Diffusion of acetonitrile in conformational isomers of an H12MDI polyurethane

The diffusion of acetonitrile in conformational isomers of the aliphatic po lyurethane, H12MDI (4,4'-dicyclohexylmethane diisocyanate)/BD (1,4-butanedi ol)/PTMO (poly(tetramethylene oxide)), was investigated at a fixed hard seg ment content of 29.9 wt%. The effective diffusion coefficient, measured exp erimentally using FTIR-ATR (Fourier transform infrared-attenuated total ref lectance) spectroscopy, decreased as the trans-trans percentage in the hard segment increased. The spectra for the polyurethanes revealed higher fract ions of hydrogen-bound C=O (carbonyl) groups at higher trans-trans percenta ges, which was consistent with higher values of hard segment T-g. During ac etonitrile diffusion experiments, a shift from hydrogen-bound to free carbo nyl groups in the hard segment domains occurred and hydrogen-bound C=N and NH peaks appeared suggesting that acetonitrile is solvating to the hard seg ments in the polymer. Based on these findings, the trend observed for the e ffective diffusion coefficient may be attributed to tortuosity and penetran t solvation in the polyurethane. (C) 1999 Elsevier Science Ltd. All rights reserved.