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We show the potential of miniemulsion photopolymerization for the continuous production of aqueous poly(acrylate) dispersions in a microreactor at room temperature. While the starting acrylate nanoemulsions are amenable to limit scattering, their polymerization within a microreactor provides additionally small microchannels and short diffusion path enabling an efficient mixing in order to alleviate the constraints associated with non-uniform through-cure in turbid medium. Two key features prove that this process design is highly eco-efficient: i) two types of energy-saving and compact UV sources (fluorescent or light-emitting diode) were employed; ii) high conversions were achieved using the fluorescent lamp with short residence times (10 min), low irradiance (3 mW cm-2) and without the need of solvent. The present study describes briefly the influence of various parameters – flow rate, photo-initiator type/concentration, droplet size, solid content, UV source – on the photopolymerization course (kinetics) and the properties of the nanolatex obtained (particle size and molecular weight).

Unlike many step polymerizations, the polymerization of bifunctional thiol and alkene monomers can be carried in emulsion to prepare a range of sulfur‐containing polymer particles differing markedly from conventional emulsion chain polymers. This study examines how the change of polymerization mechanism affects polymer molecular weight, structure and composition. A 2,2′‐dimercaptodiethyl sulfide/diallyl phthalate emulsion is photopolymerized in a photochemical stirred‐tank reactor equipped with Light‐emitting diodes (LEDs) to yield a 30% solids content latex with a high weight‐average molecular weight (100 kDa) and a broad molecular weight distribution (Đ = 8.5). Intramolecular cyclization occurs during polymerization by the addition of a thiyl radical to the unsaturated end group of the same molecule. Irreversible ring‐closure takes place to produce "dead" cyclic oligomers in the early stage of the reaction, whereas chain‐growth continues at high conversion. Consequently, the particles are composed of high molecular weight linear chains and a fraction of stable oligomer cycles, showing a broad and bimodal molecular weight distribution. The linear poly(thioether) chains include occasionally disulfide units due to thiyl radical recombination. The reversibility of disulfide bonds causes a decrease of molecular weight during storage. The addition of radical inhibitor to the latex stops fragmentation of SS bonds. [ABSTRACT FROM AUTHOR]

In the present study, a novel single hybrid monomer combining a vinylether and trimethoxysilane groups in the same molecule was synthesized by chemoselective hydrosilation and subjected to UV-irradiation in the presence of a triarylsulfonium salt. Through the UV-decomposition of this photoacid generator, two acid-catalyzed processes occurred simultaneously: the cationic polymerization of the vinyl ether functions and the sol-gel polycondensation of the alkoxysilyl groups, leading to a type II polyvinyl-polysilicate nanocomposite film. Both reaction kinetics were efficiently monitored by real-time Fourier transform infrared spectroscopy, and the influence of different key experimental parameters was investigated (laminated conditions, UV irradiation equipment, and film thickness). A particular attention was also given to the complete characterization of the hybrid microstructure by associating 29Si and 13C solid-state NMR. POLYM. ENG. SCI., 51:1466-1475, 2011. © 2011 Society of Plastics Engineers, INTRODUCTION In contrast to free-radical polymerization, calionic polymerization has been seldom the method of choice in nanocomposite chemistry. Relatively, few studies addressing cationic polymerization for the synthesis of organic-inorganic hybrid [...]

Recently, photo‐controlled reversible addition‐fragmentation chain transfer (RAFT) polymerization has been successfully applied in digital light processing 3D printing. It provides a convenient way to tune the surface properties of the 3D printed object. However, so far, 3D micro‐ and nanostructures and reconfigurations based on photo‐induced RAFT polymerization have not been presented. In this work, one macro‐photoiniferter, synthesized by photo‐controlled RAFT polymerization is applied, to 3D direct laser writing. Thanks to the exquisite spatial control of the photoreaction, 3D microstructures with feature sizes of around 500 nm are successfully obtained. Taking advantage of the presence of dormant polymeric RAFT agents, photo‐induced post‐modification of the printed microstructures is highlighted via the elaboration of multi‐chemistry patterns including thermo‐responsive ones. These results open new perspectives in multi‐material and 4D micro‐printing. [ABSTRACT FROM AUTHOR]

A photocatalytic thiol‐ene aqueous emulsion polymerization under visible‐light is described to prepare linear semicrystalline latexes using 2,2'‐dimercaptodiethyl sulfide as dithiol and various dienes. The procedure involves low irradiance (3 mW cm−2), LED irradiation source, eosin‐Y disodium as organocatalyst, low catalyst loading (<0.05% mol), and short reaction time scales (<1 h). The resulting latexes have molecular weights of about 10 kg mol−1, average diameters of 100 nm, and a linear structure consisting only of thioether repeating units. Electron‐transfer reaction from a thiol to the triplet excited state of the photocatalyst is suggested as the primary step of the mechanism (type I), whereas oxidation by singlet oxygen generated by energy transfer has a negligible effect (type II). Only polymers prepared with aliphatic dienes such as diallyl adipate or di(ethylene glycol) divinyl ether exhibit a high crystallization tendency as revealed by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. Ordering and crystallization are driven by molecular packing of poly(thioether) chains combining structural regularity, compactness, and flexibility. [ABSTRACT FROM AUTHOR]