GB883850A - Process for controlling the molecular weight of vinylidene chloride polymers - Google Patents

Abstract

A process for producing relatively low molecular weight copolymers of vinylidene and vinyl chlorides, containing at least 70 weight per cent of vinylidene chloride, comprises polymerizing the monomers in the presence of from 5,0 to 0,05 weight per cent of a perhalomethane chain-stopper having the general formula Y-C-X3 wherein Y is bromine or iodine and X is any halogen atom. Specified perhalomethanes are carbon tetrabromide, bromotrichloromethane, dibrodichloromethane, chlorotribromomethane, bromotrifluoromethane, dibromodifluoromethane, fluorotribromomethane, bromochlorodifluoromethane, carbon tetraiodide, bromotriiodomethane, dibromodiiodomethane, iodotribromomethane, chlorotriiodomethane, dichlorodiiodomethane, iodotrichloromethane, fluorotriiodomethane, difluorodiiodomethane and iodotrifluoromethane. Any known polymerization technique may be employed, but aqueous suspension using a water-dispersible granulating agent, such as a water-soluble cellulose ether, is preferred. The perhalomethane is preferably added to the monomer charge before dispersion in the aqueous phase. In examples, 68 parts of vinylidene chloride and 12 parts of vinyl chloride are copolymerized, using methyl cellulose as suspending agent and lauroyl peroxide as catalyst, in the presence of various chain-transfer agents. The effect of several of the above specified perhalomethanes on the per cent conversion and solution viscosity is compared with that of the following previously known chain-transfer agents: lauryl mercaptan, carbon tetrachloride, chlorodibromo methane, bromochloro methane and bromoform. Another example shows the effect of different amounts of carbon tetrabromide on the solution viscosity obtained in the above polymerization at 80% conversion.ALSO:A process for producing relatively low molecular weight copolymers of vinylidene and vinyl chlorides, containing at least 70 weight per cent of vinylidene chloride, comprises polymerising the monomers in the presence of from 5.0 to 0.05 weight per cent of a perhalomethane chainstopper having the general formula Y-C-X3 wherein Y is bromine or iodine and X is any halogen atom. Specified perhalo methanes are carbon tetrabromide, bromotrichloromethane, dibrodichloromethane, chlorotribromomethane, bromotrifluoromethane, dibromodifluoromethane, fluorotribromomethane, bromochlorodifluoromethane, carbon tetraiodide, bromotriiodomethane, dibromodiiodomethane, iodotribromomethane, chlorotriiodomethane, dichlorodiiodomethane, iodotrichloromethane, fluorotriiodomethane, difluorodiiodomethane and iodotrifluoromethane. Any known polymerisation technique may be employed but aqueous suspension using a water-dispersible granulating agent such as a water-soluble cellulose ether is preferred. The perhalomethane is preferably added to the monomer charge before dispersion in the aqueous phase. In examples 68 parts of vinylidene chloride and 12 parts of vinyl chloride are copolymerised, using methyl cellulose as suspendihg agent and lauroyl peroxide as catalyst, in the presence of various chain-transfer agents. The effect of several of the above specified perhalomethanes on the per cent conversion and solution viscosity is compared with that of the following previously known chain-transfer agents: lauryl mercaptan, carbon tetrachloride, chlorodibromo methane, bromochloro methane and bromoform. Another example shows the effect of different amounts of carbon tetrabromide on the solution viscosity obtained in the above polymerisation at 80% conversion.