Formation of Linear and Graft Block Copolymers at a Polymer/Polymer Interface: How Copolymer Brush and Microdomain Morphology Control Heterogeneous Reactions

Abstract

Irreversible coupling between immiscible melts of two functionalized macromonomers A and B of different lengths resulting in the formation of a linear or graft block copolymer AB was modeled by dissipative particle dynamics. Recently (Macromolecules 2011, 44, 112), we investigated the mechanism of the instability caused by saturating an A/B interface with the copolymer product, which leads to a microdomain structure formation. The present simulations were focused on the influence of copolymer composition and architecture on the microstructure development and characteristics of different kinetic regimes. Nearly symmetric copolymers form bicontinuous microdomains facilitating mass transfer and resulting in the exponential coupling kinetics. Strongly asymmetric copolymers promote fragmentation of a minor phase into isolated domains hardly accessible for the remaining reactants so that the linear or even slower kinetics is observed. At an equal concentration of functional groups, grafting proceeds always slower than end-coupling since branched copolymers form less penetrable brushes at the interface than linear diblocks. The most effective screening is achieved with symmetric copolymers. Both end-coupling and grafting produce long-lived nonuniform microstructures, with the size and shape of domains monotonously changing along the distance from the initial A/B interface. In the interface vicinity, minor phase micelles can form ordered layers.