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ABSTRACT: To explain the kinetic features of particle formation and growth in unseeded emulsion polymerization initiated by oil-soluble initiators, a mathematical kinetic model is proposed, based on the assumption that when initiator radicals or monomer radicals in the water phase enter monomer-solubilized emulsifier micelles, initiate polymerization, and propagate to a chain length which is long enough not to desorb from the micelles, the micelles are regarded to be transformed into polymer particles. It is demonstrated by comparing the experimental results obtained in the emulsion polymerization of styrene initiated by the oil-soluble initiator, 2,2'-azobisisobutyronitrile, with sodium lauryl sulfate as emulsifier that the proposed kinetic model satisfactorily explains the kinetic features such as the effects of initial emulsifier, initiator, and monomer concentrations on both the number of polymer particles produced and the monomer conversion versus time histories. © 1993 John Wiley & Sons, Inc.
Journal of Polymer Science Part A Polymer Chemistry 03/2003; 31(8):2103 - 2113. · 3.92 Impact Factor
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ABSTRACT: In order to clarify the general kinetic behavior of emulsion polymerization initiated by oilsoluble initiators, the emulsion polymerization of styrene initiated by 2,2′-azoisobutyronitrile was as a typical example, investigated thoroughly. The variations of the polymerization rate and the number of polymer particles produced with changes in emulsifier (sodium lauryl sulfate), initiator, and monomer concentrations initially charged and the reaction temperature were determined. It is shown from these experimental results that the kinetic behavior of this emulsion polymerization system is quite similar to that of styrene emulsion polymerization initiated by the water-soluble initiator, potassium persulfate despite the difference in the principal loci of radical production in both systems.
Journal of Polymer Science Part A Polymer Chemistry 03/2003; 29(7):987 - 994. · 3.92 Impact Factor
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ABSTRACT: The rate coefficient for radical desorption from the polymer particles is derived for an emulsion copolymerization system, assuming, for simplicity, that only monomer radicals can desorb from the particles. The effect of free radical desorption on the rate of emulsion copolymerization and the copolymer composition is theoretically analyzed, using the rate coefficient for radical desorption developed in this paper and a mathematical reaction model proposed earlier by the present authors for an emulsion copolymerization system where the average number of total radicals per particle does not exceed 0.5. The validity of the analysis is demonstrated experimentally using the seeded emulsion copolymerization of styrene (ST) and methyl methacrylate (MMA). Radical desorption from the particles does not affect the copolymer composition, but the desorption of MMA—monomer radicals plays an important role in determining the rate of emulsion copolymerization, while the desorption of ST—monomer radicals from the particles can be neglected from a kinetic point of view.
Journal of Applied Polymer Science 03/2003; 27(7):2483 - 2501. · 1.29 Impact Factor
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ABSTRACT: Continuous emulsion polymerizations of vinyl acetate were carried out at 50 °C in a single continuous stirred-tank reactor using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator. It was found that (1) the so-called limit cycles could take place in monomer conversion, the number of polymer particles and the molecular weight of polymers produced under certain operating conditions, (2) the time-average steady-state monomer conversion was proportional to the 0.31 power of the emulsifier concentration in the feed, to the 0.50 power of the initiator concentration, to the −1.0 power of the monomer concentration, and to the 0.90 power of the mean residence time, and (3) the time-average steady-state number of polymer particles produced was proportional to the 2.1 power of the emulsifier concentration in the feed, to the −0.80 power of the initiator concentration, to the 0 power of the monomer concentration, and to the −0.92 power of mean residence time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2748–2754, 2002
Journal of Applied Polymer Science 12/2002; 86(11):2748 - 2754. · 1.29 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 03/2002; 40(9):1275 - 1284. · 3.92 Impact Factor
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ABSTRACT: The low incidence of atherosclerosis and other degenerative disease, including urolithiasis, in the Greenland Eskimo has been attributed to their high consumption of oily fish with its high concentration of eicosapentaenoic acid (EPA). With a westernized diet, the oxygenated products of renal prostaglandin synthesis are metabolites of the n-6 series and these are known to play important roles in several pathophysiological processes involved in calcium stone formation. Buck's group presented a hypothesis that the initiating factor for lithiasis triggers prostaglandin synthesis, and showed that this influenced by EPA treatment.
In order to ascertain the effects of EPA on plasma lipids and urinary parameters, we undertook a clinical study whereby a highly purified preparation was administrated (1,800 mg/day) to 88 patients with urinary stones for 3 months (short term) and 18 months (long term).
