Aliphatic poly(alkylene dithiocarbonate)s: Thermal properties and structural characteristics of poly(hexamethylene dithiocarbonate)

Aliphatic poly(alkylene dithiocarbonate)s are an interesting class of potentially biodegradable and biocompatible materials in analogy with their homologous poly(alkylene carbonate)s. In this paper, the properties of poly(hexamethylene dithiocarbonate) (SSR6) are compared to those of poly(hexamethylene carbonate) (HMC) in order to study the effect of the substitution of oxygen atoms with sulphur atoms in the polymer backbone. SSR6 presents a higher level of crystallinity and a faster crystallisation rate with respect to HMC. The melting temperature in SSR6 is about 60 °C higher, due to a solid-solid transition between phase I, stable at room temperature, and phase II, present at high temperature. HMC crystallises only in phase I and melts at a relatively low temperature (30 °C). The capacity of SSR6 to crystallise in phase II has been attributed to the higher flexibility and mobility of the chains containing -S-CO-S- groups with respect to the chains containing -O-CO-O- groups. The pure phase II in SSR6 has been obtained in isothermal conditions and its crystallisation rate and mechanism have been analysed.