In situ preparation of branched styrene-acrylic copolymer via free radical polymerization using functional chain transfer monomer

A neoteric vinyl compound named 2-(3-mercaptopropionyloxy) ethyl methacrylate (MPOEM) with chain transfer group was designed and synthesized, which can be used for in situ formation of the branching structure by free radical polymerization. The branched styrene-acrylic copolymers were creatively prepared using styrene, methyl methacrylate, hydroxypropyl acrylate, 2-ethylhexyl acrylate, n-butyl acrylate and methyl acrylate as monomers, benzoyl peroxide as initiator and MPOEM as functional chain transfer monomer (CTM) at 135 °C. The formation of branching and the variation of molecular weight were analyzed by using triple detection size exclusion chromatography. The viscosity of branched styrene-acrylic copolymer and that of its linear analog were characterized by rotational rheometer and the Grignard tube. The effects of solid content of copolymer solution and the degree of branching on the viscosity of styrene-acrylic copolymer were investigated. The results showed that under the condition of similar molecular weight, the higher the branching degree of the copolymer, the lower is the viscosity of the copolymer solution. By adding 0.4% MPOEM of the total monomer mass, the styrene-acrylic copolymer with higher branching degree was obtained (M_w.MALLS) = 38,200 g/mol, g′ = 0.7) but its viscosity was found to be lower than those of linear analogs of lower molecular weight (M_w.MALLS = 34,500 g/mol) and branched copolymers with lower branching degree (M_w.MALLS = 35,000 g/mol, g′ = 0.84).