High-Molecular-Weight Poly(tert-butyl acrylate) by Nitroxide-Mediated Polymerization: Effect of Chain Transfer to Solvent

Tert-Butyl acrylate (TBA) was polymerized by nitroxide-mediated polymerization (NMP) using BlocBuilder initiator and 4.5 mol-% additional SG1 (N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide) relative to BlocBuilder (2-methyl-2-[N-tert-butyl-N-(diethoxylphosphoryl-2,2-(dimethylpropyl)aminooxy]propionic acid) at 115 degrees C in bulk and in various solvents. In all cases, number average molecular weight ((M) over bar (n)) increased linearly up to 35% conversion. k(p) K values (k(p) = propagation rate constant, K = equilibrium constant) for TBA agreed well with literature data. For higher target (M) over bar (n) > 50 kg.mol(-1), solution polymerizations used to reduce viscosity were problematic as chain transfer reactions became noticeable, particularly when block copolymers with styrene were desired. A better strategy to obtain high (M) over bar (n) block copolymers involved a semi-batch feeding in bulk of styrene monomer to a poly(TBA) macroinitiator which resulted in high (M) over bar (n) gradient blocks with low polydispersity ((M) over bar (n) = 54.7 kg.mol(-1), (M) over bar (w)/(M) over bar (n) = 1.3).