Effect of the soft segment on the fatigue behavior of segmented polyurethanes

Effect of the soft-segment structure and molecular weight on the microphase separation in segmented polyurethanes (SPU) was determined by means of dif ferential scanning calorimetry, small-angle X-ray scattering, dielectric co nstant measurement, pursed nuclear magnetic resonance, and thermoluminescen ce. Possible changes in the structural properties of SPU after cyclic mecha nical fatigue were monitored using the same techniques as described above. Samples were divided in two series according to their soft-segment structur e, i.e., one is linear poly(tetramethylene glycol) (PTMG), and another one with a methyl group on the PTMG chain. Hard segment consisted of 4,4'-diphe nylmethane diisocyanate (MDI), and 1,4-butanediol (BD) as chain extender in both sets. It was found that phase separation increased for both types of SPU as the soft-segment molecular weight increased. Samples with methyl gro up showed little soft-segment crystallization. Upon fatigue, samples with a methyl group demonstrated a better fatigue resistance. (C) 2000 Elsevier S cience Ltd. All rights reserved.