Aqueous phase monomer ratio

Effect of aqueous phase monomer ratio. A series of experiments was carried out to investigate the effect upon polymerisation rate of varying the ratio of aqueous phase to monomer phase, the composition of both phases being kept nominally constant. 

The results are given In Figure 3. They show that, except at very low aqueous phase monomer ratios, the rate of polymerisation per unit quantity of aqueous phase Is essentially Independent of the phase ratio. This Implies that the total rate of conversion of butadiene to polybutadiene is directly proportional to the volume of the aqueous phase. If the compositions of the two phases are kept constant. This observation is consistent with the view that the polymerisation takes place within the aqueous phase of the system. 

Figure 21.3 Effect of the nature of the oil and monomer on the percentage of surfac-tant(s) necessary for the formation of microemulsions as a function of HLB (oil to aqueous phase weight ratio 1) at 20 °C. For , A, the aqueous (diase comptis water 55%. AM 40°%, sodium acetate 5% and the oils were Isopar M, a cyclohexane, toluene. For A the aqueous phase comprised water 50%, MADQUAT 50% and the oil was cyclohexane. Suifactant(s) GCI) used were , A. polyoxyethylene sorbitol monooleate with 40 ethylene oxide residues (G 1086)+sorbitan sesquioleate (Arlacel 83) and A Soibitan monooleate with 20 ethylene oxide residues (Tween 80) + Arlacel 83 [67]...

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

Selective extraction experiments were then performed to see transference of some transition elements (Cu ", Ni ", Co ", and Fe " ) from the aqueous phase to the organic phase by the synthesized polymeric calixarenes. Phase-transfer studies in water-chloroform confirmed that polymer 2b and 3b were Fe ion-selective as was its monomer (1). Extraction of Fe " cation with 2b and 3b was observed to be maximum at pH 5.4. Only trace amounts of other metal cations such as Cu, Ni ", and Co " were transferred from the aqueous to the organic phase (Table 3). Furthermore, the extracted quantities of these cations remained unaffected with increasing pH. The effect of pH on the extraction of 3b was lower and 56% extraction was accomplished even at pH 2.2. The extraction experiments were also performed with calix[4]arene (1) the ratio was 8.4% at pH 2.2. The polymeric calix[4]arenes were selective to extract Fe " from an aqueous solution, which contained Cu +, Ni, Co ", and Fe " cations, and it was observed that the... 

In normal emulsion polymerization the diffusion of monomers from droplets allows particles to grow. The polymerization is usually initiated in the aqueous phase and the oligomeric radicals either enter micelles or merge with other growing species. In the crosslinking ECP of EUP the ratio EUP/comonomer and the solubility or insolubility of both components and the initiator in the aqueous and non-aqueous phases respectively are parameters which decide whether diffusion of the reactants in the aqueous phase plays a role and where the initiation takes place. 

A suspension process using redox initiation in a water medium was developed. The redox system is a combination of persulfatesulfite. Often ferrous or cupric salts were added as a catalyst for the redox reaction. Polymerizations were run in water at low temperature (20-25°C) and low pressure (65-85 psi). Monomer to monomer-plus-water weight ratios of 0.20 to 0.25 were used. Good agitation was required to keep an adequate monomer concentration in the aqueous phase. Yields ofup to 100% were obtained with polymer inherent viscosities of0.4 to 1.5 dl/g in C6F5C1. Reactions were run on both a 1-gal and a 100-gal scale. 

The view that the monomers are confined to the reverse micellar pseudophase is supported by interfacial tension data (67), which demonstrate that in a two-phase octane/water system, partially hydrolyzed TEOS species partition preferentially into the aqueous phase. The interfacial tension determined at the octane/water interface for samples prepared with precursor ethanolic solutions of different water-to-TEOS molar ratios (h - 0, 0.29, and 0.55) are presented in Figure 2.2.14 (67). As can be seen, for TEOS concentrations below about 4 X 10- 1 M, the octane/water interfacial tension is independent of the concentration of TEOS species in the organic phase... 

