Gallol-containing homopolymers and block copolymers: ROMP synthesis and gelation properties by metal-coordination and oxidation

Abstract

Gallol-functionalized polymers are highly desirable for their addressable functions in the fields of materials science, nanotechnology and biomedicine, owing to gallol's unique chemistry including excellent chelating properties to metals, easily oxidability and superior ability to bind proteins. Herein, we report the controlled synthesis of the first polynorbornene-based side-chain gallol-containing homopolymers and block copolymers with pendent triethylene glycol (TEG) moieties by the ring-opening metathesis polymerization (ROMP) using the 3rd generation Grubbs catalyst 1 as the initiator. We describe the direct synthetic route by the ROMP of a gallol-containing norbornene monomer, and the indirect approach via an acetoxyl protection/deprotection route. Among the tested metal ions of Fe3+, Mg2+, Cr3+ and Al3+, Fe3+ is the most effective metal ion to induce the gelation of the present gallol-containing polymers, and UV–visible spectroscopy indicates that bis-coordinated state dominates for the interaction between side-chain gallol groups and Fe3+ ions in DMF. The gelation rate, interior structure, thermal and mechanical properties of the Fe3+-induced metallogels can be effectively tuned by changing the gallol/Fe3+ molar ratio, polymeric molecular weight, and by introducing of organic TEG block. Furthermore, the oxidant-induced organogels were fabricated by adding the oxidant of NaIO4 into the DMF solution of the gallol-containing polymers, and the gelation rate highly depends on the gallol/IO4− molar ratio and the introduction of TEG block. We are convinced that the effective synthesis of well-defined gallol-containing polymers, as illustrated by the present work, will pave the way for their functional applications as smart organogels, coatings, adhesives, capsules, etc.