Performing Ring Opening Metathesis Polymerization (ROMP) Reactions and Post-Polymerization Modifications Under Flow Conditions

Ring opening metathesis polymerization (ROMP) reactions of norbornene derived monomers and Grubbs 3rd Generation catalyst were run under continuous flow conditions. Typically, ROMP reactions are performed using “batch” reaction conditions that involve the use of round-bottomed flasks and mechanical stirrers to allow for mixing. Further, these experiments are typically carried out under inert atmospheres to achieve oxygen exclusion and prevent catalyst death, which can affect the expected monomer to initiator ([M]:[I]) ratio of the polymerization reaction. However, under continuous flow conditions, the ROMP reactions in this study were performed under air atmosphere using a simple bench-top setup with syringe pumps, segments of reaction tubing, connectors and syringes that allowed for betting mixing, and excessive reaction times which can lead to less controlled polymerization reactions. Nuclear magnetic resonance (NMR) analysis provided percent conversion of monomer to polymer, and gel permeation chromatography (GPC) analysis provided number-average molecular weights (Mn) and polydispersity index (PDI, Đ) values. Homopolymerization reactions were performed with residence times (tR) of 22.5 s and 7.5 s. Đ values ranged from 1.14-1.33 and 1.07-1.18 for tR =22.5 s and tR=7.5s, respectively, for most norbornene derived monomers studied. Monocyclic monomers such as cyclopentene, cyclooctene and cyclooctadiene were not able to be successfully analyzed post polymerization under flow conditions to give an indication of control over the reactions. Block copolymers consisting of a block of norbornene followed by a block of exo-functionalized norbornene were synthesized using a tR of 22.5 s. Percent conversions were >95% for all block copolymerization reactions. Thio-bromo click reactions were performed in flow where an exo-α-bromo ester functionalized norbornene monomer was polymerized in flow and subsequently followed in-line with a solution of thiol and triethylamine for a “click” reaction to occur. Both the polymerization and the thio-bromo click reaction percent conversions were >95% as determined by 1H NMR