Characterization and Chain Structure of PEG/PBT Copolymer with the Constant Mass Ratio of Soft to Hard Segment

A series of polyether ester thermoplastic elastomers based on polyethylene glycol(PEG) and poly (butylene terephthalate) (PBT) are synthesized and characterized by means of NMR, FTIR and DSC and mechanical testing. The influence of the constant mass ratio (70/30) of soft to hard segment on the copolymer's thermal and mechanical properties is investigated. It is found that, firstly, the length of hard segments is increased with increasing PEG molecular weight from 400 to 4 000(M̄_n); secondly, four domains corresponding to the amorphous and the crystal phase of soft and hard segments coexist in some compositions; thirdly, the glass transition temperature(T_g) of the soft segment is decreased, meanwhile its molten point(T_m) and the degree of crystal(w_c) are increased with the increase of its molecular weight; finally, the inherent viscosity changes from 1.23 to 1.64 dL/g with ascending PEG molecular weight and shows a slight depression after the molten moulding which can be ascribed to a thermooxidative degradation. All copolymers are distinguished by the high elastic deformation in the stress-strain curves. With the increase of PEG molecular weight, the elongation at break ε_b, the tensile strength σ_b and the yield stress σ_y are all improved, while the elastic modulus E changes slightly around 9 MPa.