Comparing Polymer-Supported TEMPO Mediators for Cellulose Oxidation and Subsequent Polyvinylamine Grafting

A new poly(acrylic acid)-grafted TEMPO (PAA-T) is compared to polyvinylamine-grafted TEMPO and free TEMPO as oxidation mediators for cellulose. The polymer-immobilized mediators require lower overall TEMPO concentrations and they restrict oxidation to the exterior surfaces of porous cellulose. On the other hand, the resulting surfaces are coated with grafted polyvinylamine and laccase, if the enzyme is used as the primary oxidant. PAA-T is anionic and does not sufficiently adsorb onto anionic cellulose to give oxidation, whereas cellulose rendered cationic by an adsorbed layer of PVAm is oxidized by PAA-T + laccase. There is no clear best choice mediator/primary oxidant combination for cellulose oxidation subsequent to PVAm grafting; the advantages of each mediator are summarized.