Green Chemical Synthesis Of Multi-Mercapto Carboxylic Esters And The Properties Of Thiol-ene Polymers

Owing to the advantages of thiol-ene photopolymerization such as step-growthmechanism, delay in gel point, uniform network formation, ease of polymerization,resistance to oxygen inhibition, solventless processing, lower shrinkage and shrinkagestress，The thiol-ene chemistry has found applications in areas such as photo-lithography, microdevice fabrication, UV-curable coatings and inks, and degradablebiomaterials. The multi-mercapto carboxylic ester is widely used in thiol-enephotopolymerization due to its low volatility and odor.The traditional synthesis process of multi-mercapto carboxylic ester containsesterification, alkaline and water cleaning. The process produces the large amount ofindustrial waste water. In this paper, a green chemical approach is designed tosynthesis these compounds taking the advantage of the dissolve difference of thereactants and products in achcol. There is no need of alkaline and water cleaning, thecatalyst and excess mercapto carboxylic acid can be reused during these processing.We’ve synthesized a series of multi-mercapto carboxylic ester with differentstructure and degree of functionality, these compounds was characterized by1H NMR.Then, we investigated the structure of thiol effects on thiol-ene polymer’s thermalproperty. The study found that the thermal transition region of polymers is single andnarrow, the glass transition temperature (Tg) enhanced with the increasing of thiolfunctionality. The Tgdecreased drasticly due to the flexible structure to thiol, whileincorporating the rigid structure it increased.Ternary thiol-ene/acrylate system was studied. The result indicated that, the thermaltransition region of polymers is broad comparing to thiol-ene system, and thepolymers’ Tgenhanced with the increasing of the concentration of trimethylolpropanetriacrylate, and descended with the increasing of the concentration of tripropyleneglycol diacrylate. While adding the allyl-funtionalized aliphatic polycarbonate-basedpolyurethane oligomers into thiol-ene system made polymer more elasticity. What’smore, the perfluoroalkyl acrylate monomers, despite their very low concentrations,caused sharp changes in the surface properties of the polymers’ film.