Computer Simulation of Controlled Radical Polymerization: Effect of Chain Confinement Due to Initiator Grafting Density and Solvent Quality in “Grafting From” Method

Abstract

We use stochastic Monte Carlo simulation following the bond fluctuation model to study the effects of grafting density of surface-anchored initiators and solvent quality on controlled radical polymerization (CRP) from flat impenetrable substrates under good and poor solvent conditions. Our CRP model includes a mechanism for activation/deactivation of the chains and neglects termination and chain transfer reactions. The system is, thus, “truly living”. We find that under these conditions, surface-initiated polymerizations at low grafting densities resemble those in the bulk. In contrast, at high initiator grafting densities, these surface-initiated polymerizations result in gradients of the free monomer and chain-end concentrations, which lead to an uneven growth of the chains and ultimately yield polymers with broad molecular weight distributions. Poor solvent conditions exacerbate this problem by collapsing the chains and in some cases forming chain aggregates, which further restrict the access of free monomers by the active polymer chain ends and contribute to their uneven growth and ultimately broader length distributions relative to good solvent conditions. While at low grafting densities the molecular weight distributions can be described by the conventional Schulz-Zimm distribution function, at high grafting densities this approach fails to describe accurately the dispersity in chain lengths.