Stability of chemical sequence in a periodic polymeric nematogen

The stability of a polymeric nematogen's chemical sequence was studied by differential scanning calorimetry, optical microscopy, and ¹³C-NMR; the nematogen studied was a thermotropic polyester and had a periodic chemical structure. Model compounds were used to investigate transesterification in the melt at different temperatures with the addition of phenol or benzoic acid as analogues of polymer end groups. Ester interchange reactions at high temperature were found to be partly suppressed when acidic end groups of the periodic nematogen were capped. However, sequence reorganization was completely suppressed in capped nematogen when temperatures remained below the isotropization transition of the nematogen investigated. Rapid disordering of the periodic nematogen was observed above the nematic-isotropic transition, suggesting that both chemical and physical factors play a role in sequence redistribution of periodic nematogens.