In homogeneous copolymerization, the instantaneous composition of copolymer is decided only by monomer reactivity ratio. On the contrary, in emulsion copolymerization, the copolymer composition depends not only on the monomer reactivity ratio but also on the distribution of monomers between oil (polymer-monomer particles) and aqueous phases (18). 

Some polymer-composition vs. conversion curves were obtained for the copolymerizations with different f s (Figure 2), and all of them seem to intersect the ordinate at 1.0. From the initial slope of the curves and the monomer ratio in the aqueous phase the monomer reactivity ratio was calculated, but the calculation resulted in a negative r2. Therefore, it was concluded that the copolymerization could not be regarded as a homogeneous one even just after the beginning of the reaction. The first stage was considered to be a transitional stage to establish the particle formation. 

Methods The polymer beads were synthesized by suspension polymerization in concentrated aqueous NaCl solution using 0.1% (of monomers) AIBN as initiator, a monomer/aqueous phase ratio of 2/5 and freshly precipitated Mg(0H)2 as suspending agent (9). The beads were Soxhlet extracted with ethanol for 24 hours and after drying classified into mesh sizes. The 30 mesh (0.59-0.70 mm ) and 18 mesh (1.00-1.19 mm 4>) fractions were used for release experiments (30 mesh for DC1 18 mesh for OX). 

Nanocapsule/nanosphere size ranges between 200 and 350 nm were observed to be affected by both the oil-ethanol ratio and the oil-monomer ratio [63, 64], It is also influenced by the particular oil, water-miscible organic solvent, and nonionic surfactant in the aqueous phase. The pH of the aqueous phase and the temperature also affect the size distribution. 

Equation (58) indicates that an increase in initiatior concentration will not enhance the rate of polymerization. It can be used for estimating the molecular mass of the polymer assuming, of course, the absence of transfer. The ratio N/q corresponds to the mean time of polymer growth and molecular mass is equal to the product of the number of additions per unit time and the length of the active life time of the radical, kpN/e. An increase in [I] also means a higher value of q, and thus a shortening of the chains. As in Phase II, the polymerized monomer in the particles is supplemented by monomer diffusion from the droplets across the aqueous phase a stationary state is rapidly established with constant monomer concentration in the particle. The rate of polymerization is then independent of conversion (see, for example the conversion curves in Fig. 7). We assume that the Smith-Ewart theory does not hold for those polymerizations where the mentioned dependence is not linear [132], The valdity of the Smith-Ewart theory is limited by many other factors. 

It can be shown [49] for two phases in equihbrium that the partial molar free energies must be equal. In an emulsion (or miniemulsion) there are three phases monomer droplets, the aqueous phase and polymer particles. Since monomer is soluble in all of these phases, the equilibrium condition requires that the three phases have equal partial molar free energies. In the presence of monomer droplets, emulsion polymer particles contain 30-80% monomer in them. Therefore, they are said to be swollen with monomer. Ugelstad et al. [48] and Azad and Fitch [50] have shown that addition of a third water-insoluble component to a swollen polymer particle can increase the monomer to polymer ratio. They have shown that an optimum chain size for the additive exists since the solubihty of the additive increases as the chain size decreases. They found... 

One of the most unique properties of miniemulsion polymerization is the lack of monomer transport. Recall from Fig. 1 that with macroemulsion polymerization, the monomer must diffuse from the monomer droplets, across the aqueous phase, and into the growing polymer particles. In contrast, in an ideal miniemulsion (nucleation of 100% of the droplets), there is no monomer transport, since the monomer is polymerized within the nucleated droplets. This lack of monomer transport leads to some of the most interesting properties of miniemulsions. For most monomers, macroemulsion polymerization is considered to be reaction, rather than diffusion limited. However, for extremely water insoluble monomers, this might not be the case. In this instance, polymerization in a miniemulsion might be substantially faster than polymerization in an equivalent macroemulsion. For copolymerization in a macroemulsion, where one of the comonomers is highly water insoluble, the comonomer composition at the locus of polymerization might be quite different from the overall comonomer composition, resulting in copolymer compositions other than those predicted by the reactivity ratios. 

