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ABSTRACT A trithiol‐triacrylate gel system for frontal polymerization was explored to establish the gelation time, shelf life, and frontal kinetics. The free‐standing gels were created by triethylamine‐catalyzed Michael addition of trimethylolpropane tris(3‐mercaptopropionate) to trimethylolpropane triacrylate such that sufficient acrylate functional groups were left unreacted to allow free‐radical frontal polymerization with the initiator 1,1‐bis(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane (Luperox 231). Systems with gelation times between 30 and 60 min that support frontal polymerization after up to 28 days of storage were achieved. The front velocity was found to depend on the 1,1‐bis(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane concentration. However, the amount of triethylamine, which was used to catalyze gel formation, did not significantly affect front velocity. The gel diameter and addition of milled carbon fiber (Zoltek px35) affected the front velocity. Cracks during frontal polymerization were reduced when Zoltek px35 was added to the formulation, which also increased the mechanical strength. Complex geometries of free‐standing gels were successfully polymerized. This system is potentially useful in situations where molding and reshaping gels are required prior to frontal polymerization, as well as enabling the ability to examine how mechanical forces like stretching and compression can affect front kinetics. 

Abstract Frontal polymerization is a process in which a localized reaction zone propagates through the coupling of thermal transport and the Arrhenius kinetics of exothermic polymerization. Most initiators that have been used produce volatile by‐products, which create bubbles and voids. Tetraalkyl ammonium persulfates have been used but these require synthesis and do not have long shelf lives. A charge transfer complex (CTC) composed of an iodonium salt, and a phosphine compound has been identified as a gas‐free initiator for free‐radical thermal frontal polymerization. This CTC has 4‐(dimethylamino)phenyldiphenly phophine (DMAPDP) as the donor and p‐(octyloxyphenyl)phenyliodonium hexafluoroantimonate as the acceptor (IOC‐8). The CTC was tested with several acrylates, and all were found to support bubble‐free fronts. We determined the CTC mole ratio for some monomers at which the front velocity reaches a plateau. 

A model was developed to help predict how enzymes can be used to temporally control the gelation of polyvinyl alcohol (PVA) with borate. 

Abstract Frontal polymerization (FP) of epoxy monomers is typically achieved with a radical‐induced cationic frontal polymerization (RICFP) process that combines a thermal radical initiator with an onium salt superacid generator. In this paper, we show that both thermal and UV‐initiated cationic frontal polymerizations are possible for common epoxy and vinyl ether monomers with only an iodonium superacid generator in the absence of a standalone thermal radical initiator. Increasing superacid generator concentration resulted in an increase in front velocity, as did the addition of vinyl ether to epoxies. The front velocity is reduced by the addition of 4‐methoxyphenol (MeHQ), indicating free‐radicals play a significant role. 

Abstract Formulations containing vinyl ethers and epoxy were successfully polymerized through a radical‐induced cationic frontal polymerization mechanism, using an iodonium salt superacid generator with a peroxide thermal radical initiator and fumed silica as a filler. It was found that an increase of vinyl ether content resulted in higher front velocities for divinyl ethers in formulations with trimethylolpropane triglycidyl ether. However, increased hydroxymonovinyl ether either decreased the front velocity or suppressed frontal polymerization. The kinetic effects of the superacid generator and thermal radical initiator with varying vinyl ether content were also studied. It was observed that increasing concentrations of initiators increased the front velocity, with the system exhibiting higher sensitivity to the superacid generator concentration.