Expanding Chitosan Reticular Chemistry Using Multifunctional and Thermally Stable Phosphorus-Containing Dendrimers

Chitosan is an astonishing building block that is extracted from marine crustacean waste, features randomly distributed amino and acetamido groups in its backbone, and can be handled in different forms, giving rise to an impressive diversity of functional nanomaterials. Hitherto, its reticular chemistry, although mandatory to circumvent its main drawback of instability, has been dominated by the use of glutaraldehyde. Unfortunately, the toxicity and inherent chemistry of the latter narrow further development of such cross-linked materials and constitute an impediment for their massive spreading and real implementation, especially in nanomedicine and related healthcare applications. Prompted by the well-established advantages of dendrimers, more distinctively those containing phosphorus in their skeleton, we herein explore the use of second-and third-generation phosphorus-containing dendrimers as cross-linkers to provide an extended covalent dendritic framework grown inside of the carbohydrate network. The presence of residual amine and aldehyde defects was explored to conjugate other chemicals (viologen-based ionic liquid and aminopropyltriethoxysilane) thereby adding more functional diversity to the assembled framework. We also leveraged on the film-forming ability of chitosan to shape the reticular network as flexible films. Despite the bulkiness of the used phosphorus dendrimers, the film-forming memory of chitosan was preserved, allowing successful preparation of highly functional, transparent, and flexible micrometer-thick bioplastics. The cross-linking seems to delay the half-weight degradation temperature of the plastics, with a significant increase in the char residue and a reduced heat release rate. Ternary objects (Congo red dye and gold nanoparticles) could also be entrapped within the transparent films without leaching or degradation, thereby expanding the usefulness of these transparent coatings as multifunctional sensors, flame retardants, biofoulants, etc.