Synthesis and characterization of polyether esters elastomer based on polyethylene glycol and poly(butylene terephthalate) - Influence of different hard segment length on polymer properties

A series of polyether esters thermoplastic elastomer, based on polyethylene glycol (PEG) as the soft segment and poly (butylene terephthalate) (PBT) as the hard segment, are synthesized by molten polycondensation and characterized by means of NMR, IR, DSC and mechanical testing. The influence of hard segment lengths on the properties of the copolymer is investigated in the case of the soft segment length remaining constant. It is observed that, first, the length of hard segments calculated from ¹H-NMR spectra is increased with the decrease of PEG content; secondly, four phases corresponding to the amorphous and the crystal phases of soft and hard segments coexist at certain temperatures; thirdly, the glass transition temperature (T_g) of the soft segment is increased, at the same time its molten point (T_m) and the degree of crystal (W_e) are decreased with the increase of the PBT segment length. Moreover, the inherent viscosity changes from 1.34 dL/g to 1.72 dL/g, and water uptake increases from 29.4% to 104.4% as the PEG content changes from 30% to 80% (wt). Although all copolymers are distinguished by a high elastic and plastic deformation and break at very high relative deformations, the sample of high PEG content displays the typical high elastic state, while the sample of low PEG centent exhibits neck-formation characteristics in the stress-strain curve. Obviously, the material's properties under constant soft segment length can be tailored conveniently by changing the weight ratio of two components in formula.