The Relative Thermal Stability of Polyurethane Elastomers: Effect of Diisocyanate Structure

Castable Polyurethane Elastomers (PUs) based on the polycaprolactone diol Capa 225 and the five different diisocyanates trans 1,4-cyclohexane diisocyanate (CHDI), p-phenylene diisocyanate (PPDI), 4,4’-diphenylmethane diisocyanate (MDI), 80:20 molar mixture of 2,4- and 2,6-toluene diisocyanate (TDI) and 4,4’-dicyclohexylmethane diisocyanate (H₁₂MDI) were synthesised by the use of 1,4-butane diol (1,4-BD) as a chain extension agent. The thermal deformation properties of the resulting polyurethane elastomers were measured by Dynamic Mechanical Thermal Analyser (DMTA) and Differential Scanning Calorimetry (DSC). The temperature at which the value of storage modulus (log E’) changes significantly is considered to indicate the limit of thermal stability of the polyurethanes. It is found that the storage modulus of the CHDI based PU only started to decrease at 181°C while the storage modulus of the H₁₂MDI based polyurethane started to decrease at the much lower temperature of 100°C. The PPDI, MDI and TDI based PUs have thermal stabilities which fall in between these two temperatures. According to this data it can be concluded that the structure of diisocyanates has a distinct influence on the thermal stability of the polyurethane and the CHDI based polyurethane can be demonstrated to have a relatively higher temperature stability than other diisocyanate based polymers.