The influence of molecular weight on the strain-dependent permeability of poly(vinylidene fluoride) (PVDF) is investigated. Permeability measurements were performed on spherulitic and fibrous PVDF at various concentration levels of ethyl acetate (EtAc). Rheo-photoacoustic Fourier transform infrared spectroscopy (RPA FTl.r.) was used as a quantitative measure of the desorption diffusion coefficient. Polymer molecular weight, crystallite size and the number of tie molecules in the network have a significant effect on the morphological changes as a result of plastic and elastic deformations. The head-to-head and tail-to-tail defect content also plays a significant role on the mechanism of plastic deformation. By reducing the stability of crystallites, higher defect contents appear to diminish the yield stresses in PVDF which result in transition to the fibrous morphology without void formation.