Bio-based (Co)polyesters Containing 1,4-Cyclohexylene Units: Correlations Between Stereochemistry and Phase Behavior

Nowadays the urgency for solving plastic waste problems is inducing academic and industrial research to develop novel environmentally friendly polymers, i.e. materials produced from alternative resources, with low energy consumption, non-toxic to the environment, and biodegradable. These biopolymers should have also good physical performances. In the field of aliphatic polyesters, novel (co)polymers, containing 1,4-cyclohexylene units, appear very promising materials, which are obtainable from biomass, potentially biodegradable and characterized by good mechanical properties. Moreover, these polyesters have the interesting peculiarity that their phase behavior is strictly connected to the ratio of the two possible configurations, cis and trans, of the cyclic units. Indeed, the trans isomer is more rigid and symmetric than the cis. Highly symmetrical units tend to improve the chain packing with a consequent increment in crystallinity and crystalline perfection. On the other hand, the cis isomer introduces kinks into the main chain, which hinder the formation of stable crystals. Thus, at high trans content the polyesters are characterized by relative high degree of crystallinity, whereas at low trans content the polymers are amorphous. Therefore, accordingly to the final cis/trans ratio, the phase behavior of the homopolymers and copolymers significantly changes and the stereochemistry of the cycloaliphatic units result to be a key factor to tailor the final thermal properties of the material. In this paper the properties of some homopolymers and copolymers, containing the 1,4-cyclohexylene units with different cis/trans ratio, are discussed just in terms of the correlations between stereochemistry and phase behavior.