Poly(dimethylsiloxane)-Stabilized Polymer Particles from Radical Dispersion Polymerization in Nonpolar Solvent: Influence of Stabilizer Properties and Monomer Type

Abstract

Particles used in electrophoretic display applications (EPD) must possess a number of specific properties ranging from stability in a nonaqueous solvent, high reflectivity, low polydispersity, and high charge density to name but a few. The manufacture of such particles is best carried out in the solvent of choice for the EPD. This opens up new interests in the study of nonaqueous dispersion polymerization methods, which deliver polymer particles suspended in low dielectric constant solvents. We explore in this article the use of a poly(dimethylsiloxane) macromonomer for the stabilization of poly(methyl methacrylate) polymer particles in dodecane, a typical solvent of choice for EPDs. The use of this stabilizer is significant for this method as it is directly soluble in the reaction medium as opposed to traditionally used poly(12-hydroxystearic acid)-based stabilizers. Additionally, the present study serves as a baseline for subsequent work, where nonaqueous dispersion polymerization will be used to create polymer particles encapsulating liquid droplets and solid pigment particles. In this article, the influence of the macromonomer molecular weight and concentration on the properties of the synthesized particles is studied. In addition, we investigate the possibility of synthesizing polymer particles from other monomers both as a comonomer for methyl methacrylate and as the only monomer in the process. The influence of macromonomer concentration is also studied throughout all experiments.

Determining the Effective Density and Stabilizer Layer Thickness of Sterically Stabilized Nanoparticles

“…Steric stabilization is widely recognized to be the most important mechanism for achieving long-term colloidal stability. 1 , 2 Unlike charge stabilization, 3 it confers thermodynamic stability at relatively high solids, is tolerant of added salt in aqueous formulations, 4 and can be designed for a wide range of media, including both polar solvents 5 − 11 and non-polar solvents 12 − 21 as well as more exotic solvents such as supercritical carbon dioxide 22 − 27 or ionic liquids. 28 , 29 In view of these many advantages, steric stabilization is now used on an industrial scale across a wide range of commercial sectors.…”

The internal structure of poly(methyl methacrylate) latexes in nonpolar solvents

“…Poly(methyl methacrylate) (PMMA) latexes, originally developed through an industrial-academic collaboration between the University of Bristol and ICI [22,23], have proved an essential tool for colloid scientists to develop new technologies and study fundamental interactions in nonpolar media. These PMMA latexes are typically sterically-stabilized with poly(12-hydroxystearic acid) (PHSA) brushes, although there is active research into developing other effective steric stabilizers [8,[24][25][26][27][28]. They are generally dispersed in either n-alkanes or in mixed solvents to achieve density or refractive index matching (typically decalin and either brominated cycloalkanes or carbon disulfide) [29][30][31][32][33][34].…”

Investigating the Effectiveness of Reactive Dispersants in Non‐Aqueous Dispersion Polymerization

“…Unlike the homopolymer dispersants in the polar solvent systems (alcohol/water), early studies with natural rubber or polybutadiene dispersants in non‐aqueous dispersions led to gel formation at high conversions, leading to the utilization of random or block copolymers or macromers as steric stabilizers for non‐polar NADs. A commercial macromer, methacryloxypropyl terminated poly(dimethylsiloxane) has been applied to make narrow distributed poly(methyl methacrylate) (pMMA) particles of 0.5–2.0 microns in dodecane and in hexane; however, attachment of the dispersant to the particle surface was low, with only 10–20% of the dispersant added found attached to the particle surface despite the reactive end groups . Poly(12‐hydroxystearic acid) (pHS) functionalized with reactive double bonds is also used as a reactive dispersant; however, as it is not completely soluble in non‐polar solvents, the resultant polymer has also been reacted with MMA to form a comb (pHS‐g‐pMMA) copolymer in a multi‐step synthesis process .…”

“…A commercial macromer, methacryloxypropyl terminated poly(dimethylsiloxane) has been applied to make narrow distributed poly(methyl methacrylate) (pMMA) particles of 0.5–2.0 microns in dodecane and in hexane; however, attachment of the dispersant to the particle surface was low, with only 10–20% of the dispersant added found attached to the particle surface despite the reactive end groups . Poly(12‐hydroxystearic acid) (pHS) functionalized with reactive double bonds is also used as a reactive dispersant; however, as it is not completely soluble in non‐polar solvents, the resultant polymer has also been reacted with MMA to form a comb (pHS‐g‐pMMA) copolymer in a multi‐step synthesis process . This dispersant was then used to produce 500–700 nm pMMA particles in dodecane with up to 50 wt% solids content; in this case, it is hypothesized that the dispersant physically, rather than covalently, attaches to the particle surface …”

“…Although the above studies are relevant, the particle sizes are generally larger than those required for coatings applications, with the objective of many of the studies to synthesize micron‐sized particles with a very narrow size distribution for applications such as electrophoretic displays, support of biological materials, and for chromatographic applications . Thus, the research has little concern for optimizing the usage of the dispersant in the system and for robustly producing dispersions with high polymer content and controlled viscosity, of paramount interest for automotive coating applications.…”