Dispersion polymerization in supercritical carbon dioxide using comb-like fluorinated polymer surfactants having different backbone structures

Abstract

Comb-like fluorinated polymers with different backbone structures, poly(heptadecafluorodecyl acrylate) (PA-R_f), poly[oxy[(2-perfluorooctylethylene)thiomethyl]ethylene] (PEO-R_f), and poly[p-[[(perfluorooctylethylene)thio]methyl]styrene] (PS-R_f), were used as surfactants in dispersion polymerization to examine the effect of backbone structure on the formation of polymer particles. Dispersion polymerization of monomers with different polarities using these comb-like fluorinated polymer surfactants in CO₂ showed that PEO-R_f containing a polar oxyethylene backbone was an effective surfactant for the dispersion polymerization of a polar monomer, such as N-vinyl-2-pyrrolidone, whereas PA-R_f was effective for less polar monomers, such as methyl methacrylate and N-vinyl caprolactam.

Introduction

Supercritical carbon dioxide (sc CO₂) has great potential as an alternative to common volatile organic solvents because it is inexpensive, environmentally benign, nontoxic, and has tunable properties. These properties render sc CO₂ a useful medium compared to other organic solvents [1], [2], [3]. Over the past decade, there have been extensive studies into its use as a solvent for polymerization. Heterogeneous polymerization techniques, including dispersion polymerization, have employed CO₂ as a solvent because it is poor solvent for most polymers but a good one for the monomers.

Comb-like fluorinated polymers are useful surfactant systems for dispersion polymerization in sc CO₂ [4], [5]. For example, poly(1,1-dihydroperfluorooctyl acrylate) has been used to prepare poly(methyl methacrylate) particles through the dispersion polymerization of methyl methacrylate in sc CO₂ [4], [5]. Other polymer particles, such as poly(styrene), poly(divinylbenzene), poly(vinyl acetate), and poly(acrylonitrile) particles were also prepared from the corresponding monomers by dispersion polymerization in sc CO₂ using comb-like poly(acrylate) derivatives as surfactants [4], [6], [7], [8], [9], [10], [11], [12], [13], [14]. In these polymerization systems, the hydrocarbon backbone region of the surfactant plays a key role in anchoring the surface of the hydrocarbon polymeric particle. However, there are only a few reports on the effect of the backbone structure of the comb-like fluorinated polymer on the formation of polymer particles through dispersion polymerization in sc CO₂ [15].

In this study, three different monomers with different polarities, such as methyl methacrylate, N-vinyl-2-pyrrolidone, and N-vinyl caprolactam, were polymerized in sc CO₂ using three different comb-like fluorinated polymers, such as poly(heptadecafluorodecyl acrylate) (PA-R_f), poly[oxy[(2-perfluorooctylethylene)thiomethyl]ethylene] (PEO-R_f), and poly[p-[[(perfluorooctylethylene)thio]methyl]styrene] (PS-R_f), as surfactants. As the chemical structure of the side groups of these comb-like fluorinated polymers is identical, the effect of the backbone structures on the formation of polymer particles with different polarities could be studied.