RIS Models and Unperturbed Chain Properties of Polyesters Containing 1,3‐Cyclobutylene and 1,4‐Cyclohexylene Linkages

Abstract

Polyesters containing 1,3‐cyclobutylene and 1,4‐cyclohexylene linkages in the main chain are investigated using conformational energy calculations. Rotational isomeric state (RIS) models are developed for poly(1,4‐cyclohexylenedimethylene terephthalate) (PCT), poly(1,4‐cyclohexylenedimethylene 2,5‐dimethylterephthalate) (DMPCT), poly(1,4‐cyclohexylenedimethylene 1,4‐cyclohexylenedicarboxylate) (PCC), and poly(2,2,4,4‐tetramethyl‐1,3‐cyclobutylene terephthalate) (CBDO). In DMPCT, the ester linkage prefers skewed conformations with respect to the phenyl group to relieve the steric strain caused by the methyl groups. The methyl groups on the cyclobutanediol moiety in CBDO restrict the rotational freedom about the oxycyclobutylene linkage. The unperturbed dimensions as described by characteristic ratio and persistence length are calculated for the trans and cis configurations of these polyesters. CBDO shows highly extended chain conformations among these polyesters indicating relative chain rigidity of the backbone. For DMPCT and PCC, in their trans configuration, the chain dimensions decrease with an increase in temperature while for their cis configurations, the chain dimensions increase with temperature, arising from basic differences in the fragment structures that control the competition of the relative populations as affected by temperature. Temperature has negligible influence on the unperturbed dimensions of both isomeric linkages of CBDO, while this is true for the trans configuration of PCT. The study shows that induction of cyclobutylene groups in the main chain results in a greater rigidity for homopolyesters than for chains with cyclohexylene groups.

Terephthalic Acid Copolyesters Containing Tetramethylcyclobutanediol for High‐Performance Plastics

“…These cis/trans ratios of TMCD and CHDM are typical of those resulting from chemical synthesis. [ 29 , 30 ]…”

“…Aliphatic diols like EG, PDO, and BDO are even more flexible than CHDM due to the absence of ring structure. [30] cis/trans ratio of CHDM affects T m as the softening point of cis CHDM is 43 °C, and trans CHDM is 67 °C. TPA‐ 30/70cis / trans CHDM polymer (PCT) and TPA‐EG polymer (PET) have T g of 88 and 80 °C and T m of 300 and 260 °C, respectively.…”

“…These cis/trans ratios of TMCD and CHDM are typical of those resulting from chemical synthesis. [29,30] CHDM increases the mobility of polymer chains as the flipping of cyclohexane confirmation causes relaxation, which increases ductile behavior. Aliphatic diols like EG, PDO, and BDO are even more flexible than CHDM due to the absence of ring structure.…”