Preparation And Properties Of Supramolecular Polymers Based On Hydrogen Bonding

Supramolecular polymers are formed by the combination of non-covalent bonds.They include hydrogen bond-based supramolecular polymers,particularly the four-hydrogen bond system of 2-ureido-4-pyrimidinone（UPy）,which imparts many special properties to the polymer,such as self-healing properties.Therefore,supramolecular polymers have important applications in molecular machinery,cell recognition,drug release,and biosensing.The polyisoprene elastomer is a general-purpose synthetic rubber obtained by polymerization of an isoprene monomer by a catalyst.Since its chemical composition is similar to that of natural rubber,it has a high degree of polymerization,excellent resilience performance,high mechanical strength and good self-adhesion.Therefore,polyisoprene elastomer is selected as the preparation target of supramolecular polymer.Polyvinyl alcohol is a biopolymer with good biocompatibility,good water solubility and easy processing.Nanocellulose is light,excellent in mechanical properties,and it has good biodegradability and reproducibility.Nanocellulose composite has high strength,low thermal expansion coefficient and high light transmittance.It is a truly renewable,environmentally friendly and new materials with superior performance.The nanocellulose is thus urethanized and a polyvinyl alcohol/modified nanocellulosecomposite is prepared.In this paper,two kinds of methods based on 2-ureido-4-pyrimidinone（UPy）were used to modify the polymer.Firstly,the UPy modified polyisoprene was obtained by bulk anion polymerization.Secondly,a composite material of polyvinyl alcohol and UPy modified nanocellulose is obtained by a method of modifying nanocellulose.The specific content of this topic has the following two aspects.（1）Preparation of UPy modified polyisoprene.The hydroxyl terminated polyisoprene（PI-OH）was prepared by anionic polymerization,and then PI-NCO and PI-UPy were separately synthesized.In the infrared spectrum,the characteristic peak of-NCO in the 2276 cm^-1 of PI-NCO disappears in PI-UPy,and the characteristic peak appears at 3326 cm^-1.In the variable temperature infrared spectrum,the characteristic peak of 3349 cm^-1 at the position shifts toward the high wave number with increasing temperature,which indicates the successful preparation of PI-NCO and PI-UPy with the formation of hydrogen bonds.TGA results show that the thermal decomposition rate of PI-UPy is relatively slow,and the DMA results show that the glass transition range of PI-UPy,which reflect the good thermodynamic properties of PI-UPy at-30°C～-10°C.The tensile test results show that the tensile strength and elongation at break of PI-UPy are 1.0 MPa and 5.5%.At the same time,the self-healing experiment also showed the self-healing effect of PI-UPy.（2）Preparation of PVA/CNC-UPy composite materials.The urethanization modification of the UPy system based on the four-fold hydrogen bonding is carried out using the hydroxyl group of the nanocellulose.The modified nanocellulose is then added to the polyvinyl alcohol solution to prepare a composite film and a composite gel.From the FTIR results,the NCO characteristic peak disappeared at 2270 cm^-1,indicating the successful synthesis of CNC-UPy.The XRD results show that UPy modification of the CNC does not change the structure of the cellulose and at the same time increases its crystallinity.The TGA results show that with the addition of CNC-UPy,the maximum weight loss rate temperature is also increasing,indicating the addition of CNC-UPy.The thermal stability of the composite is enhanced.The DMA data shows that the more the CNC-UPy is added,the smaller the internal friction of the composite material,thus indicating that the rigidity of the material is better.It reflects the good dynamic properties of PVA/CNC-UPy composites.At the same time,the self-healing performance test also demonstrated the good self-healing properties of the polyvinyl alcohol composite gel.