ESR study of the polymerization of methyl methacrylate photoinhibited by butyl nitrite

Volumetric Photopolymerization Confinement through Dual-Wavelength Photoinitiation and Photoinhibition

“…Moreover, the polymerization rate recovered promptly after cessation of near-UV exposure at t = 1 min, indicating rapid consumption of BN-derived inhibiting radicals in the absence of BN photolysis. Sadykov et al 28 reported extended postirradiation induction times for the thermal polymerization at 60 °C of methyl methacrylate formulations containing benzoyl peroxide as a thermal initiator and BN, potentially attributable to the low radical generation rate under the conditions used. Nevertheless, under the conditions used here, photoinhibition of free-radical chain-growth photopolymerization via BN photolysis can be rapidly switched on and off by cycling the incident near-UV light.…”

“…Whereas inorganic nitrite salts can react with water to form nitric oxide and nitrous oxide species, 26 organic nitrites reportedly require activation to effect polymerization inhibition. 28 Higher molecular weight nitrites have been explored to inhibit styrene and butadiene polymerization during distillation, generally requiring low concentrations (0.0001−0.1%) to be effective. 27 Although alkyl nitrite photolysis has been extensively investigated, 29,30 their use as photoinhibitors has been limited to an examination of butyl nitrite (BN) as a UVactivated inhibitor of thermally initiated, radical-mediated chain-growth polymerization.…”

“…27 Although alkyl nitrite photolysis has been extensively investigated, 29,30 their use as photoinhibitors has been limited to an examination of butyl nitrite (BN) as a UVactivated inhibitor of thermally initiated, radical-mediated chain-growth polymerization. 28 The photochemical decomposition of organic nitrites results in the formation of nitric oxide, an efficient inhibitor of radical-mediated polymerizations, and alkoxide radicals 29 capable of polymerization initiation. As summarized in Scheme 1, this UV-induced photoinhibition was attributed to the photolysis of BN, generating nitric oxide (1) that in turn affords a nitroso spin trap upon chain termination (2).…”

“…24 Negligible polymerization was observed for triethylene glycol dimethacrylate (TEGDMA)/ bisphenol A glycidyl dimethacrylate (bisGMA) resin formulations containing BN upon irradiation at 365 nm (see Figure 2 and Table S1); an extended induction period occurred even in the absence of BN (Figure 2A), demonstrating the low initiating radical generation rate afforded by the CQ/EDAB photoinitiator system under near-UV irradiation. Sadykov et al reported that, whereas BN acts as a photoinhibitor of the thermal bulk polymerization of methyl methacrylate under near-UV irradiation, 28 it does not affect the polymerization without photoactivation. In contrast, both the polymerization rate and overall conversion of the methacrylate formulations examined here under exclusively blue irradiation progressively decreased with raised BN concentration (see Figure 2), with negligible polymerization observed for the formulation containing 3 wt % BN.…”

“…Nitrites, both inorganic , and organic, , are known to be inhibitors or retarders of free-radical chain-growth polymerization. Whereas inorganic nitrite salts can react with water to form nitric oxide and nitrous oxide species, organic nitrites reportedly require activation to effect polymerization inhibition .…”