UV-Induced [2+2] Grafting-To Reactions for Polymer Modification of Cellulose

Benzaldehyde-functional cellulose paper sheets have been synthesized via tosylation of cellulose (Whatman No 5) followed by addition of p-hydroxy benzaldehyde. Via UV-induced Paterno-Büchi [2+2] cycloaddition reactions, these aldehyde functional surfaces are grafted with triallylcyanurate, trimethylolpropane allyl ether, and vinyl chloroacetate. In the following, allyl-functional polymers (poly(butyl acrylate), pBA, M_n = 6990 g mol^-1, D strok sign = 1.12 and poly(N-isopropyl acrylamide), pNIPAAm, M_n = 9500 g mol^-1, D strok sign = 1.16) synthesized via reversible addition fragmentation chain transfer polymerization are conjugated to the celloluse surface in a UV-induced grafting-to approach. With pBA, hydrophobic cellulose sheets are obtained (water contact angle 116), while grafting of pNIPAAm allows for generation of "smart" surfaces, which are hydrophilic at room temperature, but that become hydrophobic when heated above the characteristic lower critical solution temperature (93 contact angle). The Paterno-Büchi reaction has been shown to be a versatile synthetic tool that also performs well in grafting-to approaches whereby its overall performance seems to be close to that of radical thiol-ene reactions. Via UV-induced Paterno-Büchi [2+2] cycloaddition reactions, aldehyde functional cellulose paper sheets are grafted with various functional enes. Further, the photochemical cycloaddition is used in a grafting-to approach to covalently attach allyl-functional poly(butyl acrylate) and thermoresponsive poly(N-isopropyl acrylamide).