Influence of Isocyanate Hard Segments on Properties of Polyurea Elastomers
The isocyanate molecular structures have great influences on the physical and chemical properties of polyurea elastomers.In order to explore the influences of the changes of isocyanate molecular structures on the self-healing efficiency and mechanical strength of polyurea elastomers,four kinds of isocyanates with different molecular structures were selected:isophorone diisocyanate(IPDI),4,4′-diisocyanate dicyclohexyl methane(HMDI),4,4′-diphenylmethane diisocyanate(MDI)and hexamethylene diisocyanate(HDI).Through the reactions between four kinds of isocyanates and polyether amine,elastomers with different hard segment structures were obtained(SPU-IP,SPU-HM,SPU-M and SPU-H).The influence mechanisms of isocyanate molecular structures on the properties of polyurea elastomers were studied by infrared spectroscopy(FTIR),X-ray diffraction(XRD),dynamic mechanical analysis(DMA)and viscosity test.The results show that SPU-M and SPU-H with rigid aromatic groups and crystalline hard segments have tight hard segment domains and higher mechanical strength.The asymmetric alicyclic structures in SPU-IP provide sufficient chain mobility and better self-healing properties.The self-healing efficiencies of SPU-M and SPU-IP are comparable.Due to the large steric hindrance of benzene rings in SPU-M,most of the hydrogen-bonded carbonyl groups exist in a disordered form,which enhances the self-healing efficiency of the materials.
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