Syndiotactic polymers, polar solutions

Solvent Polarity Effects. To investigate the effect of solvent polarity on these systems, a series of polymerization reactions was performed using mixtures of 2 solvents with different dielectric constants (e) methylene chloride (e=14.8) and hexane (e-2.0). As seen in Table V, the solvent polarity had a great effect on the tacticity of the resultant polymers. Predominately syndiotactic polymers were formed in the more polar solutions as previously found ( ), and the level of isotacticity increased as the solutions became less polar. These results support the proposal that isotactic sequences come from backside attack on... 

There are a few exceptions to this general rule. One of the few examples of an effect on polymer stereochemistry was provided by Dais et who found that polymerization of 31 above the cmc initiated by y-irradiation at 25 C yields polymer composed entirely of syndiotactic dyads P m) =0. When the double bond was distant from the polar head group in 32, the tacticity observed was similar to that observed in solution polymerization 18. Polymerization of 31 at... 

Free-radical polymerizations were conducted under a wide range of conditions that included photochemical, thermochemical, and low-temperature alkylborane-oxygen initiation methods. Both bulk and solution methods were used with somewhat unexpected results. Temperature appeared to have relatively little effect on the tactic order (percent syndiotacticity) of VTFA polymers. Polymerization temperatures ranged from -80 to 150 C and gave syndiotacticities between 50 and 55% by triad analysis. Polar solvents affected tacticity more. For example, polymerization in 1,2-dichloro-ethane resulted in a syndiotacticity of 43%. Presumably, such effects were related to a disruption of the association of VTFA monomer with the growing chain end. 

Polyvinyl chloride (PVC) has peculiar material characteristics because of its high level of syndiotactic vinyl chloride units. The polymer as a result has a low to modest level of crystallinity (-10%). The uncrystaUized regions in PVC are subject to dissolution by polar solvents. The solutions formed have exothermic heats of mixing and negative deviations from ideality. Non-volatile polar liquids, which dissolve amorphous PVC, are called plasticizers . PVC now becomes an elastomeric mixture of small crystalline regions and a solution phase. These materials are called plasticized polyvinyl chloride. 

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