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00:00OK, let me continue from this slide, molecular weight.
00:10We know about the molecular weight for any chemicals.
00:14We sum all the atomic weight for that molecule.
00:21In the case of this polymer, we have many, many atoms because they are connected through.
00:33So molecular weight can be calculated the same way.
00:38So that's the mass of a mole of chains, just one mole, 6 times 10 to the 23rd.
00:48How can we measure the number of the molecule by this amount?
00:58We don't know that much, right?
01:00So that method, how can we calculate the molecular weight of this polymer?
01:06That's totally different class.
01:08And then we are not going to handle that part at this moment.
01:13But you know, the colligative properties in Korean, that's 총괄성.
01:18We can guess how many molecules are existing to obtain certain physical properties.
01:28For example, the melting point can be changed by a certain amount.
01:34That is also the result of the number of molecules.
01:39That's colligative properties.
01:41It doesn't depend on what kind of a chemical that is.
01:46Only it depends on the number of molecule or their numbers.
01:53So basically, we know like polymers are not like single length chain.
02:03So here, if we have like two carbon ethylene group, one, two, three, four, five.
02:12So five ethylents are connected through make this just one polymer chain.
02:18That might be like a low molecular weight.
02:24And sometimes they can grow further.
02:27So here, let's see, I don't want to count all that.
02:30But obviously, the higher number of the methylene, the unit cell, I'm sorry, unit chain,
02:43much, much larger.
02:46That's high molecular weight.
02:48It's obvious.
02:49When we synthesize the polymers, sometimes this A and B, they both can exist in the same batch.
02:59So we do not know which can be like a major length and which is not.
03:07So that's going to be calculated.
03:11We are going to talk about that one soon.
03:14So if we have this low molecular weight and high molecular weight, we need to have certain criteria to determine the molecular weight.
03:29But we already have it like average one.
03:33So how can we average the molecular weight of the polymers?
03:40That's the issue at this moment.
03:45Because the molecular weight is changing a lot of the physical properties such as the flexibility and the melting point and the toughness.
03:59A lot of things are directly connected to this, the molecular weight.
04:05So determining molecular weight is also determines its physical properties too.
04:12Okay.
04:14Here is the definition for here, the molecular weight.
04:22So if you see that N is existing there or sometimes you see like W, that's weight and this is number.
04:35So we can average the molecular weight by counting just the number itself or weight itself.
04:47So their names are different.
04:50In this case, number average molecular weight and this is weight average molecular weight.
05:00Do you clearly see this part?
05:04So let's say I have a small ball here, one, two, three and big ball.
05:11If we average them, then maybe the result could be a little bit larger size this way.
05:21If we do weight average one, then this is number average one.
05:33If we do weight average one, it's getting a little bit bigger than this one.
05:40So when we have like a higher weight, the molecule that overwhelm the other molecules because that determines most of the physical characteristics.
05:56So in that part, we need to calculate number average molecular weight and weight average molecular weight too.
06:05So we can compare them to determine the distribution.
06:10So here the word distribution.
06:13So when we synthesize the polymer, we do not obtain just like a highly ordered just one type of chain length molecular weight.
06:26So the here molecular weight can be high or low.
06:31There might be a lot of different kinds of polymers.
06:34They are synthesized at the same time.
06:38So the number average molecular weight is normally the place at around here.
06:46Then weight average one is much higher than the number average molecular weight because if we have some high molecular weight,
06:55that their strength is much larger than the small molecules, the physical properties.
07:12Let's do a quick analogy calculation using student weights here.
07:18Number one is this is pound.
07:22I don't remember that pound, but it's like half and a little bit bigger or something.
07:30So we don't care much.
07:32But here we see 104, 116, 140, 43 and a quite large number.
07:41Oh, this one is almost like four times.
07:45So by just simply looking at those data set, what could be the average value?
07:58Maybe because it's already ordered in the, what is that, like ascending order,
08:08then we can get some around here because number five is the center.
08:17So we can simply guess maybe average could be around 180 or something.
