| http://www.w3.org/ns/prov#value | - The polyurethane block comprises a diisocyanate, typically 4,4???-diphenylmethane diisocyanate, 4,4???-dicyclohexylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, para-phenylene diisocyanate or mixtures thereof, chain extended with a diol such as 1,4-butanediol, a dithiol such as 1,4-butanedithiol, a thio-substituted alcohol, such as 1-thiolbutane-4-ol, or mixtures thereo
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