Microsuspension polymer

Figure 11. Conversion vs. time data of an inverse microsuspension polymer-ization of acrylamide and DMAEM at 60 °C and 50 wt % total monomer concentration (fio = 0.875). The phase ratio of water to oil was 0.74 1, with 10 wt % sorbitan monooleate based on the organic phase). Polymerization was initiated with 3.329 X 10 mol L AIBN. The solid line is the model...

High molecular weight of microsuspension polymers (K number of 90) may act as antiblocking and matting agents. Antiblocking is achieved with less than 1 phr addition. A 2-3 phr addition results in bubble-fiee film with fewer flow lines, and with 4 phr addition, a matt surface is usually obtained. 

From the point of view of the polymerization process, bulk (mass) polymerization produces the purest PVC because only initiators and vinyl chloride are used in the process. Bulk polymerization is capable to yield 99.9% pure polymer. In suspension polymerization, a suspending agent is added in addition to initiator, which decreases the purity of suspension PVC to about 99.8%. Microsuspension polymer contains emulsifier and its piuity can be approximately 98.8%. Emulsion polymer may contain more emulsifier and initiator rests and its purity can be estimated as 98%. All these results are quite good for commercial product and PVC can be considered as a relatively pure polymer. More admixtures are usually introduced on the compounding stage from various contaminations and brought together with additives. 

The use of core-shell impact modifiers for sPS is also patented in EP 318793 [15] (see Table 19.1). These impact modifiers are usually prepared using the emulsion polymerization process, although other methods such as the microsuspension polymerization process are possible. The core usually consists of polymers prepared from an acrylate, especially butyl or 2-ethylhexyl acrylate or butadiene. These rubber particles are then grafted with vinyl monomers, where... 

Emulsion polymerizations normally produce polymer particles with diameters ofO.I-l pm(l pm= I micron= 10 cm), although much larger particles can be made by special techniques mentioned in Chapter 8. Tlie polymer particles made by suspension reactions have diameters in the range of 50-500 pm. Recall that free-radical initiation in suspension reactions is in the monomer phase, whereas the aqueous phase is the initiation site in emulsion polymerizations. The two processes often dilTer also in the types of stabilizers that are used. Microsuspension polymerization is an alternative technique which can yield particles in the same size range as emulsion processes. This method uses a monomer-soluble initiator and anionic emulsifiers similar in nature and concentration to those used in emulsion polymerizations. A microdispersion of the mixture of the reaction ingredients is first produced mechanically and is then polymerized to provide polymer with essentially the initial fine particle size distribution. 

Poly(diallyldimethylammonium chloride) was the first quaternary ammonium polymer approved for potable water clarification by the United States Public Health Service, and has historically been the most widely produced cationic polyelectrolyte. There have been several studies on the kinetics (26-37) and uses of diallyldimethylammonium chloride (DADMAC) (38-45) however, there have been no investigations in inverse microsuspension, the most common industrial method of polymerization. Furthermore, there is considerable disagreement between published reactivity ratios, probably because no satisfactory analytical methods have been described in the literature for residual monomer concentration or copolymer composition. For other commercially important quaternary ammonium polymers, such as dimethylaminoethyl methacrylate and dimethylaminoethyl acrylate, few kinetic data are available (46-51) only Tanaka (37) measured the reactivity ratios. 

Inverse microsuspension is a commercial process for the production of high molecular weight, water-soluble polymers. Monomers are dispersed in a continuous organic phase, usually paraffinic, and sterically stabilized. Polymerization can be initiated with an oil- or water-soluble initiator. 

PVC (all types of polymer (emulsion, suspension, microsuspension, and mass) are used in blending which helps to modify rheological properties of plastisols molecular weight varies widely from low to ultrahigh)... 

Other Components. The smaller the particle size, at a given phase ratio, the more difficult it is to ensure colloidal stability (cf Fig. 5). This means that for aqueous heterophase polymerizations in the order suspension < microsuspension < emulsion < miniemulsion < microemulsion, the stabilizer concentration increases. Contrary to the simple polymerization of st5Tene in water, polymerization recipes for industrially important polymer dispersions comprise up to six monomers, frequently more than two emulsifiers, more than one initiating system, and a few other aids like biocides, defoaming agents, plasticizers for supporting film formation (39). The monomer-to-water ratio is adjusted in such a way that a solid content results typically between 40 and 60% or even higher. The amoimts of surfactants and initiator (mainly peroxodisulfate) are typically between 0.5 and 2% (w/w) relative to the monomers and 0.5% (w/w) relative to water, respectively. 

PlaStiSOlS. Plastisol-forming pol5rmers are produced by microsuspension polymerization or dispersion polymerization (9). Microsuspension produces very fine particles of monomer to ensure that small particle sizes of polymer are produced. In emulsion or dispersion polymerization the vinyl chloride is dispersed in a water-soluble initiator the vinyl chloride particles are small and stabilized using surfactants. There are also several variations of these two basic techniques. 

