The Relative Thermal Stability of Polyurethane Elastomers: 2. Influence of Polyol-diisocyanate Molar Block Ratios with a Single and Mixed Diisocyanate System

Castable polyester polyurethane elastomers (PU's) based on the system polycaprolactone diol (Capa 225)/trans 1, 4–cyclohexane diisocyanate (CHDI)/1,4 butane diol (1,4–BD) were synthesised to study the effect of various polyol-diisocyanate block ratios on thermal stability. The influence of mixed diisocyanates on thermal stability was also investigated by using CHDI as co-diisocyanates in both Capa 225/H ₁₂ MDI/1, 4–BD and Capa 225/TDI/1,4–BD based PU elastomers. Experimental techniques utilised to assess thermal stability were Dynamic Mechanical Thermal Analysis (DMTA) and Differential Scanning Calorimetry (DSC). Improved thermal stability was observed in both the higher block ratio PU's and in the mixed diisocyanate systems (H ₁₂ MDI or TDI with CHDI). The temperature resistance was found to increase about 20°C when the block ratio changed from 1/2/1 to 1/3/2 in comparative systems. Hard segment transition temperatures were also found to increase as the block ratio increased. It was also found that changing from the mixed H ₁₂ MDI+CHDI based PU to a TDI+CHDI system increased thermal stability by 25°C.