高分子物理（浙江大学） 1 高分子的链结构 Chain Structure of Polymers-2.ppt

1、高分子的链结构,1 Chain Structure of Polymer,Polymer 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 structure,Polymer is composed of many structural units linked by chemical bonds.,The

2、molecular 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.,Cros

3、slinking may 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

4、(三次结构),近程结构(一次结构),远程结构(二次结构),chemical composition regioisomerism stereoisomerism branching 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.,synthesi

5、s： processing： blending：,short range structure and long range structure,long range structure and aggregate structure,textural structure,1.2 高分子链的近程结构,Short-range structure of polymer chain,1.2.1 结构单元的化学组成 Composition of structural unit,Structural unit Main chain Side chain group or substituent,e.g.

6、Polyvinyl Chloride - PVC,Polymerization degree, 碳链高分子Carbon chain polymer 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

7、烯 PP Polypropylene,聚异丁烯 PIB Polyisobutylene,聚丙烯酸 Polyacrylic acid,聚甲基丙烯酸甲酯PMMA Polymethyl methacrylate,聚醋酸乙烯酯PVAc Polyvinyl acetate,聚乙烯基甲基醚PVME Polyvinyl 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 PVDC Polyvinylidene chloride,聚四氟乙烯 PTFE Polytetrafluor

8、oethylene (Teflon),聚丙烯腈 PAN Polyacrylonitrile,杂链高分子 Heterochain polymer,The polymer main chains 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：go

9、od thermal stability, high strength Disadvantages：easy to hydrolyze and decompose in alcohol 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 PPO Polyphenylene

10、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 Polyether ether Ketone,对苯二甲酰对苯二胺 PPTA Kevlar Poly(p-phenylene-terephthalamide),聚酰亚胺 Polyimide,polysulfone,polyester聚酯,polyurethane 聚氨酯,元素有机高分子Elementary organic polymer There is no carbon atom in t

11、he polymer main chains, but the side chains contain carbon atom.,Possessing both thermal stability of inorganics and elasticity and plasticity of organics, but the strength is low., 无机高分子 Inorganic polymer The polymer are composed of non-carbon atoms.,Only partial non-metal elements in A, A, A, A ca

12、n 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(dichloro phosphazene),1.2.2 分子构造,单链 Single chain,Molecular architecture,梯型聚合物 Ladder chain,Carbon fiber,Features of ladder polymers: excellent thermal stability. When single chain in a ladde

13、r ring is broken upon heating, the molecular weight of the polymer is unaffected.,Branching,Effects on polymer properties： crystallinity, flexibility, hardness, density, melting temperature, etc. short branchesregularity, crystallinity, density, melting temperature long branchesdissolving property a

14、nd rheology in the melt,Influence of grafting and crosslinking on the properties of polyethylene,Crosslinking polymers：undissolvable, unmeltable strength 、thermal stability Thermoset resin and vulcanized rubber are crosslinking polymer materials.,交联 crosslinking,Vulcanization of rubber,Cure of therm

15、oset plastics,Crosslinking of saturated polyolefins: radical attack (for example：irradiation crosslinking),1.2.3 键接异构 Bond order isomer,Regio-selectivity of structural units in polymerization,vinyl monomers (CH2=CHR) head-head tail-tail head-tail,affecting crystallizability, mechanical properties an

16、d thermal stability,头尾,头头,+ Zn ZnCl2,86%,Head-tail structure is the majority in polymers of vinyl monomers.,Head-to-tail,Head-to-head,Head-head and tail-tail structures leading to more hydroxyl left, thus the ability of water absorption increases and strength is reduced.,Diene monomers,？,How to dete

17、rmine regio-regularity?,NMR, IR, chemical reaction, etc.,1.2.4 立体异构 Stereoisomerism,旋光异构 Optical isomerism,Due to co-existence of meso- and racemic isomers, the whole polymer material exhibits no optical activity.,After polymerization, a chiral carbon atom is produced for vinyl monomers, thus there

18、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 isomers. uniform and crystallizable.,Polymer chains ar

19、e composed of two alternative optical isomers, uniform and crystallizable.,Polymer chains are randomly composed of two optical isomers. non-uniform and non-crystallizable,The former two are stereo-regular PP, and the last one is stereo-irregular PP.,Stereo-configuration affect polymer properties,PS：

20、 isotactic PS：crystallizable，Tm=240 C ，uneasy to dissolve atactic PS：soft temperature 80 C ，soluble in benzene PP： isotactic PP： Tm=175 C ，high strength, used as fiber and engineering plastic atactic PP： soft, additive for paving asphalt,Is stereoregularity the necessary condition for polymer crysta

21、llization?,Under most cases it is, but some exceptions：,poly(fluoroethylene) poly(vinyl alcohol) poly(trichloro fluoroethylene),similar sizes of F and H,strong H bond,Cl is slightly larger than F， But strong repulsion between F atoms.,几何(顺反)异构 Geometrical (cis-/trans-) isomerism For 1,4-addition of

22、diene monomers,cis-1,4-butadiene, rubber,transs-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 copolymers,copolymerization can improve some specific properties of polymers,P

23、MMA: 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 as oil-resistant parts).,

24、无规共聚物 (random copolymer) Two or more monomer units distribute along the polymer chain randomly ABAABABBAAABABBAAA The interaction among structural units and the intermolecular interaction are altered. The solution properties, crystallizability and mechanical properties of the copolymer are different

25、 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),AAAAAAAAABBBBBBBBB polyA-b

