Emulsion polymerization utility

Typical emulsion polymerizations utilize oil-soluble monomers dispersed in an aqueous media with a water-soluble initiator, whereas inverse emulsions employ water-soluble monomers dispersed in an organic medium containing an oil-soluble initiator. The insoluble polymer particles that result from these reactions are stabilized as colloids in solution by repulsive forces imparted by a small molecule ionic surfactant and/or an amphiphilic macromolecular stabilizer (56,57). These reactions produce high molecular weight, spherical polymer particles with sizes typically smaller than 1 fj,m. Since most common monomers are highly soluble in CO2, there are very few examples of C02-based emulsion poljnnerizations. However, acrylamide is a rare example of a vinyl monomer that has a low solubility in CO2 at moderate temperatures and pressures. The AIBN-initiated water-in-oil or inverse emulsion polymerization of acrylamide has been attempted at 65°C in 35.2 MPa (352 bar) CO2 (41,58) (eq. (3)). 

The surfactants used in the emulsion polymerization of acryhc monomers are classified as anionic, cationic, or nonionic. Anionic surfactants, such as salts of alkyl sulfates and alkylarene sulfates and phosphates, or nonionic surfactants, such as alkyl or aryl polyoxyethylenes, are most common (87,98—101). Mixed anionic—nonionic surfactant systems are also widely utilized (102—105). 

Emulsion Process. The emulsion polymerization process utilizes water as a continuous phase with the reactants suspended as microscopic particles. This low viscosity system allows facile mixing and heat transfer for control purposes. An emulsifier is generally employed to stabilize the water insoluble monomers and other reactants, and to prevent reactor fouling. With SAN the system is composed of water, monomers, chain-transfer agents for molecular weight control, emulsifiers, and initiators. Both batch and semibatch processes are employed. Copolymerization is normally carried out at 60 to 100°C to conversions of - 97%. Lower temperature polymerization can be achieved with redox-initiator systems (51). 

M ass Process. In the mass (or bulk) (83) ABS process the polymerization is conducted in a monomer medium rather than in water. This process usually consists of a series of two or more continuous reactors. The mbber used in this process is most commonly a solution-polymerized linear polybutadiene (or copolymer containing sytrene), although some mass processes utilize emulsion-polymerized ABS with a high mbber content for the mbber component (84). If a linear mbber is used, a solution of the mbber in the monomers is prepared for feeding to the reactor system. If emulsion ABS is used as the source of mbber, a dispersion of the ABS in the monomers is usually prepared after the water has been removed from the ABS latex. 

Third Monomers. In order to achieve certain property improvements, nitrile mbber producers add a third monomer to the emulsion polymerization process. When methacrylic acid is added to the polymer stmcture, a carboxylated nitrile mbber with greatly enhanced abrasion properties is achieved (9). Carboxylated nitrile mbber carries the ASTM designation of XNBR. Cross-linking monomers, eg, divinylbenzene or ethylene glycol dimethacrylate, produce precross-linked mbbers with low nerve and die swell. To avoid extraction losses of antioxidant as a result of contact with fluids duriag service, grades of NBR are available that have utilized a special third monomer that contains an antioxidant moiety (10). FiaaHy, terpolymers prepared from 1,3-butadiene, acrylonitrile, and isoprene are also commercially available. 

Utilization of another function of the macroinitiator was tried in emulsion polymerization [30]. An MAI composed of PEG (molecular weight of a segment is 1000) linked with AGP units was confirmed to be usable as a surface active initiator (Inisurf) for preparing PSt-b-PEG [30]. A higher molecular weight block copolymer was obtained in comparison with the case of solution copolymerization. 