08:23So this data set really want us or you to experience the calculation based on the number fraction of students in each mass range.
08:42And what is the average weight, something, something based on the weight fraction.
08:47So they already calculated in this slide.
08:50So we don't have to do all the math.
08:52They already did some range, weight range and then student number of students and the mean weight to some sort of this kind of table.
09:14And then they calculated the fraction or you can just simply do all that integration by like multiplying one student by 110, not 110.
09:35You know, they did just statistics, but you can use, we can use just like a raw data.
09:44104 plus 116 plus 140.
09:51And then we divide by all that, the sum by 10, right?
09:56That's like a number averaged one.
09:58That's obvious.
09:59But weight one is a little bit different.
10:02But in this case, to make it some statistics one, they did some other way like a fraction.
10:11And also they averaged it.
10:13So each average can have only just one vote.
10:18So if we do this calculation, the result might be the same as the one we previously have done.
10:29So in the case of weight average, that's a little bit different.
10:35So just to follow the one, the equation is given.
10:41So if we do all that equation, that molecular, I'm sorry, number averaged molecular weight is 188 pounds.
10:52But in the case of weight averaged molecular weight, that's 218 pounds.
11:00So normally, as we saw this before, that the weight averaged molecular weight is a little bit or sometimes much higher than just the number averaged molecular weight.
11:19And here, it's around 30 pounds distance changes, right?
11:29So that's what happens for the number averaged molecular weight and the mass averaged molecular weight.
11:36Then why do we need to have this, the both data?
11:41Because normally the physical properties are based on this, the weight averaged molecular weight.
11:51So if we have like a higher molecular weight for the weight averaged one, then their characteristics are determined by this value, not this value.
12:10But this value is also giving some information because if we have like a large gap between this number averaged one and the weight averaged one, that means its distribution is quite large.
12:29So if we have large distribution or small distribution, then these two graphs are showing different the molecular weight, average molecular weight gap.
12:52So the, you know, as I mentioned before, low molecular weight normally has the, what is that, higher flexibility and also it's, it's softer.
13:11And then higher molecular weight is dense and then also they're like a, they can resist higher power.
13:22So if we have a broader distribution, that means it has, it has the, a lot of mixed the characteristics inside actually, right?
13:36So outside, if we take a look at, from the, from the outside, they might look quite strong or the powerful, but actually inside the molecule, inside that material, there could be some cracks occurring and some of the molecules are very soft.
14:02So when we use that material for some other mechanical uses, then internal cracks or internal, the, the fatigue might cause that the materials, the rupture or the failure, right?
14:25So if we have a narrow gap, that may have like higher cost because there are the, the molecules are characteristics are evenly distributed in that material.
14:41Okay.
14:42Okay.
14:43Okay.
14:44Let's move to the degree of polymerization.
14:46Okay.
14:47Let's move to the degree of polymerization.
14:50So here, the definition is the average number of repeat units per chain.
14:55As I explained in the before, so he, in this case, at a length, at a one, two, three, four, five, six.
15:04So degree of polymerization is six.
15:05So degree of polymerization is six.
15:07That easy.
15:08That, that, that's much easier, right?
15:11Because then that number average, the molecular weight divided by just the, the average molecular weight of a repeat unit.
15:20In this case, that could be, uh, ethylene.
15:23So in the case of co-polymers, we need to add some sort of a fraction, uh, term inside.
15:34So for example, uh, ethylene has a 30% and the acetylene has a 70%.
15:43Then we may have that the mass 30% of ethylene and 70% of acetylene, and then we should make the average between them.
15:57Right.
15:58That's quite obvious, I guess.
16:00And, uh, the, you know, like, um, if we have a longer chain, then more, uh,
16:13the higher number of just a unit, unit cell, right?
16:19Unit, I'm sorry, not, I'm just saying unit cell, but unit, um, what is that?
16:25Unit chain, repeat per chain, and then, uh, repeat unit.
16:31Sorry, this word.
16:36Okay, and then, um, we just observed, like, chains, right?
16:45This is the polymer chains.
16:47Chains can, um, organize four ways.
