Structure and elasticity of crosslinked polymer blends

We consider a blend of mutually incompatible homopolymer species, A and B, that are randomly crosslinked to form a network. In such a network there is a competition between the repulsion of the A and B polymers (which favors the demixing of the two species) and the crosslinking (which prohibits complete demixing) [1,2].~ We treat the system by means of a model of flexible polymers, which are permanently crosslinked (with statistics modeled by the Deam-Edwards distribution) and have species-dependent excluded-volume interactions [3].~ As expected, the model shows that at sufficiently low temperatures the demixing tendency drives microphase separation, with a characteristic scale set by the network localization length.~ It also shows that if the system is strained after crosslinking, correspondingly anisotropic microdomains are generated in the pattern of A-B polymer concentration fluctuations trapped in by the network and, furthermore, allows the impact of microphase separation on the elastic properties of the network to be determined.\\[4pt] [1] P.G. de Gennes, J. Phys. (Paris) Lett., 40 (1979) L-69. \newline [2] D.J. Read, M.G. Brereton and T.C.B. McLeish, J. Phys. II, 5 (1995) 1679. \newline [3] C. Wald et al., Europhys. Lett. 70, 843--849 (2005); J. Chem. Phys. 124, 214905 (2006).