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Semi-crystalline poly(thioether) prepared by visible-light-induced organocatalyzed thiol-ene polymerization in emulsion

Cuong Minh Quoc Le, Gautier Schrodj, Ibrahima Ndao, Brahim Bessif, Barbara Heck, Thomas Pfohl, Günter Reiter, Justine Elgoyen, Radmila Tomovaska and Abraham Chemtob. Macromol. Rapid Commun. 2021, 2100740

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 has 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.

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