Emulsions with poly polymer

Latex Types. Latexes are differentiated both by the nature of the coUoidal system and by the type of polymer present. Nearly aU of the coUoidal systems are similar to those used in the manufacture of dry types. That is, they are anionic and contain either a sodium or potassium salt of a rosin acid or derivative. In addition, they may also contain a strong acid soap to provide additional stabUity. Those having polymer soUds around 60% contain a very finely tuned soap system to avoid excessive emulsion viscosity during polymeri2ation (162—164). Du Pont also offers a carboxylated nonionic latex stabili2ed with poly(vinyl alcohol). This latex type is especiaUy resistant to flocculation by electrolytes, heat, and mechanical shear, surviving conditions which would easUy flocculate ionic latexes. The differences between anionic and nonionic latexes are outlined in Table 11. 

With emulsion polymerization it is possible to prepare very high-molecular-weight polymers at high rates of polymerization. The required reaction temperatures are low and can even be below 20 °C when redox systems are used for initiation (see Examples 3-11). Polymer emulsions with solid contents of 50% and higher can be very stable. In many cases, e.g., poly(vinyl acetate), they are directly used as paints (paint latices), coatings, or adhesives (see Sect. 2.5.4). 

C.D. Smith, Vinyl acetate ethylene emulsions stabilized with poly(eth-ylene/poly (vinyl alcohol) blend, US Patent 6 673 862, assigned to Air Products Polymers, L.P. (Allentown, PA), January 6, 2004. 

The parameter r2 is independent of the initiator type for the emulsion, however, and is slightly higher than that obtained in benzene (r2=1.23) (Table 3). This behavior results from good compatibility of the macromonomer with poly-BzMA. Therefore the reactivity of the macromonomer does not depend so much on the reaction medium type. In contrast, reversed apparent reactivity was observed in heptane in which the clear solution of monomer turned into a polymer suspension upon polymerization. Since BzMA is soluble in the medium, it has been suggested that the polymerization occurs preferentially on the (inverse) micelle surface which is enriched by the macromonomers. 

I. J. Synthesis and characterization of exfoliated poly(styrene-co-methyl methacrylate)/clay nanocomposites via emulsion polymerization with AMPS, Polymer (2003), 44(20), 6387-6395. 

Adhesive Emulsions. Thermoplastic, synthetic polymers can be prepared as emulsions for use as adhesives. For example, while EVAc hot-melt adhesives described in the previous section contain less than 40% VAc, when the content of VAc in the copolymer is increased to 60%, and the copolymer is prepared in the form of aqueous emulsions, a very useful and versatile adhesive polymer is obtained. Although the VAc homopolymer, poly(vinyl acetate), is a brittle solid, with a Tg = 28 °C, the ethylene units present in the EVAc copolymer act as an internal plasticizer, and lower the Tg to below room temperature. The plasticization results from the reduction of interchain interaction of the VAc polymer chains by the ethylene units interspersed among the strongly interacting VAc units. This reduction of the Tg has important consequences because the formation of a flexible adhesive film from the emulsion depends upon the Tg of the polymer. 

Stable aqueous emulsions of poly(2-ethylhexyl acrylate) (PEHA) were also produced by RESAS from CO2 (68). In this case, a polymer suspension in CO2 was expanded instead of a dissolved solute. A C02-philic surfactant, Monasil PCA (PDMS-g-pyrrolidonecarboxylic acid), was utilized in dispersion polymerization to form a stable polymer suspension at 65°C and 345 bar. A hydrophilic surfactant, (e.g., SAM 185, Pluronic L61, or Pluronic L62), that is soluble in CO2 and CO2/2-EHA monomer mixtures as well as water was added to CO2 to stabilize the suspension after it had been rapidly expanded through a capillary into aqueous solution. The resulting aqueous emulsion with up to 15.6 wt % polymer content was stable for weeks with an average particle size of 2 to 3 pm. Another approach is to introduce the hydrophilic surfactant in the aqueous phase in addition to the surfactant in the CO2 phase. This approach is more general, since many hydrophilic surfactants are not soluble in CO2. During expansion of the suspension into an aqueous solution, the hydrophilic surfactant—for example, triblock Pluronic copolymers—dilfuses to the particle surface to provide stabilization. The resulting aqueous latexes were stable for 100 days for a polymer content reaching 12.7 wt %. 

FIG. 11 Pseudophase diagram for 30 wt% cyclohexane in water stabilized by PAA (Carbopol 980). The c values are shown as the curve drawn in the bottom left-hand corner of the diagram. (Reprinted from Colloids and Surfaces A Physicochem Eng Aspects, 88, Lockhead RY, Rulinson CJ, An investigation of the mechanism by which hydrophobically modified hydrophilic polymers act as primary emulsifiers for oil in water emulsions. 1. Poly(acrylic acids) and hydroxyethyl celluloses. 27-32, Copyright (1994), with permission from Elsevier Science.)... 

In Section 4 on the preparation of poly(vinyl acetate) suspension polymers, mention was made of the preparation of polymer beads by adding a methanol solution of that polymer to an aqueous solution of poly(vinyl alcohol). By varying the concentration of emulsifying agent and the rate at which solvents are distilled off, it is possible to develop conditions for the generation of emulsions with polymer particles of diameter between 1 and 3 /im. [121]. 

By use of between 0.1% and 1% of a non-ionic surfactant of HLB-value between 8 and 15 and surface tension less than 30 dyne/cm, poly(vinyl fluoride) emulsions with particle diameter less than 5 /im have been prepared at 30°-45°C [54]. Procedure 2-6 is a patented process given here for reference only. It is of interest because the incorporation of an iodine-containing compound such as ammonium iodide, 2,2 -azobisisobutyramidine hydroiodide, potassium iodide, iodine in isopropanol, isopropyl iodide, tetraiodoethylene in tert-butanol, iodo-benzene, 2-iodothiophene, or ethyl iodide give rise to polymers of improved thermal stability and resistance to color deterioration [55]. The process does not seem to involve the use of an emulsifying agent. 

Styrene-butadiene rubber latex (SBR, GRS) and acrylonitrile-butadiene rubber latex (NBR) are two of the earliest to arrive on the market. Since then, many other types have appeared, with poly(vinyl acetate) and copolymers, acrylics (generally polymers and copolymers of the esters of acrylic acid and methacrylic acids), and carboxylic-SBR types being the major products. Since latices are aqueous emulsions, less... 

Adhesive abbreviations are as follows EP, amine-cured epoxy P, polysulfide rubber flexibilizers EP/20P, EP/ 40P, and EP/60P, amine-cured epoxy with 20, 40, and 60 parts polysulfide flexibilizer EPI, emulsion polymer isocyanate ISO, isocyanate MF, melamine-formaldehyde PF, phenol-formaldehyde PF/PVA, phenol-formaldehyde flexibilized with poly(vinyl acetate) PVA, poly(vinyl acetate) PRF, phenol/resordnol-formaldehyde RF, resorcinol-formaldehyde UF, urea-formaldehyde UF/filler, UF with wheat flour UF/MF/fiUer, UF/MF copolymer with wheat flour. 

Tauer, K. (1995) Block-copolymers prepared by emulsion polymerization with poly(ethylene oxide)-azo-initiators. Polym. Adv. Technol., 6, 435. 

---