Cyclodextrin-based biodegradable polymer stars: synthesis and fluorescence studies

Polymer stars built using aliphatic polyester arms and a beta-cyclodextrin (beta-CD) core are prepared by two synthetic methodologies. The CD core stars offer the intriguing potential of loading molecules of interest into two zones by exploiting the host-guest chemistry of the hydrophobic CD core and by physical trapping in the polymer arms. Core-first syntheses were achieved through the ring-opening polymerization of rac-lactide, L-lactide, beta-butyrolactone and lactide/glycolide monomers generating seven-armed stars with a heptakis(2,6-di-O-methyl)-beta-CD core. Arm-first syntheses were achieved through the copper-catalyzed azide-alkyne cycloaddition of alkyne-terminated poly(lactic acid)s, poly(3-hydroxybutyrate) and a heptakis-azido-beta-CD. For both synthetic strategies, use of the industry standard catalyst, Sn(Oct)(2), gave polymers with broadened dispersities (1.3-1.7) when compared to aluminum complexes supported by salen ligands (<1.2). Synthetic strategies were compared by both measures of reaction control (molecular weight, dispersity, conversion) and controlled release (fluorescence spectroscopy of hydrolytic and enzymatic degradation), each offering benefits to the synthetic polymer chemistry, variable sustainability and scalability and a clear direction for further star design. Fluorescence-based controlled release studies were performed in water or methanol, releasing the encapsulated 7-methoxycoumarin fluorescent probe through both hydrolytic and enzymatic degradation. The release was shown to be strongly accelerated in the presence of the enzyme. This article contains supporting information that will be made available online once the issue is published.