00:39:47,585 --> 00:39:50,254 Oh, it keeps strength-- 866 00:39:50,254 --> 00:40:01,899 here's another thing-- below 40 degrees C. We can't do that. 867 00:40:01,899 --> 00:40:04,935 Just take a rubber ball and put it at that low of a temperature 868 00:40:04,935 --> 00:40:05,803 and try to bounce it. 869 00:40:05,803 --> 00:40:07,171 It's going to shatter. 870 00:40:07,171 --> 00:40:07,705 Right? 871 00:40:07,705 --> 00:40:11,409 Spider silk can keep that strength and not break. 872 00:40:11,409 --> 00:40:14,945 Its elastic, so it's got-- 873 00:40:14,945 --> 00:40:19,717 throughout all of this, it's got an elastic property of 4x, 874 00:40:19,717 --> 00:40:22,186 so it can be stretched to four times its original strength. 875 00:40:26,157 --> 00:40:27,725 Compare that with nitrile. 876 00:40:27,725 --> 00:40:31,162 Nitrile rubber could also go to very, very 877 00:40:31,162 --> 00:40:34,432 high elastic elongation. 878 00:40:34,432 --> 00:40:34,932 All right? 879 00:40:34,932 --> 00:40:37,601 So if you go back to nitrile-- 880 00:40:37,601 --> 00:40:39,437 here it is in the table. 881 00:40:39,437 --> 00:40:41,338 We're very happy with this, but this only 882 00:40:41,338 --> 00:40:44,008 had two monomers to play with. 883 00:40:44,008 --> 00:40:44,542 Right? 884 00:40:44,542 --> 00:40:46,544 We played with two monomers, and we got to here, 885 00:40:46,544 --> 00:40:49,580 and look at the sacrifice in the strength. 886 00:40:49,580 --> 00:40:52,082 Look at how much we had to sacrifice strength. 887 00:40:52,082 --> 00:40:53,918 Spiders don't have to do that. 888 00:40:53,918 --> 00:40:57,488 OK, and oh, here's the last one. 889 00:40:57,488 --> 00:41:05,362 Fully recycles-- now the thing is that this is actually 890 00:41:05,362 --> 00:41:06,564 kind of incredible. 891 00:41:06,564 --> 00:41:09,800 Spider webs get dusty. 892 00:41:09,800 --> 00:41:12,336 They lose their stickiness. 893 00:41:12,336 --> 00:41:16,307 So many spiders know this and just simply 894 00:41:16,307 --> 00:41:18,976 have to weave a new web every day, 895 00:41:18,976 --> 00:41:21,378 but they don't leave the old web there. 896 00:41:21,378 --> 00:41:26,550 They actually eat it, and they fully recycle it, fully. 897 00:41:26,550 --> 00:41:27,051 Right? 898 00:41:27,051 --> 00:41:30,154 They eat the web, fully recycle it, process it, 899 00:41:30,154 --> 00:41:34,058 have this condensation polymerization work, 900 00:41:34,058 --> 00:41:36,093 and make a new one the next day. 901 00:41:36,093 --> 00:41:38,362 All right? 902 00:41:38,362 --> 00:41:41,866 So we don't come close to this spider. 903 00:41:41,866 --> 00:41:46,570 We don't even come anywhere near it in terms of where we are. 904 00:41:46,570 --> 00:41:48,906 Even though I gave you all these wonderful things 905 00:41:48,906 --> 00:41:50,407 that we're doing with engineering, 906 00:41:50,407 --> 00:41:53,777 we still have so far that we could go if we could just 907 00:41:53,777 --> 00:41:56,313 figure out how nature works. 908 00:41:56,313 --> 00:41:57,915 OK? 909 00:41:57,915 --> 00:42:00,751 And this gets me to what we do, and so I've 910 00:42:00,751 --> 00:42:02,720 got my "why this matters" now. 911 00:42:02,720 --> 00:42:07,458 And so a spider eats its web, fully recycles it, 912 00:42:07,458 --> 00:42:09,193 spins a new web the next day. 913 00:42:09,193 --> 00:42:14,598 Here's what we do with our polymers. 914 00:42:14,598 --> 00:42:17,635 I already talked about the oceans. 915 00:42:17,635 --> 00:42:20,271 Here's what we do on land. 916 00:42:20,271 --> 00:42:21,572 These are tires. 917 00:42:21,572 --> 00:42:23,374 Now, tires are very difficult to recycle. 918 00:42:23,374 --> 00:42:23,874 Why? 919 00:42:23,874 --> 00:42:26,243 Because they're too vulcanized. 920 00:42:26,243 --> 00:42:27,578 They've got too much cross-link. 921 00:42:27,578 --> 00:42:30,381 Remember, if the cross-link density is too strong, 922 00:42:30,381 --> 00:42:35,920 which you need to make a tire, then you can't recycle it. 923 00:42:35,920 --> 00:42:37,755 And in fact, what happens is-- 924 00:42:37,755 --> 00:42:39,490 and there's a tire mound. 925 00:42:39,490 --> 00:42:41,258 Here's it is from a satellite picture. 926 00:42:41,258 --> 00:42:43,093 Those are tires. 927 00:42:43,093 --> 00:42:44,128 Those are tire mounds. 928 00:42:44,128 --> 00:42:45,896 Here's what happens when one catches fire. 929 00:42:45,896 --> 00:42:47,998 Here's what happens when many catch fire. 930 00:42:47,998 --> 00:42:48,966 All right? 931 00:42:48,966 --> 00:42:53,504 It's actually a very hard fire to control once they catch. 932 00:42:53,504 --> 00:42:55,773 But we don't really know how to recycle them 933 00:42:55,773 --> 00:42:57,441 well yet. 934 00:42:57,449 --> 00:43:00,411 What can we do? 935 00:43:00,411 --> 00:43:03,581 On the science and engineering side, the fact of the matter 936 00:43:03,581 --> 00:43:05,349 is there is a lot of work to do, but there 937 00:43:05,349 --> 00:43:06,717 are promising directions. 