Synthesis and characterization of MDI-butanediol urethane model compounds

Hard-segment model compounds containing one to five 4,4′-methylene bis(p-phenylisocyanate) (MDI) units extended with 1,4-butanediol (BD) were synthesized. The ends of the model compounds were reacted with ethanol. The melting point (T_m) of the model compounds increased with the number of MDI units to an extrapolated value of 299°C for the homopolymer using Flory's equation accounting for chain end defects. The ΔH of fusion was 5.3 kcal/mol. Intrinsic viscosity measurements in DMA solutions revealed a Mark Houwink exponent of 1.43 suggesting that the hard-segment model compounds are rodlike in solution. Wide-angle X-ray diffraction showed that the percentage of hard-segment crystallinity decreased as the oligomer length increased. Infrared spectroscopy studies showed that the distribution of hydrogen bond distances between C?O and NH groups became broader with increasing segment length.