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ABSTRACT This report introduces a novel UV-curing technology based on thiol-thiol coupling for polydisulfide network formation. Beginning with a model tris(3-mercaptopropionate) trithiol monomer and xanthone propionic acid-protected guanidine as photobase generator, a comprehensive characterization based on spectroscopic techniques supports the reaction of thiols into disulfides without side reactions. The best experimental conditions are described as regards to film thickness, irradiance, emission wavelength, and atmosphere composition. The results shed light on a step-growth photopolymerization mechanism involving two steps: first, the formation of thiyl radicals by thiolate air oxidation or/and thiol photolysis, and second, their recombination into disulfide. By varying thiol functionality and structure, oligomer chain length and monomer/oligomer ratio, the network architecture can be finely tuned. The molecular mobility of the polydisulfide network is crucial to high thiol conversion rates and yields as revealed by 1H T2 NMR relaxation measurements. Ultimately, spatial control enables the formation of a photopatterned poly(disulfide) film, used as next-generation high refractive index photoresist. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 117-128. [ABSTRACT FROM AUTHOR]

ABSTRACT Diphenyl iodonium hexafluorophosphate salt and N-alkyl morpholino acetophenone were shown to be effective photocatalyst generators for the cross-linking of α,ω-silanol terminated silicone oligomers. These two photoacid and photobase-induced polycondensation pathways provided an attractive and efficient alternative to toxic and expensive organometallic catalysts. The utility of this novel UV-curing process was demonstrated with a combination of time-resolved infrared spectroscopy to follow the fast reaction kinetics and solid-state 29Si nuclear magnetic resonance to investigate the polysiloxane network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39875. [ABSTRACT FROM AUTHOR]

Abstract: Two lamellar organosilica films made up of stacks of head-to-head and head-to-tail alkyl bilayers were synthesized by a UV-driven polymerization of n-C18H37SiCl3 and n-C18H37Si(OCH3)3, respectively. In addition to thermogravimetry and small-angle X-ray scattering, the characterization of these multilayer systems was focused on a variety of multinuclear solid-state NMR methods (1H, 29Si, 13C, 2D WISE). The chemical structure of the siloxane interlayer, the alkyl chain conformation and thermal stability were systematically investigated and compared. Through its marked sensitivity to molecular motion, solid-state NMR was used to investigate the effect of interdigitation on alkyl chain dynamics. [Copyright &y& Elsevier]

The article discusses the synthesis of a novel single hybrid monomer combining a vinylether and trimethoxysilane groups in the same molecule through chemoselective hydrosilation. It was also subjected to ultraviolet (UV)-irradiation in the presence of a triarylsulfonium salt. A type II polyvinyl-polysilicate nanocomposite film resulted from the simultaneous occurrence of two acid-catalyzed processes. Parameters such as laminated conditions, UV irradiation equipment and film thickness were also investigated.

Hybrid sol-gel films were prepared via a simultaneous organic-inorganic UV-curing process using a diaryliodonium salt as a superacid photogenerator. In this single-step procedure, an epoxy functionalized reactive resin mixed with a variable amount of either of two epoxy trialkoxysilane precursors was UV-irradiated, causing both the initiation of epoxy ring-opening copolymerization and the catalysis of trialkoxysilyl sol-gel reactions. The concomitant photo-induced sol-gel process was found to have a significant effect on the two related propagation mechanisms in competition for the oxirane ring-opening-the active chain-end and the activated monomer mechanisms-as proved by a systematic examination of the hybrid material microstructure through 29Si and 13C solid-state NMR spectroscopy. The effect of the oxo-silica network generation on the epoxy reaction kinetics was also evaluated using real-time Fourier transform infrared spectroscopy upon varying the epoxysilane structure and its concentration. Thermal and dynamic mechanical analyses were systematically performed on these hybrids, by studying thoroughly their structure-property interdependence. Other mechanical characterizations through tribological and scratch tests suggested that the present photopolymer-silica hybrid material provides a powerful tool to tailor mechanical property profiles. Copyright © 2010 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

A UV photoinduced cross-linking of non-modified commercial poly(disulfide) resins (Thioplast) is reported via the air oxidative photocoupling of terminal thiol functions. Catalyzed by a photogenerated guanidine base (TBD), this step-growth photopolymerization is useful to maximize disulfide functions content. The mechanism proceeds through thiol deprotonation into thiolate anions, further oxidized into thiyl radicals, eventually dimerizing into disulfide cross-links. Starting with a detailed structural characterization of the thiol-terminated resin, photooxidative kinetics are studied under exposure to a polychromatic medium-pressure Hg arc using Raman and infrared spectroscopy. The effects of irradiance, film thickness, photobase concentration, resin molar mass, and content of an additional polythiol monomer (reactive diluent) have been investigated. In an effort of upscaling, irradiation under a 365 nm LED panel has enabled the fast preparation of 1.5 μm thick cross-linked poly(disulfide) coatings in a matter of minutes. Capitalizing on the ability of residual thiol groups to react with silver cations, a post-functionalization has been successfully performed, leading to films exhibiting at their surface stable thiolate-silver bonds as proved by X-ray photoelectron spectroscopy. Despite the well-established biocide action of silver ions, no antibacterial action has been evidenced by confocal fluorescence microscopy because of insufficient release. [ABSTRACT FROM AUTHOR]

Photoacid-catalyzed sol–gel polymerization isnow recognizedas a powerful single-step synthetic approach to the synthesis of hybridfilms, which can be distinguished from conventional sol–gelmethods by higher reactivity and a solvent-free process. Despite itsutility, the mechanism is not yet understood, in particular what chemical,physical, and photochemical parameters determine the precise sequence,kinetics, and advancement of this UV inorganic photopolymerization.Here, using mainly transmission real-time Fourier transformed infrared(RT-FTIR) spectroscopy, we characterize in situthehydrolysis–condensation reactions of oligomeric silicon alkoxidesand the formation of byproducts. Systematic review and assessmentof numerous processing variables (relative humidity, film thickness,precursor structure, nature, and the concentration of photoacid generator)prove that the reaction kinetics are controlled by the two independentphenomena: the intrinsic chemical reaction rates and the water vaporpermeation into the film. [ABSTRACT FROM AUTHOR]