Enhancing Temporal Control and Enabling Chain‐End Modification in Photoregulated Cationic Polymerizations by Using Iridium‐Based Catalysts

• Published in: Angewandte Chemie International Edition 2018-07, Vol.57 (27), p.8260-8264
• Main Authors: Kottisch, Veronika, Supej, Michael J., Fors, Brett P.
• Format: Article
• Language: English
• Subjects: Addition polymerization; Catalysis; Catalysts; Cationic polymerization; Control stability; homogeneous catalysis; Iridium; Monomers; photocontrol; Polymerization; Polymers; Salts
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201804111

Gaining temporal control over chain growth is a key challenge in the enhancement of controlled living polymerizations. Though research on photocontrolled polymerizations is still in its infancy, it has already proven useful in the development of previously inaccessible materials. Photocontrol has now been extended to cationic polymerizations using 2,4,6‐triarylpyrylium salts as photocatalysts. Despite the ability to stop polymerization for a short time, monomer conversion was observed over long dark periods. Improved catalyst systems based on Ir complexes give optimal temporal control over chain growth. The excellent stability of these complexes and the ability to tune the excited and ground state redox potentials to regulate the number of monomer additions per cation formed allows polymerization to be halted for more than 20 hours. The excellent stability of these iridium catalysts in the presence of more nucleophilic species enables chain‐end functionalization of these polymers. Three iridium complexes are designed to enable superior temporal control in the photocontrolled cationic polymerization of vinyl ethers. Photocatalysts (PC) with high stabilities and finely tuned redox potentials give no background reaction in the dark for long off‐periods and at high conversions. Moreover, the increased stabilities of these complexes facilitate efficient chain‐end functionalization in a one‐pot setup.