Graft Polymerization from a Silica Surface Initiated by Adsorbed Peroxide Macroinitiators. I. Adsorption and Structure of the Adsorbed Layer of Peroxide Macroinitiators on a Silica Surface Olena Shafranska, † Viktor Tokarev,* ,† Andrej Voronov,* ,‡ Orysya Bednarska, † and Stanislav Voronov † Lviv Polytechnic National University, 12 Bandera Str., UA-79013 Lviv, Ukraine, and Fridrich-Alexander University Erlangen-Nuremberg, Institute of Particle Technology, Cauerstrasse 4, D-91058 Germany Received July 13, 2004. In Final Form: December 10, 2004 The adsorption features of two peroxide macroinitiators (PMIs) with various functionalities from their semidilute solutions on the silica surface were thoroughly investigated in the present work. These investigations include the study of the adsorption kinetics of PMI in diverse solvents and a detailed examination of the adsorbed layer structure with the aid of ellipsometry, scanning force microscopy (SFM), and contact angle measurements. Rearrangements of PMI macromolecules at the solid surface are supposed to be the main reason for the appearance of extremes on the kinetic curves and, besides, have a more pronounceable effect on adsorption rate than their diffusion rate to the surface even at the initial stage of the process. Both islandlike and densely packed structures of absorbed layers were revealed by combining contact angle measurements and SFM. Surprisingly, even in the case when saturation of the adsorbed layer is reached, PMI does not completely occupy the substrate surface which is at least particularly reachable for the wetting liquids. PMIs adsorbed at the solid surface are intended for the formation of tethered polymer “brushes” via the initiation of “grafting from” polymerization. Introduction Graft polymerization from a solid surface is a powerful technique used for obtaining polymer chains tethered to modified surfaces, so-called “polymer brushes”. 1,2 That allows one to alter the surface properties in a wide range, thereby controlling diverse interfacial phenomena, for example, wettability, adhesion, and compatibility, includ- ing biocompatibility, as well as enhancing the stability of various colloid systems. 3,4 To initiate the growth of brushlike polymer chains from the surface, different techniques are employed 2,4,5 among which the immobili- zation of radical initiators on the solid surface is one of the simplest, cheapest, technically available, and effective approaches. Earlier, we found that peroxide macroinitiators (PMIs), for example, those derived from peroxide monomer (PM) - 5-methyl-5-tert-butylperoxy-2-hexen-3-yne and maleic anhydride (MA), 6,7 can serve as effective interfacial macroinitiators, facilitating the formation of polymer chains grafted to mineral or polymer surfaces. 6,8-15 For instance, PMIs have been employed for the modification of dispersed mineral fillers such as calcium carbonate (chalk), 6,8-10 aluminum oxide (R-alumina) 11 and aluminum hydroxide, 12 zinc and titanium oxides, 13 and barium sulfate; 12 the surface of carbon black was modified as well. 14 Mainly, these investigations were targeted at the creation of improved polymer composite materials 9,16 and less attention has been paid toward studying the structure of adsorbed PMI layers. However, such information could be of high importance for effective control of subsequent stages of the graft polymerization and formation of tethered polymer brushes. The presented work aims were to establish the main adsorption features of peroxide macroinitiators on the silica surface and to reveal the structure of the adsorbed layers. To achieve these aims, the detailed structure of the adsorbed layers of PMI on oxidized silicone wafers was * To whom correspondence should be addressed. E-mail: vtokarev@polynet.lviv.ua (V.T.); andrejvoronov@hotmail.com (A.V.). † Lviv Polytechnic National University. ‡ Fridrich-Alexander University Erlangen-Nuremberg. (1) Halperin, A.; Tirrell, M.; Lodge, T. P. Adv. Polym. Sci. 1992, 100, 31-71. (2) Zhao, B.; Brittain, W. J. Prog. Polym. Sci. 2000, 25, 677-710. (3) Garbassi, F.; Morra, M.; Occhiello, E. Polymer Surface. From Physics to Technology; J. Wiley & Sons Ltd.: Chichester, U.K., 1994; p 465. (4) Fukada, T.; Tsuji, Y.; Ejaz, M. Macromolecules 1998, 31, 5934- 5936. (5) Suzuki, M.; Kishida, A.; Iwata, H.; Ikada, Y. Macromolecules 1986, 19, 804-1808. (6) Tokarev, V.; Kucher, R.; Voronov, S.; Ryabova, O.; Minko, S.; Kurgansky V. Dokl. Akad. Nauk SSSR 1987, 293 (1), 166-169 (in Russian); CA 106: 196838d. (7) Voronov, S.; Tokarev, V.; Oduola, K.; Lastukhin Yu. J. Appl. Polym. Sci. 2000, 76, 1217-1227. (8) Voronov, S.; Tokarev, V.; Petrovska G. Heterofunctional Polyper- oxides. Theoretical Basis of Their Synthesis and Application in Compounds; Lviv Polytechnic State University Press: Lviv, Ukraine, 1994; p 86. (9) Voronov, S.; Tokarev, V.; Datsyuk, V.; Seredyuk, V.; Bednarska, O.; Oduola, K.; Adler, H.; Puschke, C.; Pich, A.; Wagenknecht, U. J. Appl. Polym. Sci. 2000, 76, 1228-1239. (10) Tokarev, V.; Wagenknecht, U.; Voronov, S.; Grundke, K.; Bednarska, O.; Seredyuk, V. In “Euro-Fillers ‘97”, Manchester (UK), 1997, 61-64. (11) Tokarev, V.; Voronov, S.; Seredyuk, V.; Kozar, M.; Bednarska, O. Adsorpt. Sci. Technol. 1996, 14 (4), 239-249. (12) Tokarev, V. S.; Sereduk, V. A.; Voronov S. A. Adsorpt. Sci. Technol. 2000, 18 (2), 135-146. (13) Tokarev, V.; Seredyuk, V.; Voronov, S.; Bednarskaja O. Ukr. Khim. Zh. 1997, 63 (12), 127-132 (in Ukrainian); CA 115: 137705w. (14) Voronov, S.; Tokarev, V.; Datsyuk V.; Kozar, M. Prog. Colloid Polym. Sci. 1996, 101, 189-193. (15) Datsyuk, V. S.; Tokarev, V. S.; Voronov, S. A.; Trotsenko, S. E.; Pich, A. Z. Dopov. Nats. Akad. Nauk Ukr., Ser. B 1998, 6, 152-157. (16) Wagenknecht, U.; Kretzschmar, B.; Tokarev, V.; Voronov, S. In “Technomer ‘97”, Fachtagung uber Verarbeitung und Anwendung von Polymeren. November 1997, Chemniz, B12, pp 1-7. 3459 Langmuir 2005, 21, 3459-3469 10.1021/la0482453 CCC: $30.25 © 2005 American Chemical Society Published on Web 03/15/2005