Synthesis And Investigation Of Polyurethane And Polyester Vitrimer Based Materials

Vitrimer is a new kind of three-dimensional network polymer with reversible covalent bonds,which combines thermosetting and thermoplastic properties.Therefore,these polymers are capable of self-healing,shape-remodeling,and physical/chemical recycling,all while retaining outstanding mechanical properties and thermal/chemical stability.However,there are still deficiencies in the synthesis and functional studies of vitrimer.First,metal/acid/base catalysts are often added to promote polymerization and bond exchange processes during vitrimer synthesis,disregarding the high costs,toxicity,precipitation,and decreased material properties that are associated with high additions of these catalysts.Therefore,there is a need to develop a catalyst-free/green organocatalyst system for the synthesis of vitrimer.Second,only the self-healing,shape remodeling and physical/chemical recycling and reprocessing of vitrimer have been researched,so it is necessary to further investigate the polar groups such as hydroxyl in its network structure,expand its functionality of vitrimer,and demonstrate its application value.To solve these problems,this paper focuses on green and efficient synthesis methods,vitrimer performance and functionality studies,develops a series of catalyst-free/green organocatalyst synthesis of vitrimer from a synthesis standpoint,and investigates its fundamental performance and functionality.In order to demonstrate their application in smart labeling,moisture electricity generation,natural polysaccharide hybrid materials,strain sensors,and reprocessable adhesives,the characteristics of the polar groups in the vitrimer network structure are extensively explored.The research methodology and findings are presented as follows:(1)Using a non-isocyanate approach and an effectivering-opening polymerization reaction between the cyclic carbonate and the amine,a carbamate(-NHCOO-)link based linear polymer chain with dangling hydroxyl groups(-OH)is formed.It was found that the presence of hydroxyl groups endowed the material with fast moisture-absorbing properties,allowing PHU vitrimer to achieve equilibrium in moisture absorption within 6 hours.The DSC and mechanical properties tests revealed that as the moisture absorption time increased,the glass transition temperature(Tg)decreased from 52℃ to 21℃;the mechanical properties changed from a rigid material(37.37 MPa,4.46%,4.51 GPa,1.15 MJ/m3)to a tough material(10.69 MPa,101.86%,0.72 GPa,9.94 MJ/m3).Next,a smart material PHU@Ti3C2 with multi-stimulus response(heat,light,and humidity)was prepared by in situ polymerization of Ti3C2 with PHU vitrimer,and a series of humidity-,heat-,and light-sensitive smart labels were developed using the multi-stimulus responsiveness of PHU@Ti3C2.In addition,inspired by PHU vitrimer’s exceptional moisture absorption capacity,we investigated its applicability in the field of moisture electricity generation.The electrodes were constructed using "screen printing" technology and a paper-cutting process,and an all-in-one moisture generating device was prepared by compounding Ti3C2 with cellulose paper.This is the first study to systematically investigate and develop the moisture absorption capabilities of vitrimer,as well as to investigate its application in the fields of smart labels and moisture electricity generation.(2)In the absence of solvents and catalysts,a series of natural polysaccharide/PHU vitrimer hybrid materials(PLs-PHU)were efficiently synthesized in the presence of natural polysaccharides(chitin,chitosan,and sodium alginate)using flexible long-chain biomass diamines(Priamine 1074)as curing agents.The results demonstrate that the strong hydrogen bonding environment in the PHU vitrimer network structure allows the natural polysaccharides to be uniformly diffused in the matrix without chemical modification,and the loading can reach up to 40%.The mechanical properties of PLs-PHU can be precisely regulated by adjusting the content of natural polysaccharides,for example,the tensile strength of the composites increased from 1.8 MPa to 10.7 MPa and the elongation at break changed from 505.7%to 40.5%when the chitosan content increased from 0%to 40%.In addition,not only do PLs-PHU composites exhibit good thermal stability and solvent resistance at room temperature,but they also benefit from the faster transcarbamoylation exchange reaction of the matrix,which has exhibits excellent scratch self-healing properties(98%)and physical reprocessability at 60℃.Also,the complete component recovery of PLs-PHU composites in n-butylamine solution was accomplished.Using the outstanding physical reprocessing properties of PLs-PHU composites to construct a conductive network with "segregated structure" in the matrix,a new type of conductive composite was prepared.The potential applications of these new conductive composites in electromagnetic shielding and flexible strain sensors are then demonstrated.This paper not only demonstrates the application of a green,efficient,low-cost and low-energy technique for the synthesis of natural polysaccharide composites,but also demonstrates the generalizability of this strategy.(3)The synthesis of polyester vitrimer by disulfide catalyzed epoxy/carboxylic acid polymerization without solvent was firstly proposed and developed.To verify the efficacy of this strategy,we employed phenyl glycidyl ether(PGE)and n-butyric acid(BA)as model compounds,and the results showed that the disulfide possessed good catalytic activity.To further validate the catalytic potential,the disulfides were further used in the polymerization reaction of epoxides and dicarboxylic acids to synthesize polyester vitrimer with excellent mechanical properties(9.94 MPa,515.05%,0.40 GPa,22.70 MJ/m3)and thermal stability(Td5=357℃).On this basis,polyester vitrimer was synthesized by the efficient solvent-free auto-catalytic polymerization of biomass-based carboxylic acid-lipoic acid(LA)with disulfide bonds as a raw material and then reacted under mild conditions(90℃)with epoxy compounds.Finally,we demonstrated that using dangling hydroxyl groups on the polymer chains of polyester vitrimer,it is possible to prepare a new type of moisture electricity generating devices(EVMEGs)with higher voltage(637 mV)and high current(5μA)output at room temperature than those prepared using PHU vitrimer,and thus can be used as a new type of moisture sensor for human breath state detection.This work not only solves the issues of high cost,high toxicity,and poor thermal stability associated with conventional catalysts,but also develops a new strategy for the synthesis of polyester vitrimer from auto-catalytic polymerization,thereby providing a new catalyst and reaction system for the synthesis of polyester vitrimer.(4)A strategy for the synthesis of polyester vitrimer by thioether-catalyzed polymerization of epoxy/carboxylic acid and epoxy/anhydride without solvents was further developed.First,the catalytic activity of thioethers was investigated.Thioethers with alkyl chains demonstrated strong catalytic activity for epoxy/carboxylic acid and epoxy/anhydride polymerization at 90℃(the epoxy group conversion rate was over 70%within 90 minutes).Therefore,using the dual catalytic property that thioether can catalyze the polymerization of epoxy/carboxylic acid and epoxy/anhydride,we achieved the tandem polymerization of epoxy/carboxylic acid and epoxy/anhydride catalyzed by thioether,thereby producing polyester vitrimer with excellent mechanical properties and physical reprocessability.Furthermore,because polyester vitrimer has the brush structure of a brush polymer,it can be employed as a new,robust adhesive for attaching various surfaces(e.g.wood,cardboard,wool felt,PVC and aluminum).In comparison to conventional adhesives,these new adhesives provide superior bonding properties(up to 28.35 J/m2),but may be recycled.This paper presents the first strategy for the synthesis of polyester vitrimer based on the thioether-catalyzed polymerization of epoxy/carboxylic acids and epoxy/anhydride,which offers several advantages over conventional catalytic systems:low cost,co-catalysts-free,metal-free,solvent-free,and highly activity under mild conditions.