Synthesis of UV-curable polysiloxanes containing methacryloxy/fluorinated side groups and the performances of their cured composite coatings

https://doi.org/10.1016/j.porgcoat.2010.07.009Get rights and content

Abstract

Three novel UV-curable polysiloxanes consisting of polysiloxane backbone with methacryloxy/fluorinated side groups were synthesized, and their structures were characterized by FT-IR, 1H NMR and 13C NMR. A series of UV-cured composite coatings based on the synthesized polysiloxanes and an epoxy methacrylate were obtained through photopolymerization. Their gel content, flexibility, hardness, gloss, contact angle, thermal behavior as well as water absorption ratio were investigated. Results found that the siloxane component could enhance the flexibility and gloss of coatings, while the presence of fluorinated groups could improve the hardness. The combination of silicon and fluorine in the same polymer could increase thermal stability and water resistance of the coatings and decrease their surface energy simultaneously. The observation of the fractured-surface morphology showed that the polysiloxanes could be well dispersed in the epoxy methacrylate to some extent. A suitable addition of such polysiloxane in photocurable coating matrixes may provide excellent properties for the cured coatings and widen their applications.

Introduction

UV-curable coatings are important among coating products, which have been greatly used for the surface protection of various materials by fast-drying varnishes or paints [1]. In order to meet the need of high-performance coatings in high-technology areas like space and marine, UV-curable coating formulations have to continue to advance [2], [3], [4]. It is known that the properties of the created polymer network are affected by the composition of UV cured formulation. Conventionally, coating formulations containing fluorinated monomers, fluorinated oligomers or copolymers demonstrate good water resistance, chemical resistance, thermal stability and weather resistance [5], [6], [7], [8]. Moreover, hydrophobicity, flexibility and thermal stability of the siloxane backbone ([Si–O]n units) make polysiloxane an excellent material for the fabrications of micro-fluidic devices (such as valves and pumps), optical fibers, electronic packings, and especially metal, plastic and glass coatings [5], [9], [10], [11]. Another advantage of polysiloxane is that its each siloxane unit can provide two sites for cross-link or functional side groups through bond formation with silicon [12]. Hence, it is valuable to develop a kind of UV-curing coating system that can combine the excellent properties of fluorine and polysiloxane. Additionally in curing process, the volatilization of fluorinated monomers is easy. If fluorinated monomers are grafted into the side groups of polysiloxane, it may be an effective method to avoid the volatilization.

So far the study concerning the preparation and application of fluorine-containing polysiloxane in UV-curable coatings is seldom reported [12]. In this work, we synthesized novel UV-curable polysiloxane containing methacryloxy/fluorinated side groups (PSMF) by reacting polymethylhydrosiloxane (PMHS) of 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFMA), allyl glycidyl ether (AGE) and methacrylic acid (MA) in turn. Furthermore, three prepared PSMFs with different fluorine concentrations were respectively added into bisphenol-A epoxy methacrylate (EMA) curing system in view of the wide use of the UV-curable epoxy oligomers [13], [14] and higher requirements for their thermal ability, flexibility and surface property. In the presence of the photoinitiator, the PSMF and EMA were cross-linked by carbon–carbon double bonds in UV irradiation, and then the PSMF/EMA cured composite coatings were fast prepared. In this way, the combination of silicon and fluorine, and the formation of siloxane-based network in EMA could lead to greatly improved properties for the PSMF/EMA composite coatings. The measured results concerning the gel content, flexibility, hardness, gloss, surface property, thermal behavior, water resistance and fractured-surface morphology of PSMF/EMA coatings were discussed in detail.

Section snippets

Materials

Allyl glycidyl ether (AGE) and polymethylhydrosiloxane (PMHS, 1.41 mol reactive hydrogen per 100 g PMHS) were purchased from Xinghuo Chemical Co. of China. Diglycidyl ether of bisphenol-A (DGEBA, Ep828, the epoxide equivalent weights: 196 g/epoxide) was from Shell Chemical Co. Hydrogen hexachloroplatinate hydrate (Pt-catalyst), tetrabutylammonium bromide (TBAB), and benzophenone (BP) were from Aldrich Chemical Co. Ethylene glycol, methacrylic acid (MA), triethanolamine and

Synthesis and characterization of PSMF

In order to study the effects of silicon and fluorine on the physical properties of UV-cured composite coatings, the three UV-curable and fluorine functionalized polysiloxanes, PSMF1, PSMF2 and PSMF3 were firstly synthesized in this work. The general synthetic process is mentioned in Scheme 1. The structures of these products were measured by FT-IR, 1H NMR and 13C NMR. The FT-IR spectra of the three products are similar and shown in Fig. 1. It can be seen that the disappearance of the

Conclusion

In our work, new UV-curable polysiloxanes containing methacryloxy/fluorinated side groups (PSMF) were synthesized, and their structure were characterized by FT-IR, 1H NMR and 13C NMR. PSMF/EMA UV-cured composite coatings were prepared by mixing PSMF and EMA under UV irradiation. Their gel content, flexibility, hardness, gloss, contact angle, thermal behavior, and water absorption ratio were investigated. Results indicated that the siloxane of PSMF could enhance the flexibility and gloss, and

Acknowledgements

This work was supported by Scientific and Technological-type, Small and Medium-sized Enterprises Technology Innovation Fund Project of China Science and Technology Ministry (06C26214401627). The authors are grateful for the financial support.

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