Incorporation of nonionic emulsifiers inside styrene–methacrylic acid copolymer particles during emulsion copolymerization

Emulsion copolymerizations of styrene and methacrylic acid with polyoxyethylene nonylphenyl ether nonionic emulsifiers having various hydrophilic–lipophilic balance (HLB) values (13.7, Emulgen 911; 15.5, Emulgen 920; 17.2, Emulgen 931) were performed. The incorporation behavior of the nonionic emulsifiers, comprising polydisperse poly(ethylene oxide) (PEO) chain lengths, inside the particles was investigated. At the completion of the polymerization, the incorporated percentage of the lowest HLB emulsifier was 61%, much higher than that of the highest HLB one (10%). In both polymerizations, the amounts of the incorporated emulsifiers increased with conversion, and shorter PEO chain (i.e., lower molecular weight) components were predominantly incorporated over longer PEO chain components.