| Blocked isocyanates have been widely studied and used due to their superiority,such as significant reduction of water sensitivity,elimination of free isocyanate toxicity,and possibility for waterborne and functional polyurethane.However,blocked isocyanates still hava some drawback to affect its application,including high curing temperature and long curing time.The kinetics and mechanisms of related deblocking and cure reactions have been rarely reported.So,blocked isocyanates need fur ther study on the synthesis,blocking and deblocking reaction.In this dissertation,based on pyridinol and quinolinol,a series of original blocked isophorone isocyanates were synthesized and characterized.The relationships between their structure and deblocking temperature were investigated systematically,and the kinetics of deblocking and cure reactions were also studied.The potential applications of blocked isocyanates in waterborne polyurethane adhesive and curing agent were discussed.It not only has significant theoretical research value,but also has important guiding significance for the development of polyurethane materials science.All the results of this study were listed as below:(1)Blocked isocyanates were synthesized with isophorone isocyanate,pyridinol and quinolinol by esterification reaction,Fries rearrangement reaction and blocking reaction.The chemical structures of all the eighteen blocked isocyanates were confirmed by FTIR,1H NMR and 13 C NMR,and the synthesis conditions were optimized by isocyanate blocking ratio method.(2)The deblocking temperature of blocked isocyanates was established by DSC,TG,phenylamine and CO2 methods.The substituent effect and electronic effect of pyridine and quinoline on deblocking temperature were investigated systematically.The results revealed that the deblocking temperature was decreased with the decrease of electron cloud density on hydroxy position of aromatic ring and with the increase of electron-withdrawing effect and steric hinerance of substituent on ortho-position.(3)Non isothermal experiments were carried out to investigate the deblocking kinetics of 4-hydroxypyridine-IPDI adduct,(4-hydroxypyridin-3-yl)(phenyl)methanone-IPDI adduct,8-hydroxyquinoline-IPDI adduct and(8-hydroxyquinoline-7-yl)(phenyl)methanone-IPDI adduct.For 4-hydroxypyridine-IPDI adduct,the deblocking activation energy calculated by FRL equation and FWO equation was 134.6 kJ·mol-1 and 126.2 kJ·mol-1,respectively.The most probable mechanism function was Jander equation,and the reaction order wasn't integer.For(4-hydroxypyridin-3-yl)(phenyl)methanone-IPDI adduct,the deblocking activation energy calculated by FRL equation and FWO equation was 111.2 kJ·mol-1 and 117.0 kJ·mol-1,respectively.The most probable mechanism function was Anti-Jander equation,and the reaction order also wasn't integer.For 8-hydroxyquinoline-IPDI adduct,the deblocking activation energy calculated by K issinger equation and FWO equation was 160.4 k J·mol-1 and 178.4 kJ·mol-1,respectively,and the reaction order also wasn't integer.For(8-hydroxyquinoline-7-yl)(phenyl)methanone-IPDI adduct,the deblocking activation energy calculated by K issinger equation and FWO equation was 138.8 k J·mol-1 and 143.8 kJ·mol-1,respectively,and the reaction order also wasn't integer.All the reaction orders were not integer,which indicates that the related deblocking reactions were complicated.(4)Non isothermal experiments were carried out to investigate the deblocking-curing kinetics of PVA-pyridinol blocked isocyanate system,melamine-pyridinol blocked isocyanate system,PVA-quinolinol blocked isocyanate system and melamine-quinolinol blocked isocyanate system.For PVA-pyridinol blocked isocyanate system,the deblocking activation energy was 138.0 kJ·mol-1,the pre-exponential factor is 3.2×1018,and the reaction order was 1.27.For melamine-pyridinol blocked isocyanate system,the deblocking activation energy was 115.6 kJ·mol-1,the pre-exponential factor was 4.5×1013,and the reaction order was 1.04.For PVA-quinolinol blocked isocyanate system,the deblocking activation energy was 181.2 kJ·mol-1,the pre-exponential factor was 2.3×1021,and the reaction order was 0.71.For melamine-quinolinol blocked isocyanate system,the deblocking activation energy was 170.4 kJ·mol-1,the pre-exponential factor is 1.3×1020,and the reaction order was 0.97.All the reaction orders were not integer,which indicates that the related deblocking and curing reactions were complicated.(5)Blocked waterborne polyurethane adhesive with about 50% solid content was synthesized with(4-hydroxypyridin-3-yl)(phenyl)methanone as blocking agent,and characterized by FTIR.The adhesion experiments showed that with the increased amount of blocking agent,adhesion property increased first and then decreased.When the curing temperature was above 70 0C,the adhesion properties for genuine leather/genuine leather,PU/PU and PVC/PVC were excellent.(6).Blocked waterborne polyurethane curing agent with about 50% solid content was synthesized with(8-hydroxyquinoline-7-yl)(phenyl)methanone as blocking agent,and characterized by FTIR.The coating properties experiments showed that the synthesized blocked waterborne polyurethane curing agent can fully mix w ith waterborne fluorocarbon emulsion,waterborne epoxy emulsion and waterborne acrylic emulsion to form two-package coating with good coating properties,which performed as well as or better than VESTAGON B1530 curing agent.Meanwhile the synthesized curing agent can be cured at lower temperature compared with VESTAGON B1530. |
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