Influence of hydrophilic–lipophilic balance of nonionic emulsifiers on emulsion copolymerization of styrene and methacrylic acid

Emulsion copolymerizations of styrene and methacrylic acid (MAA) with various nonionic emulsifiers having a hydrophilic–lipophilic balance (HLB) range of 13.7–17.2 were performed to clarify the influence of emulsification state on polymerization. The emulsification state with a lower-HLB value emulsifier was worse than that with a higher one. In the lowest HLB value, MAA was predominantly polymerized over styrene in the early stage of the copolymerization, resulting in predominant (heterogeneous) distribution of MAA units in the inside of the final polymer particles. In the higher-HLB emulsifiers, styrene and MAA were simultaneously copolymerized, resulting in a homogeneous MAA distribution. The percentage of incorporation of the nonionic emulsifier inside the particles was the highest (49% based on the total amount of the emulsifier) in the lowest HLB, whereas it was 1% in the highest HLB.