Emulsions radical polymerization

The red-luminescence (612 nm) europium complex is an excellent luminescer in commercial use however, the green-luminescence Tb +-cored dendrimer complex enables a simultaneous assay at another wavelength (545 nm). The latex formation was carried out by mini-emulsion radical polymerization of the monomers dissolving the Tb +-cored dendrimer complexes. The polymeriza-... 

Detailed studies were performed on the copper-catalyzed suspension or emulsion polymerizations.249 Living or controlled emulsion radical polymerization of nBMA can be achieved in the presence of nonionic poly(oxyethylene)-based surfactants such as Brij 97, Brij 98, and Tween 20 with the F21 (X = Br)/CuBr/ L-3 or L-4 system.249,251,252 The Mn increased in direct proportion to monomer conversion up to 5 x 104 (MJ Mn = 1.1 —1.2). The particle sizes are around 1000— 4000 nm, suggesting a suspension, but can be reduced to about 300 nm with the use of hexadecane as a cosurfactant along with ultrasonication.249 252... 

The so-called reverse atom-transfer radical polymerization is feasible in aqueous emulsion too. This system enables the formation of initiating radical species in the water phase with the use of water-soluble initiators such as 1-39, 1-40, and 1-41 as in conventional emulsion radical polymerization.184,249,252,255 The copper-catalyzed emulsion radical polymerization of nBMA afforded polymers with narrow MWDs (MJMn = 1.1—1.4), but the Mn values were much higher than the calculated values due to the termination between the initiating radicals in the aqueous phase.184,255 The emulsions are relatively stable and their particle sizes are around 100—300... 

ORGANIC COATINGS BASED ON ACRYLIC LATICES. I. LATEXES PREPARATION BY EMULSION RADICAL POLYMERIZATION. PROCESS THEORY... 

Methods and Processes of Polymerization. For economic reasons, only emulsion radical polymerization at 40°C is utilized for its production this relatively low temperature leads to both a high content in 1,4-trans units and a low content in polymeric gel (resulting from side reactions). The initiators utilized are redox systems. 

There is a great deal more that could be said about emulsion polymerization or, for that matter, about free-radical polymerization in general. We shall conclude our discussion of the free-radical aspect of chain-growth polymerization at this point, however. This is not the end of chain-growth polymerization, however. There are four additional topics to be considered ... 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Vlayl fluoride undergoes free-radical polymerization. The first polymerization iavolved heating a saturated solutioa of VF ia tolueae at 67°C uader 600 MPa (87,000 psi) for 16 h (24). A wide variety of ioitiators and polymerization conditions have been explored (25—27). Examples of bulk (28,29) and solution (25,28,30,31) polymerizations exist however, aqueous suspension or emulsion methods are generally preferred (26,32—40). VF volatiflty dictates that moderately high pressures be used. Photopolymerizations, usually incorporating free-radical initiators, are also known (26,28,29,35). 

There are two problems in the manufacture of PS removal of the heat of polymeriza tion (ca 700 kj /kg (300 Btu/lb)) of styrene polymerized and the simultaneous handling of a partially converted polymer symp with a viscosity of ca 10 mPa(=cP). The latter problem strongly aggravates the former. A wide variety of solutions to these problems have been reported for the four mechanisms described earlier, ie, free radical, anionic, cationic, and Ziegler, several processes can be used. Table 6 summarizes the processes which have been used to implement each mechanism for Hquid-phase systems. Free-radical polymerization of styrenic systems, primarily in solution, is of principal commercial interest. Details of suspension processes, which are declining in importance, are available (208,209), as are descriptions of emulsion processes (210) and summaries of the historical development of styrene polymerization processes (208,211,212). 

Free-Radical Polymerization. The best method for polymerising isoprene by a free-radical process is emulsion polymerisation. Using potassium persulfate [7727-21-1] as initiator at 50°C, a 75% conversion to polyisoprene in 15 h was obtained (76). A typical emulsion polymerisation recipe is given as follows (77). 

An emulsion polymerization reaction follows three conventional steps, namely, initiation, propagation, and termination. These steps can be described by the conventional reactions that are valid for any free radical polymerization. Smith and Ewart [10] proposed that a forming latex particle in an ideal emulsion polymeriza-... 

