(112f) Monomer-by-Monomer Sequences along Gradient Copolymer Chains Predicted by Kinetic Monte Carlo Simulations

Gradient copolymers, which are expected to have an intermediate chain architecture between conventional block copolymers and random copolymers, have attracted much interest in a wide range of applications. Because of the well-ordered variation in chain structure, gradient copolymers have been theorized to exhibit interfacial activities superior to block copolymers of the same composition. However, the sequences in gradient copolymers cannot be determined directly by experimental methods. To address this challenge, we developed kinetic Monte Carlo (KMC) models to predict explicit monomer-by-monomer sequence along the copolymer chain, which is not possible with traditional moment-based continuum models.

We demonstrate our approach using styrene/methyl methacrylate gradient copolymerization with nitroxide-mediated controlled radical polymerization(NM-CRP). It was found that the variation in the average sequence length as a function of chain length does not resemble that of the instantaneous composition, which has been considered to be sufficient to characterize gradient copolymers. Our findings indicate that copolymers with compositional gradients may have chain sequences resembling those of statistical copolymers and suggest that characterization of ?structural? gradients is warranted.

In order to unravel the impact of monomer sequences on the physical properties of gradient copolymers, there must be a shift from a focus on control of composition to control of sequence. We show that KMC simulations are a powerful tool to predict the explicit sequence of copolymers and can serve as a companion to experimental efforts to precisely design the sequence length distribution of copolymers.