Enzymatic graft polymerization from cellulose acetoacetate: a versatile strategy for cellulose functionalization

A novel approach was developed to prepare cellulose acetoacetate-graft-copolymers via horseradish peroxidase (HRP)-mediated polymerization. Cellulose acetoacetate (CAA), the macroinitiator, was obtained by transesterification between tert-butyl acetoacetate (t-BAA) and cellulose in ionic liquid. The CAA-graft-polyacrylamide (CAA-g-PAM) was synthesized using a ternary initiator system consisting of CAA, HRP and hydrogen peroxide (H₂O₂). The results of surface-initiated polymerization showed that the formation of free polymers could be inhibited in this process. The kinetics exhibited that this method is a powerful tool for obtaining graft copolymers. The effects of H₂O₂ concentration and reaction temperature were investigated to explore the optimal conditions for the process of enzymatic initiation. The synthesized copolymers were characterized by FT IR, NMR, TGA and elemental analysis to confirm the successful grafting of polyacrylamide chains onto the cellulose backbones. Furthermore, generality of the HRP-mediated graft polymerization approach was demonstrated using various monomers, including 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) and sulfobetaine methacrylate (SBMA). This efficient and robust strategy has great potential in fabrication of cellulose-based functional polymers.