Synthesis and properties of poly (alkylene trans-1,4-cyclohexanedicarboxylate)s with different glycolic subunits

Abstract

This work explores one of the numerous playgrounds offered by polyesters. A series of poly (alkylene trans-1,4-cyclohexanedicarboxylate)s were synthesized combining trans-1,4-cyclohexane dicarboxylic acid with four diols containing an increasing number of methylene groups ($n_{{\mathrm{CH}}_2}$ = 3, 4, 5 and 6). The resulting polyesters are fully aliphatic. Their backbones contain cyclic aliphatic moieties and linear aliphatic segments in different relative contents depending on $n_{{\mathrm{CH}}_2}$. The flexibility of these polyesters can be finely tuned ($T_g$ decreases proportionally to the increase in $n_{{\mathrm{CH}}_2}$), however the microstructure dramatically changes depending on whether $n_{{\mathrm{CH}}_2}$ is an odd or an even number (odd-even effect). On one hand, the odd-numbered samples are easier to melt-quench to a fully amorphous glassy state; on the other hand, the even-numbered samples are prone to crystallization and crystallize very fast. The developed microstructure is complex because of the probable coexistence of different crystalline structures, mesophases, and molecular arrangements depending on the cis/trans isomerism of the cyclohexane moiety. Preliminary tests provided mechanical and barrier properties that could make these polyesters suitable for packaging applications. Composting tests showed that increasing $n_{{\mathrm{CH}}_2}$ could eventually improve the biodegradation rate of these polyesters, although crystallinity remains the most influencing parameter.