Branched Amino Acid Based Poly(ester urea)s with Tunable Thermal and Water Uptake Properties

Abstract

A series of amino-acid based poly­(ester urea)­s (PEU) with controlled amounts of branching was synthesized and characterized. The mechanical properties, thermal characteristics and water absorptions varied widely with the extent of branch unit incorporation. Herein, the details of the synthesis of a linear bis­(l-phenylalanine)-hexane 1,6-diester monomer, a branch tri-<i>O</i>-benzyl-l-tyrosine-1,1,1-trimethylethane triester monomer and a series of copolymers are described. The extent of branching was varied by adjusting the molar ratio of linear to branched monomer during the interfacial polymerization. The elastic moduli span a range of values (1.0–3.1 GPa) that overlaps with several clinically available degradable polymers. Increasing the amount of branching monomers reduces the molecular entanglement, which results in a decrease in elastic modulus values and an increase in values of elongation at break. The l<i>-</i>phenylalanine-based poly­(ester urea)­s also exhibited a branch density dependent water uptake ability that varied between 2 and 3% after 24 h of immersion in water. Nanofibers incorporating 8% branching were able to maintain their morphology at elevated temperature, in hydrated conditions, and during ethylene oxide sterilization which are critical to efforts to translate these materials to clinical soft tissue applications