Microstructure aspects of radiation-cured networks: Cationically polymerized aromatic epoxy resins

Kowandy, C.; Ranoux, Guillaume; Walo, Marta; Vissouvanadin, B.; Teyssèdre, G.; Laurent, Christian; Berquand, Alexandre; Molinari, Michaël; Coqueret, Xavier

doi:10.1016/j.radphyschem.2017.09.006

Cited by 10 publications

(8 citation statements)

References 16 publications

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“…UV-irradiation provokes the photochemical reactions of the polymer chains that was experimentally testified as decrease of the hardness of the polymer coatings due to the observed increase of the surface porosity. However, it is depends strongly photoinitator chemistry and content [59]. Generally, coating systems containing iodonium SbF 6 type salts exhibited higher yellowness and lower hardness in long-term than based polymers based on sulfonium hexafluorophosphates salts [60].…”

Section: Resultsmentioning

confidence: 99%

UV-light-induced curing of branched epoxy novolac resin for coatings

Gaidukovs¹,

Medvids²,

Onufrijevs³

et al. 2018

Express Polym. Lett.

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Usually, the processing technology of the thermoset polymers is characterized by the use of the two component formulations, which generally consist of a polymer resin and a hardener. These two component polymer formulations need to be hardened for almost 12 hours at room temperature [1, 2]. Generally, extra heating at 60-160°C is necessary to facilitate the hardening process [3]. The conventional curing process has several relevant disadvantages. Firstly, as the prerequisite condition for acceptable final properties of the produced material, the following thermal treatment is always desirable as a post-curing process [4]. Secondly, there are difficulties with producing large monolith constructions and coating large surfaces that can be sensitive to heating and/or when heating is even impossible [5]. For example, the repair service protective coatings applications for ships in the maritime industry, and for power generators in the energy generation sector [6]. The market of ultraviolet (UV) curable polymers is growing very rapidly, especially in the last decades [7]. This market is anticipated to grow by 7.0% from 2013 to 2019 and is expected to reach USD 7.930

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Section: Resultsmentioning

confidence: 99%

UV-light-induced curing of branched epoxy novolac resin for coatings

Gaidukovs¹,

Medvids²,

Onufrijevs³

et al. 2018

Express Polym. Lett.

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“…But if our aim is to synthesize a crosslinked polymer structure of the size of a single coiled macromolecule (usually not more than 100 nm when in solution), we have to run the reaction in suitable "nanocompartments", i.e., in micelles. Since we are mostly interested here in hydrophilic nanogels, and thus the monomers, crosslinkers and the resulting polymer structures should be soluble in water, synthesis should be performed in reverse miniemulsion or reverse microemulsion, having small droplets of the aqueous phase dispersed in the continuous oil phase [247,248].…”

