Degradation of Block Copolymer Films Confined in Elastic Media

We performed coarse-grained molecular dynamics simulations of swelling and degradation of glycine, valine, and phenylalanine-based poly(ester urea) copolymer films confined within polymer networks with different values of shear modulus. The microphase separated copolymer films are shown to degrade by surface and bulk erosion depending on the relative rates of chain breaking and water diffusion into the copolymer film. The degrees of swelling of the hydrophobic domains controlled by copolymer composition have a strong effect on degradation kinetics of the films. The competitive substitution of the solvent by hydrophilic fragments is influenced by their affinities to the network strands. The network interface dynamics are driven by the diffusion of solvent into the film which is manifested in a t^1/2 scaling dependence. The evolution of the film structures is quantified by analyzing the film scattering function S(q). The peak position in the scattering function associated with interdomain spacing shifts toward smaller q values and disappears as copolymers degrade. The dispersity of the degraded fragments is found to be a universal function of the fraction of broken bonds, independent on the copolymer composition and structure.