Effects Of Substituents On Properties Of Dynamically Adaptive Polyurethane Elastomers

The introduction of dynamic covalent bonds into cross-linked polymers can promote the self-healing and reprocessing of polymer networks because the dynamic covalent bonds have the characteristics of dynamic exchangeability.However,there is no clear understanding of the impact of dynamic covalent group structure on the performance of covalent adaptable polymer networks,which needs to be further studied.Polyurethane has a microphase-separated structure of hard and soft segments,so its mechanical properties can be adjusted by changing the type and ratio of hard and soft segments.Although the carbamate is an exchangeable group,its stimulation temperature is high(130 °C).The incorporation of substituent into carbamate group is aimed at lowering its stimulation temperature,while the effects of substituent on carbamate exchange and cross-linked polyurethane properties are explored.The crosslinked polyurethane elastomers were prepared from Polytetrahydrofuran ether glycol(PTMG3000),diphenylmethane diisocyanate(MDI),hexamethylene diisocyanate trimer(tri HDI),and difunctional tertiary alcohol(2,5-dimethyl-2,5-hexanediol)as a chain extender.The control polyurethane elastomers were prepared from difunctional primary alcohol and difunctional secondary alcohol as chain extenders.The structures of crosslinked elastomers were characterized by infrared spectroscopy,swelling degree,differential scanning calorimetry.The properties were characterized by tensile test and thermogravimetric analysis,and the dynamic reversibility was studied by stress relaxation and self-healing experiments.The results show that the polyurethane obtained by chain extension of difunctional tertiary alcohol has excellent mechanical properties and thermal stability,and the steric hindrance of tertiary alcohol decreases the temperature of carbamate exchange in the polyurethane.The crosslinked polyurethane elastomers containing tertiary amine group were prepared from PTMG3000,MDI,triethanolamine and 1,4-butanediol.The results show that the polyurethane crosslinked by triethanolamine has good mechanical properties and thermal stability,and the neighboring catalysis of substituent accelerates the exchange rate of carbamate.