Cationic photopolymerization of epoxide monomers in thick sections

SCHROEDER WALTER F.; SILVANA ASMUSEN; ARENAS GUSTAVO F.; CLAUDIA I. VALLO

Bahía Blanca

Congreso; IX Simposio Argentino de Polímeros SAP 2011; 2011

Photoinitiated ring opening polymerization of epoxy monomers has been the subject of extensive studies during the last two decades. Significant advances in the photocuring of such monomers have been achieved since the discovery of cationic initiators such as onium salts (ie. diaryliodonium, triarylsulfonium). These salts possess high photolysis quantum yields and are efficient photoinitiators of cationic polymerization when irradiation is carried out using light in the short- to mid-wavelength UV regions (230-300 nm). In recent years, special interest has been directed toward the development of strategies to make onium salts responsive to visible light (Yagci et al, 2010). The free radical promoted cationic polymerization has been recognized as an interesting indirect activation method where radicals are produced from usual type I or type II radical photoinitiator and oxidized by an onium salt to generate polymerization-initiating cations (Scheme 1).Photopolymerization at high initiator concentration is attractive because as initiator concentration increases, polymerization rate typically increases. However, the absorption of light by the initiator causes attenuation of the curing light along the beam direction. Light attenuation results in a gradient of conversion due to the different initiation rates occurring through the irradiation path. Thus, for photocuring products that have larger than millimeter dimensions it is advantageous to use photobleaching initiators in which light absorption by the initiator products is lower than that by the original photoinitiator molecules, thereby allowing more light to pass through the depth. In the present work we investigate the photobleaching behavior, the reactivity and final properties of epoxy monomers as these are photopolymerized using an onium/camphorquinone (CQ) initiating system in thick sections.