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

Abstract

AbstractTert‐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 ($\overline M _{\rm n}$) increased linearly up to 35% conversion. kpK values (kp = propagation rate constant, K = equilibrium constant) for TBA agreed well with literature data. For higher target $\overline M _{\rm n}$ > 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 $\overline M _{\rm n}$ block copolymers involved a semi‐batch feeding in bulk of styrene monomer to a poly(TBA) macroinitiator which resulted in high $\overline M _{\rm n}$ gradient blocks with low polydispersity ($\overline M _{\rm n}$ = 54.7 kg · mol−1, $\overline M _{\rm w} /\overline M _{\rm n}$ = 1.3).magnified image