Preparation And Properties Of Degradable Polymer Gels With Multiple Responses

Chemical gels are cross-linked polymeric materials consisting of a three-dimensional network joined by covalent or dynamically reversible covalent bonds that can be swollen in an organic solvent or water but do not dissolve.Chemical gel materials have been used as drug delivery agents,biological tissue engineering materials and other areas,and showed an important application prospects,and began to turn to artificial organs and other more advanced application areas.However,during the application process,it was found that the self-healing and degrading properties of the gel crosslinked structure are also very important.The study of self-healable gel can not only simulate the life of the repair process,but also reveal the mystery of life self-healing.At the same time,the degradation of cross-linked structure under mild conditions can eliminate the side effects of the cross-linked structure,and enhances the safety of its application and expands its application areas.Based on the above ideas,this paper focuses on(1)Easy degradable polymeric gel with extremely base-labile cross-linking;(2)Self-activated healable hydrogels with reversible temperature responsiveness,(3)Self-healable polymer gels with multi-responsiveness of gel-sol-gel transition and degradation.1.Through micro-phase separation and cross-linking,nano-material with spherical morphology was obtained with PtBA as continous phase and PGMA as dispersed phase.Then the material was swelled to prepare chemical cross-linked polymer gel with phenolic ester cross-linking.Also a phenolic ester bond connected polymer gel was prepared by copolymerization of tBA and HDA.Above two polymer gels can be degraded by NaHCO3 to obtain nanospheres and linear PtBA respectively.Also they can be hydrolyzed into hydrogel by CF3 COOH.Above results proved the phenolic ester bond are pretty stable in acidic hydrolysis process but very sensitive to aqueous sodium bicarbonate solution.This study provides a new idea for the preparation of degradable chemically crosslinked gels.This kind of materials with mild condition degradability have improved potential application in the field of drug loading and delivery and biologically friendly disposable materials.2.Hydrogels with reversible thermal responsiveness and self-healing property were prepared from copolymers of N-isopropylacrylamide and acylhydrazide with PEO dialdehyde as crosslinking agents.Hydrogels formed and self-healed through dynamic acylhydrazone bonds exchange without any external stimuli and catalysis.In addition to the self-healing and pH triggered gel-sol-gel transition behavior catalyzed by acid and anilline,the hydrogel can self-heal triggered by excess of hydrazide groups.The gel also showed temperature responsiveness due to the temperature responsivity of the PNIPAM segment of the polymer.By adjusting the excess of hydrazide groups,the phase transition temperaturecan be regulated to body temperature.Such hydrogels prepared from biocompatible polymers without additional catalyst can be used in the field of biotechnology with better persistence.3.P(N-isopropylacrylamide-4-formylphenylacrylate)P(NIPAM-co-FPA)copolymer containing a benzaldehyde pendant group linked by an base labile phenolic ester bond was designed and synthesized.Polymer gels with self-healing properties were prepared with PEO dihydrazide as a cross-linking agent without additional catalyst.This kind of polymer gels have better persistence and ensured better durability and do not need to worry about the toxicity and loss of the catalyst.Unlike the previously reported physical cross-linked PNIPAM repair hydrogels,this gel is a chemically crosslinked self-repairing gel based on dynamic acylhydrazone bonds.Results showed that acetic acid as a catalyst can accelerate the reaction rate of gel formation,but not a key factor in self-repairing.The gel can be self-catalyzed but self-healing properties depend on the crosslinking density.The self-repairing performance of the polymer is improved with the decrease of the crosslinking density;the decrease of the crosslinking density depends on the decrease of the FPA component,the increase of the molecular weight of the crosslinking agent and the decrease of the gelator concentration.Based on the reversible conversion of the dynamic acylhydrazone bond,the polymer gel showed a gel-sol-gel transition to the pH and group ratios.Because the phenolic ester bondis extremely base labile,the gel was able to degrade sodium carbonate in aqueous solution.However,the sodium bicarbonate is not sufficient to degrade the gel because the conjugated structure formed in the gel and reduce the degradation reactivity.This study provides a practical method for the preparation of self-healable polymer gels that are degraded in alkaline solutions.