Elsevier

Progress in Organic Coatings

Volume 76, Issues 2–3, February–March 2013, Pages 471-476
Progress in Organic Coatings

Synthesis and cationic photopolymerization of a difunctional episulfide monomer

https://doi.org/10.1016/j.porgcoat.2012.10.022Get rights and content

Abstract

Sulfur-containing compounds have attracted many interests in the UV curing field. A new episulfide monomer, 1,4-butanediol episulfide (BDDGE-PSTC (BPT)), was synthesized via replacement of the oxygen atoms in 1,4-butanediol diglycidyl ether (BDDGE) with sulfur atoms. Its structure was confirmed by FTIR, 1H NMR and ESI/MS. The photopolymerization kinetics of BPT was studied by real-time infrared spectroscopy (FTIR), under conditions with different photoinitiator concentration and type, atmosphere and so on. Physical properties such as refractive index and adhesion strength of the cured BPT polymer were studied. It was found that the cured BPT polymer showed higher refractive index and better adhesive strength on polyethylene terephthalate (PET) and iron in comparison with BDDGE. Thermal and mechanical properties of UV-curing BPT films were also investigated by TGA and DMA.

Highlights

▸ Difunctional episulfide (BPT) was successfully synthesized. ▸ The reactivity of BPT was higher than that of BDDGE (about 25 μm film). ▸ The cured BPT had higher refractive index compared to BDDGE. ▸ BPT polymer had better adhesive strength on PET and iron than that of BDDGE.

Introduction

The photopolymerization process is widely used for rapidly producing highly crosslinked polymer networks [1], [2]. It is of great interest in many industrial applications: the formulations are solvent-free, the production rates are high, and the energy required is much less than that of thermal curing. These advantages have led to the rapid growth of this technique in different fields such as films, adhesives, varnishes, dyes, spherical lenses, inks, and coatings on a variety of substrates including paper, metal, and wood [3]. In UV curing, free radical and cationic species are generated by the interaction of the UV light with suitable photoinitiators, which induce the curing reaction of suitable reactive monomers and oligomers.

Cationic photopolymerization has received considerable attention due to its advantages, such as lack of inhibition of oxygen, low shrinkage, good mechanical properties of UV cured materials and good adhesion properties. In addition, monomers used are generally characterized by being less toxic and irritating [4], [5]. Different types of monomers including epoxides, vinyl ethers, propenyl ethers, oxetanes, and many others have been employed and reported [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16].

Episulfides containing one sulfur atom in the ring [17], [18], [19], have significant advantages over epoxy monomers: short gelation time, low water absorption, and high refractive index. Moreover, episulfide monomers generally polymerize more readily than epoxy monomers in thermocuring episulfide/amine systems [20], [21], [22]. In UV curing, a lot of researches on the cationic polymerization of epoxy monomers have been reported, but there were few researches on the cationic polymerization of episulfide monomers [14], [23]. Moreover, there is no study reported that the cationic polymerization of episulfides could improve the refractive index and adhesion to metal materials, and that was the focus of our work.

In this study, the synthesis of a new episulfide based on 1,4-butanediol diglycidyl ether (BDDGE) was reported, and their behavior during cationic photopolymerization was studied. The refractive index and adhesive strength of the obtained photocured films were also investigated.

Section snippets

Materials

1,4-Butanediol diglycidyl ether BDDGE (S-27, 99.3%, EEW 99.2, Viscosity 9.8 mPa S) was donated from SY NASIA (Suzhou) Co., Ltd. Potassium thiocyanate (PSTA) KSCN was obtained from Tianjing wen Da Xi Gui Agent Chemical Plant. Ethanol, chloroform and anhydrous sodium sulfate were supplied by Beijing Chemical Plant (Beijing, China). The photoinitiator UVI-6976 (triarylsulfonium salt) was donated by Runtech Chemical (PR China). Iodonium bis(4-methylphenyl)hexafluorophosphate (IHT-PI 440) was donated

Photopolymerization kinetics

During the polymerization of BPT, the IR-signals of episulfides (1046 and 617 cm−1 for symmetric and asymmetric deformation of thiirane ring) [20] could be used to monitor the degree of conversion of episulfides. Due to the higher intensity and unique position in the IR spectrum, the band at 617 cm−1 was used for the analysis of the episulfide consumption. Fig. 1 showed IR-spectra of BPT during photopolymerization. The result revealed that the episulfide signals at 617 cm−1 gradually disappeared.

Conclusions

Difunctional episulfide (BPT) was successfully synthesized based on 1,4-butanediol diglycidyl ether (BDDGE) and potassium thiocyanate (PSTA). It found that the reactivity of BPT was higher than that of BDDGE in cationic photopolymerization (∼25 μm film). The cured BPT polymer showed higher refractive index and better adhesive strength on polyethylene terephthalate (PET) and iron in comparison with BDDGE.

Acknowledgements

This work was supported by the Open Fund from State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology. This study was also supported by the Natural Science Foundation of Jiangsu Province (BK2010190), Key Laboratory for Green Chemical Process of Ministry of Education (GCP201002).

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