Polymer colloids: Particle formation in nonmicellar systems

Fitch, Robert M.; Tsai, C. Y.

doi:10.1002/pol.1970.110081007

Cited by 104 publications

(48 citation statements)

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“…The polymerization technique, the preparation of polymer latex for size measurements, the estimation of particle number were the same as described earlier. 15 Limiting viscosity numbers [] of polyacrylamide were determined with Ubbelohde viscometer in water at 30 C. The viscosity-average molecular weight, M v , of polyacrylamide was calculated from ½ ¼ 6:31 Â 10…”

Section: Recipe and Proceduresmentioning

confidence: 99%

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Inverse Emulsion Polymerization of Acrylamide Initiated by Oil- and Water-soluble Initiators: Effect of Emulsifier Concentration

Capek

2004

Polym J

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ABSTRACT:The nature of the reaction loci in inverse emulsion polymerization of acrylamide (AAm) initiated by oil (2,2 0 -azoisobutyronitrile, AIBN)-and water-soluble (ammonium peroxodisulfate, APS) initiators was investigated.The rate of polymerization (R p,max , Interval 2) increases with increasing the emulsifier concentration up to a certain critical concentration and then decreases. The rate of polymerization and the polymerization rate per particle are somewhat larger in the APS-initiated polymerization than in the AIBN-initiated one. For both initiators the polymerization rate per particle is proportional to the particle size and decreases with increasing the emulsifier concentration and the decrease is much more pronounced at the high emulsifier concentrations. The similar kinetic dependences for both initiators were discussed in terms of the formation of monomeric or oligomeric radicals with the similar nature, mobility via the reaction system and partitioning between the oil and water phases. The similar radicals carrying the initiator fragment were formed by the addition of one or two (or several) units to the primary radicals (SO 4 À or 2-cyanoisopropyl). The estimated average number of radicals per particle ( n n) is much below 0.5. The low radical concentration in the polymer particles was discussed in terms of the desorption of monomeric and emulsifier radicals. The desorption of radicals was confirmed by both the Nomura model (N model , k With the increased interest in the technological exploitation of inverse emulsion polymerization as a method for the preparation of water soluble polymers has come the need to understand microscopic kinetic events that govern both the particle nucleation and the polymer growth in the polymer particles. The conventional processes such the initiation, propagation, termination and chain transfer are all operative in the inverse emulsion or microemulsion polymerizations. The inverse microemulsion polymerization processes (water-in-oil systems, w/o) are well known.1-4 The polymerization is very fast and the process is described by two non-stationary rate intervals. This is ascribed to two opposing effects; the continual increase of particle number and continual decrease of monomer at the reaction loci. The microdroplets saturated with the aqueous solution of monomer act as reaction loci and the reservoir of monomer. The rate of inverse microemulsion polymerization increases with increasing the initiator concentration but strongly decreases with increasing the emulsifier concentration. The study devoted to the inverse miniemulsion (homogenized emulsion) polymerization led to the conclusion that the addition of lipophobe to the inverse miniemulsion generated the long term stability against Ostwald ripening.5 The inverse emulsion polymerization of acrylamide produced turbid, viscous and unstable dispersions at the outset and during the intermediate stages of the polymerization. [6][7][8] It was observed that the initial rate of inverse emulsion polymerization is first or...

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Section: Recipe and Proceduresmentioning

confidence: 99%

“…27,30 The parameter x ¼ 0:5 indicates that the emulsifier acts as the stabilizer and generator of polymer particles as well. The decrease in the polymerization rate at the highest emulsifier concentration ( Figure 5, curves 4 and 5) deviates from the micellar model.…”

Section: Polymerization Ratementioning

confidence: 99%

Inverse Emulsion Polymerization of Acrylamide Initiated by Oil- and Water-soluble Initiators: Effect of Emulsifier Concentration

Capek

2004

Polym J

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“…The best-known alternative theory for particle nucleation is that of "homogeneous nucleation" which includes the formation of particle nuclei in the continuous aqueous phase. This theory is proposed by Priest, Roe and Fitch and Tsai, and extended by Hansen and Ugelstad (HUFT) describes the emulsion polymerization of watersolubble monomers such as vinyl acetate and acrylonitrile, their water solubility though low (< 3%) is much in excess of the amount of monomer which may be solubilized by the emulsifier [43][44][45][46][47][48]. It is also the only mechanism which can apply to monomers of low watersolubility, such as styrene, in emulsifier-free reaction system, and also in reaction system which contain a micellizing emulsifier but at such a concentration that is below the CMC.…”

