Polymer Brushes on Cellulose Nanofibers: Modification, SI-ATRP, and Unexpected Degradation Processes

Controlled surface-initiated atom transfer radical polymerization (SI-ATRP) has previously been described as a versatile method that allows grafting polymer brushes on purely cellulosic forms of nanocelluloses, i.e., cellulose nanocrystal (CNC) nanorods and bacterial cellulose (BC) networks. However, corresponding SI-ATRP on long and entangled cellulose nanofibers (CNFs), having typically more complex composition and partly disordered structure, has been only little reported due to practical and synthetic challenges, in spite of technical need. In this work, the feasibility of SI-ATRP on CNFs is exemplified on the polymerization of poly(n-butyl acrylate) and poly(2-(dimethyl amino)ethyl methacrylate) brushes, both of which showed first order polymerization kinetics up to a chain length of ca. 800 repeat units. By constructing high and low initiator densities on CNF surfaces, we also show that, surprisingly, a higher grafting density of polymer brushes around CNF causes noticeable degradation of the CNF na...