Hyperlipemia improved the affected individuals and urinary calcium was significantly reduced in the hypercalciuric but not in the normocalciuric group. Conclusion: The results suggest that EPA by reducing urinary calcium might favorably affect urine composition in a way that possibly reduces the risk of calcium stone formation.
European Urology 06/2001; 39(5):580-5. · 8.49 Impact Factor
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ABSTRACT: The inhibitory effect of allopurinol on calcium oxalate urolithiasis has been reported, but its effect on stone matrix proteins has not been studied in vivo. To clarify the effect of allopurinol on the matrix, we investigated its effect on the expression of osteopontin (OPN), which we previously identified as an important stone matrix protein.
Control rats were not treated. Rats of the stone group were given ethylene glycol (EG) and vitamin D(3), while the allopurinol groups (low-dose group and high-dose group) were treated with allopurinol in addition to receiving EG and vitamin D(3).
The rate of renal stone formation was lower in the allopurinol groups than in the stone group. This was associated with a low expression of OPN mRNA in allopurinol-treated rats relative to that in the stone group.
Allopurinol was effective in preventing calcium oxalate stone formation and reduced OPN expression in rats. Our results suggest that allopurinol prevents renal stone formation by acting against not only the control of oxalate but also OPN expression.
Nephron 03/2001; 87(2):170-6. · 13.26 Impact Factor
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ABSTRACT: Madin-Darby canine kidney (MDCK) cells have been used in research on crystal adhesion to epithelial cells. Recently, matrix proteins were identified, and studies of the genes and proteins expressed in renal epithelial cells have become active. The present study confirms the usefulness of the NRK-52E cell line, derived from the rat, in the study of attachment with calcium oxalate crystals. The calcium oxalate crystal suspension was distributed on top of the cells. After incubation, the monolayers were rinsed to remove non-associated crystals. After fixation, the association of crystals and NRK-52E cells was visualized using scanning electron microscopy. Calcium oxalate crystals were attached to the surface of NRK-52E cells. Under high magnification, many of the microvilli of the cells had elongated towards the crystals, and microvilli projections appeared to catch the crystals. The NRK-52E cell line is useful in the study of attachment between crystals and urinary epithelial cells in the kidney, especially for the regulation and analysis of genes and proteins.
Urologia Internationalis 02/2001; 67(1):73-6. · 0.99 Impact Factor
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ABSTRACT: Osteopontin (OPN) is one of the most important components in calcium stone matrix, but its role in stone formation is not clear. Since quantitative data regarding the excretion of OPN are necessary to assess its role, we have developed a quantitative enzyme-linked immunosorbent assay (ELISA) for OPN, and measured the urinary OPN concentrations in urolithiasis patients. Forty-seven men with urinary stones composed chiefly of calcium oxalate participated in the study. The controls were 13 normal healthy male volunteers. Urine samples were collected early in the morning and analyzed by a quantitative ELISA employing purified polyclonal antibodies to synthesized OPN aminopolypeptides. The urinary ratio of the concentrations of OPN and creatinine (OPN/Cre) in the urolithiasis patients (0.039 +/- 0.029) was significantly lower than that in the control subjects (0.062 +/- 0.030) (P<0.05). Single stone formers (n = 26; 0.050 +/- 0.020) had significantly higher OPN/Cre ratios compared with recurrent stone formers (n = 21; 0.031 +/- 0.021) (P<0. 05). The results show that OPN excretion in urolithiasis patients was lowered, presumably because of the incorporation of OPN by kidney stones.
Urological Research 09/1999; 27(4):225-30. · 1.23 Impact Factor
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ABSTRACT: It has been reported that osteopontin (OPN) plays an important role during urolithiasis as well as bone formation. Generation of stones in the urinary tract may be associated with osteoporosis and bisphosphonates are potent inhibitors of bone resorption, being used with effect in the management of bone disease. We therefore investigated the relationship between alendronate, a bisphosphonate derivative, and OPN expression in the kidney. Alendronate was administered to rats made hypercalcemic by treatment with parathyroid hormone-related peptide (PTHrP). The renal expression of OPN was then evaluated at both protein and mRNA levels. OPN expression was enhanced in the distal tubular cells of hypercalcemic rats and was decreased by alendronate. The observed inhibition of OPN expression suggests an ability of alendronate and other bisphosphonates to act as inhibitors of stone formation in the urinary tract.
Urological Research 02/1998; 26(5):355-60. · 1.23 Impact Factor
