Explicit Sequence of Styrene/Methyl Methacrylate Gradient Copolymers Synthesized by Forced Gradient Copolymerization with Nitroxide-Mediated Controlled Radical Polymerization

In spite of many efforts made to study gradient copolymers, the monomer-by-monomer sequence along the chain is still obscure. A general computational framework based on kinetic Monte Carlo simulations was developed to predict the explicit sequence of copolymers. We demonstrate our approach using styrene (S)/methyl methacrylate (MMA) gradient copolymers synthesized by a semibatch process with nitroxide-mediated controlled radical polymerization (NM-CRP). It was found that the variation in the average segment length as a function of chain length does not resemble that of the instantaneous composition. Our findings indicate that copolymers with compositional gradients may have monomer-by-monomer sequences resembling those of statistical copolymers. It was also found that the explicit sequence can significantly deviate from that of the instantaneous composition as a function of chain length when combination is the favored termination mode. These details of explicit sequence revealed by KMC simulations are obscured by only considering fractional composition measures to characterize the gradient shape.