Iridium complexes incorporating coumarin moiety as catalyst photoinitiators: Towards household green LED bulb and halogen lamp irradiation

Household LED bulbs and halogen lamps are used to promote the ring-opening photopolymerization of epoxides in the presence of a new series of iridium(III) complexes (IrCs) exhibiting enhanced visible light absorption properties through the introduction of a coumarin moiety. These latter complexes are used as catalyst photoinitiators in an oxidative cycle in combination with a silane and an iodonium salt. Remarkably, even under the selected very soft irradiations (e.g. light intensity lower than 2 mW/cm²), excellent polymerization profiles are obtained (conversions > 80%). The mechanisms are investigated by ESR and luminescence experiments.     

Rogue components: their effect and control using logical analysis of data

There is a small subset of any repairable component population that can develop a failure mode outside the scope of the standard repair and overhaul procedures, which makes them “rogue”. When this happens, a Darwinian-like “natural selection” phenomenon ensures that they will be placed in the most disadvantageous position in the asset management program, negatively affecting multiple aspects of the operational and maintenance organizations. Rogue components have long plagued the airline industry and created havoc in their asset management programs. In this paper, we describe how these rogues develop, outline the natural selection process that leads to their hampering the asset management program, and examine some of the negative impacts that ensue. Then we propose a Condition based maintenance approach to control the development of these components. We explore the use of a supervised learning data mining technique called Logical analysis of data (LAD) in CBM for the purpose of detecting rogues within a population of repairable components. We apply the resulting LAD based decision model on an inventory of turbo compressors belonging to an airline fleet. Finally, we evaluate the applicability of LAD to the rogue component detection problem and review its efficiency as a decision model for this type of problem.     

Fault diagnosis in power transformers using multi-class logical analysis of data

This paper presents the implementation of a novel multi-class diagnostic technique for the detection and identification of faults based on an approach called logical analysis of data (LAD). LAD is a data mining, artificial intelligence approach that is based on pattern recognition. In the context of condition based maintenance (CBM), historical data containing condition indices and the state of the machine are the inputs to LAD. After training and testing phases, LAD generates patterns that characterize the faulty states according to the type of fault, and differentiate between these states and the normal state. These patterns are found by solving a mixed 0–1 integer linear programming problem. They are then used to detect and to identify a future unknown state of equipment. The diagnostic technique has already been tested on several known machine learning datasets. The results proved that the performance of this technique is comparable to other conventional approaches, such as neural network and support vector machine, with the added advantage of the clear interpretability of the generated patterns, which are rules characterizing the faults’ types. To demonstrate its merit in fault diagnosis, the technique is used in the detection and identification of faults in power transformers using dissolved gas analysis data. The paper reaches the conclusion that the multi-class LAD based fault detection and identification is a promising diagnostic approach in CBM.     

Oxygen mediated and wavelength tunable cationic photopolymerization reactions under air and low intensity: A new concept

A new concept which allows efficient cationic photopolymerization reactions under air, at any excitation wavelength in the UV–visible range and under low light intensities (conventional Xe lamp and/or laser diodes) is presented. It is based on the use of a versatile free radical promoted cationic process for the photoinitiation step which only requires a radical source, a silane and an usual iodonium salt and takes advantage of the presence of oxygen. The tunable character of the absorption is connected with the choice of the radical source. The oxygen enhancement is due to the particular role played by the silane. In every case, the silylium cation is the most efficient structure for the cationic ring opening reaction. Examples of the performance achieved (e.g. a conversion close to 100%) with such systems over the 390–580 nm range using various irradiation devices is shown and discussed.     

Radical photopolymerization reactions under air upon lamp and diode laser exposure: The input of the organosilane radical chemistry

A new concept based on the conversion of the peroxyl radicals generated under air (ROO) with the concomitant formation of new initiating radicals to overcome the oxygen inhibition in particular free radical photopolymerization reactions (low intensity, low viscosity, relatively low film thickness) is proposed. This is achieved using organosilanes and the specific input of this new radical chemistry to various Type I or Type II photoinitiating systems (PI). Through many selected examples corresponding to a broad choice of experimental conditions—lamps (UV or visible lights) and laser diodes, the outstanding performance of a lot of organosilanes containing photoinitiating systems is disclosed.     

Household LED irradiation under air: cationic polymerization using iridium or ruthenium complex photocatalysts

Household LED bulbs are used to promote the ring-opening photopolymerization of epoxides in the presence of a photocatalyst (here tris(2-phenylpyridine)iridium [Ir(ppy)₃] or tris(1,10-phenanthroline)ruthenium(II) [Ru(phen)₃²⁺] complex) and a silyl radical source. Remarkably, even under this very soft irradiation (light intensity lower than 10 mW/cm2), excellent polymerization profiles are obtained i.e., this is the first reported use of such very convenient irradiation devices for photopolymerization processes. The role of the silane and other hydrogen donors is outlined.     

Photoinitiators based on a phenazine scaffold: High performance systems upon near-UV or visible LED (385, 395 and 405 nm) irradiations

Novel photoinitiators based on a phenazine scaffold are proposed for the ring opening polymerization of epoxy monomers as well as the free radical polymerization of (meth)acrylates. Good to excellent polymerization profiles can be obtained upon different easily accessible, energy saving and cheap LEDs (385, 395 and 405 nm) as well as a diode laser at 405 nm or halogen lamp opening new fields for polymer synthesis upon soft and convenient irradiations. These compounds can be particularly attractive as high performance photoinitiators in the 350–425 nm range. The initiation mechanisms are investigated in detail through fluorescence, cyclic voltammetry, steady state photolysis and electron spin resonance (ESR) experiments.     

Photoredox catalysis for polymerization reactions

Photoredox catalysis is now well-known in organic synthesis for the formation of free radicals under very soft irradiations conditions (e.g. sunlight, household fluorescence or LED bulbs, Xe lamp). This method has been introduced here to the polymer chemistry area to initiate ring opening polymerizations (ROP) or free radical polymerizations (FRP). The present paper will give an up-to date situation of the photocatalyst achievements in FRP and ROP.