Theory for the diffusion of large molecules in amorphous polymers. Application to the PVC-plasticizer systems

The diffusion of large molecules within polymers is a subject of great technological importance from both standpoints of processing and useful properties. In the present context, a penetrant molecule is considered to be 'large' if its size exceeds that of a chain segment of the host polymer by a reasonable amount. The authors have initiate a penetrant shape-dependent, largely free volume-based diffusion model that utilizes theoretical conformational analysis to generate specific low-energy penetrant molecular shapes and predict diffusion coefficients (D) for large diffusants within amorphous polymers, that can also be either crosslinked or semicrystalline, above their glass transition temperatures. The underlying theory has been presented in earlier reports by K.A. Mauritz et al. In this paper, the general equations developed in the model, as well as the technique of theoretical conformational analysis, to calculate, a priori, values of the diffusion coefficient for selected members of a homologous series of di-n-alkylphthalate plasticizers have been applied and then these results are compared with previously-reported experimental diffusion data for these systems.