Polymerization emulsion homopolymerization

Continuous polymerization systems offer the possibiUty of several advantages including better heat transfer and cooling capacity, reduction in downtime, more uniform products, and less raw material handling (59,60). In some continuous emulsion homopolymerization processes, materials are added continuously to a first ketde and partially polymerized, then passed into a second reactor where, with additional initiator, the reaction is concluded. Continuous emulsion copolymerizations of vinyl acetate with ethylene have been described (61—64). Recirculating loop reactors which have high heat-transfer rates have found use for the manufacture of latexes for paint appHcations (59). 

It is clear from Eq. 1 that the monomer concentration in a polymer particle is one of the three key factors that control the particle growth rate, and accordingly, the rate of polymerization. In emulsion polymerization, the course of emulsion polymerization is usually divided into three stages, namely. Intervals I, II and III. In Intervals I and II of emulsion homopolymerization, the monomer concentration in the polymer particles is assumed to be approximately constant. In Interval III, it decreases with reaction time. Two methods are now used to predict the monomer concentration in the polymer particles in emulsion homopolymerization empirical and thermodynamic methods. 

Massebeuf, S., Fonteix, C., Hoppe, S. and Pla, F. (2003). Development of new concepts for the control of polymerization processes multiobjective optimization and decision engineering. I. Application to emulsion homopolymerization of styrene, J. Appl. Polym. Sci, 87, pp. 2383-2396. 

Open-loop control strategies were developed and implemented to allow for reduction of transition times during grade transitions in continuous high-impact styrene polymerizations [61]. Similar strategies were also used to control the MWDs in emulsion homopolymerizations and to control the copolymer composition and the MWDs simultaneously in non-hnear emulsion polymerizations [36,37,182]. 

Seeded emulsion polymerization can be used with batch, semi-continuous, or continuous polymerization to give the desired value of N, In batch or semi-continuous emulsion polymerization, seeding ensures batch-to-batch reproducibility of the final particle size in continuous emulsion polymerization, it ensures the reproducibility, not only of the final particle size, but also of the conversion of the exit stream. Seeded emulsion polymerization is equally adaptable to emulsion homopolymerization and copolymerization. Moreover, two-stage or multiple-stage polymerizations can be used to produce core-shell latex particles the variation of the process type---batch, semi-continuous, continuous----as well as the para-... 

Divinylbenzene is easily radically polymerized or cationically polymerized thus it is necessary to store or ship it in small quantities and add a large amount of polymerization inhibitor. Homopolymerized or copolymerized with vinyl polymers. Forms a reactive microgel with double bonds by emulsion polymerization. 

Sajjadi [85] investigated the diffusion-controlled nucleation and growth of particle nuclei in the emulsion homopolymerizations of styrene and methyl methacrylate. The polymerization starts with two stratified layers of monomer and water containing surfactant and initiator, with the water layer being stirred gently. In this manner, the rate of transport of monomer becomes diffusion-limited. As a result, the rate of growth of particle nuclei is reduced significantly, and more latex particles can be nucleated in emulsion polymerization. 

The Smith and Ewart-Stockmayer-O Toole treatments [48-50] (see Chapter 4) that are widely used to calculate the average number of free radicals per particle (n) are based on the assumption that the various components of the monomer-swollen latex particles (e.g., monomer, polymer, free radicals, chain transfer agent, etc.) are uniformly distributed within the particle volume. A latex particle in emulsion homopolymerization of styrene involves uniform distribution of monomer and polymer within the particle volume except perhaps for a very thin layer near the particle surface. In the case of free radicals, this uniform distribution would only hold in a stochastic sense. However, as illustrated in Eq. (8.1), free radicals are not distributed uniformly in the latex particles when water-soluble initiators are used to initiate the free radical polymerization. The assumption of uniform distribution of free radicals in the latex particles would be valid only if the particles are very small or chain transfer reactions are the dominate mechanism for producing free radicals. If such a nonuniform free radical distribution hypothesis is accepted, the very basis of the Smith and Ewart-Stockmayer-O Toole methods might be questioned. Despite this potential problem, the Stockmayer-O Toole solutions for the average number of free radicals per particle have been used for kinetic studies of many emulsion polymerization systems. The theories seem to work reasonably well and have been tested extensively with monomers such as styrene. 

