Effect of orientation on thermoset frontal polymerization

Abstract

We observed that the velocities of descending thermoset polymerization fronts were strongly affected by the orientation of the tube. The front remained approximately perpendicular to the gravitational vector but propagated almost 1.8 times as fast at 75° along the axis of the tube. We performed a study of the velocity and front‐shape dependence on orientation with propagating fronts of triethylene glycol dimethacrylate with peroxide initiator and acrylamide/bisacrylamide polymerization in dimethyl sulfoxide with persulfate initiator. The percentage increase of velocity was independent of the initiator concentration but strongly dependent on the viscosity. Convection under the front flowed away from the tube wall nearest the vertical axis and was stronger as the angle increased. The front shape also changed, becoming significantly distorted near the wall from which the convection originated. We applied a simple geometric argument to explain the angular dependence for small angles on the basis of the assumption that convection did not affect the velocity of propagation normal to the front. The increase in velocity along the tube axis could be explained by a projection of the normal velocity onto the tube axis, following a 1/cosθ dependence. For higher angles, the convection was not sufficiently strong to maintain a level front. When the difference from a 180° orientation was considered, the velocity dependence exactly followed the geometric relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3504–3508, 2002

Frontal Polymerization

“…If the reactor is not vertical, there is no longer the question of stability-there is always convection. Bazile et al studied descending fronts of acrylamide/bisacrylamide polymerization in dimethyl sulfoxide (DMSO) as a function of tube orientation [81]. The fronts remained nearly perpendicular to the vertical but the velocity projected along the axis of the tube increased with the inverse of the cosine of the angle.…”

UV‐ignited frontal polymerization of an epoxy resin

“…If the amount of dissipated heat is not too great, then a sufficient quantity of energy able to induce the polymerization of the monomer close to the hot zone is provided. The result is the formation of a hot polymerization front capable of self‐sustaining and propagating throughout the reactor 20–36…”

“…The first studies on FP were performed in the former Union of Soviet Socialist Republics on methyl methacrylate that was polymerized under drastic pressure conditions (>3000 atm) 20, 21. Several other vinyl monomers have been polymerized at ambient pressure by Pojman and coworkers 22–25. Also, epoxy monomers have been frontally polymerized by reaction with a stoichiometric amount of a curing agent by stepwise‐growth kinetics 26–29…”

Frontal Polymerization Synthesis of Starch‐Grafted Hydrogels: Effect of Temperature and Tube Size on Propagating Front and Properties of Hydrogels

“…To investigate the front velocity functional dependence on initial temperature, we carried out additional experiments with different tube sizes. Figure 1 shows an Arrhenius plot of front velocity against initial temperature for three different tube diameters (15,20, and 25 mm). As can be seen, straight lines can be obtained over low initial temperature of 25-50 8C for tube sizes of 15 and 20 mm and 25-40 8C for tube size of 25 mm.…”

“…In all previous works on FP a number of aspects have been explored, such as the effect of initiator type and concentration on front velocity [10,12,13] and the effect of pressure [14] and tube orientation, [15] the dependences of front velocity and front temperature on reaction components. [9,11] In fact FP is performed in a nonadiabatic reactor under the atmosphere in order to test the applicability of this technique to process conditions often found in practice.…”