Thin-film behavior of poly(methyl methacrylates) (PMMA). 7. Stereocomplexation in mixed monolayers of isotactic PMMA and partially hydrolyzed syndiotactic PMMA

Abstract

In an attempt to find a monolayer stereocomplexing system in which phase separation phenomena are less restrictive than for the s-PMMA/i-PMMA couple, the monolayer behavior of partially hydrolyzed syndiotactic poly(methyl methacrylate) (s-PMMA) was studied. For low carboxyl group contents, the behavior of these materials is similar to that of the parent material, with an extra contribution of repulsive Coulombic forces originating from the ionized carboxyl groups when using basic subphases. The partially hydrolyzed materials are shown to retain their ability to exhibit a pressure-induced stereocomplexation in monolayer mixtures with isotactic poly(methyl methacrylate) (i-PMMA). When higher molecular weight parent materials for the syndiotactic component are used, aggregation processes can be observed to be suppressed for the partially hydrolyzed samples due to the aforementioned repulsive Coulombic forces, overcompensating the attractive cohesive interactions between the MMA segments and resulting in a high stereocomplexation efficiency. This efficiency is observed to strongly depend on the subphase pH, which regulates the degree of ionization of the incorporated acid groups.