A highly branched polythiourethane acrylate used for UV-curable high antireflection coatings

A series of highly branched polythiourethane acrylates (BPTUAs) were prepared through the double thiol-ene click reaction of thiol-endcapped difunctional thiourethane as an oligomer A(2) (Oligo-TU) with trimethylolpropane tri(thioglycolate ethylene glycol acrylate) (TMPTTA) as a trifunctional monomer B-3 in different ratios. The Oligo-TU was synthesized via the addition reactions of 2,4-toulene diisocyanate with 1,4-butanediol, and further with 4,4'-thiobisbenzenethiol. The TMPTTA was synthesized by the thiol-ene click reaction of trimethylolpropane tri(thioglycolate) (TMPTT) with an excess of ethylene glycol diacrylate. For comparison, a tetrafunctional thiourethane acrylate (TUA) was also synthesized. Finally, the obtained BPTUA and TUA were further modified with 2-mercaptobenzothiazole, 2-mercaptothiazoline and mercapto-5-methyl-thiadiazole, respectively, to form highly branched polyfunctional thiazole-based acrylates BPTUA-TAs and TUA-TAs. The molecular structures were confirmed by FT-IR and H-1 NMR analyses. The number average molecular weights and their polydispersity were determined by GPC spectroscopy. The UV irradiation using a medium pressure mercury lamp was applied to prepare the optical films in the presence of a photoinitiator. The refractive indices of UV-cured films were measured using a He-Ne laser at 632.8 nm. The results showed that both BPTUA and TUA films possess the similar refractive indices in the range of 1.592-1.604. However, the higher refractive indices in the range of 1.603-1.620 with BPTUA-TA films than 1.601-1.609 of TUA-TA films were obtained. All samples showed the high pencil hardness and impact resistance, as well good flexibility. (C) 2013 Elsevier B.V. All rights reserved.