Monomer and initiator must be soluble in the liquid and the solvent must have the desired chain-transfer characteristics, boiling point (above the temperature necessary to carry out the polymerization and low enough to allow for ready removal if the polymer is recovered by solvent evaporation). The presence of the solvent assists in heat removal and control (as it also does for suspension and emulsion polymerization systems). Polymer yield per reaction volume is lower than for bulk reactions. Also, solvent recovery and removal (from the polymer) is necessary. Many free radical and ionic polymerizations are carried out utilizing solution polymerization including water-soluble polymers prepared in aqueous solution (namely poly(acrylic acid), polyacrylamide, and poly(A-vinylpyrrolidinone). Polystyrene, poly(methyl methacrylate), poly(vinyl chloride), and polybutadiene are prepared from organic solution polymerizations. 

Utilizing the seed latex polymerization method to avoid the occurance of new particle formation, the kinetic treatment of an emulsion polymerization is quite straight forward. Assuming that all the particles are the same size, the rate of polymerization,... 

The use of a precision digital density meter as supplied by Mettler Instruments (Anton Paar, Ag.) appeared attractive. Few references on using density measurements to follow polymerization or other reactions appear in the literature. Poehlein and Dougherty (2) mentioned, without elaboration, the occasional use of y-ray density meters to measure conversion for control purposes in continuous emulsion polymerization. Braun and Disselhoff (3) utilized an instrument by Anton Paar, Ag. but only in a very limited fashion. More recently Rentsch and Schultz(4) also utilized an instrument by Anton Paar, Ag. for the continuous density measurement of the cationic polymerization of 1,3,6,9-tetraoxacycloundecane. Ray(5) has used a newer model Paar digital density meter to monitor emulsion polymerization in a continuous stirred tank reactor train. Trathnigg(6, 7) quite recently considered the solution polymerization of styrene in tetrahydrofuran and discusses the effect of mixing on the reliability of the conversion data calculated. Two other references by Russian authors(8,9) are known citing kinetic measurements by the density method but their procedures do not fulfill the above stated requirements. 

The objective of this paper is to illustrate, by simulation of the vinyl acetate system, the utility of the analytical predictor algorithm for dead-time compensation to regulatory control of continuous emulsion polymerization in a series of CSTR s utilizing initiator flow rate as the manipulated variable. 

The utility of the analytical predictor method of dead-time compensation to control of conversion in a train of continuous emulsion polymerizers has been demonstrated by simulation of the vinyl acetate system. The simulated results clearly show the extreme difficulty of controlling the conversion in systems which are operated at Msoap-starvedM conditions. The analytical predictor was shown, however, to provide significantly improved control of conversion, in presence of either setpoint or load changes, as compared to standard feedback systems in operating regions that promote continuous particle formation. These simulations suggest the analytical predictor technique to be the preferred method of control when it is desired that only one variable (preferably initiator feed rate) be manipulated. 

The 121 sample films were formulated into a replicate series. Those utilizing emulsion polymerized PVC were cast from plastisol onto glass plates and fused in a circulating hot air oven. Those incorporating suspension polymerized PVC were fluxed via a Banbury and two-roll compounding mill and finished on an inverted L 8-inch X 16-inch four-roll calender. Plastisol films were of nominal 8-mil thickness calendered film was 4 mils. 

Acrylates are primarily used to prepare emulsion and solution polymers. The emulsion polymerization process provides high yields of polymers in a form suitable for a variety of applications. Acrylate polymer emulsions were first used as coatings for leather in the early 1930s and have found wide utility as coatings, finishes, and binders for leather, textiles, and paper. Acrylate emulsions are used in the preparation of both interior and exterior paints, floor polishes, and adhesives. Solution polymers of acrylates, frequently with minor concentrations of other monomers, are employed in the preparation of industrial coatings. Polymers of acrylic acid can be used as superabsorbents in disposable diapers, as well as in formulation of superior, reduced-phosphate-level detergents. 

Novel shellwall chemistry has been developed that produces an encapsulating shellwall around pesticide emulsion droplets utilizing a single monomer or prepolymer dissolved in the pesticide. Heating the emulsion and use of catalyst produces shellwalls. This process is referred to as in-situ polymerization. 

