Hydrogen-Bonded Multilayer Films Based on Poly(<i>N</i>‑vinylamide) Derivatives and Tannic Acid

Layer-by-layer (LbL) assembly based on hydrogen-bonding interactions is generating great interest for biomedical applications because it is composed of neutral polymers, while LbL assembly based on electrostatic interaction requires polycations which may induce toxicity issues. As a neutral polymer, poly­(<i>N</i>-vinylamide), which has low toxicity compared to poly­(acrylamide), has the potential to fabricate LbL thin films via hydrogen-bonding interactions. Herein we report interpolymer complexes of poly­(<i>N</i>-vinylamide)­s and natural polyphenol tannic acid to form the multilayered thin film. Poly­(<i>N</i>-vinylformamide) and poly­(<i>N</i>-vinylacetamide), which are water-soluble and insoluble in acetonitrile, could not form complexes with TA in water. On the other hand, <i>N</i>-alkylated poly­(<i>N</i>-vinylamide) such as poly­(<i>N</i>-ethyl-<i>N</i>-vinylformamide) and poly­(<i>N</i>-methyl-<i>N-</i>vinylacetamide) was soluble in acetonitrile and allowed the LbL assembly to proceed with TA. Furthermore, the QCM frequency shift with films composed of poly­(<i>N</i>-ethyl-<i>N-</i>vinylformamide) and TA were stable in water, while those of poly­(<i>N</i>-methyl-<i>N</i>-vinylacetamide) and TA were instable in water, possibly because formamide has lower steric hindrance compared to acetamide to allow stronger hydrogen-bonding interactions to take place. Thus, LbL assembly reactions with alkylated poly­(<i>N</i>-vinylamide)­s and TA were investigated and revealed that poly­(<i>N</i>-ethyl-<i>N</i>-formamide) and TA, which are water-soluble, effectively interacted with one another to generate water-stable hydrogen-bonded multilayered films