Molecular dynamics of Poly(propylene 1,4- cyclohexanedicarboxylate) and its copolymers with Poly(neopenthyl glycol 1,4-cyclohexanedicarboxylate) as revealed by broadband dielectric spectroscopy

Nowadays aliphatic polyesters have attracted considerable attention as they combine the features of biodegradability and biocompatibility with physical and chemical properties comparable with some of the most extensively used polymers (LDPE, PP, etc.). In particular, polyesters based on 1,3-propanediol (1,3-PD) have attracted increasing interest in the last few years, being 1,3-PD obtainable by renewable feedstocks[1]. Dimethyl trans-cyclohexane-1,4-dicarboxylic (DMCEDA) acid, which can also be considered a bio-based monomer, contains an aliphatic ring in the monomeric unit, whose stereochemistry strongly influences the final properties of the material [2]. A series of novel random copolymers of poly(propylene 1,4-cyclohexanedicarboxylate) (PPCE) containing neopenthyl glycol sub-unit (P(PCExNCEy)) were synthesized and their structure-dynamics relationships have been investigated by means of X-ray scattering and dielectric loss spectroscopy experiments. The subglass dynamics of the polymers as revealed by dielectric spectroscopy is characterized by the existence of two processes, γ and β in order of increasing temperature. We propose that the high frequency(lower temperature) γ-relaxation is associated to the ester oxygen linked to the aliphatic carbon of the diol subunit, whereas the low frequency(higher temperature) β-relaxation has been assigned to the carbon of the ester groups linked to the aliphatic ring.