Effect of transfer agent, temperature and initial monomer concentration on branching in poly(acrylic acid): A study by ¹³C NMR spectroscopy and capillary electrophoresis

Branching has been investigated in poly(acrylic acid) synthesized by conventional radical polymerization with and without chain transfer agent (CTA) at different temperatures and initial monomer concentrations. The average number of branches per monomer unit (i.e. degree of branching) was quantified by solution-state ¹³C NMR spectroscopy. The heterogeneity of branching (dispersity of the electrophoretic mobility distributions) was measured by capillary electrophoresis in the critical conditions (CE-CC). The degree of branching (DB) increases with the reaction temperature due to a rise in the frequency of reactions leading to branches, while the heterogeneity of branching remains steady. DB is lower in polymer synthesized with CTA. This decrease is due to either the CTA quenching the mid-chain radicals or a reduction of the rate of chain transfer to polymer relative to (chain-end) propagation. No influence of initial monomer concentration on DB and on the heterogeneity of branching was observed