高分子物理1高分子的链结构ChainStructureofPolymers-2-PPT课件

1、高分子的链结构1 Chain Structure of PolymerPolymer Physics高分子物理1.1 高分子结构的特点和分类Characteristic and classification of polymer structure Structure and Property of Polymer高分子结构与性能1.1.1 高分子的结构特点Characteristics of polymer structurePolymer is composed of many structural units linked by chemical bonds.The molecular

2、weight of polymer is very high and has polydispersity.The main chains of polymer can rotate, leading to flexibility of polymer chains. Due to thermal motion, the shape (conformation) of polymer chains change with time.The Van der walls force among structural units is very important.Crosslinking may

3、greatly change properties of polymers.The aggregate state of polymer may be crystalline or amorphous. The order of polymer in crystalline state is smaller than that of small molecules，but the order in amorphous state is higher than that of small molecules.1.1.2 高分子的结构层次链结构高次结构聚集态结构(三次结构)近程结构(一次结构)远程

4、结构(二次结构)chemical compositionregioisomerismstereoisomerismbranching & crosslinkingbonding sequence in copolymersize (molecular weight and distribution)conformation (flexibility and rigidity)crystalline stateliquid crystallineamorphous stateorientation state高分子结构Configurationclassification of polymer

5、structureShort range structureLong range structureChain structureAggregate structuretextural structuretextural structureShort range structurestructural unit or local chain segment is involvedLong range structureentire single polymer chain is involvedAggregate structuredifferent polymer chains are in

6、volvedHow about double helix structure of DNA?Polymer structures at different levels are different but correlated!Polymer structure is the sum of structures at different levels, which contribute to apparent polymer properties.stereo-regularitystructure of monomersequence of comonomermolecular weight

7、crystallizability, etc.conformation; liquid crystal; etc.phase separation; crystallizability; etc.miscibility, etc.Regulation and improvement of polymer properties can be approached by change of polymer structures at different levels. synthesis： processing： blending：short range structure and long ra

8、nge structurelong range structure and aggregate structuretextural structure1.2 高分子链的近程结构Short-range structure of polymer chain1.2.1 结构单元的化学组成 Composition of structural unitStructural unitMain chainSide chain group or substituente.g. Polyvinyl Chloride - PVCPolymerization degree 碳链高分子Carbon chain pol

9、ymer The polymer main chain are totally composed of carbon atoms linked by chemical bonds (most are prepared by addition polymerization)Difficult to hydrolyze, good processibility, poor thermal stability, easy to flame and age.聚丙烯PP Polypropylene聚异丁烯PIB Polyisobutylene聚丙烯酸Polyacrylic acid聚甲基丙烯酸甲酯PMM

10、APolymethyl methacrylate聚醋酸乙烯酯PVAc Polyvinyl acetate聚乙烯基甲基醚PVMEPolyvinyl methyl ether聚丁二烯PB Polybutadiene聚异戊二烯 PIP Polyisoprene聚氯乙烯 PVC Polyvinyl chloride聚偏二氯乙烯 PVDCPolyvinylidene chloride聚四氟乙烯 PTFE Polytetrafluoroethylene (Teflon)聚丙烯腈 PAN Polyacrylonitrile杂链高分子 Heterochain polymerThe polymer main c

11、hains are composed of carbon atoms and other atoms (for example: O, N, S, P et al.) linked by chemical bonds.Prepared by condensation or ring-opening polymerization.The main chains has polarity. Advantages：good thermal stability, high strengthDisadvantages：easy to hydrolyze and decompose in alcohol

12、or acid.Applications: engineering plastics.聚甲醛 POM Polyformaldehyde 聚己二酰己二胺 Polyhexamethylene adipamide (Nylon6-6)聚氧化乙烯 PEO Poly(ethylene oxide)聚己内酰胺 Poly(-caprolactam)i.e Nylon 6聚苯醚 PPOPolyphenylene oxide, or Polyphenylene ether聚对苯二甲酸乙二酯 PET Polyethylene terephthalate聚碳酸酯 PC Polycarbonate聚醚醚酮 PEEK

13、Polyether ether Ketone对苯二甲酰对苯二胺 PPTA Kevlar Poly(p-phenylene-terephthalamide)聚酰亚胺 Polyimidepolysulfonepolyester聚酯polyurethane 聚氨酯元素有机高分子Elementary organic polymer There is no carbon atom in the polymer main chains, but the side chains contain carbon atom.Possessing both thermal stability of inorgani

