Vinyl acetate Ziegler-Natta polymerization

The polymerization proceeds spontaneously at room temperature or elevated temperatures. The proposed matrix of the comonomer complexes is described in Reference 96. Examples of alternating acrylonitrile copolymerizations involve vinyl cyclohexanes with AlEC2H5tCl2 (97), vinyl acetate with ZnCl2 (98) or Ziegler-Natta catalyst (99), and styrene. 

PB base polymers are semicrystalUne isotactic thermoplastic polyolefins. They are derived from the polymerization of butene-1 monomer with or without other alpha-olefin monomers utilizing a Ziegler-Natta type of catalyst. Their unique crystallization behavior means longer open times of adhesive and sealant formulations compared to other commonly used polymers such as polyethylene and ethylene-vinyl acetate copolymer (EVA). Polybutylene (PB), also called polybutene-1 or poly-1-butene, is different from polybutene or polyisobutylene (PIB). PIB is amorphous and rubbery, and comes in the form of a viscous liquid or big, hard block (6 in. in length and width or could be larger). PB base polymers are sup-pUed in the form of small pellets (about 0.25 in. in diameter) or nibs. 

Normally, free radical polymerization results in essentially atactic polymers although steric and electrostatic effects generally favour one configuration or the other and truly random polymers are probably rare. In some cases, free radical polymerization results in polymers which are largely syndiotactic examples of monomers which behave in this way are chlorotri-fluoroethylene, methyl methacrylate and vinyl acetate. More commonly, however, highly tactic polymers are prepared by means of ionic polymerizations. Most of the common vinyl polymers have been obtained in isotactic and syndiotactic forms by the use of ionic initiators, particularly lithium alkyls and Ziegler-Natta catalysts. 

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