The effect of copolymerization of cyclic dioxolane moieties on polyamide properties

Upon copolymerization of carbohydrate-based cyclic moieties, they offer a variety of new functionalities and a convenient way to modify the properties of the material. Structurally the electronegative sites present in the cyclic structures have a major influence on hydrogen bonding. In this study the consequences of the incorporation of 2,3:4,5-di-O-methylene-galactarate (GalXH) and 2,3:4,5-di-O-isopropylidene-galactarate (GalXMe) cyclic moieties in aliphatic polyamides are investigated by FT-IR and solid state NMR and a correlation is made with the thermomechanical properties and crystallinity of the copolyamides. The analysis is complemented by the theoretical calculations, which suggest that the amide proton of such polyamides tends to form hydrogen bonds with the acetal oxygen of neighboring GalX (intramolecular) and therefore prevents the interchain hydrogen bonding, resulting in decreased hydrogen bonding density. Despite the conformational rigidity of the GalX comonomers, the decrease in interchain hydrogen bonding leads to a counter intuitive decrease in glass transition temperature with increasing mole percentage GalX comonomer. As suspected the copolymerization of GalX with aliphatic monomers suppresses the crystallinity which is more pronounced for bulkier monomers.