THERMAL SEQUENCE RANDOMIZATION OF A WHOLLY AROMATIC COPOLYESTER HAVING AN ORDERED SEQUENCE

A wholly aromatic copolyester having an ordered comonomer sequence was prepared from 2,7-naphthalenediyl bis(4-hydroxybenzoate) and terephthalic acid following a method reported previously. This polymer was subjected to thermal treatment at 305-degrees-C under nitrogen atmosphere and the sequence randomization process was quantitatively analysed by C-13 n.m.r. spectroscopy. The melting temperature of the original polymer was 290-degrees-C. According to the results of analysis for various triad formation, the ester bonds in the triad of terephthaloyl-p-oxybenzoyl-oxynaphthyleneoxy (TPN) sequence were found to undergo very fast exchange reactions at the treatment temperature. The formation of PPP triad was evident after 30 min at 305-degrees-C, whereas PP dyad was formed after only 10 min. Although the sequence changes occurred rather rapidly, complete randomization was not attained even after 1 h.