Section: The Initial Stage (Interval I)mentioning

confidence: 99%

Emulsion Polymerization: Effects of Polymerization Variables on the Properties of Vinyl Acetate Based Emulsion Polymers

Yamak¹

2013

Polymer Science

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“…According to the hypothesis of the formation mechanism of PMP for homogeneous nucleation [27,[35][36][37][38][39][40][41][42], the formation of particles or macromolecules derived from the radicals who have reached the critical length (j ), where they lose solubility and precipitate in the aqueous phase. Further growth of the polymer particles dropped in the water is treated differently.…”

Section: The Mechanism Of Homogeneous Nucleationmentioning

confidence: 99%

An Advanced Approach on the Study of Emulsion Polymerization: Effect of the Initial Dispersion State of the System on the Reaction Mechanism, Polymerization Rate, and Size Distribution of Polymer-Monomer Particles

Khaddazh¹,

Литвиненко²

2012

Polymerization

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According to these ideas, in the presence of surfactants, the initial emulsion consists of two kinds of particles of different sizes: the monomer droplets with diameters of 5-20 microns and colloidal degree of dispersion and monomer-swollen surfactant micelles (5-10 nm).The mechanism of Harkins-Yurzhenko lied in the base of Smith and Ewart quantitative theory [5][6][7], with further refinements in the works of other authors . The main aspect of this theory is that radicals formed in the aqueous phase are trapped by the monomer swollen surfactant micelles and turn to PMP. It is assumed that only one out of every 100-1000 micelles captures a radical and becomes PMP, and the rest of the micelles are spent to stabilize the growing PMPs. Polymer-monomer particles formation ends with the disappearance of micelles of the emulsifier in the aqueous phase, after which the number of particles remains constant.Initial system contains monomer droplets with a diameter of 5-15 microns, their concentration being 10 12 -10 14 droplets/l, the monomer-swollen micelles with diameters of 5-10 nm and the number of micelles 10 18 -10 21 l -1 , and a water-soluble initiator (usually potassium persulfate) at a concentration of 1% per monomer [8]. Only a small fraction of the molecules of the monomer is located in the interior of the micelles (1-2%) and is dissolved in the aqueous phase (0.03% for styrene). In the aqueous phase, 10 14 -10 16 PMP / l are formed with a diameter in the range of 20-200 nm. Monomer droplets due to their relatively small surface area hardly compete with micelles in capturing radicals.In the polymerization process PMPs increase their size due to the diffusion of the monomer from droplets and monomer-swollen micelles which contains no radicals [1-3, 5, 9-15].Three limiting cases were considered:1. The number of free radicals in the particles is small compared with the total number of radicals, thus the average number of radicals per particle is much less that unity. 2. The average number of radicals per particle is equal to 0.5. This case is realized under following conditions: the activity of the radical in the particle persists as long as the second radical enter the particle, and the time of chain-breaking is small as compared with the average time interval of successive absorption of radicals by the particle. The authors believe that case 2 corresponds to the emulsion polymerization of styrene in the presence of potassium persulfate [5]. The rate of formation of primary radicals is equal to 10 13 radicals• ml -1 s -1 . The average number of polymer particles is of the order of 10 14 -10 16 in 1 ml of the system. If all the radicals formed by the decay of the initiator enter the polymer particles, the average frequency at which a radical enters a particle is once per 10 -100 sec. At any time, the particle contains either one radical or does not contain radicals at all, since it is assumed that chain termination occurs immediately in contact with the second radical in the particle. The particle is inactive unt...

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Polymer colloids: Particle formation in nonmicellar systems

Cited by 104 publications

References 6 publications

Inverse Emulsion Polymerization of Acrylamide Initiated by Oil- and Water-soluble Initiators: Effect of Emulsifier Concentration

Inverse Emulsion Polymerization of Acrylamide Initiated by Oil- and Water-soluble Initiators: Effect of Emulsifier Concentration

Emulsion Polymerization: Effects of Polymerization Variables on the Properties of Vinyl Acetate Based Emulsion Polymers

An Advanced Approach on the Study of Emulsion Polymerization: Effect of the Initial Dispersion State of the System on the Reaction Mechanism, Polymerization Rate, and Size Distribution of Polymer-Monomer Particles

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