Effect of mixed chain extenders on the macroscopic properties of polyurethane elastomers

A series of polyurethane elastomers have been synthesized from prepolymers (component A) and chain extenders (component B). The prepolymers were prepared using 4, 4'-diphenylmethane diisocyanate (MDI) and polytetrahydrofuran polyols (PTMG). The chain extenders were mixtures of trihydroxy polyether polyols (330N) with 1, 4-butanediol (BDO) or ethylene glycol (EGO). The thermal and mechanical properties of polyurethane elastomers based on two different systems (330N/BDO and 330N/EGO) for a range of different mass ratios in each system were investigated. Differential scanning calorimetry (DSC) showed that the glass transition temperature of soft segments (T_gs) was lower in the 330N/BDO systems, whilst the melting heat of hard segments was higher in the 330N/BDO systems. The values of T_gs and the melting heat of hard segments increased with the decreasing 330N:BDO and 330N:EGO mass ratios. Measurements of mechanical properties and dynamic mechanical thermal analysis (DMTA) showed that tensile strength and the hardness were higher for the 330N/EGO system, while the elongation and hysteresis loss (tanδ) were lower. With decreasing 330N:BDO and 330N:EGO mass ratios, the tensile strength and hardness increased, but elongation and hysteresis loss (tanδ) decreased.