Preparation And Performance Of UV Curable Polyurethane Adhesive Based On Thiol-ene Click Chemistry

UV light curing adhesives are mainly acrylic ester radical type, this kind of adhesivesmaintain a rapid growth rate in many areas because of its advantages such as a widesource material, fast curing, zero VOC emissions, maturity curing process, etc.. Butthere is oxygen inhibition, dark curing hard, thick layer, and the color system with insufficientcuring difficult in radical curing via acrylate double bond. In addition to the advantages ofconventional UV curing system, the thiol-ene click reaction system also has thebenifits of simple reaction conditions, fast curing speed, insensitive to water andoxygen, low shrinkage rate et al. Thiol-ene system is widely used in many fileds, suchas biochemistry and biomedical, polymer modified, coatings.Thiol-ene based UV lightcurable adhesives can effectively overcome the deficiencies of traditional UV-curingadhesives.In this paper, the CO-based urethane acrylate prepolymer was synthesized with Castoroil, IPDI and HPA as raw materials. And then1,4-butanediol, trimethylolpropane,pentaerythritol and castor oil was used to esterify with3-mercapto propionic acid respectivelyto synthesize the four kinds of thiol-compounds. The urethane-acrylate prepolymer andthiol-compounds were blended with addition of photo-initiator in certain proportions in orderto form polyurethane curing film under UV irradiation. The structure and properties ofsynthesized products were analyzed by NMR, FT-IR, TG and DSC. Residual NCO contentand the acid value were measured by chemical titration. In addition, the viscosity of theadhesive; the T-peel strength, hardness and the shrinkage rate of the curing membrane werealso tested. The appropriate technological parameters were obtained through above analysisand compare.The results showed that the thiol-ene addition reaction between the urethane acrylatesand the thiol-compounds was preceeded. The best conditions for the synthesis of prepolymerwas the nHPA/nCO/nIPDIratio of0.7/0.48/1or1/0.37/1, the reaction temperature70℃, thecatalyst dosage200ppm. The synthesis conditions of CO-based thiol compound were differentwith those of alcohol-based thiol compounds. When the reaction temperature was125℃,catalyst dosage was4%(wt), the molar ratio of [-COOH] of MPA and the [-OH] of CO was 1.1, the reaction had the best productivity. With the increase of functionality ofmercaptopropionic acid ester, the thermal stability improved, and the T-peel strengthenhanced. When the moral ratio of C=C in urethane acrylates and SH-in trithiol was1.5, theadhesive showed the best mechanical properties and thermal stability with curing time80s,shrinkage rate10.8%，T-peel strength116N/m and50%mass loss at369℃. The CO-basedUV-cured films showed better mechanical properties with curing time90s, T-peel strength120N/m, and shrinkage rate6.5%,50%mass loss at375℃.