16:51One, two, three, four.
16:53I don't think this can be seen that easily.
16:56This is very rare.
16:58So, um, we don't expect this one, but if that can be, uh, the fabricated in the easier way, this might be very useful.
17:11But when we synthesize polymer, normally that goes to one of these three types.
17:18Linear one, and, uh, that's a single chain, right?
17:23And lots of secondary, the bonding between chains.
17:27Here, uh, van der Waals spores, and sometimes hydrogen bonding inside.
17:33And, uh, branched one, side chains reduce packing, right?
17:38So, uh, they have, like, uh, the low density.
17:43And often, uh, lower crystallinity, too, right?
17:49And, uh, cross-linked one, uh, in, you know, when we mentioned this branched one, they, the branch is, uh, is located this way.
17:59But if they are making bonds between these chains, that's cross-linked one.
18:06That's quite strong, and, uh, the, um, sometimes they can, the, what is that, elongate.
18:18So, that makes some flexibility, and, uh, make some soft one, depending on the situation.
18:27Sometimes if that bond is very strong, then, um, that could be very fragile, or, let's see, what is that, very, um, it doesn't have a resilient setup inside.
18:47And, uh, this network, three-dimensional covalent connections.
18:52Um, I don't think we, we will see this kind of polymers often.
18:57But, the, sometimes that occurs if we control very carefully.
19:04Um, as I mentioned before, real polymers often mix these, uh, these features.
19:12Most likely, this, one of these threes.
19:15And, uh, molecular shape, and, uh, conformation, we are going to learn two words.
19:25Like, the first one is conformation, and the second one is configuration.
19:30In the case of conformation, that's just a regular molecular shape.
19:35We do not need to cut or break the bonds.
19:38That's conformation.
19:40For example, like, chain binding and twisting are possible by rotation of carbon atoms.
19:47So, uh, I already showed you, like, this one.
19:50Uh, only sp3 orbital hybridized one.
19:55Then, they can rotate.
19:57But, in the case of, um, double bond, if there is a double bond, that doesn't, uh, allow the molecules rotation.
20:06So, uh, if we only have this single bond between the carbon, and then, that, that, let the molecule, the, move around.
20:18Or, just, uh, the, give some, or is that, like, flexibility.
20:24So, um, the, when we, like, uh, when we have this kind of polymer, they normally, um, they are not linear one.
20:41Sometimes they coil or entangle.
20:44And, uh, the, if we force outside, that stretches elastically.
20:50That's all happens due to this kind of conformation changes.
20:57This conformation may, uh, cause all this entanglement.
21:03And then, um, we, it, it, it could be some sort of a random walk.
21:10And then, we do not know where the end of the molecule can exist.
21:16So, uh, that's chain end-to-end distance.
21:20The picture, a long chain, uh, the, the rendering randomly like this.
21:26It's total, uh, contour length is huge.
21:30But, uh, end-to-end distance, like R, is much smaller due to all that, the bands and, uh, kinks.
21:41Polymers from entangled coils imagine a, uh, a tangled fishing line.
21:47Uh, that entanglement explains large, and this large elastic, the extensions in rubbers.
21:55And, uh, high viscosity of melts.
22:00And here, like a configuration.
22:04That word is different from conformation we just, uh, the, we just went through.
22:12Configuration is, uh, the another expression.
22:15To change the configuration, we must break.
22:20And reform primary bonds.
22:25Two ideas are here.
22:28The head-to-tail or, like, a head-to-head arrangement.
22:33That will be, uh, explained in the next slides.
22:36The tacticity.
22:38So, uh, um, configuration, conformation.
22:43They are different.
22:45So, uh, here's the isomer.
22:47Do you remember the isomer?
22:49The, the total number of carbon or hydrogen.
22:52The elemental, the number is the same.
22:55But they are all, the, the, what is that?
22:58Their, uh, placements are different.
23:02So, uh, for example, the, let's say we have ethylene, which has one alkyl group or some functional group, R, here.
23:14If it's, uh, chlorine, that's the vinyl chloride.
