Degradation of Block Copolymer Films

We use coarse-grained molecular dynamics simulations to study degradation of films of multiblock copolymers in a solvent. Our simulations were designed to mimic degradation dynamics of glycine, valine, and phenylalanine based poly(ester urea)s in vitro. Simulations show that the rate of copolymer degradation is a result of a fine interplay between chain breaking kinetics, solvent diffusion, and swelling of the domains made of solvophilic blocks. The evolution of the film structure during the degradation process was monitored by calculating the scattering function S(q) of the copolymer film. The solvent diffusion into the films results in a monotonic shift of the peak position to smaller q. This shift is also accompanied by the increase in scattering intensity at q << 1 in such a way that the peak completely disappears at the later stages of the film degradation. This results in the scattering function S(q) to have two characteristic power law regimes with S(q)~1/q² and S(q)~1/q⁴, represented by interconnected vesicles with thin shells. The number average degree of polymerization of the copolymer fragments monotonically decreases with time. However, the polydispersity index of the copolymer fragments first increases as a function of time and then decreases.