METHOD FOR THE PREPARATION OF A VINYL CHLORIDE-BASED POLYMER

摘要

An improvement is proposed for the method of suspension polymerization of vinyl chloride monomer or a monomer mixture mainly composed thereof to produce a polyvinyl chloride resin powder having excellent absorptivity of plasticizers and containing a greatly decreased amount of fish eyes. The improvement consists in the use of a specific suspending agent which is a combination of (a) a modified, partially saponified polyvinyl alcohol, of which the modifying monomeric unit is an ethylene unit having a pyrrolidone group, caprolatam group, oxazolidinone group or 5methyloxazolidinone group as the modifying group and (b) a hydroxypropyl methyl cellulose of specified degrees of substitution of the methoxyl and hydroxypropoxyl groups and a specified viscosity of a 2% aqueous solution thereof. The improvement can be further enhanced by using, in addition to the above mentioned two, a third polymeric suspending agent which is a partially saponified polyvinyl alcohol of a low degree of saponifilcation and a low average degree of polymerization.