Influence of poly(N-isopropylacrylamide) grafting density on the temperature dependent fibril formation of methylcellulose

Methylcellulose (MC) is a water-soluble cellulose ether that is used in a variety of commercial products due to its thermoreversible gelation at ca. 60 °C, near the lower critical solution temperature (LCST) of MC. It is known that this gelation is caused by the formation of a fibrillar network upon heating. Recently, we demonstrated that the MC fibril structure can be modified and that the fibril formation can be suppressed by grafting short poly(ethylene glycol) (PEG) chains onto the MC backbone. With this new understanding, we have grafted poly(N-isopropylacrylamide) (PNIPAm) chains onto the MC backbone at various grafting densities; PNIPAm displays LCST behavior in water at ca. 32 °C. Utilizing static and dynamic light scattering, we characterize the chain conformation and variation in the overall radius of the chains as a function of grafting density and temperature. Small-amplitude oscillatory shear reveals changes in the gelation behavior and modulus of the two polymers. Fibril formation and fibril structure are studied using small-angle X-ray scattering and cryogenic transmission electron microscopy. The influence of PNIPAm grafts on the temperature dependence of MC fibril formation is compared with the results from PEG-grafted MC.