Chapter 9: The chemical reaction of polymer  9.1 The character and influencing factor of polymeric chemical reaction  9.2 The chemical alteration of polymer  9.3 The degradation of polymer  9.4 The aging and anti-aging of polymer

The chemical reaction of polymer  The chemical modification of polymer;  Synthesize the macromolecule material which have special function;  Study the chemical structure, destruct factor and rule of polymer.

The types of polymeric chemical reactions ：  The chemical reactions of polymer are divided into three types, base on the change of degree of polymerization and group (side or end):  （ 1 ） The degree of polymerization changeless, the reaction only occur at side group and/or terminal group is called similar transformation. （ 2 ） The degree of polymerization largen, as cross link, block, graft, chain expand. （ 3 ） The degree of polymerization decrease, as depolymerization( 解聚 ), degradation.

9.1 The character and influencing factor of polymeric chemical reaction  The character of polymeric chemical reaction The molecular weight is very large; Polydispersity and multi-level of structure; The aggregative structure and solution behavior of polymer are fairly different from those of the small molecule. The chemical reaction of polymer have different character with small molecule compound.

（ 1 ） The chemical reactions of polymer always incomplete  As the reaction of hydrolysis polyacrylonitrile to polyacrylates--- 丙烯酸盐 聚丙烯腈 异链聚合物 The transformation ratio not the yield rate is used as the reaction extent of functional group. Character: With the different reaction extent, the reaction depth is different, too. 水解

(2) The chemical reaction of polymer are very complex  It is hard to reflect the truth ratio and inextenso 全部的 For instance, polyvinyl acetate polyvinyl alcohol The equation cannot show: 1. How many groups of moleculal chain participate in the reaction ； 2. It can’t be interpreted as that all the ester group has been transformed.

9.1.2 The influential factor of functional group reactive ability （ 1 ） Physics factor  The diffuse speed and local concentration of reactant are reflection of mainly physical factor. Include crystal and amorphous polymer linetype, branch chain and crossline polymer, different chain conformation and so on. 链构象 The reaction is homogeneous or Heterogeneous. 均相或者非均相 They have different effect on the diffuse of small molecule, and then affect the reaction ability of the group.

（ 2 ） Chemical factor  The proximity group and probability effect are primary.  Proximity group effect: Static electrification, the different of steric hindrance and configuration 构型 Proximity group effect lie on: The property of function group ； The type of reaction ； Sterochemistry 。

（ 2 ） Chemical factor Probability effect when the adjacent functional group of polymer react randomly( 作无 规成对反应时 ),there are sigle unreacted group, which restrict the highest transformation ratio. The residue ratio of hydroxyl of the chain decrease to about 10%

9.2 Chemical transformation of polymer  The similar transform of polymer  When polymer reacts with small molecule compound, the transform only occur on side or end group, and the degree of polymerization does not change basically. It called the similar transform of polymer.  The reaction of polymer function group[esterify( 酯化 ), etherification （醚化）, halogenation （卤化）, nitration （硝化）, amidation （氨化）, acetalization （缩醛化）, hydrolyze （水解）, alcoholysis( 醇解 )]  The cyclization in macromolecule chain  Hydrogenation( 氢化 ) of unsaturated polymer  The polymerization degree of the chemical translate largen crosslink, block, graft and extend chain.

9.2.1 Similar transfer of polymerization (1) Substitution of aromatic nucleus reaction Give a illustration with ion exchange resin similarly Substitution aromatic nucleus reaction can occur sulfonation,chloromethylation Sulfonation—strong acid Positive ion exchange resins Chloromethylation （ 氯甲基化作 用） — negative ion exchange resins equation

The reaction of ion exchange resin sulfonation chloromethylation Important function macromolecule material 氯代二甲基醚

（ 2 ） The reaction of fibrin  Fibrin is composed of glucose units with three hydroxide in every ring, and can react with many reagent to create many important ramification.— 分支

The reaction creating ramification of fibrin (1) Nitration 硝化 fibrin Cell is the framework of fibrin Use N% as the degree of nitration ：  N%=12.5 ～ 13.6,it is high-nitrogen nitrocellulose, produce cordite— 无烟火药 ；  N%=10.0 ～ 12.5, pyroxylin— 硝酸纤维素 ；  N%=11, the plastic produce celluloid;  N%=12, dope （涂料） and negative. 衍生物

（ 2 ） The reaction of polyvinyl acetate Vinyl alcohol does not exist. Poly vinyl alcohol is produced by alcoholysis polyvinyl acetate with methanol. 醇解 Both acid and alkali can catalyse this reaction, but people often use alkali due to the high efficiency and have little side reaction. The degree of alcoholysis of the reaction have different request.

（ 3 ） The reaction of polyvinyl acetate Polyvinyl alcohol create polyvinyl, and react with aldehyde, then synthesis polyvinyl acetal— 聚乙烯醇缩醛 : The aldehyde used are formaldehyde and butyraldehyde, namely R is H or -C 3 H 7 The pioloform( 聚乙烯醇缩醛 ) can produce the bond of safety glass, electrical insulative film and dope- 涂料

(4) Chlorination— 氯化处理  The chlorination and hydrogen chlorination of natural rubber The rubber which is not crosslinking is dissolved in the hydrochloric ether or arene as solution, and the homogeneous phase reaction occur. 氯代烃 芳烃 By the Markownikoff rule, chlorin add on third class carbon.

