Synthesis and characterization of poly(butylene terephthalate)‐co‐poly(butylene succinate)‐block‐poly(ethylene glycol) segmented block copolymers

Abstract

Abstract Poly(butylene terephthalate)‐ co ‐poly(butylene succinate)‐ block ‐poly(ethylene glycol) segmented random copolymers, with poly(butylene succinate) (PBS) molar fraction ( M PBS ) varying from 10 to 60 %, were synthesized through a melt polycondensation process and characterized by means of GPC, NMR, DSC and mechanical testing. The number‐average relative molecular mass of the copolymers was higher than 4 × 10 4 g mol −1 with polydispersity below 1.9. Sequence distribution analysis on the two types of hard segments by means of 1 H NMR revealed that the number‐average sequence length of PBT decreased from 2.80 to 1.23, while that of PBS increased from 1.27 to 4.76 with increasing M PBS . The random distribution of hard segments was also justified because of the degree of randomness around 1.0. Micro‐phase separation structure was verified for the appearance of two glass transition temperatures and two melting points, respectively, in DSC thermograms of most samples. The crystallinity of hard segments changed with the crystallizability controlled by the average sequence length and reached the minimum value at an M PBS of about 50–60 mol%. The results can also be ascribed to the co‐crystallization between two structurally analogous hard segments. Mechanical testing results demonstrated that incorporating a certain amount of PBS moieties (less than 30 mol%), at the expense of a minute depression of the elastic modulus, that higher relative elongation and more flexibility of polymer chain could be expected. Maximum equilibrium water absorption and faster degradation rates were observed on samples with higher M PBS values and lower crystallinity of hard segments were better hydrophilicity of the polymer chain, through in vitro degradation experiments. Copyright © 2003 Society of Chemical Industry