Surface Properties of Cationic Ultraviolet-Curable Coatings Containing a Siloxane Structure M. Sangermano, 1 R. Bongiovanni, 1 G. Malucelli, 1 A. Priola, 1 A. Pollicino, 2 A. Recca, 2 S. Jo ¨ nsson 3 1 Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, C. so Duca degli Abruzzi 24, 10129 Torino, Italy 2 Dipartimento di Metodologie Fisiche e Chimiche per l’Ingegneria, Universita ` di Catania, V. le A. Doria, 6, 92125 Catania, Italy 3 Fusion, Inc. Systems, 910 Clappers Road, Gaithersburg, Maryland 20878-1357 Received 27 August 2003; accepted 9 December 2003 DOI 10.1002/app.20484 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A polysiloxane diglycidyl ether was used as a comonomer of epoxy resins to obtain coatings through the ultraviolet curing technique. Notwithstanding its very low concentration (1 wt %), the siloxane monomer caused a change in the surface properties of the films. Selective sur- face stratification was evidenced by X-ray photoelectron spectroscopy analysis, and an interesting surface modifica- tion was achieved without changing the bulk properties of the films or the rate of polymerization. © 2004 Wiley Periodi- cals, Inc. J Appl Polym Sci 93: 584 –589, 2004 Key words: cationic polymerization; polysiloxanes; surfaces INTRODUCTION The past 15 years has witnessed a tremendous resur- gence of interest in all types of reactive silicone fluids for ultraviolet (UV)-curable coatings. 1 It is well known that the rapid development of silicone polymers is due to a number of highly desirable properties, including high thermal resistance and resistance to chemicals, ozone, and UV-induced degradation. 2 Moreover, the radiation curing technique is advan- tageous: the formulations are solvent free, the produc- tion rates are high, and the energy required is much less than for thermal curing. These advantages have led to the rapid growth of the technique in different fields, mainly in the production of films, inks, and coatings on different substrates but also in the fabri- cation of a variety of high-tech and electronic applica- tions, such as printed circuit boards. 3 In UV curing, the cationic process, suitable for epoxy resins, vinyl ethers, and oxetanes, presents some advantages over the radical one, 4 in particular the lack of inhibition by oxygen, the low shrinkage of the products, the good mechanical properties of the UV-cured materials, and the good adhesion to various substrates. In addition, the monomers used are generally characterized by low irritation and toxicity properties. 5 Therefore, great effort has been focused on the preparation of epoxy- functional silicone fluids; both glycidyl siloxanes and cycloaliphatic epoxy silicone derivatives have been prepared and characterized. Dicycloaliphatic polysi- loxane oligomers can be readily synthesized by plati- num-catalyzed hydrosilation of an epoxy compound bearing a vinyl group, such as 4-vinylcyclohexene ox- ide, with an appropriate ,-dihydrogen silane; 6–8 analogous diglycidyl ether polysiloxanes have been obtained by the hydrosilation of allyl glycidyl ether. 9 In Scheme 1, both synthetic routes are reported. Photopolymerizable silicones, by virtue of their unique properties, are well suited for specific applica- tions of the curing technique, such as ophthalmic de- vices, medical applications, optical fiber coatings, elec- tronic circuits, gas membranes, release applications, and pressure-sensitive adhesives; 10,11 they have the advantages of softness, biological inertness, relatively good thermal stability, excellent dielectric proper- ties, good substrate wettability, and permeability of gases. 12 The main disadvantage is that the dimethyl silicones are nonpolar and nonmiscible with other res- ins. Moreover, the onium-type photocatalysts, such as the iodonium salts, used in cationic curing are often also immiscible in the silicone media unless sufficient polar organofunctionality is designed into the silicone to render them compatible with the cationic catalyst. 13 Alternatively, a catalyst with low polarity can be used. 14 Interesting results were obtained when low polarity curable products were used as comonomers in UV formulations: fluorinated epoxy monomers added in a very low amount (1 wt %) into traditional epoxy systems changed the surface properties of the films, Correspondence to: M. Sangermano (marco.sangermano@ polito.it). Journal of Applied Polymer Science, Vol. 93, 584 –589 (2004) © 2004 Wiley Periodicals, Inc.