 The chlorination and hydrogen chlorination of natural rubber Chlorine react with chloroform or carbon tetrachloride solution in 80 ～ 100 ℃ ; 氯仿

 The chlorination of saturation hydrocarbon polymer 饱和 Polyethylene, polypropylene, polyisobutylene, PVC, other saturation polymer and copolymer can be chloridized. The mechanism of reaction is free radical. Heat, initiator of free radical polymerize and ultraviolet light can initiate reaction.  Reaction is take place in solid phase or solution  When the solution is unhomogenized, the reaction occur on the surface of the polymer, then low chlorine produce is created. It is advantageous to improve surface performance and have no effect to the mechanical property of main body.

（ 5 ） Cyclization 环化 When some polymers are heated, they can cyclize through side group reaction. Such as polyacrylonitrile form ladder structure through preoxidation or cyclization.— 预氧化或环化 At last it is heated in 1500 ～ 3900 ℃. It separate out other element beside carbon, then form carbon fiber. This is a new type high strength and modulus material ， which can produce the excellent complex material with metal, ceramics, rosin, and it is wide used in high tech and space navigation.

9.2.2 The chemical transform that the degree of polymerization largen  This kind of reaction is: cross linking, block, graft and extend chain. （ （ 1 ） Cross linking With the action of heat, light, radiant energy or cross linking reagent, the molecule chain link up through the chemical bond and form three dimensional reticular structure. 三维空间网状结构

① The sulfuration of rubber 橡胶硫化  The cross linking of rubber is called sulfuration.  The early meanings of sulfuration (narrow sense of sulfuration)----is the chemical process that the rubber transformed to cross linking reticulation polymer by sulfur (thermal sulfuration) or SCl 2 (cold sulfuration)  Then----the chemical reaction which cross link the rubber by peroxide, diazocompound, Se, Te and other metallic oxide is also called sulfuration. More than that ， broad sense of sulfuration is the general designation of rubble cross linking caused by chemical or physical factor.

② The cross linking of polyolefins 聚烯烃  The main chain of polyethene, ethylene – propylene copolymer and polysiloxane is not contain double bond, so they cross link through peroxide, not sulfur.  The free radicals, which are created by the thermal decomposition of peroxide, take the hydrogen on macromolecule, and then form the macromolecule free radicals and coupling cross link.

（ 2 ） Graft copolymer  Graft reaction ： the chemical process that some side chains transplant to the main chains, which are different from the latter in the structure and compose of structural unit.  The graft copolymer’s performance is decided by the composition, structure and length of the main and side chains, and the number of side chains.  Graft is one of the important means of polymer modification

 There are two means to produce graft copolymer ： polymerization ： Polymerization occur on the active induction point of polymer main chain, then form side chains, include big monomer, initiator, chain transfer, radiation polymerization, photopolymerization and mechanical process coupling ： This means make use of the side function of main chain macromoleculer and the polymer which has end function

（ 3 ） Block copolymer  Most block copolymer are type AB and ABA. Some else are ABAB or ABC, such as SBS (S is the chain segment of styrene, B is the chain segment of butadiene).  The means of synthesize block copolymer isn’t free radical. It need special technique.

① The active polymerization that add different monomer in turn It is the most frequent way to synthesize block polymer that add different monomer in turn to polymerize subsection by means of living polymerization initiatory First initiatory A Then initiatory B Pay attention the order of adding monomer

① Active polymerization that add different monomer in turn  Several means to synthesize SBS (1) BuLi is the initiator, then add styrene, butadiene, styrene in turn to polymerize. S → B → S (2) Naphthalin natrium polymerize the butadiene and form double negative ions, then styrene polymerize on the double end. S ← B → S (3)First form SB ， then connect with propriety coupling agent. 适当的 S → B…X…B ← S

② Use the reaction between performed polymer that have end group to synthesize.  Such as: the esterify between polystyrene and polymethacrylate can synthesize block copolymer. – 聚甲基丙烯酸酯 ③ Synthesize through the exchange reaction of polycondensation. such as: heat polyester and polyamides, through the transfer chain to synthesize the block copolymer of them.

④ Special initiator  Using the double function free radical initiator which work independently in different condition can also synthesize block copolymer.  As show below ： + styrene (  ) decompose at the bond of carbon nitrogen cause the styrene polymer The end group ester peroxide can be activate by amine

⑤ Force chemistry Two homopolymers or one homopolymer and another monomer plasticate( 塑炼 ) heat and machine shearing force chain rupture to free radical Block copolymer The biradical termination between two chain free radical cause the polymer of second monomer

⑥ Photolysis— 光解作用  Irradiated by UV, as show below ： The polystyrene dissolve in MMA Uv irradiate C--Br Produce free radical Initiate the polymerization of MMA, form the block copolymer

(4) Extend chain  Extend chain ： The reaction connect the performed polymers that have lower molecular weight through propriety means, increase the molecular weight.  远螯聚合物  Telechelic oligomer and liquid rubber, can form high molecular weight polymer though extend chain. This can replace traditional complex sulfuration— 硫化  All the performed polymers have active end group such as hydroxide, carboxyl, amidocyanogen, carbimide can extend chain. 氨基 异氰酸脂  Polycondensation, free radical, and negative ion can synthesize end group telechelic oligomer.

(4) Extend chain  Example ： preparation of telechelic oligomer with hydroxyl and carboxyl Initiator is naphthalen natrium Telechelic oligomer with hydroxyl and carboxyl Double negative ion active polymer

(4) Extend chain Extend chain polymerization such as PET,PBT  Hydroxide: the extend chain agent is double acid anhydride or diisocyanate  Carboxyl: the extend chain agent is Oxazoline 唑啉 , bicyclic oxide 双环氧化物. 如： the structur of dioxazoline is: 二喹啉 Very active Reaction with carboxyl PET-D-PET ； PET-D-PBT ； PBT-D-PBT 酐 二异氰酸盐 ( 酯 )