Synthesis And Properties Of Thermally Responsive Isocyanate Cross-Linked Polymers

Isocyanates(-NCO)have shown promising applications in polyurethane and other fields due to their high activity and easy structural design.Although isocyanate applications have been widely reported,its high activity also poses difficulties such as short storage cycles and high requirements for use conditions.Block of isocyanates is an important way to solve the above problems.In this dissertation,thermally responsive isocyanate cross-linked polymers were prepared based on blocked isocyanates and isocyanates functionalized with disulfide bonds.The mechanical properties and self-healing properties of the resulting products were investigated.The phenol-2,4-toluene diisocyanate(Blocked Isocyanate,BI)was prepared by molecular design using a confinement reaction.The unblocking temperature was determined by simultaneous thermal analysis(SDT).Fourier infrared testing(FTIR)determined the unblocked product as free isocyanate.A series of blocked isocyanate cross-linked polymers with different numbers of hydroxyl groups was synthesized by thermal cross-linked reaction using BI and polyol as raw materials.DSC,TGA and tensile tests were performed,and the results showed that the polymer T_gincreased with the increase of polyol hydroxyl number.The elongation at break increased.A series of blocked isocyanate interpenetrating network polymers(IPN)with different numbers of hydroxyl groups was synthesized by optical and thermal cross-linked reactions using light-curing resins,BI and polyol as raw materials.The properties were investigated by DSC,TGA,DMA and SEM tests.The results showed that the elongation at break increased and then decreased with the increase of the closed product/polyol content,and the T_gincreased with the increase of the number of hydroxyl groups.The tensile strength and elongation at break increased and then decreased with the increase of the number of hydroxyl groups.The number of cracks increases and the cracks become finer as the number of hydroxyl groups increases.The two-phase descriptiveness is good.A thermally responsive isocyanate cross-linked polymers were synthesised by cross-linking reactions using dithiobis(isocyanate)(DTSA),hexamethylene diisocyanate trimer(tri-HDI),low molecular weight hydroxylated poly(10-hydroxydecanoate)(PHDA)and poly(ethylene glycol)(PEG)as raw materials.The thermal properties,shape memory behaviour and self-healing properties were investigated by DSC,DMA,POM,tensile testing and macroscopic characterisation.The results showed that the T_mof PHDA and PEG segments increased with increasing PEG content.The elongation at break before and after self-healing was 650.5%and 481.8%,respectively and the self-healing efficiency was 78.3%.The polymer has both triple shape memory and self-repair ability.