Benzoylformamides (BFAs) are proposed as photocaged bases for redox free radical photopolymerization (FRP). Initially the dissolving capacity of BFAs was evaluated. Besides our previously reported photo-latent anion polymerization, BFAs, as versatile photocaged bases, can not only initiate the FRP of acrylates unassisted, but also perform redox FRP in combination with a benzoyl peroxide initiator. We detail a model photopolymerization in the presence of BFA-dBA ( N , N -dibenzyl-2-oxo-2-phenylacetamide) as the photocaged base. In combination with a benzoyl peroxide initiator, BFAs are able to initiate the amine-mediated redox photopolymerization of acrylates, and enhance the photopolymerization rate. Finally, we investigated the mechanism of the radical formation to initiate the redox FRP, as exemplified by BFA-dBA.
Ming-Hui He,Mei-Lin Su,Zhao-Hui Yu,Guang-Xue Chen,Zhao-Hua Zeng,Jian-Wen Yang
Benzoylformamide (BFA) derivatives are proposed as new photocaged bases with good solubility in epoxy resin. Initially their structures were confirmed by 1 H NMR, 13 C NMR, and elemental analysis. Next, we detail their thermal stability, solubility behavior, and photolysis products. Furthermore, the model photo-latent anion polymerization (AP) of epoxide system in the presence of BFA-dBA ( N , N -dibenzyl-2-oxo-2-phenylacetamide) as a photocaged base has been investigated, and excellent photopolymerization profile is obtained.
Minghui He,Guangxue Chen,Xun Huang,Ruixin Xu,Zhaohua Zeng,Jianwen Yang
N-Phthaloyltranexamic acid ammonium salt derivatives integrating with peroxides can invoke redox photopolymerization and propagating polymerization. A series of N-phthaloyltranexamic acid ammonium salt derivatives based on benzophenone, thioxanthen, and naphtha chromophores as novel photocaged bases were synthesized and characterized. In combination with a benzoyl peroxide initiator, these structures were able to initiate the amine-mediated redox photopolymerization of acrylates. In particular, the covalent binding of N-phthalimidoamino acid and type II chromophores (thioxanthone, benzophenone) improved remarkably the photoreactivity of photocaged bases (thioxanthen-DBU and benzophenone-DBU) compared to the parent compound. Furthermore, naphthal-DBU matches well the emission spectra of the mercury lamp with a dominant emission wavelength at 365 nm. More importantly, phthal-DBU & BPO as a new photocaged redox combination can invoke controlled redox polymerization within an irradiation time of 3 min. Finally, due to the persistent interaction of the produced longeval amine with peroxides, remarkable post conversion after irradiation, which is significant for preparation of photo-screened materials, was thus initially achieved in the redox photopolymerization.
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