ABSTRACT: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.

The influence of the total comonomer concentration (TCC; 30-42 wt %), emulsifier concentration (EC; 7.3-23 wt %), hydrophilic-lipophilic balance (HLB; 9-9.9), crosslinking agent (N,N 0 -methylene bisacrylamide) concentration (CAC; 0-122.8 ppm with respect to TCC), and isopropyl alcohol (chain-transfer agent) concentration (IPC; 0-1.5 wt % with respect to TCC) on the flocculation performance (FP) of 80/20 wt % acrylamide (AM)/[2-(acryloyloxy)ethyl]trimethylammonium chloride (ADQUAT) copolymers obtained by semicontinuous inverse microemulsion copolymerization was studied with capillary suction time testing for FP assessment on anaerobic digested sludges. FP increased as TCC decreased, was nearly unaffected by EC, was maximum with an HLB of 9.5, decreased strongly with CAC, and showed a peak value with an IPC of 1 wt %. At a very high TCC, copolymer growth in a highly collapsed state resulted in greatly structured, high weight-average molar mass flocculants with decreased swelling capacities (SCs), which did not favor bridging flocculation, and in increased shielding of their positive charges, which did not favor charge neutralization flocculation. However, industrially needed latices with both high TCC and good FP could be obtained by the addition of isopropyl alcohol, which, below a concentration of 1 wt %, improved FP by decreasing the weight-average molar mass and thereby enhancing SC while maintaining long enough chains to be effective for bridging flocculation. On the basis of the results, new star-shaped ADQUAT/AM copolymers are envisioned as flocculants with superior FP. A synthetic route is proposed.