A Capping Method for Nitrogen Anion Initiated Living Anionic Polymerization for Synthesizing Alkyl Methacrylate Macromonomers

Lithium alkylamides are important functional initiators for anionic polymerization of methacrylates, but only sterically hindered ones can initiate a successful living polymerization. A capping method is reported here to modify nitrogen anion initiators (capping reaction) for living anionic polymerization of alkyl methacrylates. Dimethylacrylamide (DMA) and tert-butyl methacrylate (tBMA) were found to be effective capping agents for lithium diallylamide. After capped with DMA or tBMA, the initiator efficiency of lithium diallylamide was increased from 0.1 to 0.9 for various monomers. Monosubstituted lithium alkylamides (vinyloxypropylamide and allylamide) could not directly initiate the polymerization of methacrylates due to severe reaction with the carbonyl groups in the monomers. After capped with DMA, the initiators polymerized methacrylates with initiator efficiency about 0.4−0.6, depending on the monomer type. tBMA was not suitable as capping agent for the monosubstituted lithium amides. Using these capped initiators, we subsequently synthesized block copolymers. 1H NMR demonstrated that all the polymers prepared had terminal unsaturated groups from the initiators.