Synthesis and characterization of putrescine-based poly(phosphoester-urethanes)

A novel set of putrescine-based segmented polyurethanes was synthesized using 1,4-butane-diisocyanate and phosphoester diols, and was characterized for its potential as a degradable biomaterial. These poly(phosphoester-urethanes) (PPU) were flexible polymers with ultimate tensile strength (UTS) from 2 to 3 MPa, elongations up to 80% and tan delta near 0.15. The incorporation of phosphoester bonds in the backbone of the polymer by using bis(2-hydroxyethyl)phosphite (BGP) and bis(6-hydroxyhexyl)phosphite (BHP) as chain extenders resulted in hydrolytic degradation which was evaluated in vitro. By varying the content of the phosphoester diol BGP, degradation rate, as followed by mass loss and GPC, could be modulated. Polymers based on the more hydrophobic monomer, BHP, showed slower degradation than corresponding BGP based polymers. Tensile properties of PPU-B2 after 22 days in vitro degradation show more than a 50% drop in UTS and ultimate elongation, likely caused by void spaces left behind in the polymer after mass loss and swelling. The attachment of a drug, PAS, pendant to the phosphoester group of the PPU was demonstrated. PAS was linked via the spacer 4-hydroxybenzaldehyde, and free, intact drug was released in about 5 h from a thin film.