New Trends in UV Curing

We present an overview of the use of photochemistry applied to polymerization and crosslinking reactions by radical or cationic process used for thin film technologies and more generally for coatings. Industrially, most of the formulations used are initiated by radical mechanism. Since the discovery by J. Crivello of iodonium and sulfonium salts, the market has been oriented to use cationic systems to crosslink monomers/ oligomers. One of the main advantage of such a system is that it is not sensitive to the presence of oxygene as it is for radical mechanisms. An overview of a photosensitive formulation is presented i.e. photoinitiators, photosensitisers, monomers and/or oligomers mainly used by formulators and additives. A new technique which has been developed to study and optimise any photosensitive formulation – differential phto calorimetry DPC – and which permits to determine kinetic parameters such as enthalpy, degree of conversion, rate constant, Arrhenius parameters, etc. is also describe. Some of the main characteristics and properties of UV cured polymers like acrylates, epoxides, vinylethers and others are correlated with their structures and the photocuring conditions. Applications to thin film technologies based on acrylates, epoxides and silicones is presented. A promising area of research which opens a new route for the obtention of new structure of alternating copolymers for coatings without the use of photoinitiator and based on charge transfer complex CTC is also presented

Synthesis of New Metallized Polyimide Films with High Optical and Physical Performances

Electroconductive and reflective metallized polyimide films have been prepared by heterogeneous chemical modification of polyimide surface. By carrying out the chemical reactions in situ in the modified layers of polyimide surface, a metal phase strongly impregnated into the polyimide surface is obtained. The steps of chemical modification have been studied on the model compound – poly(amic acid) on the basis of isophthaloylchloride and methylenedianthranilic acid which forms insoluble sodium or potassium poly(amic acid) salts (polyamate). Metallization of Kapton® HN & JP (from DuPont) and Upilex S® (from Ube) films has been carried out and the films have been characterized by X-ray diffraction (XRD), X-ray fine diffraction (XRFD), measurements of reflectivity in the visible range and surface resistivity at elevated temperatures. It is shown that reflectivity coefficients of silvered films are 90-92% and surface resistivity is about 0.5 Ω/sq

Copolymers Formation by Photopolymerization of (Meth)acrylates Containing Dissolved Polyheteroarylenes

International audienceRadical photopolymerization of (meth)acrylates in the presence of dissolved polyheteroarylenes has been investigated. The kinetics of radical polymerization of unsaturated monomers in the presence of polyheteroarylenes and model compounds has been studied by Differential Scanning Photocalorimetry and Infrared Spectroscopy. From the results of investigations into the kinetics and the polymer structures (Fourier Transform Infrared Spectroscopy, Nuclear Magnetic Resonance, Size-exclusion Chromatography, Thermogravimetric analysis), it has been established that radical photopolymerization of vinyl monomers in the presence of polyheteroarylenes leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. Using Electron Spin Resonance Spectroscopy the novel radicals upon the addition of model compounds for the polyheteroarylenes have been detected, and a mechanism of copolymer formation has been proposed

Preparation and Characterization of Sulfonated Polyphenylquinoxalines

International audiencePoly(phenylquinoxaline)s.(PPQs) are a family of aromatic condensation polymers known for their outstanding thermal and chemical stability. The pendant phenyl groups and chains isomerism improve the solubility and processing characteristics of these polymers. PPQs have also been shown to possess excellent thermo-oxidative stability and thermohydrolytic stability. This stability makes these polymers candidates for development as proton exchange membranes (PEMs) to be used in fuel cells. In addition to thermohydrolytic stability, PEMs require high protonic conductivity and, in order to achieve this they also require high water uptake. Aromatic condensation polymers do not possess these properties, but ionomers derived from them may. The usual method to derivatiziting these polymers is through sulfonation. In the frames of the present investigation we have carried out sulfonation of two PPQs using an H2SO 4—oleum mixture (4 : 1) as sulfonating agent at 125 3C. As a quinoxaline ring is readily formed in acidic medium synthesis of sulfonated PPQs (SPPQs) was also carried out directly from monomers using an H 2SO4—oleum mixture as solvent, catalyst and as sulfonating agent. Depending on the conditions of the reaction (temperature, duration, and the ratio of components in a sulfonating mixture) the polymers containing 0.2—6.7% S were prepared. SPPQs are soluble in polar organic solvents1 from the solutions of SPPQs high strength films (3 = 80—100 MPa) were cast. On the basis of sulfonated PPQs new cation-exchange membranes were prepared and investigated. Among the cation-exchange membranes developed those of the greatest interest are proton-exchanging membranes for fuel cells. Proton conductivity of the membranes prepared strongly depends on relative humidity and comparable with the conductivity of Nafion 117

Novel phosphonated poly(1,3,4-oxadiazole)s: Synthesis in ionic liquid and characterization

International audienceA new class of poly(1,3,4-oxadiazole)s (PODs) with pendant phosphonic acid groups was synthesized via direct polycondensation of dicarboxylic acids and their dihydrazides using ionic liquid, namely 1-methyl-3-propylimidazoluium bromide ([mpim]Br), as a reaction medium, and triphenyl phosphite as a reaction activator. The polymers were obtained with inherent viscosities equal to 0.46–0.58 dL/g in two steps starting from polyhydrazides formation followed by thermal polycyclization under high vacuum. Polymers derived from 5-phosphonoisophtalic acid were soluble in traditional organic solvents, while application of 2-phosphonoterephthalic acid resulted in formation of insoluble gels. Such properties as thermal stability, glass transition temperatures, water uptake, molecular weights and proton conductivity of novel polymers were investigated in detail. A comparison between common poly(1,3,4-oxadiazole)s and their phosphorylated or phosphonated analogs having the same polymer backbone demonstrated that PODs with pendant phosphonic acid groups possess approximately the same thermal stability, but greater glass transition temperatures along with reduced solubility. Transparent flexible films cast from such novel polymers were characterized by high tensile properties, namely tensile strength of about 90–100 MPa and elongation up to 8%. The proton conductivity values measured at the temperature range from 20 to 90 °C varied from 4 × 10−7 to 5 × 10−6 S/cm at 100% relative humidity