Water is extensively used to produce emulsion polymers with a sodium stearate emulsifrer. The emulsion concentration should allow micelles of large surface areas to form. The micelles absorb the monomer molecules activated by an initiator (such as a sulfate ion radical 80 4 ). X-ray and light scattering techniques show that the micelles start to increase in size by absorbing the macromolecules. For example, in the free radical polymerization of styrene, the micelles increased to 250 times their original size. 

Polymerization, including radical polymerization, in supercritical C02 has been reviewed.1 6 137 It should be noted supercritical C()2 while a good solvent for many monomers is a very poor solvent for polymers such as the (meth)acrylates and S. As a consequence, with the exception of certain fluoropolymers and polymerizations taken to very low conversion, most polymerizations in supercritical CCb are of necessity precipitation, dispersion or emulsion polymerizations. 

Vinyl chloride Free radical polymerization in bulk or emulsion rapid in presence of peroxides susceptible to photochemical polymerization —CH2—CH— 75 Largely amorphous, except when highly oriented by stretching. Hard. Soluble in ketones and esters... 

Chemical methods for structure determination in diene pol3 mers have in large measure been superseded by infrared absorption techniques. By comparing the infrared absorption spectra of polybutadiene and of the olefins chosen as models whose ethylenic structures correspond to the respective structural units, it has been possible to show that the bands occurring at 910.5, 966.5, and 724 cm. are characteristic of the 1,2, the mns-1,4, and the m-1,4 units, respectively. Moreover, the proportion of each unit may be determined within 1 or 2 percent from measurements of the absorption intensity in each band. The extinction coefficients characteristic of each structure must, of course, be known these may be assigned from intensity measurements on model compounds. Since the proportions of the various units depend on the rates of competitive reactions, their percentages may be expected to vary with the polymerization temperature. The 1,2 unit occurs to the extent of 18 to 22 percent of the total, almost independent of the temperature, in free-radical-polymerized (emulsion or mass) poly butadiene. The ratio of trans-1,4 to cfs-1,4, however,... 

Morton and Salatiello have deduced the ratio kpp/kp for radical polymerization of butadiene by applying the above described procedure, appropriately modified for the emulsion system they used. The primary molecular weight was controlled by a mercaptan acting as chain transfer agent, as in the experiments of Bardwell and Winkler cited above. Measurement of the mercaptan concentration over the course of the reaction provided the necessary information for calculating % at any stage of the process, and in particular at the critical conversion 6c for the initial appearance of gel. The velocity constant ratios which they obtained from their results through the use of Eq. 

Free-radical polymerization of alkenes has been carried out in aqueous conditions.115 Aqueous emulsion and suspension polymerization is carried out today on a large scale by free-radical routes. Polymer latexes can be obtained as products (i.e., stable aqueous dispersions... 

Capek, I. and Chern, C.-S. Radical Polymerization in Direct Mini-Emulsion Systems. Vol. 155, pp. 101-166. 

The principle free radical polymerization techniques are bulk, solution, suspension, and emulsion. Tables 6.5 and 6.6 briefly describe these techniques. 

Working in emulsion is essentially limited to radical polymerization in water. Similar to suspension polymerization, the basic principle is to disperse a sparingly water-soluble monomer in water and bring about polymerization in this state. There are, however, some essential differences between the two procedures ... 

The purification procedures to be applied depend on the monomer, on the expected impurities, and especially on the purpose for which the monomer is to be employed, e.g., whether it is to be used for radical polymerization in aqueous emulsion or for ionic polymerization initiated with sodium naphthalene. It is not possible to devise a general purification scheme instead the most suitable method must be chosen in each case from those given below. A prerequisite for successful purification is extreme cleanliness of all apparatus (if necessary, treating with hot nitrating acid and repeatedly thorough washing with distilled water). 

The spectra may first be evaluated qualitatively.The polyisoprene prepared in solution shows a pronounced band at 888 cm which indicates a high proportion of 3,4-link-ages. For the product of bulk polymerization this band is much reduced in favor of absorptions at 1127 and 1315 cm indicating predominantly c/s-1,4-linkage of the monomeric units in this case.The polymer made by radical polymerization in emulsion (see Example 3-12) shows the presence of all possible structural units,although the proportion of c/s-1,4-linkages is low. 

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