Emulsion homopolymerization or copolymerization of MMA is usually carried out in a pressurized batch reactor with a water-soluble initiator and surfactant. The polymerization temperature may be varied from 85 C to 95 C to achieve high conversion. Bacterial attack, common in acrylic polymer... 

Different approaches are used to prepare polymer particles with attaching to surface-functionalized groups. In majority of the cases, they consist of step-batch or -semibatch polymerizations in dispersed media, being among them pulsion polymerization (emulsifier-free or not) the most used polymerization process (i) emulsion homopolymerization of a monomer containing the desired functional group (functionalized monomer), (ii) emulsion copolymerization of styrene (usually) with the functionalized monomer, (iii) seeded copolymerization to produce composite functionalized latexes, and (iv) surface modification of preformed latexes. 

Polymerization takes place, in the following manner in the presence of suitable peroxide catalyst these compounds polymerize with themselves (homopolymerizatiOn) in aqueous emulsion. When the reaction is complete, the emulsified polymer may be used directly or the emulsion coagulated to yield the solid polymer (312). A typical polymerization mixture is total monomer (2-vinylthiazole), 100 sodium stearate, 5 potassium persulfate, 0.3 laurylmercaptan, 0.4 to 0.7 and water, 200 parts. 

Copolymerization is effected by suspension or emulsion techniques under such conditions that tetrafluoroethylene, but not ethylene, may homopolymerize. Bulk polymerization is not commercially feasible, because of heat-transfer limitations and explosion hazard of the comonomer mixture. Polymerizations typically take place below 100°C and 5 MPa (50 atm). Initiators include peroxides, redox systems (10), free-radical sources (11), and ionizing radiation (12). 

The resulting complexes can be effectively employed as single component catalysts to homopolymerize ethylene or copolymerize ethylene with acrylates [50, 51] and a variety of other polar monomers including vinyl ethers, [51,52] vinyl fluoride [53], iV-vinyl-2-pyrrolidinone, and AMsopropylacrylamide [54], In fact, the resulting catalysts are so robust that they can be used as single component catalysts in aqueous emulsion homo-polymerization of ethylene and copolymerization of ethylene with norbomenes and acylates [55]. 

As already discussed for homopolymerization, radical copolymerizations can be carried out in bulk, in solution, and in dispersion. The composition of the copolymer obtained in suspension or emulsion may be different from that obtained by polymerization in bulk or solution if one of the monomers is more soluble in water than the other. In such a case the composition of the monomer mixture in the organic phase, or in the micelles where the copolymerization takes place, is not the same as the original composition. 

Homopolymerization. The free-radical polymerization of VDC has been carried out by solution, slurry, suspension, and emulsion methods. Slurry polymerizations are usually used only in the laboratory. The heterogeneity of the reaction makes stirring and heat transfer difficult consequently, these reactions cannot be easily controlled on a large scale. Aqueous emulsion or suspension reactions are preferred for large-scale operations. The spontaneous polymerization of VDC, so often observed when the monomer is stored at room temperature, is caused by peroxides formed from the reaction of VDC with oxygen, fery pure monomer does not polymerize under these conditions. Heterogeneous polymerization is characteristic of a number of monomers, including vinyl chloride and acrylonitrile. 

The homopolymerization of DADMAC is possible in several organic solvents such as acetone, l-methyl-2-pyrrolidone, tetramethylurea, or dimethylform-amide. Various initiation methods including radical, ionic, or x-ray induced polymerization have been employed [19]. Since the monomer solubility is limited in these solvents, and the resulting homopolymer is soluble only in water, methanol and acidic acid, the polymerization in aqueous solutions are preferred. Polymerization in both homogeneous and heterogeneous systems have been studied and the kinetics and mechanisms were investigated in aqueous solution and in inverse-emulsion [6-16,52,53]. 

Figure 1. Styrene homopolymerization— limiting conversions (Equations 1 and 2 with parameters Tgp = 93.5°C Tym = -88.2°C atp = 0.48 X lO C 1 am = 1.0 X 10 3oC 1). Experimental limiting conversions (bulk, suspension, and emulsion polymerization)—(O) present data (%)from Ref. 12.

