Miniemulsion Radical Photopolymerization Of Acrylate Monomers

HOIJEMBERG, PABLO ARIEL; CHEMTOB, ABRAHAM; CROUTXÉ-BARGHORN, CÉLINE

Villeneuve d'Ascq

Jornada; GFP2P Journées de Printemps; 2010

Groupe français de photochimie, photophysique et photosciences

Industrial application of photopolymerization in colloid polymer science has been limited so far to latex film photoreticulation through UV irradiation or electron beam. A vast majority of the studies on emulsion polymerization processes focus primarily on thermally-initiated polymerization. Nevertheless, there have been a few examples of photoinduced polymerization in aqueous dispersed media since the 80s, mainly relying on microemulsion or micellar techniques.1,2 Latex synthesis via photoinduced polymerization is certainly a non mature research field, which is poorly understood and explored. Switching to a photochemical way may lead to important improvements with respect to conventional thermal methods: polymerization time is significantly reduced due to the high reactivity of the photochemical processes (a few minutes against several hours), the absence of external heating and the low exothermicity of the reactions could limit the risks of colloidal destabilization, etc. This study describes the radical photopolymerization of acrylate monomers in miniemulsion at laboratory scale. Starting from nanosized acrylate droplets (smaller than 100 nm) which encapsulate a type I radical photoinitiator bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide (BAPO), UV irradiation led after a few minutes to the formation of polymer nanoparticles of similar size. The present study deals with the kinetics aspects of this reaction and the colloidal properties of the resulting polymer dispersions. Real-time Fourier transform near-infrared spectroscopy (RT-FTNIR) in transmission was implemented to follow continuously the fast photopolymerization process.3 In order to shed light on the reaction kinetics, the ratio between the light absorbed by the photoinitiator and the light scattered by the monomer miniemulsion droplets was estimated by spectroscopical studies. In addition to this first pathway, two innovative photochemical approaches without conventional photoinitiators species have been investigated. The first one relies on the self-initiated photopolymerization of acrylate monomers under proper irradiation conditions, while the second one takes benefit from the photoinitiating ability of a phenyloxide-based surfactant. [1] Kuo, P. L.; Turro, N. J.; Tseng, C. M.; El-Aasser, M. S.; Vanderhoff, J. W. Macromolecules, 1987, 20, 1216. [2] Carver, M. T.; Dreyer, U.; Knoesel, R.; Candau, F.; Fitch, R. M. J. Polym. Sci., A: Polym. Chem., 1989, 27, 2161. [3] Chemtob, A.; Kunstler, B.; Croutxé-Barghorn, C; Fouchard, S. Photoinduced Miniemulsion Polymerization. Accepted in Colloid Polym. Sci. (2010). DOI 10.1007/s00396-010-2190-1