A Tandem Continuous Flow Process for the Synthesis of Functionalized PDMS

The traditional industrial production of functionalized polydimethylsiloxane (PDMS) consists of a two-stage batch process, i.e., the ring-opening polymerization (ROP)/equilibrium of cyclic siloxane monomer followed by attaching functional groups to PDMS through hydrosilylation. In this study, we developed a continuous tandem flow process combining the two stages for the synthesis of functionalized PDMS using octamethylcyclotetrasiloxane (D4) as the monomer. We investigated the kinetics of ROP/equilibrium reaction of D4 using a flow tube reactor filled with the cationic resin catalyst Amberlyst 35. The reaction was found to be complete within a short residence time, 2-3 min, giving steady flow-out of the reaction mixture containing ca. 80% nonvolatile content for a period of up to 90 min. The catalyst was reusable for up to 80 times by rinsing with methyl isobutyl ketone (MIBK). The resulting PDMS-SiH, bearing two terminal -SiH groups, was used for subsequent hydrosilylation reaction with different vinyl compounds in the presence of the Speier catalyst. PDMSs possessing functionalities such as ethylene glycol (EG), epoxy (EPO), methacrylate (MA), and hydrocarbon chain were prepared through continuous tandem ROP/equilibrium and hydrosilylation reaction. These products exhibit excellent defoaming performance that is comparable with the commercial products from a batch process. The present study paves the way to a more efficient production of functionalized silicone oil through a flow reaction process.