Free Radical Polymerization of 1,1-Difluoroethene in a Supercritical Carbon Dioxide Medium

A novel process has been devised and demonstrated at the laboratory scale that produces polyvinylidene fluoride from 1,1-difluoroethylene monomer utilizing supercritical carbon dioxide. Notably, the process has been shown to produce unimodal, gel-free polymer with molecular weights of 1.5 million. In the process, the role of 1,1-difluoroethene is two-fold; one as a reacting monomer and the other as a supercritical co-solvent in a binary mixture with CO2. The process concept was demonstrated using an agitated 300 ml bolt closure, stainless steel reactor. Reaction studies involved varying the total pressure (12 to 31 MPa), the partial pressures of CO2 and monomer, the temperature (325 to 400 K), and involved several commercially available organic peroxide initiators. While demonstrating the feasibility of the novel synthesis process route, unique high-quality polymer products were produced. Another process benefit is the substantially lower risk of temperature runaway compared to the conventional emulsion polymerization process, due to the excellent heat and mass transfer characteristics of the supercritical fluid medium. Experimentally, the yields were high with excellent reproducibility. In this paper, the effects of the polymerization conditions and the type of free radical initiators on the resultant polymer resin properties and the product yield are discussed