Photoactivation of organotellurium compounds in precision polymer synthesis: Controlled radical polymerization and radical coupling reactions

Abstract

Organotellurium chain transfer agents (CTAs) used for organotellurium-mediated radical polymerization (TERP) are highly photosensitive and generate radicals by carbon-Tellurium bond homolysis upon absorbing UV-vis light at approximately 350500 nm. The controlled radical polymerization of various vinyl monomers takes place in the presence of organotellurium CTAs under photoirradiation. The use of low-intensity light is important to attain structural control because of the need to maintain a low radical concentration. Photo-TERP not only preserves the synthetic advantages of TERP under thermal conditions, as exemplified by its high versatility in polymerizable monomer families, but also attains new benefits, including decreasing the amount of dead polymers, increasing the control of the macromolecular structure, lowering the polymerization temperature, and providing temporal control. In contrast, irradiation of a polymer prepared by TERP in the presence of dienes and styrenes with high-intensity light selectively gives the dimer via a polymer-end radical coupling reaction. Various symmetrical telechelic and mid-chain-functionalized polymers and ABA-Triblock copolymers can be synthesized. Due to the mild conditions for both photo-TERP and the coupling reaction, unique macromolecular structures, and high structural control, these methods provide a new method in macromolecular engineering for fabricating functional polymer materials with improved and/or new functions.