Influence of the photoinitiating system on the properties of photopolymerized methylmethacrylate: the role of the ketyl radical in type II photoinitiators

The photopolymerization of methylmethacrylate using different initiating systems strongly affects its glass transition temperature and dispersity.

Isomerization controlled photopolymerization: effect of dye photophysics on photoinitiation efficiency

The efficiency of free radical polymerization by photoinitiating systems based on two Astrazon orange cyanine dyes was shown to be directly related to the isomerization process of the dye in the excited states. The impact of resin viscosity on photopolymerization reactions was measured and related to the overall radical quantum yields. The quantum yields were calculated according to the photocyclic behaviour of the initiating systems based on the Astrazon orange dyes. These dyes are characterized by a viscosity dependent photophysics, which leads to an isomerization-diffusion-controlled photopolymerization. Besides this demonstration, Astrazon orange dyes appeared to be very good candidates for free radical photopolymerization in the visible, presenting high absorption coefficient, low cost and good sensitivity.

Preparation of antibacterial keratin fabrics via UV curing and click chemistry

A clean and cost-effective surface modification method of keratin fabrics was proposed by UV curing and thiolene click reaction.

Optimization of a Safranine O three-component photoinitiating system for use in holographic recording

The coupling between a holographic resin, combining multiple monomers and additives, with photoinitiating systems (PIS) is not straightforward. In this paper, a classic PIS based on Safranine O (SFH+) as dye, an amine (ethyl-4-(dimethylamino)benzoate) as electron donor, and a triazine derivative (2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine) as electron acceptor for holographic recording was studied using time-resolved spectroscopic experiments. By taking into account the viscosity of the matrix, a method to evaluate the overall quantum yield of radicals released is proposed and the contribution of singlet and triplet excited states of SFH+ in the formation of radicals is evaluated. Then the corresponding photopolymerization efficiencies of the PIS, studied by real-time FTIR, are compared with holographic recording experiments: this system allows the formation of a hologram with high diffraction efficiency (0.9) in 3 s of irradiation time. It is shown that besides holographic resin formulation, the photochemistry of PIS also impacts the hologram formation.

Extended mechanistic aspects on photoinitiated polymerization of 1,6-hexanediol diacrylate by hexaarylbisimidazoles and heterocyclic mercapto compounds

Chlorine substituted hexaarylbisimidazole (o-Cl-HABI) efficiently initiates radical polymerization of multifunctional acrylic esters in the presence of a heterocyclic mercapto compound if the latter can form its tautomeric thione. Exposure of o-Cl-HABI results in lophyl radicals, which efficiently add to the thione in the first step while the second step releases a highly reactive thiyl radical from this intermediate. LC-MS and CID-MS measurements support this reaction scheme. Furthermore, photo-DSC experiments applying UV light between 320 and 380 nm showed that mercaptotriazole and phenylmercaptotriazole exhibited the best reactivity in the monomer 1,6-hexanediol diacrylate (HDDA) while alkyl substituted mercaptotriazoles showed less reactivity. Change of the triazole heterocycle by mercaptoimidazole resulted in a significant decrease of photoinitiation efficiency. This heterocycle does not form the corresponding thione in HDDA as shown by NMR measurements. Replacement of mercaptotriazole by an alkylthiol leads to a system showing the lowest photoinitiation efficiency in this series. Formation of thione structure in the case of heterocyclic mercapto compounds may cause higher reactivity of the heterocyclic mercapto compounds with the lophyl radical in the monomer chosen.

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

The combination of a dye which absorbs the photon, an electron acceptor and an electron donor leading to energy conversion through electron transfer, was the basis of the so called three-component systems. In this paper, an experimental work combining Rose bengal dye with a triazine derivative as electron acceptor and ethyl 4-(dimethylamino)benzoate as electron donor, will underline the benefit of the photocyclic behavior of three-component systems leading to the dye regeneration. A thermodynamic approach of the photocycle is presented, followed by a mechanistic and computational study of ideal photocycles, in order to outline the specific kinetics occuring in so called photocatalytic systems. The simple kinetic model used is enough to outline the benefit of the cyclic system and to give the basic requirements in term of chemical combination needed to be fulfilled in order to obtain a photocatalytic behavior.

Photopolymerization of methyl methacrylate: effects of photochemical and photonic parameters on the chain length

The effects of photochemical and photonic parameters are investigated on the chain length of poly(methylmethacrylate) (PMMA) as formed by the free radical photopolymerization process.

Quaternary ammonium salts of phenylglyoxylic acid as photobase generators for thiol-promoted epoxide photopolymerization

A novel series of photobase generators (PBGs), which are quaternary ammonium salts of phenylglyoxylic acid (PA) having the ability to generate strong bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) or 1,1,3,3-tetramethylguanidine (TMG), was synthesized.