Synthesis of million molecular weight polyacrylamide with droplet flow microreactors

Microreactors are good platforms to study polymerization, but the production of high molecular weight polymers in small reaction space is rather difficult. To obtain million grams/mole molecular weight product, we developed two microreactors to implement inverse suspension polymerization in separated droplets, working as mini-reactors. Protecting by the lubricant film around droplets, 3600 kg/mol polyacrylamide (PAM) was successfully prepared in 38 min residence time, without any clogging issues. Advanced to the batch reactors, the microreactors offered precise control over the whole polymerization process in terms of reaction time and properties of the products, which facilitated the understanding of the basic laws of reactions. Thermal-initiated and redox-initiated radical polymerizations were both investigated, and the thermal-initiated reaction was found to be suitable for preparing high molecular weight polyacrylamide (>1000 kg/mol). The redox-initiated polymerization was a mixing-controlled reaction, which finished quickly in the microreactor.