Ambidextrous Surfactants for Water-Dispersible Polymer Powders from Dispersion Polymerization in Supercritical CO₂

Abstract

A new concept is introduced in which a surfactant, poly(dimethylsiloxane)-b-poly(methacrylic acid) (PDMS-b-PMA) (Mw ) 5500 g/mol PDMS, 900 g/mol PMA), is utilized to stabilize an organic latex in either a nonpolar medium, dense CO2, or water. The latex particles, in this case poly(methyl methacrylate) (PMMA), were synthesized by dispersion polymerization in supercritical carbon dioxide. In CO2, the PDMS block provides steric stabilization while the PMA block adsorbs to the particle surface. Upon transfer to water, the PDMS block collapses onto the surface and the PMA block ionizes for pH > 5 to stabilize the latex by electrostatic repulsion, as shown by zeta potential measurements. The surfactant is "ambidextrous" in that it provides stabilization in either CO2 or water, by different mechanisms in each medium. Smaller more uniform particles were produced in CO2 with a mixture of the commercially available surfactant, PDMS-g-pyrrolidonecarboxylic acid (PDMS-g-PCA) (Mw ) 8500 g/mol, ∼2 PCA groups) and PDMS-b-PMA.

Steric Stabilization of Colloids by Poly(dimethylsiloxane) in Carbon Dioxide: Effect of Cosolvents

“…In addition, the particles are much less agglomerated, on the basis of much lower sedimentation rates during polymerization and the SEM images. Previous work has shown that the monomer, methyl methacrylate, enhances steric stabilization, which is lost as the monomer is consumed (15,16). By adding a relatively unreactive cosolvent, it is possible to stabilize the reaction to completion.…”

“…Recently, PDMS-based surfactants have been used to stabilize latexes formed during heterogeneous polymerization of methyl methacrylate (14-16) and styrene (17) in supercritical CO 2 . At low conversions, where monomer acts as a cosolvent, the latexes are stable, but become unstable at high conversions, indicating limitations in the solvation of PDMS by pure CO 2 (15,16). This instability, which is not predicted by simulation studies of symmetric systems, warrants further study.…”

Frontiers in green chemistry utilizing carbon dioxide for polymer synthesis and applications

“…A new concept for the preparation of water-dispersible polymer particles in CO 2 has been developed by Johnston [34]. PMMA was synthesized in CO 2 using an "ambidextrous" surfactant.…”

Micelle Formation and Surface Interactions in Supercritical CO2. Fundamental Studies for the Extraction of Actinides from Contaminated Surfaces.

“…thick) perpendicular to the axis with 180 o separation so that UV-Vis spectra of the cell contents could be collected. 19 Another cell was equipped with three 5/8 in. sapphire windows mounted perpendicular to the cell axis with 90 o separation enabling collection of steady state emission and lifetime data.…”