Nonisocyanate Thermoplastic Polyhydroxyurethane Elastomers via Cyclic Carbonate Aminolysis: Critical Role of Hydroxyl Groups in Controlling Nanophase Separation

Thermoplastic polyhydroxyurethanes (PHUs) were synthesized from cyclic carbonate aminolysis. Because of the hydroxyl groups in PHU, the choice of soft segment has a dramatic influence on nanophase separation in polyether-based PHUs. Use of a polyethylene glycol-based soft segment, which results in nanophase-separated thermoplastic polyurethane elastomers (TPUs), leads to single-phase PHUs that flow under the force of gravity. This PHU behavior is due to major phase mixing caused by hydrogen bonding of hard-segment hydroxyl groups to the soft-segment ether oxygen atoms. This hydrogen bonding can be suppressed by using polypropylene glycol-based or polytetramethylene oxide (PTMO)-based soft segments, which reduce hydrogen bonding by steric hindrance and dilution of oxygen atom content and result in nanophase-separated PHUs with robust, tunable mechanical properties. The PTMO-based PHUs exhibit reversible elastomeric response with hysteresis, like that of conventional TPUs. Because of nanophase separation with broad interphase regions possessing a wide range of local composition, the PTMO-based PHUs also demonstrate potential as novel broad-temperature-range acoustic and vibration damping materials, a function not observed with TPUs.