Characterization of water‐soluble oligomer in acrylic acid‐styrene emulsion copolymerization

Low molecular weight species, formed during the emulsion copolymerization of styrene and acrylic acid, were isolated and characterized. Samples of the reaction mixture were taken at different times during seeded and unseeded batch reactions. Reactions were stopped via injection of the samples into hydroquinone solutions and cooling with dry ice. Low molecular weight copolymers were separated and FTIR spectroscopy, mass spectroscopy, and 13C–NMR spectroscopy techniques were used to measure the oligomer composition, molecular weight, and copolymer sequence distribution, respectively. The molecular size measurements should relate to the size of oligomeric radicals that grow in the water phase and enter polymer particles and the measurements should also relate to any water‐soluble polymer that is formed by termination in the aqueous phase. The molecules, found for copolymers formed from 90/10 weight ratios of styrene and acrylic acid, were comprised of 6–9 monomer units with 2–3 being styrene. Those formed from 60/40 styrene/AA ratios contained 13–16 monomer units with 1–2 styrene. Differences were observed between seeded and unseeded systems, especially in the amount and nature of the water‐soluble material formed early in the reaction.