Vinyl chloride polymerization tacticity

It seems likely that other polymerizations will be found to depart from Bemoullian statistics as the precision of tacticity measurements improves. One study12 indicated that vinyl chloride polymerizations are also more appropriately described by first order Markov statistics. However, there has been some reassignment of signals since that time. 4 25... 

In practice, however, vinyl chloride polymerized commercially does not have regular tacticity because the growing end of the chain is a free radical at an sp hybridized carbon center which can freely rotate. This rotation rate varies with temperature by polymerizing vinyl chloride at very low temperature the rotation can be slowed significantly, preferentially trapping certain conformations and allowing for polymerization of a more syndiotactic polymer. 

Since metallocene catalysts have coordination power for chain staeoregularity, efforts are made to produce tactic polymers from nonolefin sources such as styrene, MMA, and vinyl chloride, which are normally polymerized using free-radical processes. Unfortunately, metallocenes based on early transition metals are too sensitive to polarity. Only styrene can be polymerized to high molecular weight. Syndiotactic PS was produced using half-sandwich metallocene in 1986 by Ishihara et The materials have high melting tempaa-... 

---