Determination of average sequence length in poly(butylene terephthalate)-poly(ethylene terephthalate-co-isophthalate-co-sebacate) segmented copolyesters

Copolyesters, namely, poly(butylene terephthalate)-poly(ethylene terephthalate-coisophthalate-co-sebacate) (PBT-PETIS) were synthesized by means of melting transesterification. In the five-component copolycondensates system, average sequence length was calculated based on the analysis of H-1-NMR spectra and the equal probability of interchange reaction for three kinds of polyester units in PETIS with PBT. The results reveal that the average sequence length of both PBT and PETIS segments vary almost linearly with reaction time. The determination of degree of randomness that lies within the range of 0.1749-0.5282 suggests the formation of segmented copolyesters.