Biobased Synthesis of Alternating Copolysaccharides Utilizing Nanofibrous Cellulose Crystallites as a Template

Alternating copolymers exhibit specific physical properties, such as a narrow glass transition temperature range and a highly uniform micelle size. Alternating copolymers are, however, synthesized from only limited combinations of monomers. Herein, we report the semisynthesis of copolymers with a basic skeleton composed of alternating glucose (G)/glucuronate (U) units via the regioselective surface oxidation of plant cellulose crystallites, followed by mechanical shearing of the oxidized crystallites in water. The molecular weights and yields of the resulting G/U copolymers varied depending on the degree of oxidation (DO) of the crystallites and method of mechanical shearing and were approximately 8000‒15000 g/mol and 4‒16%, respectively. Interestingly, the molecular chain length distributions of the G/U copolymers were in good agreement with the length distributions of the dent defects formed on the crystallite surfaces. We conclude that the oxidized surface molecules of the crystallites were stripped during the mechanical shearing process to yield the G/U copolymers, and these parts of the surfaces were identified as the crystallite defects. Thus, novel biobased alternating copolymers, which cannot be artificially synthesized, are produced via the chemical functionalization of plant cellulose crystallites utilizing the two-fold helix structure of the surface molecules as a template.