Synthesis and thermal stability of oligourethanes based on the cycloaliphatic diisocyanate trans,trans‐4,4′‐methylenebis(cyclohexylisocyanate)

The synthesis of molecularly uniform and isomerically pure oligourethanes is described. The compounds are models for the hard segments in polyurethane elastomers based on the aliphatic trans,trans‐4,4′‐methylenebis(cyclohexylisocyanate) (ttHMDI)/butanediol system. The thermostability of the urethanes was determined by differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and temperature‐dependent FT‐IR spectroscopy. The aliphatic urethane group was found to be more stable than urethanes based on the corresponding aromatic 4,4′‐methylenebis(phenylisocyanate) (MDI). The stability also depends on the physical properties and morphology of the oligourethane. The ttHMDI urethane group does not decompose up to the individual melting point of the oligomer, whereas in aromatic MDI diisocyanate systems decomposition occurs already significantly below the melting; the MDI‐specific transurethanization is not observed in the ttHMDI‐based urethanes.