Monomer/modified nanosilica systems: Photopolymerization kinetics and composite characterization Mariola Sadej-Bajerlain a , Hubert Gojzewski b, c , Ewa Andrzejewska a, * a Faculty of Chemical Technology, Poznan University of Technology, pl. Marii Sklodowskiej-Curie 2, 60-965 Poznan, Poland b Institute of Physics, Poznan University of Technology, ul. Nieszawska 13A, 60-965 Poznan, Poland c Max Planck Institute for Polymer Research, Ackermannweg 10, 55-128 Mainz, Germany article info Article history: Received 1 September 2010 Received in revised form 16 December 2010 Accepted 30 January 2011 Available online 24 February 2011 Keywords: Nanosilica Photopolymerization Kinetics abstract The article describes the influence of the amount and type of organically modified nanosilica (surface and structure modified Aerosil 7200 and surface-modified Aerosil R711) on the photopolymerization kinetics of tetraethylene glycol dimethacrylate and on the physical properties of nanosilica dispersions in the monomer and the polymer matrix. Kinetic measurements showed that silica addition can accelerate or retard the polymerization depending on the silica content; the magnitude of this affect depends on the type of silica modification and can be associated with stability of silica dispersion (as measured by Zeta potential value). The highest reactivity showed compositions containing 4e5 wt.-% of silica and accel- eration of the polymerization seems to result mainly from the increase in the propagation rate coeffi- cient. The composites obtained show a uniform dispersion of nanoparticles within the polymer matrix for the silica content at least several wt.-%. The size of aggregates covered with the polymer layer is between 50 and 150 nm for Aerosil R7200 and 75e300 nm for Aerosil R711. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction In recent years much attention has been focused on development of new inorganic-organic composite materials of prospective use in many areas [1e3]. A nanocomposite can be defined as a material resulting from the association of particles having at least one of their dimensions in the range of a few nanometers, dispersed or organized in a polymer matrix [4], and nanohybrid can be defined as nano- composite for which there exists a relatively strong chemical bond between the nanoparticles and the macromolecular chains that compose (at least partly) the continuous phase [5]. It is well known that nanocomposites can combine advantages of organic polymers and the inorganic materials, which results in an enhancement of various properties including viscoelastic characteristics, fire resis- tance [6] and barrier properties [7], resistance to scratching [8,9], abrasion [9e11], as well as other mechanical properties [2,10,11]. From among the inorganic substances, silicon dioxide has become of greatest importance as an active filler of polymers because of its good resistance to heat and electricity, mechanical stability, relatively low costs and high specific surface area [11,12]. Silica has been widely applied in various industries. Besides common plastics and rubber reinforcement, many other potential and practical applications of polymer/silica nanocomposites have been reported: coatings, flame- retardant materials, optical devices, electronics photoluminescent conducting film, ultrapermeable reverse-selective membranes, proton exchange membranes, grouting materials, sensors, etc. [13]. An easy way to disperse silica in a polymer is the preparation of the composite “in situ”, by the polymerization of a monomer that contains dispersed silica. Especially useful method is the UV-induced process, which is solvent-free, energy efficient, economical in space and can be realized at ambient temperature with the high speed. These features, along with the spatial and temporal control of the curing, make the photopolymerization an attractive method for generating of high performance materials. Photopolymerization found extensive applications in producing photoactive polymer- based systems used in coating industry, paints or printing inks, adhesives, composite materials, printing plates, photo- and stereo- lithography, holographic recordings, and dental restorative formula- tions. UV-irradiation in the presence of a suitable photoinitiator is one of the most efficient methods for the generation of highly crosslinked polymers from multifunctional monomers. Polymerization can be carried out under a wide range of conditions, including varying monomer structure, number and type of reactive functional groups, temperature, atmosphere, irradiation rate and photoinitiator type. * Corresponding author. Tel.: þ48 61 6653637; fax: þ48 61 6653649. E-mail address: ewa.andrzejewska@put.poznan.pl (E. Andrzejewska). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2011.01.058 Polymer 52 (2011) 1495e1503