Structure-Property Relationship of Polymer Blends with Co-Continuous Structures Prepared by Photo-Crosslinking

Abstract

Polymer blends with co-continuous structures in the micrometer scale were obtained by photo-cross-linking of poly(2-chlorostyrene)/poly(vinyl methyl ether)(P2CS/PVME) mixtures undergoing the spinodal decomposition process. The reaction was carried out with UV light at 365 nm to induce the photodimerization of anthracenes labeled on the P2CS chains (P2CS-A). To obtain the blends with co-continuous structures of varying length scales (λ), P2CS-A/PVME blends having the same cross-link density were prepared by irradiation and subsequently annealed over different time intervals. The resulting morphology was observed by using phase-contrast optical microscopy and was analyzed by digital image analysis. It was found that the time evolution of these co-continuous structures follows the power law λ ∞ t α , where α is close to 1/4. This value is smaller than 1/3, as predicted by the Lifshitz-Slyozov-Wagner law, indicating that the spinodal decomposition was slowed down by the presence of cross-links. The physical properties of these photo-cross-linked blends were examined by dynamic mechanical measurements. For the same cross-link density, the storage modulus E' of P2CS/PVME blends increases with λ, whereas the loss peaks of these co-continuous structures shift to the high temperature side. These experimental results suggest that the combination of photo-cross-linking reactions and the phase separation kinetics of polymer blends has the potential of providing a new way to design multiphase polymer materials with controllable co-continuous structures in the micrometer range.