Preparation And Properties Of Strong And Functional Polyurethane-urea Supramolecular Hydrogels

Hydrogels are high water containing but water insoluble three dimensional networks.With their high water contents and flexibility,hydrogels are very similar to many native soft tissues.Thus,they have been explored for a variety of applications in biomedical field.The 3D network can be covalently or noncovalently crosslinked,which are named as chemical or physical(e.g.supramolecular)hydrogels,respectively.Chemical hydrogels often show highly stable and high mechanical properties.While,the physical hydrogels or supramolecular hydrogels which are crosslinked by noncovalent interactions,including metal-ligand interaction,H-bonding,host-guest interaction,Van der Waals’ force and hydrophobic force etc.,often show reversible or dynamic properties,such as sol-gel transition and self-healing property.Based on the work of H-bonding and hydrophobic force cooperatively induced strong and tough polyurethane-urea supramolecular hydrogels previous in our group,here,in this study,different kinds of functional units were further induced into the hard segments in the main chain of the copolymers to endow the resultant strong and tough supramolecular hydrogels with various stimuli responsive properties.Main contents of the present studies are as follows1),A series of polyurethane-urea linear copolymers with various functional units within the hard segments in the main chain were prepared via a simple one-pot with two-step methods using polyethylene glycol with different molecular weight(PEG4k,PEG6k and PEG 10k),1,12-diisocyanatododecane and functional unit containing diamine small molecules(chain-extender)as raw materials.The obtained copolymers were characterized by 1H NMR,FTIR and GPC.2),The above obtained PUU copolymers were further transformed into corresponding supramolecular hydrogels via solution casting technique.The hydrogels’equilibrium swelling water content,mechanical strength,microstructure and so on were studied by tensile testing,rheology,SEM,TEM etc.Results showed that the hydrophilic PEG chains endows the resultant hydrogels with relatively high equilibrium water content;the hydrophobic spacer shielded bis-urea hard segments aggregated into nanodomains to act as physical crosslinking points,these strong H-bonding domains provide the resultant supramolecular hydrogels with excellent mechanical properties.3),Stimuli response experiments showed that:the dynamic covalent bonds(S-S or C=N)containing hydrogels showed reduction or pH stimuli responsive gel-to-sol transition behavior;addition of metal ions into the pyridine containing supranolecular hydrogels will not only improve the mechanical properties,but also can enhance or quench the fluorescence of the hydrogels;the azobenzene unit containing hydrogel showed UV-Vis responsive reversible mechanical properties changing behavior;all obtained supramolecular hydrogels have water-responsive shape memory property.