Polystyrene seed particles

Step II Swelling of polystyrene seed particles with CDD... 

Seeded polymerization using a slight amount of monomer leads to the surface modification without changing particle size. The resulting particles are a kind of core-shell particles or, more exactly, core-skin particles (Fig. 12.2.4C). Seeded polymerization of sugar-units-containing styrene derivative on polystyrene seed particle was carried out to obtain latex particles covered with sugar units (17). A necessary condition for this is that the monomer is more hydrophilic than the seed polymer. If not, the monomer permeates into the seed particle and only a small fraction remains on the... 

Rate of Swelling of Polystyrene Seed Particles by Toluene... 

The dynamic swelling method (DSM) [10] has also been described for the preparation of crosshnked microspheres with free vinyl groups [78]. Therefore, polystyrene seed particles (1.9 pm) prepared by dispersion polymerization are dispersed in ethanol-water (7/3, w/w) containing divinylbenzene (DVB), benzoyl peroxide, and poly(vinyl alcohol) (PVA). The slow drop-wise addition of water to the mixture causes the DVB phase to separate, and it is continuously imbibed by seed particles to produce relatively large swollen particles (4.3 pm), which are then polymerized to afford the respective PS-PDVB composite particles with free vinyl groups. DSM has recently been developed in order to prepare hohow microspheres and various oddly-shaped polymer particles, including a rugby ball, red blood cells, or snowman structures [79-83]. 

Later, Hosoya et al. 1931 prepared monodisperse polymer-based CSPs from chiral methacrylamides by co-polymerization onto the surface of polymeric particles. These are synthesized by a staged templated suspension polymerization using a two-step swelling method starting from polystyrene seed particles of 1 pm size used as shape templates, onto which methyl methacrylate and later the chiral methacrylamide is co-polymerized. 

The method of preparing superparamagnetic particles developed by Charmot [109] uses hydrophobic non-porous polystyrene seed particles of narrow size distribution. A seeded polymerization is carried out to increase the particle size (1.35 pm) and a terpolymer is formed around the seed particles by a dispersion polymerization of styrene, DVB and 4-vinylpyridine in toluene. The toluene containing cobalt precursor swells the latex particles, which results in a homogeneous distribution of the metal precursor. A thermolysis reaction is conducted in the presence of 4-vinylpyridine, and the release of carbon monoxide indicates the decomposition of the metal salt into cobalt. The main problem of this method is the particle surface deformation during the evolution of carbon monoxide. The amount of crosslinker, however, cannot be reduced below a certain level without significantly modifying the properties of the particles. 

Fig. 8. Scanning electron micrograph showing the 2 ym polystyrene seed particles protruding from the surface of 10 ym poly(styrene (80 %)/methacrylic acid (20 %)) particles.

Fig. 9. Scanning electron micrograph illustrating the expulsion of 1 jam polystyrene seed particles from 4.2 ym poly(methyl methacrylate (73 %)/hydroxethyl methacrylate (20 %)/ethylene glycol dimethacrylate (7 %)) particles.

Figure 8.2. Profiles of the calculated average number of free radicals per particle (n, or n ) as a function of monomer conversion for the experiment at SCC with the weight fractions of polystyrene seed particles (154nm in diameter), the second-stage monomer (methyl methacrylate), and the weight fraction of initiator (potassium persulfate) equal to 0.06, 0.09, and 9.62 X 10 , respectively.

A somewhat different approach is where an organic solvent is used to extract to core material. In one example (Okubo etal, 1991 Okubo Nakagawa, 1994) large polystyrene seed particles, produced by dispersion polymerisation, are used as a seed in a second stage polymerisation where a shell of polystyrene-divinylbenzene was polymerised around the core. The core material was then extracted with toluene under reflux. Depending on the... 

Figure 9.15 Monodisperse polystyrene latexes prepared by reverse recondensation method (A) 1.5 pm polystyrene seed particles, (B) 5.2 pm, (C) 7.5 pm, (D) 10.2 pm particles swelled from (A) particles (Reproduced by permission of Elsevier Science from ref. 87)...

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