Chain copolymerization stereoblock

It is known the case of i-PP, for which the copolymerization with small amounts of ethylene tends to stabilize the y form [84] for instance, by melt crystallization of a copolymer with 6% by mol of ethylene more than 80% of the crystalline phase is in the y form [85], It is also known that the obtainment of the y form by melt crystallization, is also favored for samples of low molecular mass [86, 87] and for stereoblock fractions [88]. This seems to suggest that, whenever the preferential crystallization of the y-form is observed, there is the concomitant occurrence of a reduction in the polymer of the length of the chain stretches with polypropylene head to tail constitution and isotactic configuration. 

Pathway (1) has recently found an interesting demonstration in the related area of ethylene/1-alkene multiblock copolymerization, with ZnR2 acting as the chain shuttling agent. In propylene homopolymerization, presumptive evidence of isotactic/atactic stereoblock chain formation with a similar mechanism was reported by Chien et al. for polypropylenes obtained with mixtures of... 

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