14、cs and elasticity and plasticity of organics, but the strength is low. 无机高分子 Inorganic polymerThe polymer are composed of non-carbon atoms.Only partial non-metal elements in A, A, A, A can form inorganic polymers二硫化硅 silicon disulfide聚偏磷酸(盐) polyphosphoric acid(or polyphosphates)聚二氯一氮化磷 poly(dichlor

15、o phosphazene)1.2.2 分子构造单链 Single chainMolecular architecture梯型聚合物 Ladder chainCarbon fiberFeatures of ladder polymers: excellent thermal stability. When single chain in a ladder ring is broken upon heating, the molecular weight of the polymer is unaffected.BranchingEffects on polymer properties： cr

16、ystallinity, flexibility, hardness, density, melting temperature, etc. short branchesregularity, crystallinity, density, melting temperature long branchesdissolving property and rheology in the meltInfluence of grafting and crosslinking on the properties of polyethylene TypePropertiesHDPELDPEXPECrys

17、tallinity, %956070Density, g/ml0.950.970.910.940.931.40Melting point, C135105Working temperature, C12080100100135Tensile Strength, MPa2040102010100Elongation, %504005080050600Crosslinking polymers：undissolvable, unmeltable strength 、thermal stabilityThermoset resin and vulcanized rubber are crosslin

18、king polymer materials.交联 crosslinkingVulcanization of rubberCure of thermoset plasticsCrosslinking of saturated polyolefins: radical attack (for example：irradiation crosslinking)1.2.3 键接异构 Bond order isomerRegio-selectivity of structural units in polymerization vinyl monomers (CH2=CHR) head-head ta

19、il-tail head-tailaffecting crystallizability, mechanical properties and thermal stability头尾头头+ Zn ZnCl286%Head-tail structure is the majority in polymers of vinyl monomers.Head-to-tailHead-to-headHead-head and tail-tail structures leading to more hydroxyl left,thus the ability of water absorption in

20、creases and strength is reduced.Diene monomers？How to determine regio-regularity?NMR, IR, chemical reaction, etc.1.2.4 立体异构 Stereoisomerism旋光异构 Optical isomerismDue to co-existence of meso- and racemic isomers, the whole polymer material exhibits no optical activity. After polymerization, a chiral c

21、arbon atom is produced for vinyl monomers, thus there are two optical isomers.(For single polymer chain, the optical activity is very weak due to the small difference between the two long chain group.)三种类型Isotactic 全同立构Atactic 无规立构Syndiotactic 间同立构Polymer chains are composed of single optical isomer

22、s. uniform and crystallizable.Polymer chains are composed of two alternative optical isomers, uniform and crystallizable.Polymer chains are randomly composed of two optical isomers.non-uniform and non-crystallizableThe former two are stereo-regular PP, and the last one is stereo-irregular PP.Stereo-

23、configuration affect polymer propertiesPS： isotactic PS：crystallizable，Tm=240 C ，uneasy to dissolve atactic PS：soft temperature 80 C ，soluble in benzenePP： isotactic PP： Tm=175 C ，high strength, used as fiber and engineering plastic atactic PP： soft, additive for paving asphaltIs stereoregularity th

24、e necessary condition for polymer crystallization?Under most cases it is, but some exceptions：poly(fluoroethylene) poly(vinyl alcohol) poly(trichloro fluoroethylene)similar sizes of F and Hstrong H bondCl is slightly larger than F，But strong repulsion between F atoms.几何(顺反)异构 Geometrical (cis-/trans

25、-) isomerismFor 1,4-addition of diene monomerscis-1,4-butadiene, rubbertranss-1,4-butadiene, crystalline, plastics 天然橡胶 Natural rubber杜仲胶 Gutta-percha Stereo-isomerism and regio-isomerism may occur simultaneously!1.2.5 共聚物的序列结构Sequence structure of copolymerscopolymerization can improve some specifi

26、c properties of polymers PMMA: poor flow behavior and not suitable for injection-molding (strong intermolecular interaction). MMA+S copolymer: improved flow behavior, suitable for injection molding S+AN copolymer: impact resistance, thermal stability and chemical resistance are improved (can be used

27、 as oil-resistant parts). 无规共聚物 (random copolymer)Two or more monomer units distribute along the polymer chain randomly ABAABABBAAABABBAAAThe interaction among structural units and the intermolecular interaction are altered.The solution properties, crystallizability and mechanical properties of the

