Study of the lower critical solution temperature behaviour of poly(vinyl methyl ether) aqueous solutions in the presence of poly(acrylic acid). The role of interpolymer hydrogen bonding interaction

The phase separation behaviour of poly(vinyl methyl ether) (PVME) aqueous solution in the presence of poly(acrylic acid) (PAA) is reported. As the PAA concentration increases, the cloud point temperature of the PVME/PAA aqueous solutions is gradually displaced to temperatures higher than 33°C, i.e. the lower critical solution temperature of the pure PVME solution, until a soluble system in the entire temperature region is obtained. At higher PAA concentrations, the system phase separates again, but no temperature dependence is observed. This phase behaviour can be explained by the formation of an interpolymer complex between the two polymers. Indeed, potentiometric, viscometric and fluorescence measurements reveal that the complex is formed through hydrogen bonding interactions between the two polymers, and that it has a compact structure and is relatively hydrophobic.