Multifaceted Synthetic Route to Functional Polyacrylates by Transesterification of Poly(pentafluorophenyl acrylates)

Abstract

Synthesis of functional polyacrylates by 4-dimethylaminopyridine (DMAP) catalyzed trans-esterification of poly(pentafluorophenyl acrylate) (polyPFPA) is reported. High fidelity and versatility of this strategy was exemplified by near quantitative conversion with diverse functional alcohols (primary, secondary as well as phenolic) featuring reactive groups like alkene, alkyne or acrylate, enabling further sequential functionalization using click chemistry. Co-integrating an equimolar mixture of allyl and propargyl alcohol produced an orthogonally clickable copolymer by thiol–ene and 1,3-cycloaddition reaction. Base catalyzed ester exchange allowed installation of acid labile Boc-l-serine to create amino acid pendent polymer keeping both NH2- and COOH-group free, thereby providing a facile route toward zwitterionic polymers. Reaction with 2-dimethylaminoethanol conferred dual pH and CO2 responsive polymers from the same reactive precursor. The synthetic strategy was further extended to attach alcohols obtained from natural resources such as geraniol, l-lactic acid or sesamol to engineer new renewable polymers. Even a graft copolymer with very high (93%) grafting density could be achieved utilizing PEG350–OH. The trans-esterification was found to be highly selective for primary alcohols over secondary alcohols and also to the activated PFP-ester over a normal ester such as poly(methyl acrylate). Using such selectivity, fluorescently tagged polymer could be synthesized by replacing only the PFP-ester of a poly(methyl acrylate-co-PFPA) with 1-pyrenemethanol. Further, PFPA was polymerized with 2.0 mol % diacrylate to produce a cross-linked gel network. The PFP-ester groups of the cross-linked gel could be quantitatively replaced with Boc-l-serine, which upon deprotection of the Boc group resulted in a novel zwitterionic hydrogel exhibiting pH-dependent swelling properties. Time-dependent FTIR experiment suggested fast kinetics of the reaction, making this synthetic route practically applicable for postpolymerization modification. Mechanistic investigation exposed involvement of both DMAP and the nucleophilic solvent N,N-dimethylformamide (DMF) in catalyzing the reaction. This also explains the reason as to why near quantitative conversion was achieved in DMF and not in the non-nucleophilic solvent 1,4-dioxane.