An enzyme-catalysed access to amphiphilic triblock copolymer of PCL-b-PEG-b-PCL: synthesis, characterization and self-assembly properties

Abstract

Biodegradable amphiphilic triblock copolymer of PCL-b-PEG-b-PCL was synthesized by a simple, environmentally friendly and one-pot biocatalytic route that employs lipase Novozym-435 as a biocatalyst and poly (ethylene glycol) (PEG) as a macromolecular initiator to induce ring-opening polymerization of ε-caprolactone (ε-CL). The structure of the prepared copolymers was characterized by gel permeation chromatography, Fourier transform infrared spectrum and nuclear magnetic resonance spectrum. The crystalline behaviours of the PCL-b-PEG-b-PCL were investigated by differential scanning calorimetry and X-ray diffraction. The self-assembly behaviours of the amphiphilic PCL-b-PEG-b-PCL were studied by fluorescence technique, dynamic light scattering instrument and transmission electron microscopy. The structure analyses indicate that PCL-b-PEG-b-PCL with desired components can be synthesized by changing the molar ratio of ε-CL monomer and PEG macroinitiator. Interestingly, the crystalline structure of PCL-b-PEG-b-PCL is mainly determined by the crystallization of PCL block, suggesting that the crystallization of PEG block in the copolymer is inhibited by the PCL block. The self-assembly behaviours of PCL-b-PEG-b-PCL in water can be adjustable according to the molar ratio of ε-CL and PEG. Size of the formed PCL-b-PEG-b-PCL micelles increased and the critical micelle concentration decreased while the polycaprolactone chain length increased.