The Mayo Lewis equation, using reactivity ratios computed from Eq. 18, will give very different results from the homogenous Mayo Lewis equation for mini-or macroemulsion polymerization when one of the comonomers is substantially water-soluble. Guillot [151] observed this behavior experimentally for the common comonomer pairs of styrene/acrylonitrile and butyl acrylate/vinyl acetate. Both acrylonitrile and vinyl acetate are relatively water-soluble (8.5 and 2.5%wt, respectively) whereas styrene and butyl acrylate are relatively water-insoluble (0.1 and 0.14%wt, respectively). However, in spite of the fact that styrene and butyl acrylate are relatively water-insoluble, monomer transport across the aqueous phase is normally fast enough to maintain equilibrium swelling in the growing polymer particle, and so we can use the monomer partition coefficient. 

Both the mini- and macroemulsion copolymerizations of pMS/MMA tend to follow bulk polymerization kinetics, as described by the integrated copolymer equation. MMA is only slightly more soluble in the aqueous phase, and the reactivity ratios would tend to produce an alternating copolymer. The miniemulsion polymerization showed a slight tendency to form copolymer that is richer in the more water-insoluble monomer. The macroemulsion formed a copolymer that is slightly richer in the methyl methacrylate than the co-... 

The monomer chemical potential in the particles is lower than that in the droplets, so that the monomer in the droplets will diffuse across the aqueous phase and into the particles, leading to changes in the monomer chemical potentials of the the particles and droplets. The change in the monomer chemical potential is illustrated in Fig. 21, where Y is defined as the swelling capacity the ratio of the weight of a swollen particle to its weight before it is swollen. 

Molar ratio HD 0PB Amount of OPB in the aqueous phase, g/dm water Amount of OPB adsorbed on monomer droplets. q/dm3 water... 

The reduction in rate per unit quantity of aqueous phase which occurs at low ratios of aqueous phase to monomer phase may be due to serious depletion of Initiator in the aqueous phase. The Initiator Is considerably more soluble in the butadiene phase than in the aqueous phase, and therefore may have been present largely In the monomer phase in those systems which contained large volumes of butadiene. 

The essential ingredients in an emulsion polymerization are the water, a monomer which is not miscible with water, an oil-in-water emulsifier, and a compound or compounds which release free radicals in the aqueous phase. Other ingredients which may be used in practical recipes are mentioned briefly later. Typical proportions (by weight) are monomers 100, water 150, emulsifier 2-5, and initiator 0.5, although these ratios may vary over a wide range. 

Note that suspension polymerization is only superficially related to emulsion polymerization, which was outlined in Chapter 8. In suspension processes the coagulation of the dispersion is controlled by agitation plus the action of a water-soluble polymer and/or a fine particle size inorganic powder. The role of water is to act primarily as a heat transfer medium. In vinyl chloride suspension polymerization the specific heat of the monomer and polymer are about equal and are one-quarter that of water, on an equal weight basis. Thus, at the typical 1.5/1 water/vinyl chloride mass ratio the heat capacity of the aqueous phase is about six times that of the organic phase. Another use of water is, of course, to keep the viscosity of the reaction medium at a useful level. Water/monomer ratios of 1.5/1 to 1.75/1 provide a good compromise between suspension concentration and viscosity. 

The polymerization was carried out by making up the aqueous phase and the monomer phase separately. The aqueous phase was made up in the flask used to carry out the polymerization. The monomer phase was prepared in another vessel and added later to the reaction flask. The weight ratio of aqueous phase to monomer phase for these syntheses was 1 12. The aqueous phase consisted of 1.645 kg of tap water, 2.0 g of 50% aqueous NaOH, 4.35 g of boric acid, 38.12 g of poly(diallydlmethylammonium chloride) aqueous solution (made from 12.5% solids), and 4.10 g of gelatin. The monomer phase consisted of 129.5 g of commercial DVB (measured by GLC to be 55.6% DVB), 42.3% EVB (97.9% polymerizable monomers), 773.2 g of styrene (99.8% pure), 600.0 g of M1BC, and 9.0 g of AIBN. 

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