Suspension technique

Emulsion polymerisation represents the next stage in development from the suspension technique and is a versatile and widely used method of polymerisation. In this technique droplets of monomer are dispersed in water with the aid of an emulsifying agent, usually a synthetic detergent. The detergent forms small micelles 10-100 /im in size, which is much smaller than the droplets that can be formed by mechanical agitation in suspension polymerisation. These micelles contain a small quantity of monomer, the rest of the monomer being suspended in the water without the aid of any surfactant. 

As emulsion polymerisation proceeds, like the suspension technique but unlike either the bulk or the solution techniques, there is almost no increase in viscosity. The resulting dispersed polymer is not a true emulsion any more, but instead has become a latex. The particles of the latex do not interact with the water hence viscosity is not found to change significantly up to about 60% solids content. 

Fluidized beds, in general, and the air-suspension technique patented by Wurster, in particular, now offer an attractive alternative to pan coating. The basic principle underlying their operation is to suspend the... 

Wurster, D.E., Air-suspension technique of coating drug particles a preliminary report, /. Am. Pharm. Assoc., 48 (1959) 451-454. 

Polymerization reactions were principally conventional emulsion types, although solution, bulk, or suspension techniques may also be used. 

The predominant method used to prepare a crosslinked polymer support is to polymerize a monovinylcompound with a small amount of a divinylcompound by radical initiators. This enables the use of suspension techniques and spherical particles are therefore available. 

There are two basic laboratory methods for the preparation of filter standards--dust generation and the liquid suspension technique. Dust generation has a distinct advantage because of the ability to produce atmospheres similar to the workplace which can then be... 

Haartz, Bolyard and Abell ( 3.) used atomic absorption spectrophotometry to check filter standards prepared by the suspension technique Zinc oxide was "spiked" on DM-800 filters and quantitated by AAS and XRD Results from these measurements are shown in Table II, An average deviation of 2 1% was found between the two techniques. Although this data does give a considerable degree of confidence to the use of the suspension procedure for standards preparation, additional data for other analytes is needed for conclusive proof. 

Although the suspension technique may be useful in extending drag release under certain conditions, it is only applicable to drags that are practically insoluble in water, such as corticosteroids. For drags that are somewhat water-soluble, the particulate approach may be considered. 

Mathir, Z. M., Dangor, C. M., Govender,T., and Chetty, D. J. (1997), In vitro characterization of a controlled-release chlorpheniramine maleate delivery system prepared by the air-suspension technique, / Microencapsul., 14,743-751. 

Deasy, R B. (1991), Microencapsulation of drugs by pan and air suspension techniques, Crit. Rev. Ther. Drug Carrier Syst., 8, 39-89. 

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. 

At first glance, radical polymerization may be considered a mature technology with millions of tons of vinyl based homo- and copolymers being produced annually. This perception of maturity is based on the fact that free radical polymerization is so widely used industrially and in research laboratories for the synthesis of a wide variety of polymeric materials. This widespread adoption is due to its versatility, synthetic ease, and compatibility with a wide variety of functional groups, coupled with its tolerance to water and protic media. These features make possible the development of emulsion and suspension techniques, which greatly simplifies the experimental set up and has led to wide commercial adoption. 

Bulk Macroporous Polymers (DVB-50-B-T, DVB-50-B-A). Comparison of DVB-50-B-T with DVB-50-S-T reveals there is little difference between polymers prepared in bulk and by suspension techniques. Both materials, prepared with toluene as cosolvent, reveal fluorescence quenching traces that are almost superimposable. There is, however, a very dramatic difference between material prepared by bulk polymerization using different cosolvents. Polymer DVB-50-B-T reveals a large fraction of all sites are quenched within 15 sec (Figure 6), a small tail on this curve indicates a component (<5%) of inaccessible sites. In contrast, the material prepared with... 

It was concluded that the suspension technique was good for fast screening of chemical instability. The other solid state procedures were found to be better predictors of the solid dosage form. 

Rather conventional means for the manufacturing of hollow microspheres with diameters between 1 and 1000 pm have been developed [11.9]. Methods include spray drying and dripping as well as emulsion or suspension techniques. The microspheres feature low effective and bulk densities coupled with high specific surfaces. Typical wall thicknesses are in the range 1-10% of the diameter. Potential wall materials include glass, ceramic and mixed oxides, silicates and aluminosilicates, polymers and polycondensates, and metals. Surface phenomena, which may be modified by chemical reactions, additives, and/or post-treatments, play an important role for microsphere formation, properties, and stability. Fig. 11.12 is the photomicrograph of a calcined hollow microsphere [11.9]. 

The effect of catalyst heat treatment on the spectra of amines adsorbed on silica-alumina catalysts was examined by Okuda and Tachibana (15) employing the suspension technique. Two bands were observed with benzeneazodiphenylamine. The band at 4400 A was attributed to the basic form of the dye, while that at 5380 A to the conjugate acid formed by reaction of the basic dye either with a proton or with an aluminum... 

Graft Polymerization of Styrene (9). Polymerization was effected by the mass-suspension technique under nitrogen. The radical initiator was added to the rubber solution in styrene, with tert-dodecyl mercaptan being added either simultaneously or later during the polymerization. For prepolym-... 

Recently an improvement in this separation technique was reported, which seemed to indicate that enantioselective inclusion in the lattices of chiral hosts could be employed on a large scale. [11] When crystalline hosts such as R,R)-(-)-S (m.p. 196 °C), [12] (/ ,/ )-(-)-9 (m.p. 165 °C), [12] and (5,5)-(-)-10 (m.p. 128 °C) are suspended in hexane or water, chiral guest molecules form the same inclusion compounds as from solution. This is by no means self-evident, since inclusion compounds have different crystal lattices than the pure host crystals. Thus crystal/liquid reactions occur, and phase rebuildings analogous to those observed in gas/solid reactions [13] must take place. Yet this suspension technique is more selective and more effective than the initially developed solution technique. Numerous racemic alcohols like 11, -hydroxy esters like 12, epoxy esters like 13, and epoxy ketones like 14 were stirred a few hours with appropriate hosts (suspensions of 8, 9, and 10) and formed 1 1 complexes that could be filtered off in yields of > 85 % and with ee values of > 97 % (the complex of 12 and 9 formed in hexane only 80% ee in one step). Recrystallization of the inclusion... 

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