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 °C in bulk and in various solvents. In all cases, number average molecular weight ( M 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 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 ₙ block copolymers involved a semi‐batch feeding in bulk of styrene monomer to a poly(TBA) macroinitiator which resulted in high M ₙ gradient blocks with low polydispersity ( M ₙ = 54.7 kg · mol −1 , M w / M ₙ = 1.3). magnified image