Morphological behavior of bi-component polymeric particles with dioctyl phthalate plasticizer

Abstract

Two-phase copolymers containing styrene-acrylate were synthesized with a soft phase consisting of methyl acrylate, butyl acrylate, or butyl methacrylate. Besides the styrenic copolymers, the copolymers containing a hard phase of methyl methacrylate were also synthesized. Comonomer droplets with a narrow size distribution were prepared using Shirasu Porous Glass (SPG) membrane having pore size 0.51 or 0.90 um. After a single-step SPG emulsification, the emulsion droplets composing mainly of monomers, hydrophobic additives, and an oil-soluble initiator were suspended in the aqueous phase containing a stabilizer and an inhibitor. It was then transferred to a reactor, and subsequent suspension polymerization was carried out. Uniform copolymer particles poly(styrene-co-acrylate)s with a mean diameter ranging from 3 to 10 ?m with a narrow particle size distribution or a coefficient of variation close to 10% were achieved depending on comonomer compositions and the recipe. The glass transition temperature measured by differential scanning calorimetry indicated that the resulting copolymer particles contained a soft phase of methyl acrylate compatibilized better with a hard phase of methyl methacrylate than styrene with dioctyl phthalate addition. Glass transition temperatures of poly[(methyl methacrylate)-co-(methyl acrylate)] particles were strongly affected by the composition drift in the copolymer caused by their high difference in reactivity ratio. Incorporation of dioctyl phthalate in the copolymer particles did not significantly affect the glass transition temperature of methyl methacrylate- or methyl acrylate-containing copolymer particles, but it did affect the styrene-containing copolymer and particle morphology of the copolymers observed by TEM technique. Incorporation of a long-side chain monomer such as butyl methacrylate or butyl acrylate in copolymerizing with styrene was more effective plasticized than that adding an external plasticizer like dioctyl phthalate. The particle morphologies were also controlled by the addition of low-molecular weight polystyrene. When viscosity of the dispersion phase was high, different morphologies such as core-shell or salami structure were observed. The film formation of copolymer and their surface morphology were studied by microscopic techniques.