Sodium dodecyl sulfate emulsifiers

Fig, 1. Dependence of tbe rate of polymerizaiion (in Interval II) of styrene emulsions on tlie concentration of the emulsifier (sodium dodecyl sulfate) at 60°C. Initiator 0.2% KjSjOg on aqueous phase. (From Al-Shahib, 1977.)... 

The reactive intermediates used in chain-growth polymerizations include radicals, carbanions, carbocations, and organometallic complexes. Of the three common metal catalyzed polymerizations - coordination-insertion, ring-opening metathesis and diene polymerization - the last appears to possess the greatest tolerance toward protic solvents. The polymerization of butadiene in polar solvents was first reported in 1961 using Rh salts [18]. It was discovered that these polymerizations could be performed in aqueous solution with an added emulsifier (sodium dodecyl sulfate, for example). 

Neelson et al. [92] followed the effect of emulsifier (sodium dodecyl sulfate) concentration on the decomposition rate of initiator and the rate of polymerization. The decomposition rate of potassium peroxodisulfate increased with increasing the emulsifier concentration. For example, with increasing [SDS]/(mol dm ) 0, 1.74, 3.47, 6.95, 13.89, and 24.3 increased kj x 10 /s 2.9, 3.6, 12.3, 16.9, and 21.9 (50 °C, [VC] = 11.5 moldm ). For the catalitic decomposition of peroxodisulfate caused by emulsifier the authors derived the following semiempirical expression... 

Decomposition of peroxodisulfates in the aqueous sodium dodecyl-sulfate solutions (below and above CMC) with and without poly(vinyl chloride) particles and/or vinyl chloride monomer was investigated by Georgescu et al. [94, 95]. They also observed the increase of peroxodisulfate decomposition in the presence of emulsifier (Fig. 4). In contrast, the decomposition rate decreased with increasing particle concentration. The dependence of the initial decomposition rate of potassium peroxodisulfate vs the emulsifier concentration is described by a curve with a maximum at CMC. The catalyzed decomposition of initiator was ascribed to the interaction of initiator with free emulsifier molecules or with emulsifier micelles. The effect of particles was ascribed to the decrease of the water-soluble fraction of emulsifier caused by adsorption of emulsifier on the polymer particle surface. The relationship of the decomposition rate constant vs the emulsifier (sodium dodecyl sulfate) concentration with and without poly(vinyl chloride) particles is described by a curve of the same shape but with different absolute values of k ka is lower in the presence of PVC particles (Fig. 4). The most intensive decomposition of initiator occurs at concentrations close to the CMC. Decomposition of peroxodisulfate recorded with vinyl chloride and poly(vinyl chloride) is faster than in pure water and slower than in emulsifier solutions. Variations in the decomposition rate results from the... 

Svoboda et al. [160] investigated the emulsion copolymerization and ter-polymerization of VC with vinyl accetate, butyl acrylate and/or ethyl acrylate. The polymerizations proceeded under batch and continuous conditions and were initiated by peroxodisulfates. Anionic emulsifiers (sodium dodecyl sulfate, sodium dodecylbenzene sulfonate,..) and blends of anionic and non-ionic emulsifiers (mostly polyoxyethylene type) were used. Copolymer latexes prepared with emulsifier blends were much more stable than those with an anionic emulsifier. As expected, the copolymers prepared by continuous polymerization gave copolymers with homogeneous composition. In the batch copolymerizations, the shift in the copolymer composition with conversion was observed and particles with broader size distribution were prepared. For example, the batch VC/ethyl acrylate polymer latexes gave particles with a diameter from 180 nra to 320 nm. 

To prepare a 340-nm sphere, the following recipe has been suggested 19.9 g of methyl methacrylate, 3.5 g of methacryUc acid, 10.5 g of hydroxy-ethyl methacrylate, 1.1 g of ethylene glycol dimethacrylate, and 0.1 g of emulsifier sodium dodecyl sulfate (SDS) are added to 64.9 g of distilled water. Polymerization is carried out for 1 hr at 98°C in a sealed tumbling container. Write down the approximate molecular structure of the surfaee and indicate whether the polymer partiele would dissolve in any solvent. 

Before we examine the polymerization process itself, it is essential to understand the behavior of the emulsifier molecules. This class of substances is characterized by molecules which possess a polar or ionic group or head and a hydrocarbon chain or tail. The latter is often in the 10-20 carbon atom size range. Dodecyl sulfate ions, from sodium dodecyl sulfate, are typical ionic emulsifiers. These molecules have the following properties which are pertinent to the present discussion ... 

