Synthesis and characterization of L-tyrosine based novel biodegradable polyphosphates and polyurethanes for biomaterial applications

Hydrolytically degradable synthetic polymers developed from natural metabolite monomers play an extremely significant role in the area of biomaterial applications because of their potential biodegradability with minimal toxicity. Natural L-amino acids, being important natural metabolites, have been investigated for development of such polymers. Homopolymers of L-amino acids, through such investigations, have generated results indicating only limited success, mainly due to several difficulties associated with their processing and fabrication. For example, most of the homopoly(amino acids) have been found to be sparingly soluble or insoluble in common organic solvents, making chemical processing of these polymers difficult. Also, because of the high degree of crystallinity of such polymers, they have been found to have very negligible glass transition but prominent melting at high temperature regions, thereby making thermal processing of these polymers difficult. Such practical difficulties have been traced back to the highly ordered amidic(peptidic) nature of the polymer backbone. Hence, modification of the backbone structure of such polymers has been thought of as a way to circumvent such difficulties.; The research described in this dissertation involves the development of natural amino-acid L-tyrosine-based polymers having alternate amide(peptide) and non-amide bonds in the polymer backbone. Hence they are aptly called “pseudo” poly(peptides). The introduction of the non-amide moiety in the backbone provides a way to induce, enhance and control several “bio-engineering” properties of the amino-acid based polymer, like, hydrolytic degradability, thermal transition temperatures, chemical solubility etc. that are pertinent to biomaterial applications. This dissertation describes stoichiometrically controlled solution polymerization processes that were developed to incorporate phosphoester and urethane moieties alternating with amide moieties in a predominantly L-tyrosine based polymer backbone structure. The monomers and the subsequent polymers were characterized by NMR, FTIR and elemental micro-analysis for their structures and constituent compositions and, by GPC for their molecular weight distributions. The polymers were also characterized for their pertinent bio-engineering properties like thermal transition temperature, thermal degradation temperature, permeability, hydrolytic degradability in simulated physiological environment, relative hydrophilicity and effect of hydrolysis on local pH. The characterization results show considerable promise towards potential biodegradability and hence potential biomaterial applications.