Abstract
4,4′-Diisocyanato dicyclohexylmethane (HMDI) is a commercially available diisocyanate used as a building block for polyurethane products that require excellent light stability and hydrolysis resistance. It consists of a mixture of three geometrical isomers, the trans,trans-, cis,trans-, and cis,cis-isomers. We found that the trans,trans-isomer leads to some interesting properties in polyurethane elastomers. Surprisingly, the hardness and percent elongation (properties that usually follow an inverse relationship) both increase with increasing trans,trans- HMDI contents. We also observed dramatic increases in the ultimate tensile strength, split-tear strength, resilience, and solvent resistance. Also, the melting temperature of the elastomers increases with increasing trans,trans content. X-ray analysis of model hard segments showed that the hard segment based ont,t-HMDI is highly ordered, leading to higher melting temperatures and better separation between the hard- and soft-segment phases.
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