Nomura et al. [360,364] first utilized a Couette-Taylor vortex flow reactor (CTVFR) for the continuous emulsion polymerization of St to clarify its char-... 

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 latexes upon which this industry developed were natural rubber and polychloroprene for solvent resistance. However, technology is advancing to permit penetration of carboxylated nitrile latex for optimized solvent resistance and tougher abrasion resistance. Among the competition to latexes in this field are poly(vinyl chloride) plastisols. As technology develops in producing small particle size latexes from polymers whose synthesis is loo water-sensitive for emulsion polymerization, the dipped goods industry will quickly convert to their utilization from the solvent-based cements of these polymers now employed Prime candidates include butyl rubber, EPDM, hypalon, and vlton. 

Styrene is frequently used as part of some terpolymers with large practical utilization. One such copolymer is acrylonitrile-butadiene-styrene terpolymer (ABS). Usually it is made as poly(l-butenylene-graft-l-phenylethylene-co-cyanoethylene). This form of the copolymer can be made by grafting styrene and acrylonitrile directly on to the polybutadiene latex in a batch or continuous emulsion polymerization process. Grafting is achieved by the free-radical copolymerization of styrene and acrylonitrile monomers in the presence of polybutadiene. The degree of grafting is a function of the 1,2-vinyl content of the polybutadiene, monomer concentration, extent of conversion, temperature and mercaptan concentration (used for crosslinking). The emulsion polymerization process involves two steps production of a rubber latex and subsequent polymerization of styrene and acrylonitrile in the presence of the rubber latex to produce an ABS latex. 

Most of the peroxodisulfate produced (>65%) is used as a polymerization initiator in the production of poly(acrylonitrile), emulsion-polymerized PVC etc. The rest is utilized in numerous applications (etching of printed circuit boards, bleaching processes etc.). 

Starved-feed emulsion polymerization can be conducted without emulsifiers if suitable comonomers and procedures are utilized.341 Polymerization of a water-soluble methacrylate like HEMA in the presence of a CCT agent is carried out initially. The resulting HEMA oligomer is further copolymerized with hydrophobic monomers so that the resulting diblock copolymer serves as a surfactant (see, for instance, sections 5.3 and 5.4). During the cross-linking process, all of this surfactant is incorporated into the polymer backbone and is thus immobilized, overcoming the problem of residual surfactant in the final product. 

When it is important that surfactants utilized in free-radical emulsion polymerization not be free to... 

In summary, this pioneering work clearly demonstrated the possibility of aqueous catalytic insertion polymerization of acyclic and cyclic olefins, as well as aqueous ROMP. On the other hand, metal salts without any additional ligands to control the properties of the metal centers were utilized, and activation to the active species was probably also relatively ineffective in most cases. Consequently, catalyst efficiencies were moderate at best. Most of the polymerizations also afforded low molecular weight materials, or employed rather special monomers. The possibility of polymer latex synthesis appears not to have received much attention, although free-radical emulsion polymerization of styrene and butadiene was already a large-scale process at the time. 

Famously, emulsion polymerization was utilized to form styrene-butadiene synthetic rubber during the... 

We are currently exploring new routes to the synthesis of ionomers with controlled architecture, i.e. with control over the amount and location of ionic groups in the polymer backbone. One of our main interests is the synthesis of ion containing block copolymers. The applicability of anionic polymerization in the synthesis of block copolymers and other well defined model systems is well documented (22-24) Not as well appreciated, however, is the blocky nature that certain emulsion copolymerizations may provide. Thus, we have utilized both anionic and free radical emulsion polymerization in the preparation of model ionomers of controlled architecture. In this paper, the synthesis and characteristics of sulfonated and carboxylated block ionomers by both free radical emulsion and anionic polymerization followed by hydrolysis will be discussed. 

---