Synthesis of core-shell PS/PMMA expandable particles via seeded suspension polymerization

Abstract

Expandable core-shell beads were synthesized by dosing methyl methacrylate (and styrene) in a constant rate and polymerizing in the presence of polystyrene seeds and pentane. The morphological studies of beads indicated that there were larger poly(methyl methacrylate)-rich domains near the shell. The sizes of these domains were decreased towards the core of the particles. For better surveying the likely structures of domains and the extent of expansion agent diffusion, the beads having the shells formed with copolymerization of styrene and methyl methacrylate in the presence of polystyrene seeds were studied. From the morphological studies, the parallel regular and the onion-like structures were recognizable. In addition, another shell was formed around the dispersed phase showing a complex core/shell structure both in particle and in domain scales. The pentane content in the beads with copolymerized styrene and methyl methacrylate monomers on the polystyrene seeds was increased compared to the beads having the shells of pure poly(methyl methacrylate). This was because the onset of gel effect was longer with adding the styrene to methyl methacrylate monomer hence there was more time for expansion agent to diffuse into the beads. The different amounts of pentane distributed in polystyrene-and poly(methyl methacrylate)-rich phases were discussed in terms of the changes in glass transition temperature of two phases.

Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers

“…The high magnification SEM images provided information about the change of the microspheres' surfaces after the seeded polymerization process. This result is in accordance with the literature [1,15,18] . These surfaces are characteristic of non-porous shells.…”

Chemical resistance of core-shell particles (PS/PMMA) polymerized by seeded suspension

“…Moreover, the presence of PMMA at the surface seems to hinder particle expansion, and a non-uniform foamed particle was obtained. This result is in agreement with a more recent study published by Heydarpoor et al [10] . The authors investigated similar systems of PS/PMMA core-shell expandable particles, by using pentane as the expansion agent.…”

“…Previous studies showed that this kind of morphology was expected [8,10] . This occurred because the polymerization rate is much faster than the diffusion of PMMA/MMA in the swollen PS particles.…”

“…In addition to typical peaks from PS and PMMA homopolymers, a new peak appears at 2.9 ppm. This signal is commonly assigned to O-CH 3 sites bonded to PS sequences [10,12] , which proves that a copolymerization reaction is taking place. By using the integrated area of the peak centered at 2.9, the percent of copolymer formed for synthesis route 1 and 2 were determined to be 1 and 6 mol% respectively.…”

Insight into the structure of polystyrene-poly(methyl methacrylate) core-shell particles synthesized by seeded suspension polymerization

“…It was reported that the average molecular weight of PMMA in core-shell particles is almost 5 times higher than the PMMA obtained in unseeded batch suspension polymerization due to high polymer concentration and diffusional limitations (gel effect) that take place from the beginning of the second step of polymerization, decreasing the termination rate. 4 Therefore, the high-molecular-weight PMMA synthesized in the second step of polymerization needed more time to be completely extracted.…”