23:18If it's, like, uh, the benzene, that's styrene, right?
23:23So, that's the one we are going to observe.
23:26But here, representing just R.
23:29And if it makes the polymerization, then it becomes a single bond.
23:34This R can exist at the lower position or higher position.
23:39Once it goes there, uh, but in this case, they can rotate.
23:44It's, uh, obviously, uh, they are the same structure at this moment.
23:49But we will see, uh, when, sometimes it's totally different one.
23:54So, uh, here in, uh, in the bottom part, we already know, like, a steroisomer.
24:01It's a chiral compound.
24:03So, it's a mirror plane.
24:05And when we have this carbon center, and then the, all the one, all the connected one is identical.
24:14They are all different.
24:15Then the mirror image is totally different from this.
24:21Right?
24:22So, this is isomer.
24:24Sometimes in our body, this isomers are very important.
24:27And some of the, the, this could be drug.
24:32And this could be poison.
24:34So, um, we have to be very careful in, in our body, the medical compound for, um, drug design.
24:44You know, that, that, fever, um, the treatment chemical, one of the, the, the one.
24:57And, uh, only the one option.
25:00If, let's say, uh, this compound is a drug and the other one is, uh, in that case, that's not a poison.
25:07But this doesn't do anything.
25:09It's just a regular, the useless compound.
25:13But this one acts as a, like a medical drug.
25:17So, we need, only need this compound.
25:20But we, when we synthesize them, this can be synthesized too.
25:26So, uh, the isolation could be very important for the medical use.
25:37So, tacticity.
25:38You know, tact means touching.
25:41Right?
25:42So, how do they touch?
25:45Like, in this case, R group can be, uh, located just alternatively.
25:51Same side of the chains.
25:53They are tacting that way.
25:56Stereo-regularity or spatial arrangement of alkyl group or the functional group, R, units along chain.
26:05So, this is just one of the normal one.
26:08And then, that's isotactic.
26:12Very similar to each other.
26:16And then, syndiotactic.
26:18They are different way.
26:21They are facing each other.
26:27In that case, this is syndiotactic.
26:30These two, uh, tacticities are very normal.
26:35We synthesize the polymer.
26:37That occurs in one of these.
26:39Like, uh, the isotactic or syndiotactic.
26:42Right?
26:43And sometimes, uh, the a-tactic.
26:45A-tactic.
26:46A-tactic.
26:47A-tactic.
26:48A-tactic.
26:49A-tactic.
26:50A-tactic.
26:51A-tactic.
26:52Random position.
26:53A-tactic.
26:54Random position.
26:55So, um, the, you know, like, uh, the isotactic, syndiotactic.
27:08they are like a totally different one we cannot just this as I explained it in
27:16the previous slide we have like confirmation or configuration in this
27:22case it's configuration not a confirmation okay and also we have some
27:27more example here the this one the we see there's are like a double bond and then
27:40this like a methyl group and methyl group is this way and then this one this way
27:50and the other way so actually the polymerization goes trans direction here
27:58cis direction right if we look at only the ethylene compound this is trans so if
28:11we this is hydrogen so this is a cis and this is trans so it's very difficult to
28:19say which one like is it trans or cis but the polymerization occurs this way so
28:25it's a cis but the polymerization of goes this trans way trans and this one is
28:33natural rubber and this one is also I think the gata percha is kind of natural
28:41rubber too but from different trees and different region and I know the lot of
28:54people know about this natural rubber like this cis form but we might be very
29:02less experienced for this gata percha but this is also very important the
29:09chemical because you know the in old ages when they the people started to make
29:18some electricity line and then also the in Europe between this England and France
29:26friends friends friends they have on the the where is that like a telephone line
29:34under the sea in that case they need a very insulating the insulating polymer to
29:43wrap that conducting material and also they should protect and water because they
29:51are putting that in under the sea so in that case they use this gata percha I'm
30:01teaching another class and then in that class I I have a chance to explain that
30:06selenium the semiconductor and that in that company is also like a gata percha they
30:16are like making some electrical insulating material for wrapping this semiconductor or
30:23the conducting material okay and then the copolymers the mixing repeat units they
