Characteristics of Frontal Polymerization

Fortenberry and Pojman studied FP of acrylamide without solvent using powdered acrylamide and persulfate [53]. They found that the initial or green density of the systems affected the front velocity. Such behavior is quite normal for self-propagating high-temperature synthesis (SHS) with inorganic components [54-56]. Solid monomers can be used in solvent as well [57]. 

We will focus henceforth on free-radical systems because they offer several control parameters. An unusual feature of free-radical systems is that they are nonstoichiometric. Adding more initiator usually does not affect the conversion 

Studies on the velocity dependence on temperature and initiator concentration have been performed [43, 58, 59]. FP in solution was performed [57], and initiators that do not produce gas were developed [60]. The velocity can be affected by the initiator type and concentration but is on the order of a few centimeters per minute for monofunctional acrylates and as high as 20 cm min for multifunctional acrylates [60]. 

Free-radical FP has been discussed in detail by Pojman et al. [43] and by Washington and Steinbock [61]. The velocity dependence on the initiator concentration has been studied for several systems [58, 59, 62] and follows a power function 

FP is not currently in commercial use, although there have been several patents issued related to it. The first is for an In depth curing of resins induced by UV radiation, which used a combination of UV hght to start free-radical FP [63]. In 2001, Gregory patented Ultraviolet curable resin compositions having enhanced shadow cure properties in which the frontal curing of cycloaliphatic epoxides was achieved with a cationic photoinitiator in tandem with a peroxide [64]. Pojman was awarded two patents on functionally gradient materials prepared by FP [65, 66]. The maker of chemical anchors, Hilti, has two patents on FP but has not commercialized either of them [67, 68]. 

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