Development of Melt Polymerization Route for Amino acid Based Functional Polymers and their Self-assembled Nanostructures

Abstract

Polymers based on biological resources have gained significant interest due to their potential application in therapeutics, biodegradable and biocompatible engineering thermoplastics. Among the natural resources, amino acids are important class of biological-monomers for producing well-defined macromolecular architectures. New synthetic approaches are urgently required for the development of amino acid based biodegradable and biocompatible polymers in biomedical field. In this thesis work, novel dual ester-urethane polycondensation chemistry has been developed for amino acid monomers with commercial diols to produce high molecular weight fibrous polymers. The new synthetic process was tested for more than ten different amino acids. Further, the chemoselective melt condensation chemistry was tailored to make diverse polymer architectures such A-B and A-B-A type species; amine functionalized linear polyesters, and cross-linked thermo-sets. The role of catalyst action on the chemoselective reaction indicated that the Ti(OBu)4 catalyst produced high chemoselectivity compared to other catalysts from alkali, alkali earth metal, transition metal and lanthanide group elements. The optical purity of the new reaction was also tested for D- and L-isomers and these new classes of functional polymers were found to be self-assembled as helical fibrous. Multi-functional amino acid monomers based on aspartic and glutamic acids produced linear functional polyesters with urethane as pendent in each repeating unit. These polymers were found to undergo reversible helical self-assemblies to produce hierarchical helical amyloid-like fibrils to charged nano particles and vice versa. New monomers were developed based on cystine to make disulfide linkage containing functional polyesters. These polymers could be degraded into small chains by DTT as redox agent. The cytotoxicity studies of amine functional disulfide polymers (cationic polymers) was performed in MCF-7 cells and the result indicated that these polymers are nontoxic to cells and are also biocompatabile in nature. The overall finding revealed that the new classes of amino acid based polymers developed by melt polycondensation process are potential candidates for thermoplastic as well as drug delivery applications.