Polystyrene seed latexes

Figure 19 The scanning electron micrographs of the polystyrene seed latex and the copolymer latices carrying carboxyl, hydroxyl and amine functional groups, (a) PS/PAA, (b) PS HEMA, (c) PS/PDMAEM. The original SEM photographs were taken with 10,000 x magnification and reduced at a proper ratio to place the figure. (From Ref. 93. Reproduced with the permission of John Wiley Sons, Inc.)...

The polystyrene seed latex was monodispersed. Even after several grow-ups (polymerizations) the final 1650 A latex was monodispersed. Hydrodynamic chromatography on the 1650 A latex gave a mean diameter of 1660 a with a size variance as small as for normal polystyrene latex standards (typical standard of 1760 8 with a standard deviation of 23 a). The final latex particle size could be accurately predicted from the initial particle size and the total amounts of monomer and polymer used. 

The present paper demonstrates that for polystyrene seed latexes and styrene-acrylic or all acrylic second stage monomers, complete association can take place when S>100%, if certain mixtures of anionic and nonionic surfactant are used. The morphology of some of the two-stage latexes is described. 

The particle size information for the latexes selected for structural characterization is shown in Table XIV. The homopolymer polystyrene seed latex was used to prepare the two-stage... 

It is noteworthy that a basic assumption made in the derivation of the free radical desorption rate constant is that the adsorbed layer of surfactant or stabilizer surrounding the particle does not act as a barrier against the molecular diffusion of free radicals out of the particle. Nevertheless, a significant reduction (one order of magnitude) in the free radical desorption rate constant can happen in the emulsion polymerization of styrene stabilized by a polymeric surfactant [42]. This can be attributed to the steric barrier established by the adsorbed polymeric surfactant molecules on the particle surface, which retards the desorption of free radicals out of the particle. Coen et al. [70] studied the reaction kinetics of the seeded emulsion polymerization of styrene. The polystyrene seed latex particles were stabilized by the anionic random copolymer of styrene and acrylic acid. For reference, the polystyrene seed latex particles stabilized by a conventional anionic surfactant were also included in this study. The electrosteric effect of the latex particle surface layer containing the polyelectrolyte is the greatly reduced rate of desorption of free radicals out of the particle as compared to the counterpart associated with a simple... 

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... 

Deionized water (720 g), sodium lauryl sulfate (4.3 g), dioctanoyl peroxide (40 g), and acetone (133 g) were emulsified using an ultrasonic probe for 10 minutes. The step 1 polystyrene seed (48.0 g seed, 578 g latex) was added to the emulsion together with lauryl sulfate (0.8 g) and acetone (29.6 g). The mixture was transferred to a flask and left to agitate at approximately 25°C for 48 hours. Acetone was then removed and the solution added to a 5-liter double-walled glass reactor. The temperature was increased to 40°C while styrene (336 g) and divinyl benzene (0.88 g) were added drop-wise over approximately 60 minutes. After 4 hours the mixture was treated with deionized water (1200 g), potassium iodide (1.28 g), and polyvinyl pyrrolidone (18.48 g) with the temperature increased to 70°C. The polymerization continued for 6 hours at 70°C and 1 hour at 90°C. Styrene-based oligomer particles with a diameter of 1.7 pm and with a narrow size distribution were obtained. 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

The technique involves first producing a seed latex by emulsifier-free emulsion polymerisation. A polystyrene latex of about 1 pva diameter is usually used. The seed particles are initially swollen using a microemulsion of a free radical initiator and a low molecular weight activating solvent , such as dibutyl phthalate, emulsified in water by sonication using sodium dodecyl sulphate as stabiliser. The seed... 

Kinetic results [11-13] The rate of styraiepolymerizaticm initiated by potassium persulfate in a monodisperse polystyrene (PS) seed latex (c. 200 run in diameter) was ctxistant from 0% up to 60% convositxi, while the monomer concentration in the particles decreased significantly. In order for the polymerization rate to remain constant while the total monomer concentration was halved, the monomer concentration at the site of polymerization must be constant. In terms of the Smith-Ewart theory. Case 2, the rate of polymerization per particle, / pp, is expressed as... 

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. 

The seed latexes used as the cores of the imprinted particles were prepared from hydrophilic or hydrophobic polymers. The hydrophilic seeds were prepared from methyl methacrylate and methyl methacrylate/ethyleneglycol dimethacrylate copolymers, while the hydrophobic seeds were composed of polystyrene or styre-ne/divinyl benzene copolymers. Hydrophilic- and hydrophobic-imprinted shells were then laid over these cores. It was found that the best cholesterol recognition was obtained with a hydrophilic-imprinted shell and a poly(methyl methacrylate) core. However, the performance deteriorated when the core was lightly cross-linked with ethyleneglycol dimethacrylate. In a second paper [10], imprinted polymers were prepared by the noncovalent approach with cholesterol rebinding relying upon hydrophobic interactions between cholesterol and the imprinted shell. To achieve this, the template was modified to give it the characteristics of a surfactant. The structure of the template surfactant is illustrated in Fig. 2. 

Acrylonitrile is also commonly found in impact modifiers, such as the acrylonitrile-butadiene-styrene (ABS) type, produced by emulsion polymerisation. Polybutadiene seed latex particles are grafted onto styrene and acrylonitrile in a seeded emulsion polymerisation process. As the styrene-acrylonitrile copolymer shell forms, polybutadiene domains are spontaneously separated within. The resulting impact modifier particles are subsequently compounded with polystyrene to product high impact polystyrene (HIPS). The impact modification properties of the latex particles may be optimised through varying the butadiene content, the particle size and structure, and the shell molecular weight. A basic formulation for an ABS impact modifier is given in Table 6. 

Ryan and Crochowski teach the use of acrylic latex IPNs dispersed in PVC copolymers to produce transparent, impact-resistant vinyls (see Table 8.1). A three-stage polymerization of the latex particles is required. A crosslinked rubbery latex such as poly(butyl acrylate) makes up the seed latex. A crosslinked vinyl aromatic, such as polystyrene, makes up network II. A linear poly(alkyl methacrylate), such as PMMA, forms polymer III. The finished latex is coagulated and blended with PVC to produce a tough, transparent plastic. Transparency is achieved by a close match of refractive indices. 

CuCl/CuCl2/bpy as the catalyst. The ATRP initiator layer on the surface of polystyrene particles was prepared by seed emulsion polymerization of 2-(2-bromoisobutyryloxy) ethyl methacrylate (BIEM) using polystyrene (PS) latex as seeds. 

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