Synthesis and ring-opening polymerisation of a new alkyne-functionalised glycolide towards biocompatible amphiphilic graft copolymers

A new functional dilactone, 3-(2-propynyl)-1,4-dioxane-2,5-dione (4), was synthesized from ethyl glyoxalate and propargyl bromide via a 4-step reaction sequence. Ring-opening (co)polymerisation of the alkyne-functionalised monomer 4 with L-lactide was carried out in dichloromethane at 30 degrees C using N,N-dimethylaminopyridine as a catalyst and benzyl alcohol as an initiator. The resulting alkyne-functionalised copolyesters were characterized by H-1 NMR, size exclusion chromatography (SEC) and MALDI-TOF spectroscopy. Azide end-functionalised PEG was then grafted onto the polyester backbone with multiple pendant alkyne moieties using copper-catalysed azide-alkyne cycloaddition (click chemistry). The graft copolymers were characterized by H-1 NMR, SEC and DOSY NMR. The aggregation behavior of the copolymers in water was investigated by fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The critical aggregation concentration was in the range of 10-50 mg L-1. The nano-sized objects were rod-like in shape with a diameter of 100 nm and a length of around 400 nm.