Section: General Synthetic Approachesmentioning

confidence: 99%

Polymerization Reactions and Modifications of Polymers by Ionizing Radiation

et al. 2020

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Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on materials, photons or high energy electrons, in both cases ions and electrons are produced. The interactions between electrons and monomers takes place within less than a nanosecond. Depending on the dose rate (dose is defined as the absorbed radiation energy per unit mass), the kinetic chain length of the propagation can be controlled, hence allowing for some control over the degree of polymerization. When polymers are submitted to high-energy radiation in the bulk, contrasting behaviors are observed with a dominant effect of cross-linking or chain scission, depending on the chemical nature and physical characteristics of the material. Polymers in solution are subject to indirect effects resulting from the radiolysis of the medium. Likewise, for radiation-induced polymerization, depending on the dose rate, the free radicals generated on polymer chains can undergo various reactions, such as inter/intramolecular combination or inter/intramolecular disproportionation, b-scission. These reactions lead to structural or functional polymer modifications. In the presence of oxygen, playing on irradiation dose-rates, one can favor crosslinking reactions or promotes degradations through oxidations. The competition between the crosslinking reactions of C-centered free radicals and their reactions with oxygen is described through fundamental mechanism formalisms. The fundamentals of polymerization reactions are herein presented to meet industrial needs for various polymer materials produced or degraded by irradiation. Notably, the medical and industrial applications of polymers are endless and thus it is vital to investigate the effects of sterilization dose and dose rate on various polymers and copolymers with different molecular structures and morphologies. The presence or absence of various functional groups, degree of crystallinity, irradiation temperature, etc. all greatly affect the radiation chemistry of the irradiated polymers. Over the past decade, grafting new chemical functionalities on solid polymers by radiation-induced polymerization (also called RIG for Radiation-Induced Grafting) has been widely exploited to develop innovative materials in coherence with actual societal expectations. These novel materials respond not only to health emergencies but also to carbon-free energy needs (e.g., hydrogen fuel cells, piezoelectricity, etc.) and environmental concerns with the development of numerous specific adsorbents of chemical hazards and pollutants. The modification of polymers through RIG is durable as it covalently bonds the functional monomers. As radiation penetration depths can be varied, this technique can be used to modify polymer surface or bulk. The many parameters influencing RIG that control the yield of the grafting process are discussed in this review. These include monomer reactivity, irradiation dose, solvent, presence of inhibitor of homopolymerization, grafting temperature, etc. Today, the general knowledge of RIG can be applied to any solid polymer and may predict, to some extent, the grafting location. A special focus is on how ionizing radiation sources (ion and electron beams, UVs) may be chosen or mixed to combine both solid polymer nanostructuration and RIG. LLET ionizing radiation has also been extensively used to synthesize hydrogel and nanogel for drug delivery systems and other advanced applications. In particular, nanogels can either be produced by radiation-induced polymerization and simultaneous crosslinking of hydrophilic monomers in “nanocompartments”, i.e., within the aqueous phase of inverse micelles, or by intramolecular crosslinking of suitable water-soluble polymers. The radiolytically produced oxidizing species from water, •OH radicals, can easily abstract H-atoms from the backbone of the dissolved polymers (or can add to the unsaturated bonds) leading to the formation of C-centered radicals. These C-centered free radicals can undergo two main competitive reactions; intramolecular and intermolecular crosslinking. When produced by electron beam irradiation, higher temperatures, dose rates within the pulse, and pulse repetition rates favour intramolecular crosslinking over intermolecular crosslinking, thus enabling a better control of particle size and size distribution. For other water-soluble biopolymers such as polysaccharides, proteins, DNA and RNA, the abstraction of H atoms or the addition to the unsaturation by •OH can lead to the direct scission of the backbone, double, or single strand breaks of these polymers.

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“…We recently reported on the advanced understanding of the build-up of thermomechanical properties of networks at nanoscale by probing with new AFM techniques and measuring the peak normal forces, which allow to quantify the local modulus, adhesion, dissipation, and deformation, while simultaneously imaging sample topography of cationically-cured DGEBA and epoxy Novolak resins [22,41].…”

Section: Heterogeneitiesmentioning

confidence: 99%

“…Liquid monomer Monolith Nanocluster formation, increase in number, growth and percolation Figure 10. Sketch representing the gradual formation of a monolithic nano-heterogeneous network upon radiation-initiated cationic polymerization DGEBA-based formulations as supported by AFM imaging [22,41].…”

Section: Progress Of Dgeba Polymerizationmentioning

confidence: 99%

Cationic Curing of Epoxy–Aromatic Matrices for Advanced Composites: The Assets of Radiation Processing

2022

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Cross-linking polymerization of multifunctional aromatic monomers initiated by exposure to high energy radiation continues to be explored as a promising alternative to thermal curing for the production of high-performance composite materials. High-energy radiation processing offers several advantages over thermosetting technology by allowing for fast and out-of-autoclave curing operations and for its adaptability in the manufacturing of large and complex structures at reduced energy costs. The present article covers the basic aspects of radiation curing by cationic polymerization of epoxy resins, providing a status report on recent investigations conducted in our group to improve the properties of epoxy matrices and gain better control over the process for producing composites. A selection of results based on blends prepared with different composition of epoxy aromatics, transfer agents, thermoplastic toughening agents and onium salt initiators exemplifies the importance of the composition on polymerization kinetics and on the properties of resulting materials. The superiority of radiation-triggered polymerization-induced phase separation of thermoplastic additives is emphasized by the obtained morphology of toughened materials. The low initial temperature and fast curing of the reactive blends limits the expansion of phase-separated thermoplastic domains, resulting in an enhancement of the toughness.

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Microstructure aspects of radiation-cured networks: Cationically polymerized aromatic epoxy resins

Cited by 10 publications

References 16 publications

UV-light-induced curing of branched epoxy novolac resin for coatings

UV-light-induced curing of branched epoxy novolac resin for coatings

Polymerization Reactions and Modifications of Polymers by Ionizing Radiation

Cationic Curing of Epoxy–Aromatic Matrices for Advanced Composites: The Assets of Radiation Processing

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