TSC/RMA study on the depolarization transitions of TDI-based polyurethane elastomers with the variation in NCO/OH content

Thermal behaviors of TDI-based polyurethanes were studied viz. depolarization relaxation transitions by TSC/RMA technique. Two relaxation transitions in T-g region were found. One is the T-g transition. The other, T-global, is the relaxation transition of global nature and dominated by the hard TDI-MOCA segment in an amorphous phase. The observed T-g is shifted from the cooperative motion of urethanic matrix dominated by the soft segment to the relaxation transition of the entire global molecular structure. As a result, a merged and widen T-g transition range was observed in TSC with supportive observations of a broadened DSC curve for the same specimens. This widened T-g transition was further analyzed by thermal windowing technique of RMA. Increases in the following T-g temperature ranges of 25 degrees C (-50 degrees C to -25 degrees C), 50 degrees C (-50 degrees C to 0 degrees C), 55 degrees C (-50 degrees C to 5 degrees C) and 60 degrees C (-50 degrees C to 10 degrees C) for 1.6, 2.4, 2.8 and 3.2 NCO/OH ratio specimens were detected in the RMA spectra. The compensation parameters (T-c, log tau(c)) of polyurethane specimens in order of NCO content are (10.1, -2.85); (39.6, -3.08), (51.8, -3.71) and (85.8, -4.49) for NCO/OH ratios 1.6, 2.4, 2.8 and 3.2, respectively. The T-global transition was observed and in association with tangent delta in the DMA measurement. (C) 1999 Elsevier Science B.V. All rights reserved.