Conformation of Methylcellulose as a Function of Poly(ethylene glycol) Graft Density

Low molecular weight thiol-terminated poly(ethylene glycol) (PEG) (M ∼ 800) has been grafted onto a high molecular weight methylcellulose (MC, M_w ∼ 150000) by a facile thiol-ene click reaction; graft densities varied from 0.7% to 33% (grafts per anhydroglucose unit). Static and dynamic light scattering reveals that the overall radius of the chain increases systematically with graft density, in a manner in excellent agreement with theory. As the contour length remains unchanged, it is apparent that grafting leads to an increase in the persistence length of this semiflexible copolymer, by as much as a factor of 4. These results represent the first experimental verification of the excluded volume theory at low grafting densities, and demonstrate a promising synthetic platform for systematically increasing the persistence length of a model semiflexible, water-soluble polymer.