Ultrafast Synthesis of Interpenetating Polymer Networdks by Photopolymerization of Expoxides and Acrylate Monomers

Interpenetrating polymer networks (IPN) can be readily synthetized by crosslinking polymerization
of two multifunctional monomers or telechelic oligomers that polymerize by different mechanisms, e.g. radical and cationic types. The main advantage of IPNs is to combine in a single material the properties of the two kinds of polymer networks. An easy way to produce lPNs is by photoinitiated polymerization of monomer blends, in particular by mixing the two types of monomers which are the most widely used in UV-radiation curing acrylates which polymerize by a radical mechanism, and epoxides which polymerize by a cationic mechanism 1.2 A distinct feature of photoinitiation lies in the high polymerization rate which can be reached under intense illumination, together with the advantage of a solvent-free formulation curable at ambient temperature. As a result, the UVcuring technology has found a large variety of applications, in particular to achieve a fast-drying of varnishes and printing inks, a quick setting of adhesives and composite materials and a selective insolubilization of photoresists in microlfthography.
The monomers selected for this study are compounds which are typically used in UV-curable
resins, namely a bisphenol A based diacrylate and a biscycloaliphatic diepoxide. Phase separation does not occur in this particular mixture which remains perfectly transparent, before and after UV-curing. As this formulation contains no volatile acrylate diluent, it does not show the strong odor and irritating character typically found in acrylate-based UV-curable formulations. We have studied the light-induced crosslinking polymerization of this monomer blend by means of real-time infrared (RTIR) spectroscopy, a technique that allows one to monitor in situ the polymerization of each monomer of the mixture and to record directly the conversion versus time
profiles in a timescale as short as I second The important kinetic parameters have thus been determined, in particular the actual polymerization rate and the final cure extent, a quantity which
governs the physico-chemical characteristics of the IPN formed.