Relationship between polydispersity of polymer glycols and mechanical properties of polyurethane elastomers

A series of eight blend poly(oxytetramethylene) glycols (PTMGs) with different polydispersity were prepared from three kinds of PTMGs with the number-average molecular weights of 278 or 642,1004, and 1918. The PUEs were prepared from the blend polymer glycols, 4,4'-diphenylmethane diisocyanate and 1,4-butanediol by a prepolymer method. The hard segment content of all PUEs was ca. 37 wt%. Thermal and mechanical properties of the PUEs were characterized by hardness, density, swelling test, gel permeation chromatography, differential scanning calorimetry, dynamic viscoelastic properties measurements, and tensile testing. With a broadening polydispersity of the soft segment, T_g of the soft segment shifted to low temperature, indicating that the phase separation became stronger. This induced a increasing Young's modulus and hardness of PUEs. Tensile strength and strain at break for the PUEs including the lowest molecular weight component (PTMG250) showed larger and smaller magnitudes, respectively. This is because PTMG250 played as physical crosslinking points and made network structure become heterogeneous.