Semicontinuous copolymerization of 80/20 wt % [2-(acryloyloxy)ethyl] trimethyl ammonium chloride/acrylamide in an inverse microemulsion at high comonomer concentrations

The semicontinuous inverse microemulsion copolymerization of 80/20 wt % [2-(acryloyloxy)ethyl]trimethylammonium chloride/acrylamide in an isoparaffin solvent at high comonomer concentrations (30-42 wt %) was studied with a mixture of nonionic surfactants (Crill 43 and Softanol 90) as the emulsifier and sodium metabisulfite as the initiator. The influence of the total comonomer concentration (TCC), emulsifier concentration (EC), hydrophilic-lipophilic balance (HLB), isopropyl alcohol (chaintransfer agent) concentration (IPC), and crosslinking agent concentration (CAC) on the weight-average molar mass (M _w), absolute viscosity (BV), and viscometric structuring index (VSI) of the obtained copolymers was analyzed. M_w and BV increased with TCC and HLB and decreased with EC. At the higher TCC, M_w decreased with IPC; meanwhile, at the lower TCC, M_w increased with IPC above 0.5 wt %. VSI increased with TCC, HLB, and IPC and decreased with EC. VSI increased dramatically with CAC, whereas BV showed a peak at the CAC of 10 ppm. In the absence of both chain-transfer and crosslinking agents, M_w increased linearly with VSI, and this suggests that linear copolymers of very high M _w values cannot be obtained by inverse microemulsion copolymerization, at least for high TCCs. The results are explained in terms of both the collapsed state of the copolymer chains inside the latex particles and changes in the interface structure and composition.