Binary Frontal Polymerization: A New Method to Produce Simultaneous Interpenetrating Polymer Networks (SINS) JOHN A. POJMAN,”* WILLIAM ElCAN,’ AKHTAR M. KHAN,’ and LON MATHIAS2 ‘Department of Chemistry and Biochemistry and ‘Department of Polymer Science, The University of Southern Mississippi, Hattiesburg, Mississippi 39406-5043 SYNOPSIS We report a new method for the preparation of a simultaneous interpenetrating polymer network (SIN) using a thermal propagating front of two independent and noninterfering polymerization mechanisms. The system consists of the free radical crosslinking of trieth- ylene glycol dimethacrylate (TGDMA) and the amine/BCla oamine curing of diglycidyl ether of bisphenol A (DGEBA). The front velocity dependence on the percentage of each monomer shows a minimum at 4570 TGDMA. Temperature profile measurements indicate that a single reaction front propagates. A colored opaque material is produced, but SEM and TEM analysis were inconclusive whether phase separation occurred. Samples as large as 5 cm in diameter were prepared with this method. We conclude that this method should be especially suited for preparing large sampIes of IPNs in which significantphase separation occurs. @ 1997 John Wiley & Sons, Inc. Keywords: IPN ● frontal polymerization . propagating front ● SIN INTRODUCTION Frontal polymerization is a mode of converting monomer into polymer via a localized reaction zone that propagates. Such fronts can exist with free rad- ical polymerization or epoxy curing. Frontal poly- merization was first discovered at the Institute of Chemical Physics in Chernogolovka, Russia, by Chechilo and Enikolopyan in 1972.’ They studied methyl methacrylate polymerization to determine the effect of initiator type and concentration on front velocity2 and the effect of pressure.3’4 A great deal of work on the theory of frontal polymerization has been performed.h ‘(’ Work has also been done with epoxy curing.’ ‘“g Davtyan et al. reviewed the field up to 1984.]s Pojman et al. have recently reviewed and analyzed the chemistry and theory of frontal polymerization.’4 Pojman et al. demonstrated the feasibility of frontal polymerization in a variety of neat monomers with thermal free radical initiators at ambient pres- sure using liquid monomers that form polymers with * To whom all correspondenceshould be addressed. .Jourrralof Polymer Science: Pan A: Polymer Chemistrs, Vol. .35,,227–230 11997) f, 1997 John Wiley & Sons. Inc CYT 0SS7-f U4X/97/020227-fM melting points exceeding the reaction temperature of the front]s-’7 and with a solid monomer.la Unsta- ble modes of propagation were found under some conditions.’g They also evaluated the factors that affect propagating fronts and the conversion and molecular weight distributions of polymers produced in them. zo’z] We expect that this approach will ultimately have three benefits over traditional methods of polymer synthesis: (1) reduced energy costs, (2) reduced waste production, and (3) unique morphologies. A unique feature of propagating fronts is their ability to con- vert monomer to polymer rapidly and uniformly. Performing an adiabatic polymerization of a neat monomer is difficult at best and dangerous at worst, but it can be advantageous because the heat of the reaction is used to increase the rate of reaction, making for very rapid conversion. Also, the lack of solvent eliminates the need to separate the polymer from the solvent and residual monomer, which re- quires energy and can have environmental ramifi- cations. Recently, Nagy et al. demonstrated that a thermochromic composite (changes color with changes in temperature) could be prepared better via frontal polymerization than with traditional ho- mogeneous methods because the rapid front pre- 227