In a series of experiments at 60 C, the rate of polymerization of styrene agitated in water containing persulfate initiator was measuredt for different concentrations of sodium dodecyl sulfate emulsifier. The following results were obtained ... 

DVB (purity > 98 %) was polymerized using sodium dodecyl sulfate (SDS) as emulsifier in the presence of various initiators, such as potassium persulfate (PPS) [51,77-82], 2,2 -azobisisobutyronitrile (AIBN) [83] and also by thermal initiation [84]. 

Emulsifier. For most of the experiments sodium dodecyl sulfate (SDS) was used as an emulsifier. A commercial product was recrystallized twice from alcohol. 

In our experiments the monomer concentration was between about 150 and 200 grams per kg. of emulsion. Sodium dodecyl sulfate in a concentration of 5 to 15 grams per kg. of water was used as an emulsifier. The reaction temperature was generally 25 °C. Only with vinylidene chloride and chloroprene a reaction temperature of 5°C. was used because of the low boiling point of these monomers. Dose rate ranged between about 500 and 2000 rads per hour but was kept constant during each experiment. 

In the present experiments greatly enhanced rates of thermal emulsion polymerization were observed when potassium octadecanoate or sodium dodecyl sulfate (at 0.12 mol dm ) whereas sodium dodecyl benzene sulfonate and Triton1 X-100 (Rohm Haas, a non-ionic emulsifier octylphenoxypoly(ethyleneoxy)-ethanol) did not enhance the rate. The conversion after 12 hr at 60 °C with potassium octadecanoate was 69 % whereas with sodium dodecyl benzene sulphonate it was only 29 % (Fig. 2). 

In Fig. 2, the weight ratio mx/m2 of hydrocarbon to water is plotted as a function of the concentration of surfactant in the continuous phase (in weight percent) when sodium dodecyl sulfate (SDS) is employed as emulsifier. The above ratio is calculated for the point at which a small amount of hydrocarbon remains as a distinct phase. The ratio mjm2 depends upon the nature of the hydrocarbon employed and increases with the surfactant concentration, more rapidly at lower concentrations. A similar behavior was observed for a non-ionic surfactant, Triton X-100 (Fig. 3), but the values of mllm2 are smaller in this case than in Fig. 2. This happens because the electrostatic repulsion responsible for the stability of the concentrated emulsion containing SDS is stronger than the steric repulsion involved in the stability of the emulsion containing Triton X-100. 

To act as solubilizing, wetting, or emulsifying agents such as Cremophor EL, sodium desoxy-cholate, Polysorbate 20 or 80, PEG 40 castor oil, PEG 60 castor oil, sodium dodecyl sulfate, lecithin, or egg yolk phospholipid. 

Aqueous emulsions of styrene, methyl methacrylate, methyl acrylate, and ethyl acrylate were polymerized with y-radiation from a Co source in the presence of sodium dodecyl sulfate or sodium laurate. The continuous measurement of conversion and reaction rate was carried out dilato-metrically. The acrylates polymerized fastest and the over-all polymerization rate increased as follows styrene < methyl methacrylate < ethyl acrylate methyl acrylate. The effects of radiation dose, temperature, and original monomer and emulsifier concentrations were studied with respect to the following factors properties of polymer dispersions, number and size of polymer particles, viscometrically determined molecular weights, monomer-water ratio, and kinetic constants. 

Dose rate 200 rad/hr. Temperature 25 °G. Monomer concn. about 1.2 moles/kg. emulsion. Emulsifier about 0.046 mole sodium dodecyl sulfate/kg. solution) Monomer... 

Properties of Dispersions and Polymers. All polymer dispersions with SDS (sodium dodecyl sulfate) as an emulsifier were stable for at least 8 months. Dispersions with Na laurate as emulsifier flocculated after a short time. Polyacrylates on drying yielded clear and coherent films polystyrene and PMMA dispersions gave opaque and brittle layers. The doses needed for polymerization were well below a dose which causes cross linking or degradation. 

Swelling of polymethyl methacrylate latex particles with methyl methacrylate. Table IV lists the swelling ratios and interfacial tensions for the different-size polymethyl methacrylate latexes with added Aerosol MA and sodium dodecyl sulfate emulsifiers. Comparison of the data with the theoretical curves from Model I (Figure 2) defines an apparent interaction parameter of 0.45 and the semi-empirical equation ... 

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