Synthesis of ultra-high-molecular-weight PVA using two-stage photo-concentrated emulsion polymerization of vinyl acetate

Abstract

This article deals with a process for synthesizing an ultra-high-molecular- weight poly vinyl alcohol (UHMW PVA) through two-stage photo-concentrated emulsion polymerization in the absence of potassium persulfate (KPS). In the first stage vinyl acetate (VAc) monomer and polyoxyethylene nonyl phenyl ether sodium sulfate (POEPES) were mixed in equal proportions and the reaction was carried out at 0°C, without any initiator, by photo-irradiation with a high-pressure mercury lamp. The reaction was stopped when the conversion rate of VAc reached 10%. The viscosity of the pre-polymer was observed to be 270 cps. The purpose of the second stage was to produce a concentrated emulsion solution which comprised a volume fraction of over 50% consisting of VAc, obtained from the first stage, POEPES and deionized water. Photo-concentrated emulsion polymerization was carried out following the same procedure as in the above mentioned stage. The conversion rate of VAc could reach more than 80% in a very short time. Furthermore, a Pn (average degree of polymerization) of PVA of 12400 could be obtained, following the hydrolysis of polyvinyl acetate (PVAc). The characteristics of UHMW PVA were as follows: the regular tactic structure was 50%; the ratio of 1,2-glycol structure was estimated to be about 1.2 mol% and saponification could reach 99.5%.