Molecular motions in bisphenol a polycarbonates as measured by pulsed NMR techniques. II. Blends, block copolymers, and composites

Molecular motions in several polyblends and composites based on bisphenol A polycarbonate were investigated over a wide temperature range by means of two pulsed nuclear magnetic resonance methods: the spin-lattice relaxation time T1 and the spin-lattice relaxation time in rotating frame T1ρ. Characteristic changes in the transitions of the polyblends and composites with respect to the transitions of unmodified homopolymers and copolymers were observed. By selecting different types and quantities of materials to modify the matrix (bisphenol A polycarbonate) these changes were analyzed. It was found that the multiple transitions in the composites and polyblends were not always combinations of the transitions present in the constituent materials, but depended on compatibility of the polymers and the type of molecular motions of the individual components. Unlike other methods of investigating polymers in bulk, nuclear magnetic relaxation methods are sensitive to supramolecular structure or morphology. Supplemented with transmission and scanning electron micrographs, the results from these experiments led to the postulation of interaction domains or zones between the two phases in certain nonhomogeneous polymer systems in which the motions in one phase (usually the continuous phase) were affected by the motions in the other phase (usually the dispersed phase). Information on the nature and extent of this interaction was obtained by the NMR relaxation methods. The experimental results reflect not only the presence of separate phases in the nonhomogeneous materials, but also the complex heterogeneity of such systems. The results suggest correlations between internal molecular motions and physical properties of the materials examined. Based on the above concepts, a mechanism of rubber reinforcement was proposed. The impact strength of a rubber-modified polymer is related to the apparent volume of the rubber phase. This volume consists of the actual volume of the rubber plus the affected portion of the surrounding glassy matrix which, assisted by the segmental motions of the rubber, assumes the same motions.