An alternative approach for producing latex with a wide particle size distribution is microsuspension polymerisation. In this process, an initiator such as lauroyl peroxide is used, which is highly soluble in the VCM, but is essentially insoluble in water. Thus, polymerisation takes place within the dispersed VCM droplets. The water insolubility of the initiator also helps to stabilise the VCM droplet, and it may be possible to use lower levels of emulsifier compared with the batch emulsion and continuous emulsion processes. Lower levels of emulsifier can be advantageous, for example for applications coming into contact with food, where water absorption or clarity is important, and also for the environmental impact of the proccess. Such latexes produce polymers which give very low plastisol viscosities, but tend to be dilatant in nature. This can be overcome by modifying the process to have a secondary particle size distribution alongside the primary one. 

The microsuspension process is not suitable for the production of polymers giving sharply pseudoplastic plastisols. 

Microsuspension Ability to produce potymers giving very low plastisol viscosities. Polymers can give coatings with very low water absorption and clarity and excellent organoleptic properties (low emulsifier levels). Product consistency. A lower consumption of emulsifier can also be an advantage regarding the environmental impact of the process. Inability to produce pseudoplastic polymers. Greater conplexity. 

When a water-miscible polymer is to be made via a suspension process, the continuous phase is a water-immiscible fluid, often a hydrocarbon. In such circumstances the adjective inverse is often used to identify the process [118]. The drop phase is often an aqueous monomer solution which contains a water-soluble initiator. Inverse processes that produce very small polymer particles are sometimes referred to as inverse emulsion polymerization but that is often a misnomer because the polymerization mechanism is not always analogous to conventional emulsion polymerization. A more accurate expression is either inverse microsuspension or inverse dispersion polymerization. Here, as with conventional suspension polymerization, the polymerization reaction occurs inside the monomer-containing drops. The drop stabilizers are initially dispersed in the continuous (nonaqueous phase). If particulate solids are used for drop stabilization, the surfaces of the small particles must be rendered hydrophobic. Inverse dispersion polymerization is used to make water-soluble polymers and copolymers from monomers such as acrylic acid, acylamide, and methacrylic acid. These polymers are used in water treatment and as thickening agents for textile applications. Beads of polysaccharides can also be made in inverse suspensions but, in those cases, the polymers are usually preformed before the suspension is created. Physical changes, rather than polymerization reactions, occur in the drops. Conventional stirred reactors are usually used for inverse suspension polymerization and the drop size distribution can be fairly wide. However, Ni et al. [119] found that good control of DSD and PSD could be achieved in the inverse-phase suspension polymerization of acrylamide by using an oscillatory baffled reactor. 

Poly (vinyl chloride) (PVC) is one of the highest tonnage polymers produced on a world-wide scale. From the beginning of production over 40 years ago, growth of PVC sales into a wide variety of applications has expanded rapidly, reaching an annual world consumption of 1.2 x 10 tes per annum in 1980 (1). PVC is prepared by four principal polymerisation processes bulk or mass, suspension, microsuspension and emulsion. In addition PVC may also be prepared by solution or dispersion polymerisation, but these remain low tonnage specialised products. 

This section also considers recent developments in microsuspension polymerisation for producing both monodisperse and polydisperse polymer latices. While spray-drying is commonly used to dry the latex, energy costs are high. Flocculation of... 

Some modifications to the microsuspension process have been developed such as a seeded process (12) and an extension to this where an emulsion polymer latex, particle size sO.lpm, is added to the seed latex and monomer at the beginning of the polymerisation (13). In the latter process it is claimed that by... 

Microsuspension polymerization is a process used in the PVC industry to produce resins for plastisols [125], In this process, which resembles miniemulsion polymerization, a mixture of monomer and an oil-soluble initiator are dispersed in an aqueous solution of surfactants using intensive shear. The monomer droplets are polymerized yielding particles usually <2 pm, which are normally isolated by spray drying as they cannot be separated by centrifuging or filtering. These particles are solid and nonporous. The polymer particles are larger than the monomer droplets (0.1-2 pm) because the combined effect of the Ostwald ripening (as no costabilizer is used in the formulation) and droplet/particle coalescence. 

Hunkeler D, Hamielec AE, Baade W. Mechanism, kinetics, and modeling of the inverse-microsuspension homopolymerization of acrylamide. Polymer 1989 30 127-142. 

Rheological studies also indicated differences in behavior as a function of concentration for these two polymers. The plots of relative and reduced viscosities for the copolymer prepared in surfactant were similar to the profile in Fig. 2.1, indicating that it behaved as a hydrophobically associating polymer in deionized water and 2% NaCl. The solution polymer, in contrast, was shown to behave as a polymeric microsuspension in these solvents. 

---