Synthesis of biomedical, fluorescence‐labelled polyesterurethanes for the investigation of their degradation

The synthesis and characterization of fluorescence‐labelled, phase segregating block polyesterurethanes based on the known biocompatible and degradable materials poly[( R )‐3‐hydroxybutyric acid] (PHB), poly(ϵ‐caprolactone) (PCL), and poly[(ϵ‐caprolactone)‐ co ‐glycolide] (PCL/PGA) is described. To introduce fluorescence labels in the amorphous domains of the polymers, phenacyl 10,11‐dihydroxyundecanoate (PDUA) was synthesized and copolymerized with a PHB diol, a PCL diol, and aliphatic diisocyanates. After cleavage of the protecting group (without degradation of the polymer backbone), the carboxyl group was reacted with a fluorescent amine (dansylcadaverine) in the presence of 4,6‐diphenylthieno[3,4‐ d ]‐1,3‐dioxol‐2‐one 5,5‐dioxide (Steglich reagent). Also a polymer containing 13 C‐labelled carboxy groups was synthesized and the labelling reaction monitored by 13 C NMR spectroscopy. To introduce fluorescence labels in the hard segment of the polymers, a new low‐molecular‐weight diol based on poly[( R )‐hydroxybutyric acid] and containing protected carboxy groups was synthesized. After the deprotection, the carboxy groups were reacted with a fluorescent amine (dansylcadaverine) in the presence of an activating system based on dicyclohexylcarbodiimide. The labelled PHB diol was then copolymerized with a poly[(ϵ‐caprolactone)‐ co ‐glycolide] diol and an aliphatic diisocyanate. The so obtained fluorescence‐labelled block polyesterurethanes are promissing materials for the investigation of the biocompatibility and degradation of the corresponding, non‐labelled materials (DegraPol®) by means of fluorescence‐aided microscopic and spectroscopic techniques.