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.