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Directly and indirectly acting photoinitiating systems for cationic ring opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) by using diphenyl iodonium salt (DPI) in the presence of benzyl alcohol were studied and mechanistic details were evaluated. In the direct system, the polymerization is initiated by a Bronsted acid formed upon UV irradiation of DPI. Polymerizations by indirectly acting photoinitiating systems proceeding via electron transfer reactions of photochemically formed electron donor radicals or excited states of polynuclear aromatic compounds with DPI were investigated. It was demonstrated that polymerizations proceed in a controlled manner by an activated monomer (AM) mechanism. Applicability of the photoinitiation to the other lactone monomers was validated on the example of delta- valerolactone (delta-VL).

In the drive toward the development of efficient and stable inorganic semiconductor materials with broadband solar absorption ability to induce various photochemical processes is a highly attractive research field. In this study, two-dimensional (2D) few-layer black phosphorus (BP) exfoliated in a solvent is utilized as photocatalyst to initiate the polymerization of various monomers under visible and near-IR (NIR) light irradiation. Upon the light exposure, few-layer BP generates excited electrons and holes, which undergo electron transfer reactions with the onium salts to form free radicals capable of initiating free radical polymerization. Among the onium salts tested, aryldiazonium salt was found to be the most efficient in the photopolymerization process owing to its favorable reduction potential with the conduction edge potential of BP. The presented strategy also provides the possibility for the in situ preparation of BP-polymer composite materials.

Various ligation processes have recently become a powerful tool in synthetic polymer chemistry. Herein, the use of a new photochemical ligation process as a versatile approach for the cross-linking polymerization, functionalization of polymer chain ends, and surface modification of various materials such as silica and graphene oxide, is demonstrated. The process is based on the formation of urethane linkages by the reaction of photochemically in situ generated isocyanates from benzoyl azides with hydroxyl moieties in the presence of organobase, bicyclo[2.2.2]-1,4-diazaoctane (DABCO) under ambient conditions. The intermediates and obtained materials are characterized by NMR, FTIR, TGA, and TEM analyses. It is believed that this simple and efficient ligation process will expand future applications to fabricate complex macromolecular structures, biomaterials, and gels.

A novel methodology for photoinduced metal-free Atom Transfer Radical Polymerization ( ATRP) by using conventional Type II photoinitiators such as benzophenone, thioxanthone, isopropyl thioxanthone and camphorquinone as sensitizers is presented. These sensitizers efficiently activate the ATRP of vinyl monomers when used in conjunction with co-initiators and alkyl halides under light irradiation. DFT calculations were performed to reveal mechanistic aspects and showed that the initiation of the controlled ATRP reaction pathway from the triplet state is energetically favoured for all sensitizers. In the case of benzophenone, however, the hydrogen abstraction pathway, which leads to free radical polymerization, is a possible side reaction. The strategy applied was proved to yield polymers with narrow molecular distribution. The chain-end fidelity of the polymer obtained was approved by chain extension and block copolymerization experiments, whereas the irradiation dependency of polymerization was confirmed by light on/off experiments.

A novel synthetic strategy involving sequential photoinduced cationic and copper-catalyzed azide alkyne cycloaddition (CuAAC) click processes for the synthesis of complex macromolecular structures such as side-chain functional polymers, graft copolymers, and organogels is described. In the approach, first a set of copolymers possessing side-chain alkyne or halide functionalities, namely, poly(cyclohexene oxide-co-glycidyl propargyl ether) (P(CHO-co-GPE)), poly(cyclohexene oxide-co-epichlorohydrin) (P(CHO-co-ECH)), and poly(tetrahydrofuran-co-epichlorohydrin) (P(THF-co-ECH)), were synthesized by photoinitiated free-radical-promoted cationic copolymerization of the corresponding monomers using phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) and diphenyl iodonium hexafluorphosphate (Ph2I+PF6-) as free radical photoinitiator and oxidant, respectively. While P(CHO-co-GPE) readily contained clickable alkyne side-chains, the halide groups of P(THF-co-ECH) were converted to azide groups by conventional azidation procedure using NaN3 in DMF. Model side-chain functionalization, grafting onto, and organogel formation were demonstrated by using P(CHO-co-GPE) and azidated P(THF-co-ECH) via photoinduced CuAAC reactions. The intermediate polymers formed in various stages and final polymers were characterized by spectral analysis and gel permeation chromatography.