Maleate Surfmers. Surfmers with allylic, acrylic and vinylic moieties tend to homopoly-merize and produce water-soluble polyelectrolytes if used above their CMC. This has shifted researchers attention to maleic derivatives that do not homopolymerize at normal temperatures because their ceiling temperature is too low. Tauer and co-workers have pioneered the synthetic work [4,15] which led originally to compounds like those given in Figure 6.49. An example of maleic-derived Surfmer used in emulsion polymerization lattices is reported in [16] and the advantages provided in commercial paint formulations are discussed later. 

Homopolymerization. The free-radical polymerization of VDC has been carried out by solution, slurry, suspension, and emulsion methods. 

Usually or most widely applied, polymer latexes are made by emulsion polymerization [ 1 ]. Without any doubt, emulsion polymerization has created a wide field of applications, but in the present context one has to be aware that an inconceivable restricted set of polymer reactions can be performed in this way. Emulsion polymerization is good for the radical homopolymerization of a set of barely water-soluble monomers. Already heavily restricted in radical copolymerization, other polymer reactions cannot be performed. The reason for this is the polymerization mechanism where the polymer particles are the product of kinetically controlled growth and are built from the center to the surface, where all the monomer has to be transported by diffusion through the water phase. Because of the dictates of kinetics, even for radical copolymerization, serious disadvantages such as lack of homogeneity and restrictions in the accessible composition range have to be accepted. 

As a model monomer for radical homopolymerization of hydrophobic monomers, styrene is described in many papers. The polymerization of acrylates and methacrylates is also well known. It could also be shown that the miniemulsion process also easily allows the polymerization of the ultrahydrophobic monomer lauryl methacrylate without any carrier materials as necessary in emulsion polymerization [71]. 

Polyacrylonitrile, which is a semicrystalline polymer, can be used for many engineering applications, such as fiber spinning or for housing and package applications. A peculiarity of polyacrylonitrile is that it is insoluble in its monomer. This makes it very difficult to homopolymerize acrylonitrile in an emulsion polymerization process since nucleated polymer particles cannot grow by monomer swelling. 

The copolymerization with alkyllithium to produce uniformly random copolymers is more complex for the solution process than for emulsion because of the tendency for the styrene to form blocks. Because of the extremely high rate of reaction of the styryl-lithium anion with butadiene, the polymerization very heavily favors the incorporation of butadiene units as long as reasonable concentrations of butadiene are present. This observation initially was somewhat confusing because the homopolymerization rate of styrene is seven times that for butadiene. However, the cross-propagation rate is orders of magnitude faster than either, and it therefore dominates the system. For a 30 mole percent styrene charge the initial polymer will be almost pure butadiene until most of the butadiene is polymerized. Typically two-thirds of the styrene charged will be found as a block of polystyrene at the tail end of the polymer chain ... 

The prinaples of latex reactor design, operation, and control will he illustrated by a consideration of the homopolymerization of styrene and vinyl acetate. Emulsion polymerization of vinyl acetate follows Case 1... 

A wider range of acrylate/styrene block copolymers have been prepared by copper catalysts, partially because the homopolymerizations of both monomers can be controlled with common initiating systems. Both AB- (B-15 to B-17)202,230,254,366,367 and BA-type (B-18 to B-21)28,112,169,230,366,368,369 block copolymers were obtained from macroinitiators prepared by the copper-based systems. The block copolymerizations can also be conducted under air230 and under emulsion conditions with water.254 Combination of the Re-and Ru-mediated living radical polymerizations in... 

Radical-Initiated Homopolymerization. When this homopolymerization is carried out with benzoyl peroxides or other radical formers in a manner analogous to emulsion polymerization of chloroprene, highly crosslinked polymers are formed. They are insoluble in organic solvents such as toluene, benzene, or chloroform. Radical polymerization in toluene, benzene, or hexane leads only to insoluble products. 

Our findings for both the copolymerization and the homopolymerization of acrylonitrile were thus unusually high, and the reason must be the emulsion polymerization process. The work of Joshi (12) on acrylamide and methacrylamide, which are water soluble, may be relevant. He reported values of 13.8 and 19.5 kcal/mole for acrylamide in hydrocarbon and in aqueous solution for methacrylamide the corresponding values were 8.4 and 13.4 kcal/mole... 

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