A C-13 NMR-STUDY OF TRANSESTERIFICATION IN MIXTURES OF POLY(ETHYLENE-TEREPHTHALATE) AND POLY(BUTYLENE TEREPHTHALATE)

Poly(ethylene terephthalate) and poly(butylene terephthalate) homopoly mers and mixtures of these two polymers have been heated in the absenc e of oxygen at 573 K for 30 min and 476 K for 6 h. The resultant polym ers have been analysed using solution viscometry, d.s.c., density dete rmination and C-13 n.m.r. Degradation has been observed when the polye sters are heated at 573 K and this is particularly evident for the pol y(butylene terephthalate). Assignment of resonances due to homogeneous and heterogeneous dyads and degradation products in the n.m.r spectra have been made using model compounds and a random copolyester which h ave been synthesized by us. Using these assignments we have calculated sequence length distributions of ethylene and butylene sequences in t he materials obtained. On heating at 573 K transesterification of the polyester present in the minority is complete and a single random copo lymer is obtained. From the melting point data, it is clear that two c opolyesters result when the mixtures are heated at 476 K for 6 h. The values for the number average sequence length suggest that block copol yesters are produced.