Physical properties of poly( n-alkyl acrylate) copolymers. Part 2. Crystalline/non-crystalline combinations

The physical properties of n-alkyl acrylate copolymers containing one crystallizeable monomer and one non-crystallizeable or slightly crystallizeable monomer, including thermal characteristics, structure as determined by small angle X-ray scattering, and gas permeability as a function of temperature, were examined in detail and compared to the corresponding homopolymers and copolymer systems containing two crystallizeable comonomers. The current copolymers exhibit melting point depression and, for a given average side-chain length, have lower heats of fusion than the corresponding homopolymers and crystalline/crystalline copolymers. Limited SAXS experiments revealed an increase in the d-spacings, above and below the melting point, with side-chain length consistent with expectations. The crystallites predominantly exhibit end-to-end packing similar to other poly( n-alkyl acrylates) previously studied. Poly( n-alkyl acrylates) exhibit a ‘jump’ in their gas permeability at the T m of the side-chain lengths that is mainly caused by a switch in the side-chain morphology from crystalline to amorphous upon melting. The reduced crystallinity of the crystalline/non-crystalline copolymers results in a smaller permeation jump, which in some cases were extremely broad. All jump breadths correlate with the melting endotherms for these copolymers as determined by DSC similar to that for homopolymers and crystalline/crystalline copolymers. The magnitude of the jump correlates with the heat of fusion, irrespective of the comonomer type, in all cases.