Super Strong Polyurethane-urea Supramolecular Hydrogel

Hydrogels are chemically or physically cross-linked3D networks which cannot bedissolved in water, but can absorb a lot of water. However, the actual utilization of classichydrogels has been seriously impeded by their poor mechanical properties.In recent years, polyurethane (PU), including polyurethane urea (PUU) hydrogelsattracted people’s great attention because PU elastomers have excellent mechanicalproperties. But the mechanical properties of PU and PUU hydrogels reported so far werenot very ideal.During the process of preparing water-borne PU dispersion, a tough and stretchablePU hydrogel was accidentally obtained in our lab. After a careful analysis，it was foundthat the hydrogel obtained was actually a polyurethane urea supramolecular (PUUS)hydrogel prepared using water as additional in-situ chain extender. Based on this finding,a PUU hydrogel with shape memory function was also investigated.The main work we have done is as follows：First, the raw materials, including hydrophilic chain extender (sodium1,2-hydroxy-3-propanesulfate DHPA, ethane diamine double-2-hydroxyl propanesulfonicacid EDHPS), polycaprolactone (PCL) with various molecular weight and threeblock copolymers (PCL-PEG-PCL), for the preparation of polyurethane urea hydrogelwere synthesized. FTIR，1H NMR and DSC were used to characterize the structure of theraw materials.Second, a novel type of transparent PUUS hydrogel with excellent mechanicalproperties and easy processability has been prepared，using water as the additional in-situextender to form urea linkages, and a series of characterization，for example，FTIR，waterabsorbance，tensile test，compression，TG，DSC，XRD，SEM on the PUUS gel has been carried out. The mechanical properties, in terms of shear modulus0.2-0.8MPa,elongation at break695%-2411%, tensile strength3.3-34MPa and compression stress36.8MPa-60MPa, of PUUS gel could be easily controlled to a great extent by simplyaltering the [NCO]/[OH] ratio. Besides, the present linear PUU polymers can bedissolved in many organic solvents, such as acetone, methanol, ethanol, DMF and so on,and thus could be made into different forms by various manufacturing methods includingsolution casting, electro-spinning, injection, compression molding etc.Third, another kind of polyurethane urea supramolecular (PCUS) gels withshape-memory function were prepared using PCL/PEG and PCL-PEG-PCL/PEG asmixed soft segments and water as in situ chain extender and a series of characterizationwas conducted. The mechanical properties of PCUS gels with different [PCL]/[PEG]ratio, in terms of shear modulus0.088-0.5MPa, elongation at break750%-1561%andtensile strength1.3-41.6MPa, could be easily controlled to a great extent by simplyaltering the [PCL]/[PEG] ratio. PCUS gel with PCL4k as soft segment has good shapememory performance. With the increase of neutralization degree, the tensile strength andelongation at break of the gels decreased，however water absorbance increased.