The Effect of Diisocyanate Isomer Composition on Optical and Adhesive Properties of Polyurethanes Based on 4,4'-dicyclohexyl Methane Diisocyanate

摘要

Polyurethanes wereprepared having 47 wt % hard segments based on 4,4'-dicyclohexyl methane diisocyanate (H12MDI) with trans, trans isomer contents in the 16 to 99 mol % range and 1,4butanediol chain extender. The soft segments is polytetramethylene glycol (PTMEG, Mw 1000). H12MDI with 25, 40, 60, 80 and 99% trans,trans isomer contents were obtained from commercial H12MDI (16% trans, trans) by fractional crystallization, and all polyurethanes were prepared by a two-step bulk polymerization procedure. The polyurethanes based on H12MDI with trans,trans contents of 40% or higher yielded materials insoluable in N,N-dimethylformaide (DMF) and were generally opaque. Mechanical properties, such as tensile strength at break, decreased with increasing trans,trans content, while the Young's modulus and Shore hardness increased. A decrease in adhesion strength is produced when content of t,t-H12MDI is above 25%. Wide-angle and small-angle X-ray scattering at room temperature were employed to characterize phase morphology. The mean macrolattice spacings between stiff fragments (STF) decreased in the order t,t-H12MDI-0.16 > t,t-H12MDI0.25 > t,t-H12MDI-0.40 > t,t-H12MDI-0.60 > t,tH12MDI-0.80 > t,t-H12MDI-0.99.