Nitroxide mediated copolymerization of acrylates, methacrylates and styrene: The importance of side reactions in the polymerization of acrylates

Abstract

The ability to (co)polymerize acrylates, methacrylates and styrene with one alkoxyamine/nitroxide has been regarded as challenging in nitroxide mediated polymerization (NMP). The alkoxyamine 3-(((2-cyanopropan-2-yl)oxy)(cyclohexyl)amino)-2,2-dimethyl-3-phenylpropanenitrile (Dispolreg 007) has recently emerged as a robust regulator to mediate the (co)polymerization of methacrylates and styrene. Herein, the versatility of the alkoxyamine is tested to produce random and block copolymers based on n-butyl acrylate (BA). The formation and influence of dead polymer (mostly macromonomers) was studied for the homopolymerziation of n-butyl acrylate. At temperatures above 100 °C, control over the polymerization could be retained up to about 50% conversion, with relatively narrow molar mass distributions (Mn = 34000 g·mol−1, Ð ∼ 1.7). Above this conversion side reactions, namely β-scission of mid-chain radicals generated by chain transfer to polymer and monomer self-initiation led to loss of control. This effect could be mitigated by lowering to 50 wt% the concentration of BA and/or by lowering the temperature, or by copolymerizing BA with MMA or styrene. The chain extension of acrylate based macro-alkoxyamines led to non linear structures, due to the presence of macromonomers and residual dead chains during the production of PBA macro-alkoxyamines.