Physical Properties of Emulsion Polymers

The mechanical properties (e.g., hardness, flexibility, impact resistance, abrasion resistance, and scratch resistance) of polymers are primarily characterized by the polymer molecular weight and molecular weight distribution, polymer morphology (e.g., semicrystalline and amorphous structures), and crosslinking reactions. The purpose of this section is to give the reader an introductory background about the important factors that affect the physical properties of emulsion polymers. 

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The completion stage is identified by the fact that all the monomer has diffused into the growing polymer particles (disappearance of the monomer droplet) and reaction rate drops off precipitously. Because the free radicals that now initiate polymerization in the monomer-swollen latex particle can more readily attack unsaturation of polymer chains, the onset of gel is also characteristic of this third stage. To maintain desirable physical properties of the polymer formed, emulsion SBR is usually terminated just before or at the onset of this stage. 

The physical properties of these polymers, as well as their transparency, is at least in part owed to their structure. Some authors have indicated that this type of structure represents a polymeric oil-in-oil (POO) emulsion (II). 

Acrylic Monomers. The physical properties of a polymer are dependent upon the monomers used in the polymerization. Impurities contained in the monomers also affect the physical properties. Acrylosilane resins and crosslinkable emulsions can be prepared using 3-(Diethoxymethylsilyl) propyl methacrylate (I) (H)). Free-radical polymerization using (I) will yield a resin... 

Journal of Polymer Science Polymer Physics Edition 39, No.ll, 1st June 2001, p.1093-106 MECHANICAL PROPERTIES OF EMULSION POLYMER BLENDS Robeson L M Berner R A Air Products Chemicals Inc. 

Fluorinated surfactants used as an emulsifier in emulsion polymerization of fluo-ropolymers improve physical properties of the polymer and increase the rate of polymerization. Because the fluorinated surfactants are more effective in emulsion polymerization than hydrocarbon surfactants alone, the total surfactant concentration can be reduced. For example, in emulsion polymerization of vinyl chloride, 160 ppm Monflor 31 can reduce the required concentration of sodium dodeylbenzenesulfonate by about 40%. 

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). 

Styrene is a colorless Hquid with an aromatic odor. Important physical properties of styrene are shown in Table 1 (1). Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, / -heptane, and ethanol. Nearly all of the commercial styrene is consumed in polymerization and copolymerization processes. Common methods in plastics technology such as mass, suspension, solution, and emulsion polymerization can be used to manufacture polystyrene and styrene copolymers with different physical characteristics, but processes relating to the first two methods account for most of the styrene polymers currendy (ca 1996) being manufactured (2—8). Polymerization generally takes place by free-radical reactions initiated thermally or catalyticaHy. Polymerization occurs slowly even at ambient temperatures. It can be retarded by inhibitors. 

The information on physical properties of radiation cross-linking of polybutadiene rubber and butadiene copolymers was obtained in a fashion similar to that for NR, namely, by stress-strain measurements. From Table 5.6, it is evident that the dose required for a full cure of these elastomers is lower than that for natural rubber. The addition of prorads allows further reduction of the cure dose with the actual value depending on the microstructure and macrostructure of the polymer and also on the type and concentration of the compounding ingredients, such as oils, processing aids, and antioxidants in the compound. For example, solution-polymerized polybutadiene rubber usually requires lower doses than emulsion-polymerized rubber because it contains smaller amount of impurities than the latter. Since the yield of scission G(S) is relatively small, particularly when oxygen is excluded, tensile... 

In the foregoing examples the synthesis of block copolymers was based on the solubility differences between two monomers, of which one is water soluble while the other is emulsified. Another polymerization technique is based on the kinetics of the emulsion polymerization. When a water emulsion of a monomer, such as styrene, is irradiated during a short time, the reaction, continues at a nearly steady rate until practically all the monomer is used up. If a second monomer is then added, it will polymerize, being initiated by the radicals occluded in the polymer particles. Although in this case also the yields of block copolymers are low, nevertheless the physical properties of the final product are markedly different from those of statistical copolymers (4, 5, 151, 176). 

It is anticipated, and in fact is true, that the physical properties and performance characteristics of emulsion polymers prepared by routes I and IV are different. The question here is whether it is possible by characterization techniques to distinguish polymers made by different routes and, more subtly, by the same nominal route but with some process aberration such as a feed upset. In order to determine the feasibility of such an approach, an emulsion copolymer system was selected the copolymer of styrene and ethyl acrylate. 

The problem of the infiuence of disorder on the physical properties of materials is very important since it has implications in many fields composite materials, polymers, emulsions, ionosphere, etc. The concept of disorder is very general and in each case it is necessary to state precisely what we mean by disorder. 

Okaya T, Tanaka T, Yuki K (1993) Study on Physical Properties of Poly (vinyl acetate) Emulsion Films Obtained in Batchwise and in Semicontinuous Systems. J. Appl. Polym. Sci. 50 745. 

It is well known that polymer miscibility is not only important in the case of simple mixture, but it also determines the physical nature of block and graft copolymers. Multi-layer structures have been studied in recent years as a means for improving physical and mechanical properties of the polymer composition. It is possible to obtain a number of functional properties by means of the multi-stage sequential emulsion polymerization. As concerns this multi -layer structure, we have already reported some interesting results in a study of the processing aid for polyvinyl-chloride, 5 which amazingly improved the processability for polyvinylchloride due to its multi-stage polymer composition produced by sequential emulsion polymerization. 

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