Hard segment connectivity in low molecular weight model ‘trisegment’ polyurethanes based on monols

Abstract

Low molecular weight model trisegmented polyurethanes based on monofunctional polyols, or ‘monols’, with water-extended toluene diisocyanate (TDI) based hard segments (HS) are investigated. The formulations of the materials generated are similar to those of flexible polyurethane foams with the exceptions that the conventional polyol is substituted by an oligomeric monofunctional polyether of ca. 1000 g/mol molecular weight; and no surfactant is utilized. Plaques formed from these model systems are shown to be solid materials at ambient even at their relatively low molecular weights of 3000 g/mol and less. SAXS, DSC, and AFM are utilized to investigate the microphase separated morphologies of the samples generated. WAXS results show that the local packing of the HS is of a similar nature as that in actual flexible polyurethane foams. AFM phase images, for the first time, reveal the ability of the HS to self-assemble through bidentate hydrogen bonding and form lath-like percolated structures, resulting in solid plaques, even though the overall volume of the system is well dominated by the two terminal liquid-like polyether segments.