Formation mechanism of silicone rubber particles with core-shell structure by seeded emulsion polymerization

Abstract

SYNOPSISSilicone rubber particles with core-shell structure were prepared by polymerization of vinyl monomers in the presence of crosslinked and linear poly(dimethy1 siloxane-methyl vinyl siloxane) latex. The monomers were added with either continuous or swelled-continuous addition mode. The core-shell morphology of silicone rubber/polystyrene [PST] and silicone rubber/poly(methyl methacrylate-divinyl benzene) [P(MMA-DVB)] composite particles were obtained. The effects of monomer addition mode, the compatibilities of the monomers or their homopolymer with silicone rubber, and the reactivity of polysiloxane with vinyl monomers on the formation of the core-shell structure were discussed. 0 1996 John Wiley & Sons, Inc. I NTRO DU CTI 0 NSince core-shell particles have plenty of applications, such as the toughening and strengthening of plastics,'-3 preparation of core-shell particles by seeded emulsion polymerization has been attracting great interest among researchers. Thus, a tremendous progress in this field has been achieved.The factors influencing the formation of coreshell particles have been extensively studied. The crucial factor is thermodynamics, which determines the formation of the core-shell or inverted coreshell s t r~c t u r e .~ Kinetic factors, such as diffusion re~triction,~ seeded emulsion polymerization rate6 and addition mode of monomers: are very important in the morphology formation of the obtained particles. However, most of the researches concentrated on the poly(meth)acrylate systems.In our previous work, we reported the preparation of the core-shell particles of silicone rubber/PMMA and silicone rubber/PGMA using one-stage method? The compatibility of vinyl monomer with silicone rubber and the reaction rate between vinyl monomers and Si-H of silicone oils affected greatly the morphology and the content of vinyl polymers in the surface layer of the obtained particles.

Preparation and characterization of core–shell polystyrene–polydimethylsiloxane particles by seeded polymerization

“…In this present work, B represents polydimethylsiloxane while A is polystyrene. According to the data reported by He et al 10, γ aw = 19.61, γ bw = 29.22 and γ ab = 2.89 dyn cm −1 , and so we can resolve the simultaneous inequalities and find that the inequality only when V b > 0.525 given by Equation (9) is tenable. However, it is impossible to satisfy this inequality since $V_{\rm a}^{2/3} - V_{\rm b}^{2/3}$ is within the range −1 to +1, while (γ aw − γ bw )/γ ab = 3.32.…”

“…We think that this is due to the high emulsifier concentration (6.67 %, relative to the amount of monomer) and the higher rate of gamma‐ray‐induced initiation when compared to chemical initiation: this produces a large number of nucleation points at the beginning of polymerization, which also results in a much smaller particle size than those obtained when employing chemical initiation. In addition the free radical yield produced from styrene was very small relative to the radicals produced from water, plus the concentration of styrene in water is very small (about 0.16 %);10 hence, there may be little homogeneous nucleation. The hydrophilicity of styrene also contributes to the narrow distribution of the latex particles because of the difficulty of monomer transfer from the droplets to the existing particles.…”

“…Composite core–shell particles are important in coatings and adhesives, impact‐resistance plastics and many other areas. Most of the research has focused on methyl methacrylate (MMA), butyl acrylate (BA), styrene (St), vinyl acetate (VAc), butadiene and N ‐isopropylacrylamide,1–7 with only a few reports available on siloxanes,8–11 in particular, polysiloxanes as the shell material.…”

Preparation and characterization of core–shell polystyrene and polymethylsilsesquioxane structure latex particles by seeded polymerization

“…Most research has been focused on methyl methacrylate, butyl acrylate, styrene (St), vinyl acetate, butadiene, N ‐isopropylacrylamide 1–7. Only a few reports are available concerning siloxanes in such systems,8–11 especially with polysiloxane as the shell.…”

Polydimethylsiloxane latexes and copolymers by polymerization and polyaddition in miniemulsion

“…As PDMS has only a low mechanical performance by itself, the PDMS is usually blocked or grafted with polyacrylates/polystyrene, giving core-shell latexes [5][6][7]. Polyurethane-polydimethylsiloxane particles of diameters in the range 500 nm up to 5 mm, have been also recently synthesized by step-growth polymerization in cyclohexaneor supercritical carbon dioxide [8].…”