Side functionalization of diboronic acid precursors for covalent organic frameworks

International audienceA series of substituted 1,4-benzenediboronic acids (BDBA) was synthesized and their thermal properties investigated. Two diboronic acids were studied as building-blocks for covalent organic framework (COF) formation, namely 2,5-dimethoxy-1,4-benzenediboronic acid and 2-nitro-1,4-benzeneboronic acid. Interestingly, substitution of the BDBA core caused a dramatic decrease of the polymerization temperature leading to the formation of a less organized structure

Sequential linking to control the growth of a surface covalent organic framework

International audienceWe report on formation of a new surface covalent organic framework (SCOF) based on a sequential polymerization in two stages. The bifunctional precursor used, p-bromo-benzene boronic acid (BBBA), was vapor deposited in ultra-high-vacuum conditions on a Au(111) surface. In a first step the boronic acid moieties reacted to form trimers linked by covalent boroxine rings. In a second step, an Ullmann coupling reaction was thermally activated to form C− C bonds between the trimers, leading to the final polymeric network. By this procedure the growth mechanism was optimized and the polymerization reaction yield could approach 100%. A well-extended network was obtained, differing from the ideal honeycomb-like network by a substantial number of nonhexagonal pores, which are intrinsic defects to the polymer structure. A comparison of the two competing reactions provides new insights into the complex mechanisms governing growth of two-dimensional covalent networks

Zinc complex based photoinitiating systems for acrylate polymerization under air; in situ formation of Zn-based fillers and composites

International audience[N,N′-Bis(salicylidene)-1,2-phenylenediamine]zinc(II) (ZnC) exhibits unexpected properties as a photoinitiator or additive for both free-radical photopolymerization reactions and in situ formation of Zn-based fillers under light activation and aerated conditions. The ZnC/2,2-dimethoxy-2-phenylacetophenone (DMPA) and ZnC/N-methyldiethanolamine (MDEA) couples are characterized by remarkable properties: (i) a photoinitiating efficiency for the radical polymerization of an acrylate matrix under air higher than that of a reference Type I photoinitiator such as DMPA (final conversion of ∼30–45% vs. 15%) and therefore a good ability to overcome the oxygen inhibition effect and (ii) a never reported in situ formation of Zn-based fillers (100 μm thick sticks) or composites. The photochemical properties of the ZnC are investigated by fluorescence and UV-visible spectroscopy and Electron Spin Resonance (ESR). The photodecomposition of ZnC under air is governed by either an addition of peroxyl radicals onto ZnC when associated with DMPA, or a H-abstraction mechanism when combined with MDEA. When using a ZnC/MDEA/silver salt photoinitiating system, a highly efficient polymerization of the acrylate matrix under air and a concomitant in situ production of Ag(0) NPs are observed

A new cleavable photoinitiator architecture with huge molar extinction coefficients for polymerization in the 340-450 nm range

International audienceA new Type I photoinitiator Tr_DMPA is described. It consists in three 2,2′-dimethoxy 2-phenyl acetophenone (DMPA) units grafted onto a truxene (Tr) scaffold. Compared to DMPA itself, the lowest electronic transition exhibits a ππ* character and the corresponding molar extinction coefficients ε are increased from about 400 M−1 cm−1 (at about 332 nm for DMPA) to 63 000 M−1 cm−1 (at 338 nm for Tr_DMPA); such huge values are exceptional in Type I photoinitiators at this wavelength. Tr_DMPA undergoes a fast cleavage and efficiently initiate an acrylate polymerization upon a Xe−Hg lamp, a halogen lamp or a laser diode exposure at 405 nm (upon very low light intensities: 2− 12 mW/cm2) in the 300−450 nm range. The polymerization of epoxides or divinylethers is also feasible in the presence of an iodonium salt at 405 nm where reference photoinitiators cannot efficiently operate. The chemical mechanisms analyzed by ESR, fluorescence, steady state photolysis, and laser flash photolysis experiments are discussed

Copper photoredox catalysts for polymerization upon near UV or visible light: structure/reactivity/efficiency relationships and use in LED projector 3D printing resins

International audienc

Novel Naphthalimide-amine Based Photoinitiators Operating under Violet and Blue LEDs and Usable for Various Polymerization Reactions and Synthesis of Hydrogels

International audienceA series of naphthalimide derivatives containing tertiary amine groups (DNNDs) have been prepared. Some of these derivatives (e.g. DNND3, DNND4 and DNND5) exhibit interesting shifted absorption so that they can be utilized as versatile photoinitiators upon exposure to various violet and blue LEDs (385, 405, 455 and 470 nm). They are particularly efficient for the cationic photopolymerization of an epoxide and the free radical photopolymerization of an acrylate. The thiol–ene photopolymerization, as well as the synthesis of interpenetrating polymer networks (of epoxide/acrylate blend) IPNs, is feasible. Remarkably, the production of hydrogels can also be easily achieved using a DNND derivative after inclusion in a cyclodextrin cavity. The photochemical mechanisms have been comprehensively investigated by steady state photolysis, Electron Spin Resonance (ESR), fluorescence, electrochemistry and laser flash photolysis and discussed in detail

Photoinitiating systems of polymerization and in-situ incorporation of metal nanoparticles in polymer matrixes upon visible lights: push-pull malonate and malonitrile based dyes

International audienceNovel push-pull dyes containing a (substituted) hydrocarbon moiety and a malonate (or a malononitrile) moiety are proposed as photoinitiators for the ring opening polymerization of epoxides as well as the synthesis of interpenetrated polymer networks (IPNs) upon exposure to visible light (laser diode, halogen lamp, etc.). Excellent polymerization profiles are obtained. The role of the acceptor and donor moieties in these dyes towards their light absorption properties, the associated photochemical processes and their photoinitiating ability is investigated. A very efficient dye has been selected for the reduction of Ag+ and the in situ formation of Ag(0) nanoparticles in the synthesized IPN

New Cleavable Photoinitiator Architecture with Huge Molar Extinction Coefficients for Polymerization in the 340–450 nm Range.

A new Type I photoinitiator <b>Tr_DMPA</b> is described. It consists in three 2,2′-dimethoxy 2-phenyl acetophenone (DMPA) units grafted onto a truxene (<b>Tr</b>) scaffold. Compared to DMPA itself, the lowest electronic transition exhibits a ππ* character and the corresponding molar extinction coefficients ε are increased from about 400 M^–1 cm^–1 (at about 332 nm for DMPA) to 63 000 M^–1 cm^–1 (at 338 nm for <b>Tr_DMPA</b>); such huge values are exceptional in Type I photoinitiators at this wavelength. <b>Tr_DMPA</b> undergoes a fast cleavage and efficiently initiate an acrylate polymerization upon a Xe–Hg lamp, a halogen lamp or a laser diode exposure at 405 nm (upon very low light intensities: 2–12 mW/cm²) in the 300–450 nm range. The polymerization of epoxides or divinylethers is also feasible in the presence of an iodonium salt at 405 nm where reference photoinitiators cannot efficiently operate. The chemical mechanisms analyzed by ESR, fluorescence, steady state photolysis, and laser flash photolysis experiments are discussed