AbstractThe pore structures of microparticulate drug carriers are important diffusion pathways, which are not a static property but rather may be changing in the case of degradable matrix polymers such as poly[(rac-lactide)-co-glycolide] (PLGA). In this study, the mutual impacts of dynamic changes in microparticle porosity and polymer degradation were analyzed for PLGA with different molecular weights and end groups as well as PLGA-based triblock copolymers. In selected cases, particularly for PLGA with hydrophilic end groups and low initial number average molecular weight of 5 kDa, pore opening/pore closing phenomena were detected during incubation in phosphate buffer at 37 °C. Initially, pore closing was induced by water-induced plasticization and the reduction of interfacial tension. The pattern of molecular weight decrease and mass loss suggested that pore closing did not result in undesired autocatalytic acceleration of degradation or delayed mass loss due to trapped acidic degradation products.