Preparation And Self-repairing Properties Of Diels-Alder Addition Polymer Modified By Polyurethane

Polymer materials have been widely used because of their have lightweight,wear-resistant and easy to be processed properties.However,due to the high temperature in the process of processing,it is easy to oxidize or decompose,which will damage the properties of materials;And in the process of using,there will be internal micro-cracks.If not effectively repaired,micro-cracks will further and become irreversible damage of macro-cracks,the extension of micro-cracks will lead to the overall failure of polymer materials and significantly shortening their life.Therefore,the key to solve the above problems is to reduce the processing temperature and endow the material with self-repairing function.Thermoplastic materials have the characteristics of secondary processing and moulding,and th eir molecular weight is generally tens of thousands to millions.High molecular weight can give excellent mechanical properties of materials,but at the same time improve their processing temperature.Thermosetting materials generally have excellent mechanical properties and solvent resistance.But because of its internal crosslinking,it loses the properties of secondary processing,which limits its application in various fields,at the same time it also causes material pollution and waste.In order to solve the above problems,in this paper based on the Diels-Alder(D-A)cycloaddition reaction of click chemistry,is used to prepare a polyurethane modified DA addition polymer.They can be polymerized at lower temperatures,depolymerized at slightly higher temperatures and have self-repairing properties.The research contents are as follows:(1)Design and synthesis of terminal furanyl prepolymer(PDGF),bisfuran chain extender(FPDF)and trifuran crosslinker(NF).The structure of the synthesized molecule was characterized by fourier transform infrared(FTIR)and nuclear magnetic resonance(NMR),and the results were cons istent with the expected targets.(2)A series of DA linear(L-DAPU)and cross-linked(C-DAPU)addition polymers were designed and synthesized by D-A cycloaddition reaction.The effects of three parameters of chain extension parameters(Rt),hard segment content(H%)and crosslink density(C%)on the mechanical properties of D-A addition polymer materials were investigated.By adjusting the formula,the tensile strength of L-DAPU can be adjusted from 3.68 MPa to 12.47 MPa and the elongation at break is between 333% and 820%.The tensile strength of C-DAPU can be from 6.47 MPa to 18.71 MPa.The elongation at break is regulated in the range of 200%~866 %.(3)The temperature of the retro-DeilsAlder of the D-A addition polymer was determined by thermogravimetric experiments(DSC).The results show that the optimum temperature of r-DA for L-DAPU is 127?,and the optimum temperature for r-DA of C-DAPU is 150?.After pyrolysis,the product slowly repolymerizes at 60°C,and the material strength can be recovered more effectively under the action of the solvent to achieve self-healing effect.Linear and cross-linked DA addition materials are rapidly converted from elastomers to viscous fluids after thermal depolymerization.The number average molecular weight of L-DAPU-8 decreased from 114,700 to 6,800 after thermal depolymerization at 127 ? for 40 minute.(4)The self repairing properties of the thermally polymerized materials were characterized by gel permeation chromatography(GPC)and optical microscope,and the mechanical properties of the thermally polymerized materials were tested.The results show that the product after thermal polymerization is converted i nto an elastomer material,and its mechanical properties are restored.Observing the self-repair process of cracks in L-DAPU-8 samples,it was found that after 16 hours of heat treatment,the cracks basically healed.The number average molecular weight of the L-DAPU-8 sample after heat polymerization increased from 6800 to 91300 within 16 hours,and the recovery rate of L-DAPU-8 sample was 81.1% under solvent-free conditions.The repair rate of C-DAPU-13 sample It is 57.8%,The repair rate of L-DAPU-8 sample was 94.0% and the repair rate of C-DAPU-13 sample was 93.4% under DMF solvent conditions.It is proved that the solvent can improve the compatibility between components and improve the self-repairing effect of the modified material.