Functionalization of hydroxyl groups in segmented polyhydroxyurethane eliminates nanophase separation

The properties of segmented, nanophase-separated polyhydroxyurethane (PHUs) were investigated before and after hydroxyl group functionalization. Segmented PHU was synthesized using polytetramethylene oxide (PTMO)-based soft segment, divinylbenzene dicyclocarbonate (DVBDCC) as hard segment, and p-xylylene diamine as chain extender at 40 wt% hard-segment content. The pendant hydroxyl groups were subsequently functionalized with benzoyl chloride, and the properties of PHUs before and after functionalization were characterized with NMR spectroscopy, small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA). ¹H and ¹³C NMR spectra confirm the successful attachment of the benzoyl group to the hydroxyl group. The FTIR spectra of PHU-Bz in the carbonyl region also show a higher proportion of free carbonyl relative to hydrogen-bonded carbonyl, indicative of phase mixing. These results show that hydroxyl group functionalization with side groups as small as an acetyl group or as large as a benzoyl group provides similar, substantial steric hindrance to interurethane hydrogen bonding, leading to phase mixing in these segmented, functionalized PHUs. SAXS experiments were performed using a Rigaku S-MAX 3000 SAXS system emitting X-rays with a wavelength of 0.154 nm.