Thermal study of polyester networks based on renewable monomers citric acid and gluconolactone

A detailed thermal study is presented of the melt polycondensation between the renewable monomers citric acid and d-glucono-δ-lactone. It was found that the polyester networks formed have glass transition temperature ranges that increase with increasing reaction temperature and time, corresponding to an increase in molecular weight. The minimum reaction temperature was investigated and found to be 130 °C for a 1/1 system. Moreover, the monomers show eutectic melt behaviour, with a eutectic melting temperature of 125 °C. A range of additional co-monomers were evaluated, revealing that aliphatic and aromatic bifunctional co-monomers result in lower glass transition temperatures. When polyfunctional co-monomers were employed it was found that the chain flexibility influenced the resulting thermal properties. Moreover, it is shown that the ring structure of d-glucono-δ-lactone plays a key role in the thermal properties of the resulting polyesters.