Fully biobased triblock copolymers generated using an unconventional oscillatory plug flow reactor

Abstract

Producing polymers in continuous flow offers significant advantages in terms of efficiency, scalability, and safety. Using conventional tubular flow reactors to synthesize polymers comes with some challenges, especially related to maintaining narrow residence time distributions (RTD) when operating with viscous fluids. Laminar flow is typically observed in tubes with restricted dimensions, and significant wall effects result in the broadening of the molar mass distributions. We envisioned that such a limitation can be overcome by the use of an oscillatory flow reactor (OFR). This work describes the use of a novel plate-type OFR to improve continuous-flow polymerization reactions for the first time. The reactor plate is equipped with millimeter-scale cubic pillars, and when combined with a superimposed oscillatory flow regime, promotes turbulent flow to circumvent detrimental wall effects during polymerizations. Additionally, the pulsatile flow intensifies mixing, and careful tuning of the pulsation amplitude and frequency lead to improved (i.e., narrowed) residence time distributions, a crucial parameter when synthesizing complex block polymer scaffolds in continuous flow. This innovative principle of implementing OFRs for improved continuous polymerization reaction is demonstrated with the benchmark ring-opening polymerization of lactide, a well-known renewable monomer. Thorough characterization using the reactor system reveals the relationships between process conditions and molecular attributes, including target molar mass and dispersity (D). Further, the OFR enabled the streamlined preparation of a series of block polymers with variable composition and low dispersity in a single experiment by judiciously adjusting the independent inlet feed rates. Finally, the OFR system allows for simple scaling without affecting the critical process parameters. As a result, a multi-gram synthetic protocol was achieved employing a biobased hydroxyl telechelic poly(beta-farnesene) macroinitiator in the ring-opening polymerization of lactide to generate fully renewable ABA-type triblock copolymers.