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

Abstract

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°C (−50°C to −25°C), 50°C (−50°C to 0°C), 55°C (−50°C to 5°C) and 60°C (−50°C to 10°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 τ 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 δ in the DMA measurement.