Synthesis of cellulose nanocrystals bearing photocleavable grafts by ATRP

Cellulose nanocrystals (CNC) were grafted with photocleavable polymeric chains using Atom Transfer Radical Polymerisation (ATRP). The nanoparticle synthesis relies on two main steps: first the grafting of a photosensitive moiety bearing an ATRP initiating site onto the surface of CNC, followed by surface initiated ATRP from the modified surface outwards. An original UV-sensitive linker bearing one ATRP initiating site and one anchoring hydroxyl functionality, which was grafted to the CNC surface using a diisocyanate linker, was designed to achieve this goal. Polystyrene (PS) was then polymerized from the modified CNC, resulting in CNC-g-photolinker-PS nanoparticles. The possibility to degraft the PS chains using UV-irradiation was further investigated, and PS grafts with a narrow polydispersity index (1.08) and molecular weights close to those of formed homopolymers through sacrificial initiator addition were obtained. This is the first example where it has been proven that good control of SI-ATRP from CNC can be achieved. It also confirms that homopolymers initiated by sacrificial initiator in the polymerization medium can be an indication of the grafted polymer brush length. These materials further offer potential as smart delivery vehicles and smart materials.