Abstract
Polyurethane (PU) elastomers based on 4,4″-diphenylmethylene diisocyanate (MDI), poly(oxytetramethylene) glycol (PTMO), and hydroxyl-terminated random copolymers of tetrahydrofuran and 3-methyl-tetrahydrofuran (THF/Me-THF) were synthesized. Purified 1,4-butanediol (BD) was used as the chain extender. Stress-relaxation, FT1R, ESR and thermal analysis studies suggest that a two-phase morphology is present in the segmented PU. The strategy adopted in the ESR study was to incorporate a nitroxide, 4-hydroxy-2,2’,6,6'-piperidine-1-oxyl (TEMPOL), in the segmented PU. At the same hard segment content, PUs from higher MW soft segments exhibited better phase separation than did their lower MW counterparts. The stress-relaxation of these elastomers conforms to at least a two-component Maxwell model. PUs having higher soft segments underwent a longer relaxation process.
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