Synthesis of poly(ethylene glycol)-co-poly(caprolactone) di- and triblock copolymers and effect of architecture, dispersity and end-functionalisation on their aqueous self-assembly

Abstract

The synthesis of block copolymers based on polyethylene glycol (PEG) and polycaprolactone (PCL) is reported. PEG-b-PCL diblock copolymers were prepared using both enzymatic and tin-mediated ring-opening polymerisation. Well-defined PEG-b-PCL-b-PEG triblock copolymers were synthesised through coupling of PEG-b-PCL diblock copolymers using hexamethylene diisocyanate. In addition, a PEG-b-PCL diblock copolymer with a single vinyl group on the PEG-terminus was prepared and this was converted quantitatively into amine end-functional copolymers through the use of photo-initiated thiol–ene chemistry in the presence of cysteamine hydrochloride. The aggregation behaviour of diblock and triblock copolymers was investigated using a direct hydration technique. The majority of the polymers formed vesicles as expected from the block composition, with the diblock copolymers generally having significantly thicker membranes than triblock copolymers of comparable composition, indicating differences in the membrane microstructure. The inclusion of 10 wt% of a protonisable amine-functional diblock at neutral pH appeared to favor cylindrical micelle (worm) formation. This morphology appeared to be stable up to 100% amine-functional diblock copolymer, thus providing a facile route to prepare worm-like micelles with a well-defined number of functionalisable surface groups.