938 00:43:06,717 --> 00:43:09,253 So I wanted to leave you with a little bit of that, 939 00:43:09,253 --> 00:43:10,988 and I'm not going to go into great detail. 940 00:43:10,988 --> 00:43:13,157 I just want to show you, and there's references here 941 00:43:13,157 --> 00:43:13,724 you can look. 942 00:43:13,724 --> 00:43:16,160 This was published a couple of years ago in Nature. 943 00:43:16,160 --> 00:43:21,165 One direction is in self-healing polymers. 944 00:43:21,165 --> 00:43:22,733 This is a very exciting direction. 945 00:43:22,733 --> 00:43:23,534 What can we do? 946 00:43:23,534 --> 00:43:26,670 Well, we can go away from this whole single-use idea 947 00:43:26,670 --> 00:43:28,772 and make stuff last longer. 948 00:43:28,772 --> 00:43:29,273 All right? 949 00:43:29,273 --> 00:43:31,308 So that would be beneficial. 950 00:43:31,308 --> 00:43:33,811 Maybe not if it ends up in the ocean, 951 00:43:33,811 --> 00:43:38,015 but in terms of just how long we can use these materials. 952 00:43:38,015 --> 00:43:40,784 So one direction is, well, you've got these polymer 953 00:43:40,784 --> 00:43:43,253 networks, and you incorporate little gels, little beads 954 00:43:43,253 --> 00:43:46,156 in here, but the beads don't open up 955 00:43:46,156 --> 00:43:48,792 until a crack comes along. 956 00:43:48,792 --> 00:43:50,394 So they're sensitive to a crack. 957 00:43:50,394 --> 00:43:53,530 And when they feel a crack in the material, they open up, 958 00:43:53,530 --> 00:43:57,334 and they pour a healing liquid that then solidifies. 959 00:43:57,334 --> 00:43:58,969 That's a self-healing kind of approach. 960 00:43:58,969 --> 00:44:00,537 You could do that at different scales, 961 00:44:00,537 --> 00:44:02,139 all the way down to the strand. 962 00:44:02,139 --> 00:44:03,507 You can do that on larger scales. 963 00:44:03,507 --> 00:44:06,110 And here's a whole system where there's actually 964 00:44:06,110 --> 00:44:09,446 this healing material being flowed through a polymer 965 00:44:09,446 --> 00:44:13,083 structure, just like arteries in our body. 966 00:44:13,083 --> 00:44:16,186 Again, always there to try to heal the material. 967 00:44:16,186 --> 00:44:17,621 Right? 968 00:44:17,621 --> 00:44:20,791 Another direction is in fully recovering. 969 00:44:20,791 --> 00:44:22,960 And again, I don't want to go into full detail here. 970 00:44:22,960 --> 00:44:24,561 You can look up some of this stuff. 971 00:44:24,561 --> 00:44:26,930 This was published last year. 972 00:44:26,930 --> 00:44:30,000 Can we take the polymer and chemically 973 00:44:30,000 --> 00:44:33,504 decompose it all the way back to the monomer? 974 00:44:33,504 --> 00:44:35,539 Can we go back to where we started? 975 00:44:35,539 --> 00:44:38,375 Can we do what the spider does? 976 00:44:38,375 --> 00:44:38,876 Right? 977 00:44:38,876 --> 00:44:41,879 The answer is no, not today. 978 00:44:41,879 --> 00:44:45,249 But if we could, that would open up 979 00:44:45,249 --> 00:44:48,318 a whole lot of doors for recycling 980 00:44:48,318 --> 00:44:49,553 that are closed today. 981 00:44:49,553 --> 00:44:52,489 Can we do this in a way that is efficient? 982 00:44:52,489 --> 00:44:53,691 Right? 983 00:44:53,691 --> 00:44:56,894 And then, another direction of work 984 00:44:56,894 --> 00:44:58,529 that I think is very important is 985 00:44:58,529 --> 00:45:02,499 in making thermosets so heavily cross-linked so you 986 00:45:02,499 --> 00:45:04,668 get all the hardness and all the properties you need 987 00:45:04,668 --> 00:45:07,538 of the polymer that's heavily cross-linked, but easily 988 00:45:07,538 --> 00:45:09,206 breakable in the cross link. 989 00:45:09,206 --> 00:45:12,142 And there is good work going on in this direction. 990 00:45:12,142 --> 00:45:15,312 Can we make degradable thermosets? 991 00:45:15,312 --> 00:45:17,581 That's another really important direction. 992 00:45:17,581 --> 00:45:20,084 And last, we should be encouraging people, 993 00:45:20,084 --> 00:45:22,186 if you can't do any of this, at least take 994 00:45:22,186 --> 00:45:24,922 the polymer out of the landfill and make something with it. 995 00:45:24,922 --> 00:45:27,624 And there are projects-- you can look at here, Waste Management 996 00:45:27,624 --> 00:45:30,527 Journal, in making bricks out of polymers, 997 00:45:30,527 --> 00:45:32,930 incorporating them into construction materials. 998 00:45:32,930 --> 00:45:33,430 Right? 999 00:45:33,430 --> 00:45:37,634 These are important directions, and we need a lot more 1000 00:45:37,634 --> 00:45:40,204 hopefully in the very near term. 1001 00:45:40,204 --> 00:45:40,270 hopefully in the very near term. 1002 00:45:40,270 --> 00:45:42,206 No more just talking about alignment. 1003 00:45:42,206 --> 00:45:43,774 OK, have a good weekend.