Ambient Temperature Synthesis of Triblock Copolymers via Orthogonal Photochemically and Thermally Induced Modular Conjugation

Abstract

A strategy for the modular ambient temperature synthesis of ABA and ABC triblock copolymers via a combination of photoinduced Diels–Alder reactions with thermal Diels–Alder reactions and azide–alkyne click chemistry is reported. Polystyrene (PS) and PMMA (PMMA) with α-2,5-dimethylbenzophenone and ω-cyclopentadienyl or ω-azide end-functionality were prepared via atom transfer radical polymerization (ATRP) and subsequent transformation of the bromine end-group. The phototriggered conjugation reaction proceeds via an in situ formation of highly reactive o-quinodimethanes. Maleimide-capped poly(tert-butyl acrylate) obtained via ATRP was employed as dienophile. Alkyne and maleimide functionalized poly(ethylene glycol) (PEG) were synthesized by esterification of monomethoxy PEG. PtBA-b-PMMA-b-PtBA and PtBA-b-PS-b-PtBA were successfully prepared in a one-pot reaction at ambient temperature combining photoinduced and thermal Diels–Alder reactions. ABC triblock copolymers (PtBA-b-PS-b-PEG) with narrow polydispersities were obtained via the combination of photoinduced Diels–Alder reactions with thermal Diels–Alder reactions as well as CuAAc chemistry. The polymers were characterized by size exclusion chromatography and 1H NMR spectroscopy.