Competition between Physical Cross-Linking and Phase Transition Temperature in Blends Based on Poly(N-isopropylacrylamide-co-N-ethylacrylamide) Copolymers and Carboxymethyl Cellulose

The combination of thermoresponsive polymers and biopolymers is growing due to the multiple benefits, owing to their tunable properties. Numerous works focus on the preparation of materials by chemical cross-linking, but physical cross-linking (based on hydrogen bonding) has not been deeply studied. In this context, questions around the hydrogen bonding of physical-crosslinking and lower critical solution temperature (LCST) need to be addressed, especially when a second comonomer is incorporated. This study is based on the preparation of blends of poly(N-isopropylacrylamide-co-N-ethylacrylamide) copolymers and carboxymethyl cellulose (CMC) by dissolution, where the LCST-transition and physical-crosslinking are studied. The results show a strong effect of the comonomer on the properties in comparison with the CMC, especially for solutions of methanol/water. Low contents of N-ethylacrylamide (NEAM) can promote physical-crosslinking and the gelation, avoiding cononsolvency observed for homopolymers. On the other hand, NEAM will disrupt the gelation when the comonomer content is high enough.