Polymers Large molecules syndiotactic

Chlorination of poly(vinyl chloride) destroys the regularity of the tacticity. Dor-restijn et al. [123] executed chlorination in two different ways. First, pol>tvinyl chloride) was chlorinated in solution so that no preference existed for the kind of hydrogen atom which was replaced by chlorine atoms the tacticity of the polymer molecules is destroyed more or less completely. Second, the polymer was chlorinated in powder form in this case there is a large preference for the amorphous parts, whereas the crystalline parts are mudi less available for chlorination and remain more or less intact Even if the polymer is attacked prrferentially at the isotactic sequences, the tendency to form gels will decrease, as the [nresence of an even number of isotactic sequences in between syndiotactic sequences causes an enormous increase in the crystallinity of polyfviny chloride) [82,84]. Dorrestijn et al. showed that chlorination had a dramatic influence on the tendency to form gels in the case of solution chlorination, whereas powder chlorination had only a minor effect despite much higher chlorine contents. 

When the polymerization of EMA was carried out in toluene with 1,1-diphenylhexyllithium as initiator at -78 C, a large amount of methanol-soluble, isotactic polymer formed with a very small amount of methanol-insoluble fraction. The latter fraction was also isotactic in this case. The results indicate the possibility that in the polymerization of EMA in toluene with BuLi the propagating species for syndiotactic polymer exist in the form of ion pairs complexed with one or more molecules of lithium ethoxide, and the isotactic active species are less connected with the ethoxide or free from it. At higher polymerization temperatures the coordination of ethoxide weakens and the rate of propagation at the chain ends becomes very rapid, which results in a decrease in the formation of methanol-insoluble, syndiotactic fraction. 

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