| Popis: |
Polychlorotrifluoroethylene (PCTFE) is ordinarily prepared by emulsion polymerization. A polymer suitable for thermal processing requires coagulation, extensive washing, and postpolymerization workup. Coagulation to provide a filterable and washable solid is a slow, difficult process and removal of surfactant is an important part of it. Complete removal may be extremely difficult depending on the extent of adsorption to the polymer particles. Consequently we set out to develop a suspension polymerization process, which would be surfactant-free and afford an easily isolated product requiring a minimum of postreaction workup. Early work at Kellog on Kel-F produced polymers with low zero strength time (ZST) values indicating low molecular weight. These polymers had poor physical properties. Tseng and Young in preliminary experiments in a water/ alcohol medium made a suspension polymer that had ZST values approximately those of an emulsion polymer. These results led us to a study of the process variables and of different initiators in the suspension polymerization of chlorotrifluoroethylene. Polymer characterization, including inherent viscosity, GPC molecular weight, and melt flow behavior, was also studied. As a result of this study a suspension process was developed that gives high-molecular-weight product with outstanding physical properties. |
