FUNCTIONAL-GROUP ACCESSIBILITY IN HYDROGEN-BONDED POLYMER BLENDS

Accessibility of functional groups is an important concept in the mixi ng of polymers and involves factors such as chain connectivity, steric shielding, etc., all of which tend to limit the number of interchain contacts formed. Infrared spectroscopy is well suited to study functio nal group accessibility in carefully selected miscible hydrogen bonded polymer blend systems, because the fraction of interchain hydrogen bo nded groups can be measured quantitatively. Such measurements have bee n made on blends consisting of a wide range of carbonyl containing (co )polymers with a 2,3-dimethylbutadiene-stat-4-vinylphenol containing 2 4 wt% 4-vinylphenol. Evidence has been obtained for decreasing accessi bility of the carbonyl groups of the poly(n-alkyl methacrylate)s due t o steric shielding from bulky side groups. Conversely, when these grou ps are spaced further apart in an ethylene-stat-vinyl acetate or ethyl ene-stat-methyl methacrylate copolymer chain, they become much more ac cessible. The effect of functional group accessibility on the scaling and transferability of self- and interassociation equilibrium constant s is discussed, together with ramifications in terms of the prediction of miscibility windows and maps for hydrogen bonded polymer blends.