Molecular and topological structures in polyester block copolymers

Abstract

The thermomechanical analysis (TMA) was used to investigate structures, molecular-weight distributions and relaxation transitions in polyester block copolymers possessing properties of thermoplastic elastomers. The copolymers were synthesized by polycondensation of polytetramethylene oxide (PTMO, molecular weight 1000), 1,4-butanediol and dimethyl terephthalate. The concentration of PTMO blocks was varied between 10 and 80 wt.%. The TMA shows changes in molecular and topological structures of the polyester copolymers when the composition is varied. The copolymers based on PTMO and polybutylene terephthalate (PBT) appeared to have a three-block (regions) topological structure at PTMO concentrations between 10 and 70 wt.%. They consist of (1) a low-temperature topological block ( T g between −27°C and −76°C), formed by most likely by PTMO enriched with the amorphous portion of PBT; (2) an intermediate ( T g varies within 94–18°C range), being postulated PBT amorphous portion enriched with amorphous PTMO; and (3) a high-temperature topological block formed by PBT chain segments, the regularity of which gets disturbed under the influence of PTMO soft chains ( T g between 197°C and 53°C). At 75 wt.% of PTMO, the three-block topological structure is transformed into a diblock one characterized by miscibility of the low-temperature and intermediate amorphous topological blocks. Complete mutual miscibility of all topological blocks and formation of a single-topological block polymer occur at 80 wt.% PTMO content.