Combining Cationic and Anionic Polymerizations using a Universal Mediator: Enabling Access to Two- and Three-Mechanism Block Copolymers

The combination of multiple polymerization mechanisms and monomer classes to make block copolymers is an ongoing challenge. In particular, the combination of cationic and anionic polymerization mechanisms commonly requires extra compatibilization steps or the use of multi-functional initiators. Herein, we report the use of thiocarbonyl thio compounds (TCTs) as universal mediators to sequentially polymerize ethyl vinyl ether via photocontrolled cationic polymerization (photo-CP) and the thiirane phenoxy propylene sulfide via thioacyl anionic group transfer polymerization (TAGT). Thermal analyses of the resulting block copolymers provide evidence of microphase separation of the blocks. The resulting diblocks can be further chain extended using photoinduced electron/energy transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT) of N-isopropylacrylamide to make a triblock terpolymer from three different monomer classes incorporated via three different mechanisms without any end group modification steps. The development of this simple, sequential synthesis using a universal mediator opens up new possibilities by providing facile access to diverse block copolymers of vinyl ethers, thiiranes, and acrylamides.