| Dynamic covalent bonds(DCBs)refer to chemical interactions which can selectively undergo reversible breakage and reformation under equilibrium conditions without any side reaction.The DCBs combine the stability of covalent bond and dynamicity of noncovalent bond in a single system.have been widely application in synthetic chemistry,materials science and medicine.As a typical dynamic covalent bond,boronate ester bond has become an effective tool to construct dynamic system.The special dynamic property,which endows materials based on dynamic boronate ester bond with special stimuli-responsive properties and self-healing ability.The boronic acid-containing polymers have been successfully used in molecular recognition and detection,drug delivery and control release,self-healable materials.This paper is mainly based on the design and synthesis of functional boronic acid-containing polymers,and use them to build dynamic crosslinking systems based on boronate ester bonds,and carry out applied research.1.Novel double DCBs-crosslinked hydrogels based on the combination of the acylhydrazone and boronate ester bonds were prepared.The functional phenylboronic-and ketone-containing diblock copolymers with controllable composition and degree of polymerization were prepared via sequential two-step reversible addition-fragmentation chain transfer(RAFT)polymerization.The double DCBs-crosslinked hydrogels were constructed by the interaction of PAD with polyvinyl alcohol and adipic dihydrazide without any external stimuli.The synergistic advantages of integrating the active boronate ester and stable acylhydrazone bond in gelation process,self-healing ability,multi-responsive properties and the tunable mechanical property of the hydrogel were studied comprehensively.The active boronate ester linkage endows the hydrogel with fast gelation kinetics and self-healing ability,while the stable acylhydrazone linkage can enhance the mechanical property of the hydrogel.Compared with its singly crosslinked hydrogels,the level of stimuli-responsiveness of the hydrogel has been enhanced.Moreover,the combination of the dual dynamic covalent bonds in hydrogel enhances the regulation and control level of the mechanical properties.The mechanical property of the hydrogel can be readily engineered not only by changing the network architecture and composition,but also by alternately controlling the formation or dissociation of one of the dynamic linkages.2.Functional phenylboronic-and hydrazide-containing of N-isopropyl acrylamide based diblock polymer,and ketone-and glucose group-containing acrylamide based diblock polymer,were prepared by RAFT polymerization.The structure and properties of the polymers were studied,and doubly dynamic hydrogel were prepared under different conditions.The main driving force of gel formation is the acylhydrazone bond formed by hydrazine and ketone group,and the boronate ester bond formed by boronic acid and glucose group.The synergistic advantages of integrating the boronate ester and acylhydrazone bond in gelation process,self-healing ability,multi-responsive properties and the tunable mechanical property were studied comprehensively.The formation of hydrogel under different pH conditions and the corresponding mechanism were emphatically studied.The active boronate bond endows the hydrogel with fast gelation kinetics and maintain the gel state,while the stable acylhydrazone bond can enhance the mechanical strength of the hydrogel gradually.Under acidic conditions,the acylhydrazone bond ensures the rapid formation kinetics and good self-healable ability of the hydrogel.Under alkaline conditions,the two dynamic covalent bonds are synergistic,giving the hydrogel multiple responsiveness and macroscopically self-healable ability.In addition,the combination of the dual dynamic covalent bonds in hydrogel enhances the regulation and control level of the mechanical properties.The mechanical property of the hydrogel can be readily engineered not only by changing the network architecture and composition,but also by alternately controlling the formation or dissociation of one dynamic linkage,meanwhile,another dynamic linkage can maintain the gel state of the system.Based on these results,this work provides a promising strategy for designing smart hydrogels with multiple responsiveness and tunable properties.3.Bulk boronate ester-based hydrogels with excellent physiological usability for wound dressing were fabricated by using the B-N coordination.The hydrogels were readily prepared by mixing a N-acryloyl-3-aminophenylboronic acid-containing copolymer and a 2-acrylamido glucose-containing copolymer in aqueous solution.Amine-containing N-(3-dimethylaminopropyl)acrylamide was incorporated into the polymer backbone to facilitate the formation and increase the stability of the boronate ester bond.The cross-linking density and inner structure of the hydrogel could be readily engineered by controlling the pH,[PBA]/[glucose]ratio,solid content of the polymer,thus offering great versatility for preparing functional hydrogels with tuneable mechanical properties.Moreover,the hydrogels exhibited excellent biocompatibility for both HEK293 cells and HeLa cells,the 24 h survival ratio was above 88%.Benefitting from the dynamic nature of the boronic ester,the hydrogels can be dissociated by adding competitive sugar molecules,making them easy to remove from medical gauze or skin in 10 min.This approach of designing polymer architecture to regulate the pH dependence and mechanical properties of a gel is a promising strategy for preparing functional hydrogels.This amine-containing dynamic hydrogel is a practical platform for designing multifunctional,smart soft materials,and has great potential for biomedical applications,especially for wound dressings.4.Micro crosslinking system based on boronic acid-containing polymers and xanthan gum was constructed to enhance the performance of xanthan gum in oil recovery.The addition of a small amount of polymer can effectively enhance the viscosity,salt resistance,anti-aging and rheological properties of xanthan gum solution,the viscosity increasing ratio can reach 70%.Meanwhile,the XG-PB system has good applicability to platform mineralized water and oil field sewage.The degradation experiments of hydrochloric acid and hydrogen peroxide/thiourea were carried out.and it was found that the system could be decomposed in 30 min.The micro crosslinking system not only can effectively improve the properties of xanthan gum solution,but also has no adverse effects on the demulsification of crude oil.5.A micro crosslinking system is formed by using diol-containing viscosity reducer and boronic acid-containing polymer through dynamic boronate ester bond to enhance the stability of the crude oil emulsion.Firstly,a series of functional polymers PAG were synthesized from acrylic morpholine and glycidyl methacrylate via free radical polymerization.The copolymer PAGC3,PAGC6,and PAGOH was obtained by modifying the PAG with n-propylamine,n-hexamine,hydrolysis ring opening,respectively.The functional polymers were studied comprehensively,and the viscosity reduction experiment on heavy oil LD-21 showed that the viscosity reducer has good viscosity reduction performance,the viscosity reduction ratio was more than 95%.The performance of the viscosity reducer was evaluated in deionized water,oilfield sewage and other conditions,which proved its good environmental adaptability.After demulsification,most of the viscosity reducer stay in the oil phase,and the distribution of viscosity reducer has basically reached equilibrium.Through the observation of the morphology of asphaltene in LD-21 before and after viscosity reduction,as well as DFT,the mechanism of viscosity reduction was explored.It is found that the viscosity reducers can effectively associate the asphaltene aggregate,mainly through the destruction of the interaction of the asphaltene.However,the crude oil emulsion is unstable.After removing the external force,the water and oil separate immediately(<60 s).The micro crosslinking system was formed by using the boronic acid-containing polymer and diol-containing viscosity reducer.The viscosity reduction performance of the micro crosslinking system in various conditions were studied.The formation of the micro crosslinking system can effectively maintain the viscosity reduction rate.The mechanism of viscosity reduction was studied by measuring the distribution coefficient and observing the morphology of asphaltene.Through the study of the stability of the crude oil emulsion,it is proved that the formation of the micro crosslinking system can effectively improve the emulsion stability,the separation time can be increased from 60 s to 17.5 min.This work has great significance to the practical application of these viscosity reducers. |
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