28、copolymer are different from the corresponding homopolymers.For example:PE and PP are plastics, but EP random copolymer is rubber.PTFE(聚四氟乙烯) is a plastics. Molten processing is impossible, but copolymer of tetrafluoroethylene and hexafluoropropylene is a thermoplastic.嵌段共聚 (block copolymer) AAAAAAA

29、AABBBBBBBBB polyA-b-polyB or poly(A-b-B) SBS (styrene-b-butadiene-b-styrene): prepared by living anionic polymerizationHardHardSoftSBS： thermoplastic elastomer high temp: can flow and can be processed by injection molding. low temp: like crosslinking rubber (PS chains at both ends are glassy, “physi

30、cal” crosslinking). PSPB接枝共聚 (graft copolymer)polyA-g-polyBABS (acrylonitrile-butadiene-styrene): ternary copolymer prepared by combination of random copolymerization and grafting polymerization. Structure P(BS)-g-P(SA) or P(AB)-g-PS or P(SA)-g- P(AB)-CH2-CH=CH-CH2- Rubber-like elasticity. High impa

31、ct resistanceGood formabilityChemical resistance, high tensile strength and hardness交替共聚物（alternating copolymer） ABABABAB An example:Styrene-maleic anhydride alternating copolymer short range structurestructure of unitcarbon chain polymerheterochain polymerelementary organic polymerinorganic polymer

32、molecular architecturesingle chainladder chainbranchingcrosslinkingbond orderisomerismvinyl monomer：H-T; H-H; T-Tdiene monomer：1,2; 1,4; 3,4stereo-isomerismvinyl monomer：optical isomerism (isotactic, syndiotactic, atactic) diene monomer：geometric isomersequence ofcopolymerrandom copolymerblock copol

33、ymergrafting copolymeralternating copolymerconfiguration1.3 高分子链的远程结构Long-range structure of polymer chainLong-range structure of polymer chain1.3.1 分子量 Molecular WeightSmall molecule：definite molecular weight for a specific substancePolymer：distribution of molecular weight (polydispersity) For the

34、details, see Chapter 4Only when MW reaches a certain value (critical MW), polymer materials exhibit useful mechanical strength. polar polymer: DPcri 40 non-polar polymer: DPcri 80Strength Molecular WeightPolarNonpolarWhen MW is very high (DP600700),strength reaches a limit, but melt viscosity is too

35、 high to process.Plastics and rubber: broad MW distribution (high MW parts contribute to strength, low MW parts improve processability.)Fiber: narrow MW distribution1.3.2 内旋转构象 Conformational Staterotation of CC single bond change of conformation larger polymerization degreeTEM of bacterias DNAThe r

36、epeating units in the main chain are connected by covalent bonds no independent motion for single unit polymer chains are poor in entropy.flexibility链段 Chain segment consisting in many units, which can move independently.considerable conformationDue to presence of H and other substituents, energy ba

37、rrier must be overcome for rotation of single bond.larger distance smaller repulsion lower energystability: trans gauche cistg-g+cistransgauche正丁烷或聚乙烯内旋转位能图 For linear PE chain, the energy level of all-trans conformation is the lowestT=0 K: planar zig-zag conformationT 0K: gauche conformation appear

38、 due to thermal motion For a with 10,000 bonds,The number of arrangements310,000=104,7711.3.3 分子链的柔顺性 Chain Flexibility Static flexibility (静态柔顺性) flexibility of polymer chain at thermodynamic equilibrium determined by the difference in the potential energy of trans and gauche conformation ()kTThe p

39、olymer chain is rigid.Dynamic flexibility (动态柔顺性) the transition rate between different conformations determined by the energy barrier between different conformations (E) p : time for transition from trans to gauche conformation E CN CO CC Side group polarity interaction flexibility PAN PVC PPnumber

40、 of polar side group flexibilitypolarity: 1,1- di-substituents size of side group flexibility PS PP PE CH2 CCl2 PVDC CH2 CHCl PVC Chain length length of main chain number of conformation flexibilitylength of side chain interaction flexibilityBut when the side chain is too long, it hinders rotation o

41、f the main chain and flexibility decreases.CH3 CH2 C COO(CH2)nCH3n: 01219201.4 高分子链的构象统计Conformational statistics of polymer chain1.4.1 自由连接链 Freely Jointed Chain Freely jointed chain is just used for theoretical calcution, and it does not correspond to any real polymer chain.The polyme chain consis

42、ts in n equal one-dimensional links of length l (with no occupied volume).There is no restriction on the angles between the links.No energy is required to change the angles. The probability of each bond at any direction is equal and the contour or fully extended length of the chain is nl.Other two t

43、erms：random walk (无规行走) one-dimensional freely jointed chainrandom flight (无规飞行) three-dimensional freely jointed chain Simulation of freely jointed chainN = 104The trace is like that of Brownian particles.The volume fraction of the units is very small.There are lot of holes inside the random coil.

