Micelles chain initiation

Monomer molecules, which have a low but finite solubility in water, diffuse through the water and drift into the soap micelles and swell them. The initiator decomposes into free radicals which also find their way into the micelles and activate polymerisation of a chain within the micelle. Chain growth proceeds until a second radical enters the micelle and starts the growth of a second chain. From kinetic considerations it can be shown that two growing radicals can survive in the same micelle for a few thousandths of a second only before mutual termination occurs. The micelles then remain inactive until a third radical enters the micelle, initiating growth of another chain which continues until a fourth radical comes into the micelle. It is thus seen that statistically the micelle is active for half the time, and as a corollary, at any one time half the micelles contain growing chains. 

Addition of a selective solvent to molecularly dissolved chains has been used by many research teams to prepare block copolymer micelles. The initial nonselective solvent can be further eliminated by evaporation or can be gradually replaced by the selective solvent via a dialysis process. The stepwise dialysis initially introduced by Tuzar and Kratochvil is now widely used for micelle preparation [6], especially for the formation of aqueous micelles [32],... 

Because of their different hydrophilicities, the two free radicals formed at the same time can separate from each other quickly which can eliminate the cage effect. In a micelle, the local BA concentration may be quite high. Once a micelle is initiated, a number of BA molecules may be added quickly. As a result, some short BA blocks would be incorporated into a poly(MAETAC) chain to form something like multi-block copoly(MAETAC-BA), as shown in Fig. 19 [170]. Surfactant should stabilize the BA blocks so that the block copolymer remains in the aqueous phase. 

The time-dependent turbidity measurements carried out by the authors of [69] suggest that the mixing of aqueous solutions of PIB-(t-PMANa micelles and P4VPQ is at first accompanied by the formation of large multimicellar aggregates, which gradually split into smaller ones. At the same time, P4VPQ+ chains initially bound... 

There are two stages involved in a typical emulsion polymerization. In the seed stage, a mixture of water, surfactant, and colloid is first heated to the reaction temperature (85-90°C). Next, 5-10% of the monomer mixture with a portion of the initiator is added. At this point the reaction mixture contains monomer droplets stabilized by surfactant, some dissolved monomei the initiator, and surfactant (in solution and in micelles). The initiator breaks down to produce radicals, when heated and these initiate the polymerization of the dissolved monomers. Growing polymer chains eventually enter a micelle, initiating reaction of the monomer inside. If a second growing polymer enters the micelle, termination can occur. 

For the purpose of formation of micelles of desired size and shape, one needs to use a combination of solvents. To start with, having the chain initiators balancing the hydrophile group will help in the formation of micelles. Then, by choosing the right type of solvent or cosurfactant, the core of the micelles can be enlarged for the removal of the oily soils from the surfaces. 

In emulsion polymerization an excess of surfactant is used. The monomer is dispersed, as in suspension polymerization, but the resulting dispersion is better stabilized. The excess surfactant is present as micelles. The initiator is water soluble. Since the monomer is at least slightly soluble in the water phase, the polymerization starts there. When the oligomer chains grow, polymer particles are... 

Owing to their lipophilic chains and their very small size, micelles are very easily dispersed in base oils and dispersion is stable for a long time. Overbased micelles, used initially as detergents, also present antiwear properties (see Chapter 4). Overbased micelles can be used in several ways (a) as thin coatings deposited on a solid surface, (b) as a colloidal dispersion in apolar medium (oil, grease, etc.) and (c) in gas phase lubrication. 

Probably the kinetic chain initiation takes place in micelle formed by absorption of a radical created in the aqueous phase. In micelle, in which a high concentration of monomer is observed, the chain grows proceeds until absorption of a next radical. Due to the very small size of the spore, in which the polymerization started, it seems likely that the second radical will react with the growing chain and will break its growth. Bu it will not start a new chain. 

