Search

NIR light-induced polymerization has attracted more and more attention in the photopolymerization field due to the possibility to use safer and more penetrating wavelengths, reducing the hazardousness. Here, a novel perspective for the free radical polymerization of acrylate-based monomers based on triplet-triplet annihilation upconversion (TTA-UC) is proposed, avoiding the introduction of heavy metals, usually required in the TTA processes. Thermal imaging experiments and Fourier transform infrared spectroscopy are respectively used to record the temperature during NIR irradiation and measure the reactive function conversion. The competition between the TTA-UC and the NIR photothermal activation is investigated to compare the relative efficiency of both NIR processes. In view of the results obtained by the different methods, the photothermal effect seems to get the upper hand over the photoactivation of the system., (© 2021 Wiley-VCH GmbH.)

The radical copolymerization of vinyl and cyclic ketene acetal (CKA) monomers is a promising way to prepare degradable vinyl polymers. The reactivity of the comonomer pair is known to be dependent of the vinyl monomer structure that requires to play with experimental conditions (feed ratio, overall monomer conversion, etc.) to target a desired cumulative (average) copolymer composition. Even if the materials are completely degradable, there is no information about the homogeneity of the degraded products. This theoretical study, using kinetic Monte Carlo simulations, allows simulating degradation at the molecular level. It is shown that disparate reactivity ratios (styrene/CKA, etc.) and also a composition drift at high conversion can lead to an inhomogeneous degraded product compared to systems with similar reactivity ratios (vinyl ether/CKA, etc.). The use of reversible deactivation radical polymerization techniques does not influence the final degraded products and is only useful for the design of advanced macromolecular architectures before degradation., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cyclic monomers bearing either vinyl or exomethylene groups have the ability to be polymerized through a radical pathway via a ring-opening mechanism (addition-fragmentation process), leading to the introduction of functionalities in the polymer backbone. Radical ring-opening polymerization (rROP) combines the advantages of both ring-opening polymerization and radical polymerization, that is the preparation of polymers bearing heteroatoms in the backbone but with the ease and robustness of a radical process. This current review presents a comprehensive description of rROP by detailing: (i) the various monomers that polymerize through rROP; (ii) the main parameters that govern the rROP mechanism; (iii) the copolymerization by conventional or controlled/living radical polymerization between rROP monomers and traditional vinyl monomers to obtain copolymers with advanced properties; (iv) the different applications (low shrinkage materials and preparation of (bio)degradable materials) of rROP monomer-containing materials, and (v) the main alternatives to rROP to induce degradability to materials obtained by a radical polymerization.

We report on the use of an alkoxyamine (AA) for fabrication of functional micropatterns with complex structures by UV mask lithography. The living character of the polymer surface and the vertical spatial control of the repolymerization reaction from few tens of nanometers to few micrometers were demonstrated. The impact of the main parameters governing the controlled polymerization and the reinitiation process activated by light or heat was investigated. Micropatterning is shown to be a powerful method to investigate the physicochemical molecular phenomena. It is possible to control the polymer microstructure thickness from few tens of nanometers to few micrometers. In the last section, some applications are provided showing the potential of the AA for generating covalently bonded hydrophilic/hydrophobic micropatterns or luminescent surfaces. This demonstrates the high versatility and interest of this route.

2-Methylene-4-phenyl-1,3-dioxolane (MPDL) was successfully used as a controlling comonomer in NMP with oligo(ethylene glycol) methyl ether methacrylate (MeOEGMA) to prepare well-defined and degradable PEG-based P(MeOEGMA-co-MPDL) copolymers. The level of ester group incorporation is controlled, leading to reductions in molecular weight of up to 95% on hydrolysis. Neither the polymer nor its degradation products displayed cytoxicity. The method was also successfully applied to methyl methacrylate.

Nine different perylene derivatives are prepared and their ability to initiate, when combined with an iodonium salt (and optionally N-vinylcarbazole), a ring-opening cationic photopolymerization of epoxides under very soft halogen lamp irradiation is investigated. One of them is particularly efficient under a red laser diode exposure at 635 nm and belongs now to the very few systems available at this wavelength. The photochemical mechanisms are studied by steady-state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry, and laser flash photolysis techniques., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Novel functionalized ketones (K_PY) incorporating one/two pyrene moieties or a pyridinium chromophore for radical and/or cationic polymerization under soft irradiation conditions (Xe–Hg lamp, halogen lamp) are proposed. These compounds exhibit red-shifted absorptions and enhanced molar extinction coefficients (e.g. for near visible lights (395 nm), the absorption can be increased by a factor of 20). The ability of the various K_PY/amine couple in the radical polymerization of an acrylate (up to 75% conversion) and the different K_PY/diphenyliodonium salt system in the cationic polymerization of an epoxide (up to 70% conversion) is often better than that of reference compounds. These structures are also very efficient to overcome the oxygen inhibition. Molecular orbital calculations, ESR experiments and laser flash photolysis allow an investigation of the absorption properties, the excited state processes and the involved initiation mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: A polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymer is synthesised in an original manner by nitroxide mediated polymerization of styrene from a PEO macroalkoxyamine. Minor amounts of side products are unavoidably present in the final polymer, including: traces of macroalkoxyamine, PEO-b-PS-b-PEO triblock copolymer—a product of the recombination of PEO-b-PS macro-radical during the initial stage of the polymerization—and hPS—a product of thermal initiation. These species do not represent more than a little percentage of the total composition. They are hardly detectable with classical SEC. We use liquid chromatography at critical conditions (LC-CC), 2D chromatography and LC-CC-NMR to get an exhaustive description of the chemical composition distributions (CCD) and of the molar mass distributions (MMD) of all the minor species quoted above. The results are consistent with the synthesis route and prove the accuracy of the LC-CC based techniques in analysing even very small amounts of species. [Copyright &y& Elsevier]