Accessing libraries of bifunctional block copolymers using two distinct pentafluorophenyl moieties†
A dual reactive block copolymer poly(methyl methacrylate-stat-pentafluorophenyl methacrylate)-b-poly(styrene-stat-pentafluorostyrene) (P(MMA-r-PFPMA)-b-P(S-r-PFS)) based on pentafluorophenyl (PFP) ester and alkyl groups was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization and evaluated as a precursor scaffold for libraries of bifunctional segmented macromolecules by amidation and para-fluoro–thiol substitution (Mn ≈ 52 000 g mol−1, Đ ≈ 1.2, average functionality ≈ 7–8 mol%). The order of functionalization was found to be relevant as fluoro thiol substitution occurred on both functional groups. Indeed, on functionalizing PFS, multiple fluorine substitutions at the para and meta positions of the PFPMA aromatic ring were observed at rates faster than for the para fluorine atom of PFS units. The reactivity of the fluorine atoms of PFPMA was investigated further to better understand their order of substitution and the implication on the activity of PFPMA towards amidation. The reactivity of fluorine atoms of both PFP units towards aliphatic thiols follows the order: para PFPMA > meta PFPMA > para PFS. In addition, the para monosubstituted PFPMA unit retains its activity towards amidation while the meta substituted products are rendered inactive. The dual reactive polymer was found to be a direct access point for block copolymers with distinct segmental reactivities when amidation was performed first on PFPMA motifs, followed by a para-fluoro thiol reaction on PFS units. This way functionalities such as allyl, norbornenyl, furfuryl, azide, and hydroxyl could be selectively introduced. An amino- and sulfhydryl-dual functionalized block copolymer could also be obtained in one pot.