RAFT Polymerization of Tert-Butyldimethylsilyl Methacrylate: Kinetic Study and Determination of Rate Coefficients

Well-defined poly(tert-butyldimethylsilyl methacrylate)s (TBDMSMA) were prepared by the reversible addition-fragmentation chain transfer (RAFT) process using cyanoisopropyl dithiobenzoate (CPDB) as chain-transfer agents (CTA). The experimentally obtained molecular weight distributions are narrow and shift linearly with monomer conversion. Propagation rate coefficients (k_p) and termination rate coefficients (k_t) for free radical polymerization of TBDMSMA have been determined for a range of temperature between 50 and 80 °C using the pulsed laser polymerization-size-exclusion chromatography (PLP-SEC) method and the kinetic method via steady-state rate measurement, respectively. The CPDB-mediated RAFT polymerization of TBDMSMA has been subjected to a combined experimental and PREDICI modeling study at 70 °C. The rate coefficient for the addition reaction to RAFT agent (k_β1, k_β2) and to polymeric RAFT agent (k_β) is estimated to be approximately 1.8 × 10⁴ L·mol^-1·s^-1 and for the fragmentation reaction of intermediate RAFT radicals in the pre-equilibrium (k_-β1, k_-β2) and main equilibrium (k_-β) is close to 2.0 × 10^-2 s^-1. The transfer rate coefficient (k_tr) to cyanoisopropyl dithiobenzoate is found to be close to 9.0 × 10³ L·mol^-1·s^-1 and the chain-transfer constant (C_tr) for CPDB-mediated RAFT polymerization of TBDMSMA is about 9.3.