Once the monomer phase is dispersed into droplets, the rate of agitation does not ordinarily affect particle size or particle size distribution. The initiator, which is water-soluble, decomposes thermally in the aqueous phase, producing free radicals that diffuse into the micelles and initiate polymerization there. Termination reactions can occur in a number of ways, but because there are very few growing chains within a micelle, the probability for termination by coupling is low thus the molecular weight of the polymer can become very high. Moreover, the emulsion has low viscosity throughout the polymerization, so... 

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. 

Radicals generated from water-soluble initiator might not enter a micelle (14) because of differences in surface-charge density. It is postulated that radical entry is preceded by some polymerization of the monomer in the aqueous phase. The very short oligomer chains are less soluble in the aqueous phase and readily enter the micelles. Other theories exist to explain how water-soluble radicals enter micelles (15). The micelles are presumed to be the principal locus of particle nucleation (16) because of the large surface area of micelles relative to the monomer droplets. 

As the quinone stabilizer is consumed, the peroxy radicals initiate the addition chain propagation reactions through the formation of styryl radicals. In dilute solutions, the reaction between styrene and fumarate ester foUows an alternating sequence. However, in concentrated resin solutions, the alternating addition reaction is impeded at the onset of the physical gel. The Hquid resin forms an intractable gel when only 2% of the fumarate unsaturation is cross-linked with styrene. The gel is initiated through small micelles (12) that form the nuclei for the expansion of the cross-linked network. 

Emulsion Polymerization. In this method, polymerization is initiated by a water-soluble catalyst, eg, a persulfate or a redox system, within the micelles formed by an emulsifying agent (11). The choice of the emulsifier is important because acrylates are readily hydrolyzed under basic conditions (11). As a consequence, the commonly used salts of fatty acids (soaps) are preferably substituted by salts of long-chain sulfonic acids, since they operate well under neutral and acid conditions (12). After polymerization is complete the excess monomer is steam-stripped, and the polymer is coagulated with a salt solution the cmmbs are washed, dried, and finally baled. 

The function of emulsifier in the emulsion polymerization process may be summarized as follows [45] (1) the insolubilized part of the monomer is dispersed and stabilized within the water phase in the form of fine droplets, (2) a part of monomer is taken into the micel structure by solubilization, (3) the forming latex particles are protected from the coagulation by the adsorption of monomer onto the surface of the particles, (4) the emulsifier makes it easier the solubilize the oligomeric chains within the micelles, (5) the emulsifier catalyzes the initiation reaction, and (6) it may act as a transfer agent or retarder leading to chemical binding of emulsifier molecules to the polymer. 

According to the other kinetic model proposed for the soapless emulsion process, the growing macroradicals may also form micelle structures at earlier polymerization times since they have both a hydrophilic end coming from the initiator and a hydrophobic chain [74]. 

Emulsion polymerisation is initiated using a water-soluble initiator, such as potassium persulfate. This forms free radicals in solution which may initiate some growing chains in solution. These radicals or growing chains pass to the micelles and diffuse into them, which causes the bulk of the polymerisation to occur in these stabilised droplets. 

A slight increase in the turbidity upon heating of aqueous solutions of the s-fractions of the NVCl/NVIAz-copolymers obtained from the feeds with initial comonomer molar ratios of 75 25 (Tcp 65 °C) and 80 20 (Tcp 66 °C) could be due to the micellization phenomena, although the absence of DSC peaks over the same temperature range testified to the non-cooperative character of the process. This could indicate that the chains of these s-type copolymers had, nevertheless, a certain amount of oligoNVCl blocks non-buried by the hydrophilic microenvironment sufficiently well and thus capable of participating in the hydrophobically-induced associative intermolecular processes at elevated temperatures. At the same time, the sequence of monomer units in the s-copolymers obtained from the feeds with the initial comonomer ratios of 85 15 and 90 10 (mole/mole) corresponded to the block-copolymers of another type. The basis for such a conclusion is the lack of macroscopic heat-induced phase separation at elevated temperatures (Fig. 3 a and b) and, simultaneously, the transi-... 

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