Comparative Characterization of Polyvinyl Alcohols for Vinyl Chloride Suspension Polymerization 1. The Degree of Hydrolysis

The suspension polymerization of vinyl chloride is a complex process and requires elaborate formulations. These include suspending agents or protective colloids that play a key role in the particle formation process. In the suspension polymerisation of vinyl chloride the bulk monomer phase is dispersed in water by vigorous stirring and the droplets produced are stabilized against coalescence by the presence of suspending agents or protective colloids. The degree of protection afforded to the monomer droplets depends on the type, properties and concentration of the protective colloids (1-5). The properties of suspension obtained polyvinyl chloride (PVC-S) depend largely on its particle structure or morphology, so significant changes in polyvinyl chloride characteristics can be achieved by changes in suspending agent systems (6-10). Polyvinyl alcohols (PVA) are among the most used suspending agents or protective colloids. They are vinyl acetate - vinyl alcohol copolymers. The basic properties of polyvinyl alcohols depend on their degree of hydrolysis, degree of polymerization, average molecular weight and distribution of hydroxyl groups on the polymer chain. Little changes in polyvinyl alcohols structure can result in important changes of polyvinyl chloride morphology, hence of polyvinyl chloride properties (8-10). For this reason we decided to perform an in-deep, comparative study on the structure of some polyvinyl alcohols used in polyvinyl chloride technology. Here, we present the comparative determination of the degree of hydrolysis of different types of polyvinyl alcohols used in PVC-S technology as basis for a new method of characterization. For reproducibility reasons, complete standard characterization of all the samples used was also performed.