Modular Synthesis of Polyferrocenylsilane Block Copolymers by Cu-Catalyzed Alkyne/Azide “Click” Reactions

This paper reports a new synthetic strategy for the preparation of polyferrocenylsilane (PFS) block copolymers. The block copolymers were prepared by Cu-catalyzed alkyne/azide cycloaddition of two homopolymer precursors that allows access to new functional PFS block copolymers (e.g., polyferrocenylsilane-block-poly(N-isopropylacrylamide)) (PFS-b-PNIPAM)). Trimethylsilyl-protected, alkyne-terminated PFS homopolymer was first prepared via living anionic polymerization, terminating living PFS with commercially available 4-[(trimethylsilyl)ethynyl]benzaldehyde. Subsequent deprotection of the trimethylsilyl group with NaOMe yielded the ethynyl-terminated PFS (ω-alkyne-PFS). This method should be readily applicable to other polymers prepared by living anionic polymerization. Subsequently, non-PFS homopolymers containing a complementary “clickable” azide functional group were synthesized either by anionic polymerization, modification of a commercially available polymer, or atom transfer radical polymerization via two different approaches. In an azide postpolymerization modification approach, polystyrene (PS) and poly(methyl methacrylate) (PMMA) were functionalized by azide substitution of the terminal halide after ATRP. Alternatively, the azide moiety was incorporated into the ATRP initiator prior to polymerization, e.g., to give PNIPAM-N3 and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA-N3). Finally, the alkyne-terminated PFS segment and the azide functionalized counter block were coupled through the formation of a 1,2,3-triazole ring. In this report, PFS-b-PNIPAM, PFS-b-PDMAEMA, PFS-b-PS, PFS-b-PMMA, PFS-b-polydimethylsiloxane, and PFS-block-poly(ethylene oxide) have been synthesized via this convenient modular protocol in high yield and high purity.