Pickering emulsions for the polymerization of ε-caprolactone in continuous flow process

Using the potential of compartmenting free enzyme in dispersion phase of Pickering emulsion, a simple continuous flow system for free enzyme catalytic cycle-opening polymerization of ε-caprolactone has been studied. In order to generate suitable and stable Pickering emulsions, silica nanoparticles(SiNPs) modified with octyltrimethoxysilane (OTMS) and aminopropyltrimethoxysilane (APTMS) are synthesized, and the modification is confirmed by Fourier transformed infrared (FTIR) spectroscopy and water contact angle (CA). It is found that CA values of modified SiNPs increased from 107° to 168° with the increase of ratio of OTMS to APTMS from 1:1 to 8:1, which indicates that wettability of SiNPs has been changed from original hydrophilic to hydrophobic and consequent has an effect on the properties of Pickering emulsions. Among the modified SiNPs, the silica modified with OTMS: APTM (2:1) can construct stable W(water)/O(toluene) Pickering emulsion, confirmed by images from confocal laser microscope. The stable Pickering emulsion comprising of Candida Antarctica lipase B dispersed in water droplets is selected as a model for investigation of conditions for ring-opening polymerization of ε-caprolactone. The high monomer conversion is achieved with amount of emulsifier and enzyme being used 5 wt% and 3 wt%, respectively, and flow rate 3 mL h−1in continuous flow process, which is higher than that in batch reaction system although the formula of Pickering emulsion is identical. Specially, the polycaprolactone (PCL) with an average molecular weight of 210151 g/mol, as per gel permeation chromatography (GPC) analysis, is achieved. The catalytic efficiency of enzyme for polymerization is not changed even after several cycles of use. The present enzyme immobilization within Pickering emulsion offers a green and prospective approach for synthesis of high molecular weight polymer in continuous flow process. [Display omitted]