Vinyl chloride suspension polymerisation and the control of polymer properties

A number of poly(vinyl alcohols), used in the suspension polymerisation of vinyl chloride, have been fractionated and characterised. The most effective had the highest molecular weight and contained the most unsaturation. The more insoluble fractions gave the best balance of product properties. Reactor sampling experiments have been used to determine the mechanism of polymerisation. In most polymerisations, the final grain size is determined by factors that control the coalescence and break‐up of the monomer droplets during the first 15% conversion. It is suggested that the structure within the grains is controlled by the formation of a continuous network of PVC primaries which retards droplet contraction.