26、-polyB or poly(A-b-B) SBS (styrene-b-butadiene-b-styrene): prepared by living anionic polymerization,Hard,Hard,Soft,SBS： 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, “physical” crosslinki

27、ng).,PS,PB,接枝共聚 (graft copolymer),polyA-g-polyB,ABS (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 impact resista

28、nce,Good formability,Chemical resistance, high tensile strength and hardness,交替共聚物（alternating copolymer）,ABABABAB An example: Styrene-maleic anhydride alternating copolymer,short range structure,structure of unit,carbon chain polymer heterochain polymer elementary organic polymer inorganic polymer,

29、molecular architecture,single chain ladder chain branching crosslinking,bond order isomerism,vinyl monomer：H-T; H-H; T-T diene monomer：1,2; 1,4; 3,4,stereo- isomerism,vinyl monomer：optical isomerism (isotactic, syndiotactic, atactic) diene monomer：geometric isomer,sequence of copolymer,random copoly

30、mer block copolymer grafting copolymer alternating copolymer,configuration,1.3 高分子链的远程结构,Long-range structure of polymer chain,Long-range structure of polymer chain,1.3.1 分子量 Molecular Weight,Small molecule：definite molecular weight for a specific substance Polymer：distribution of molecular weight (

31、polydispersity) For the details, see Chapter 4,Only when MW reaches a certain value (critical MW), polymer materials exhibit useful mechanical strength.,polar polymer: DPcri 40 non-polar polymer: DPcri 80,When MW is very high (DP600700),strength reaches a limit, but melt viscosity is too high to pro

32、cess.,Plastics and rubber: broad MW distribution (high MW parts contribute to strength, low MW parts improve processability.),Fiber: narrow MW distribution,1.3.2 内旋转构象 Conformational State,rotation of CC single bond change of conformation larger polymerization degree,TEM of bacterias DNA,The repeati

33、ng 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 conformation,Due to presence of H and other substituents, energy barr

34、ier must be overcome for rotation of single bond.,larger distance smaller repulsion lower energy stability: trans gauche cis,cis,trans gauche,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 lowest T=0 K: planar zig-zag conformation T 0K: gauche conformation appe

35、ar due to thermal motion,For a with 10,000 bonds, The number of arrangements 310,000=104,771,1.3.3 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 (),

36、kTThe polymer 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 kT transition from trans to gauche conformation can be comple

37、ted in 1011s.,small p : good dynamic flexibility large p : poor dynamic flexibility,Temperature Force Solvent,External Factors,Internal Factors,Structure of main chain Substitutes Branching and cross-linking Length of polymer chain Intermolecular force Crystallization, Factors affecting flexibility

38、of polymer chain, Main chain structure,length of single bond,conjugated double bond rigidity,H bond rigidity,isolated double bond flexibility,SiO CN CO CC, Side group,polarity interaction flexibility PAN PVC PP number of polar side group flexibility polarity: 1,1- di-substituents 1-mono-substituents

39、）, CHCl CHCl poly(1,2-dichloroethylene), CH2 CHCl PVC,size of side group flexibility PS PE, CH2 CCl2 PVDC, CH2 CHCl PVC, Chain length,length of main chain number of conformation flexibility length of side chain interaction flexibility But when the side chain is too long, it hinders rotation of the m

40、ain chain and flexibility decreases.,n: 01920,1.4 高分子链的构象统计,Conformational statistics of polymer chain,1.4.1 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 consists in n equal one-dimensio

41、nal 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 terms： random walk (无规行走

42、) one-dimensional freely jointed chain random flight (无规飞行) three-dimensional freely jointed chain, Simulation of freely jointed chain,N = 104,The 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., End-to-end dist

43、ance (末端距), Mean-square of end-to-end distance (均方末端距 ),Total n terms,ij,The conformation of freely jointed chain is far from that of extended chain!,extended chain,Origin of rubber elasticity,mass of unit: mi coordinate of ith unit:, Radius of gyration (旋转半径 ),coordinate of center of mass,n 时,also

44、applicable to freely rotating chain and Gaussian chain,Radius of gyration is suitable for polymer chains with multiple chain ends.,freely jointed chain,1.4.2 自由旋转链Freely Rotating Chain,Model with fixed valency angle The angle are restricted to lie on a cone, but the bond can rotate freely on the sur

45、face of the cone., Mean-square of end-to-end distance,Total n terms,Total 2(n-1) terms,Total 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 = 1/3,1.4.3 受阻内旋转链 Hindered Rotation Chain,For a real polymer chain, the rotation of the bonds on th

46、e 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, 298K,1.4.4 高斯链 Gaussian

47、Chain,The 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:,*

48、The same : =Nele2 le=/L,*The same contour length: L=Nele=nlsin(/2), can be experimentally measured.,For PE,For freely rotating chain: contour length: Nele=Nlcos(180-)/2=Nlsin(/2) =Nele2=2Nl2 le=2Nl2/Nlsin(/2)=2.45l,(Note: Only for freely jointed chain the contour length is Nl. For other chains, the

49、contour length is Nlsin(/2).,Equivalent freely jointed chainobey Gaussian distribution; the motion unit is a segment; correspond to real polymer chain Freely jointed chainobey Gaussian distribution; the motion unit is a single bond; only used for theoretical study,Probability distribution function o

50、f 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) Where is the last step (the other end of the chain) located ?,End-to-end distance of Gaussian chain from stati

51、stical 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 Y,Probability distribution function in three dimension,三维空间几率分布函数 W(xyz),Probability,The probability distribution

52、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)： When 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+