Chemical Engineering Journal, Vol.357, 611-624, 2019
Structure evolution during order-disorder transitions in aliphatic polycarbonate based polyurethanes. Self-healing polymer
The aliphatic polycarbonate based polyurethanes (PU) from poly(hexamethylene) carbonate diol (PC), hexamethylenediisocyanate and hexanediol were synthesized, characterized and designed as promising self healing polymers. The symmetrical linear PU structure containing the hexamethylene sequences results in a high degree of ordering and strong superstructures, manifested by a high crystallinity of the PC soft phase and a strong self-assembly of linear hard segments (HS). At the optimum composition, both supramolecular structures percolate resulting thus in the singnificant reinforcement. The PU, undergoing order-disorder transitions, involves three types of physical crosslinks with different thermal stability; PC crystalline phase, HS domains and in addition the entanglements. The structure evolution and reversible sol-gel transition during formation/breaking of the corresponding physical networks was followed by rheology, DSC and FT-IR. The kinetics of build-up and stability of physical networks is governed by the content of HSs. The investigation contributed to the understanding and control of the thermal phase transitions of supramolecular structures in aliphatic PCPUs. The strong supramolecular structure undergoing order-disorder transitions, presence of thermally stable entanglement network and excellent mechanical properties make the PCPU suitable as a strong self-healing polymer. Two structural motifs are present: the thermally sensitive structure generating self-healing properties and the shape persistent entanglement network structure preventing the irreversible deformation. The efficient healing and restoration of the original structure and mechanical properties after damage of the polymer were checked by microscopy and tensile testing.