Synergistic aerobic ATRP/DT polymerization in emulsion: operating window, mechanism, and limits

Concurrent ATRP with degenerative transfer (DT, the RAFT mechanism) enables aerobic emulsion polymerization of butyl methacrylate (BMA). We studied the effects of the initiator-to-chain transfer agent ratio and nature, halide type, temperature, pH, targeted degree of polymerization, and monomer fraction on the kinetics, molecular weight, dispersity, and colloidal properties of the resulting polymers. The optimal conditions were [R-Br]/[CTA] = 1–2 with 0.1 M NaBr or NaCl at pH 5–10, 70–95 °C, and ≤ 30 vol% BMA, which yielded high conversion (97%) with stable latexes, predictable molar masses (up to 76 × 10 3 Da), and low dispersities ( Đ ≤ 1.26) using 1 mM Cu catalyst (∼350 ppm). Very low dispersity ( Đ = 1.02) can be achieved also with hydrophilic CTAs. The rate constants increased from 0.033 to 0.174 h −1 increasing temperature from 50 to 95 °C (activation energy: 38.6 ± 7.7 kJ mol −1 ). Chain-end fidelity was demonstrated using a PBMA macroinitiator to produce a PBMA- b -PDPA copolymer in emulsion. Fast oxygen and hydrogen peroxide reduction reactions (ORR and HPRR with k ORR > 10 8 M −1 s −1 ) enabled by [Cu I TPMA] + permitted ATRP/DT polymerization without degassing the mixture. These results delineate the operational limits and opportunities for extending ATRP/DT polymerization.