30:36create copolymers two or more monomers are polymerized together but you can
30:43easily see like a random case just a random one one three two one random one
30:49and the alternating one a B a B a B a B a B a B that's alternating right and then
30:58blocking just the block one block two block three four different block or
31:03grafting grafting this main polymerization and there's some grabs occur but that's
31:12that's obvious right so the pro polymer designs choose the properties and that's why people
31:21are trying to use there's a polymer co-polymer designing the impact resistance and rubber
31:28elasticity and barrier performance for example like a styro and battalion rubber that's just the
31:36random co-polymer used in tires no but if we use only the polystyrene that's that's that can be easily
31:45broken down and polyethylene is also it's not that much flexible but if we mix them up then they can show the
31:56tire properties now we move to like a crystallinity and polymers you know the
32:07crystallinity is the words for the metallic compound at the very beginning so people
32:13didn't believe that polymer or organic compound may have some sort of like the
32:19crystallinity but later on the the scientists figured out the this the organic chains may organize
32:33very clearly that order the atomic arrangement involving molecular chains that's due to that
32:41van der Waals force so if we have a long chain they have a strong interaction because they have the higher
32:48number of electrons inside that what is that like induced type moment interaction so this is just a regular
33:00polyethylene unit cell they make some sort of the crystallinity the degree of polycrystallinity depends
33:11on like cooling rate and chain regularity and the side group symmetry something like that the more crystalline
33:22polymers are typically stronger and more heat resistance turned and then more amorphous ones are like a clearer
33:33and then and also more flexible let's be more specific polyethylene forms on the orthoramic unit cell it says that way we
33:48don't have to know about that one the chains like a zigzag and peg tightly we can estimate percent crystallinity by
33:59by comparing like densities crystalline regions pack the closer than amorphous region in this case they look
34:09all like a crystaline part the formula uses and like specimen density and densities of fully amorphous and
34:19fully crystalline material and then here uh thin uh plate let thin plate let's whether like chain folds at faces
34:35uh you know some sort of let's
34:39So let's
34:41um
34:45한국말로 하면 여기 약간선
34:48alpha
34:53적휠고 같은 뭐 그런 애들 처럼 생긴 애들을 얘기하는 건데요 Let's like Let's, Let's like let's like little and lemon a little like in common
34:59as made like little things you or you don't be like little doя
35:00이런 애들을 좀 얘기하는 게 있잖아요. A capaciti for the equations that are all
35:03몇iler are less than those兩個 however you know that's right
35:05그런 식으로 되어 있다고 하고 있습니다 Ahan
35:06going to talk about it
35:09OK, the polymers rarely 100% crystalline, we already know about it, right?
35:20Because if the polymers can have some defects, even like metal cannot have perfect crystallinity.
35:33Difficult for all regions of all chains to become aligned.
35:38And degree of crystallinity that can be just calculated as I just mentioned.
35:45And also due to that tacticity and a lot of things, then we can guess how many percentages can be highly oriented or some percentages are just a more personal.
36:05And people tried to figure out this structure and then they observed some polymer single crystal electron microscope.
36:17And then I do not actually know about this, the whole part, but you know, it has a certain angle.
36:28And then some artists said this terrace.
36:35And that's a regular style for just the metallic compound, right?
36:42That's what we already observed in the highly organized crystalline metal compound.
36:50They show almost the same way.
36:52And then they also have done some sort of the optical properties.
37:01And before that they suggested this one.
37:04In bulk, the semi-crystalline polymers nucleate from the melt and then grows spirolytes.
37:17Roughly like a spherical aggregation of chain folded lamellae radiating from a center and separated by amorphous region.
37:29And this is the material.
37:34So they suggest this way.
37:35And then they observed it through the high, the, what is that, high-powered and high-resolution SEM image and TAM images too.
37:48And finally, they have done some sort of, I'm sorry, I thought I had one more thing, but I'm sorry.
37:59That's the end.
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