44、End-to-end distance (末端距) Mean-square of end-to-end distance (均方末端距 )Total n termsijThe conformation of freely jointed chain is far from that of extended chain!extended chainOrigin of rubber elasticitymass of unit: micoordinate of ith unit: Radius of gyration (旋转半径 )coordinate of center of massn 时 a

45、lso applicable to freely rotating chain and Gaussian chainRadius of gyration is suitable for polymer chains with multiple chain ends.r012i质心rifreely jointed chain1.4.2 自由旋转链Freely Rotating ChainModel with fixed valency angle The angle are restricted to lie on a cone, but the bond can rotate freely o

46、n the surface of the cone. Mean-square of end-to-end distance Total n termsTotal 2(n-1) termsTotal 2(n-m) terms=l2n+2(cos+cos2 +cos3 +cosn-1 ) (cos + cos2 +cosn-2 )(cos + + cosn-3 ) +.+ cos n四面体构型 cos = 1/31.4.3 受阻内旋转链Hindered Rotation ChainFor a real polymer chain, the rotation of the bonds on the

47、cones is not free. Energy barrier must be overcome for rotation of the bonds. The energy barrier for rotation is not a constant, but it varies with rotation angle .Bond angle键角Conformation angle构象角For PE，trans: =0, U(t)=0; gauche (g or g) =120 , U(g or g)=3.34kJmol-1, 298K1.4.4 高斯链 Gaussian ChainThe

48、 distribution of “equivalent chain” obeys Gaussian distribution. Gaussian chain(1) The polymer chain comprises N hypothetical segments.(2) Each segment has a length of l and is rigid.(3) Segments are freely jointed and there is no restriction on angles.Equivalent freely jointed chain:*The same : =Ne

49、le2 le=/L*The same contour length: L=Nele=nlsin(/2) can be experimentally measured.For PEfreely jointed chainfreely rotating chainunder conditionextended chainNl22Nl26.76Nl22/3 N2l2Kuhn lengthl (bond length)2.45l8.28 l0.82NlFor freely rotating chain: contour length: Nele=Nlcos(180-)/2=Nlsin(/2) =Nel

50、e2=2Nl2 le=2Nl2/Nlsin(/2)=2.45l(Note: Only for freely jointed chain the contour length is Nl. For other chains, the contour length is Nlsin(/2).Equivalent freely jointed chainobey Gaussian distribution; the motion unit is a segment; correspond to real polymer chainFreely jointed chainobey Gaussian d

51、istribution; the motion unit is a single bond; only used for theoretical study Probability distribution function of end-to-end distance for freely jointed chain in one-dimensional space W(x)Start from zero point (one end of the chain)Each step l (bond length), n steps of random walk (number of bonds

52、) Where is the last step (the other end of the chain) located ? End-to-end distance of Gaussian chain from statistical method The probability distribution function for other end W(x) is: One end is fixed at x=0, y=0, z=0 P is the probability of the other end located in the space dxdydz Z dxdydz X YP

53、robability distribution function in three dimension三维空间几率分布函数 W(xyz)Probability The probability distribution function in three-dimensional space W(xyz): Usually only the distance of the ends is cared, and the the direction of the ends is ignored.radiant distribution function W(R)Meaning of W(R)： Whe

54、n one end of the chain is fixed at the zero point, W(R) is the probability density for the other end appearing in the spherical shell from radius R to R+dR.RdR均方末端距R The most probable end-to-end distance R* Mean end-to-end distance Mean square root end-to-end distanceFor PE, n=1000, l=1.54Three type

55、s of end-to-end distance1.4.5 柔顺性的表征 Characterization of Flexibility2) 空间位阻参数(刚性因子) Undisturbed mean square end-to-enddistance under condition flexibility3) undisturbed dimension A (无扰尺寸)A flexibility1) characteristic ratio C (特征比)C flexibility4) Kuhn链节长度 Kuhn Segment LengthL 高分子链围线尺寸 Contour length of the chainKuh