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

The poly(butylene terephthalate)-co-poly(butylene succinate)-6- poly(ethylene glycol) segmented block copolymers (PBT-co-PBS/PEG) with PBS molar fraction (M_PBS) varying from 10% to 60 mol% were synthesized by melt polycondensation technique and characterized structurally by means of NMR, DSC, GPC, etc. The analysis on the sequence distribution of two hard segments in the copolymer chain reveals that the average sequence length of hard segment PBT decreased from 2.80 to 1.23, while that of PBS increased from 1.27 to 4.76 with the increase of PBS molar fraction, and the random distribution of the two hard segments was justified for the location of randomness around 1.1. Microphase-separation structure was demonstrated for the appearance of the two glass transition temperature (T_g,s, T_g,h) and two melting points (T_m,s, T_m,h) in DSC curves of most of the samples. Especially, the co-crystallization between two hard segments might be responsible for the minimum value of the melting point and crystallinity of the hard segments where M_PBS reached 50-60 mol%. It can be concluded that incorporation of aliphatic moiety PBS in PEGT/PBT copolymer, will impart higher flexibility and hydrophilicity and faster degradation rate to the polymer chain.