Direct Evidence for Sequence Ordering of Random Semicrystalline Copolyesters during High-Temperature Annealing

Abstract

In an effort to study sequence ordering during annealing in semicrystalline copolyesters, the carbonyl carbon of p-hydroxybenzoic acid was 13 C tagged and then solution polymerized with 2-hydroxy-6-naphthoic acid to form a low molecular weight, 50/50, random copolyester. The random copolyester was annealed at 40 deg below the crystal nematic transition temperature (Tcn). DSC results indicated a large increase in crystallinity; however 13 C NMR analysis showed no change in the benzoic-naphthoic (BN) and benzoic-benzoic (BB) diad sequence peak ratios. When the random copolyester was annealed near the Tcn, DSC results indicated a large increase in the transition temperature, no increase in crystallinity, and a shift in the BN:BB peak ratio indicating a significant increase in alternating sequences. On the basis of these results, the dramatic increase in transition temperature during annealing near Tcn is best interpreted as sequence ordering via interchain transesterification reactions within the existing crystalline regions.

Crystallization and Melting Behavior of Liquid Crystalline Copolyesters Based on Modified Poly- [(p-hydroxybenzoic acid)-co-(ethylene terephthalate)]

“…[30,32,33] One interesting proposal is sequence ordering through a crystallization induced reaction (CIR), [34] which was recently conclusively confirmed. [35] In CIR process, the non-crystallizable comonomer units adjacent to the crystalline domains are replaced by the crystallizable units through an interchange reaction, and the latter then crystallize into the crystalline domain, thus increasing the crystal size, crystallinity and melting point. The higher temperature crystallization conditions (200 8C for up to 24 h) afford an opportunity for ester interchange and solid phase polymerization, well known for these materials.…”

Thermal decomposition behavior of main-chain thermotropic liquid crystalline polymers, Vectra A-950, B-950, and Xydar SRT-900

“…Several review articles and books have described the scientific progress on this subject. [1][2][3][4][5][6][7][8] Two approaches have been developed to exhibit a polymer in a LC state. One is to form LC behavior in a solution (lyotropic LCP), and the other is in a melt (thermotropic LCP).…”

Structure and Properties of Phosphorous‐Containing Thermotropic Liquid‐Crystalline Aliphatic–Aromatic Copolyesters

“…This phenomenon of multiple melting was reported in many papers as a feature in common for liquid crystalline polyesters. [8,10,[37][38][39] The multiple melting behavior has been previously attributed to reasons including the presence of different crystal structures, [40,41] or to crystal reorganization, [42,43] or to different components of the morphology formed in multiple stages of crystallization. [44] DSC traces of polymers 4a-4d have similar features.…”