首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Emulsion polymerization of styrene in the absence of emulsifier with K2S2O8 as initiator produced uniform latices. Incorporation of ca. 0.5% ionic comonomer (sodium styrenesulfonate) reduced the particle size from the range 0.5–1.0 μm achieved in prior emulsifier free formulations to a range of 0.15–0.40 μm. Some advantages achieved by incorporation of ionic comonomer were higher polymer content and independently controllable surface charge density. Particle diameter varied as the 0.64 power of the ratio of ionic strength to comonomer, as the ?0.20 power of initiator concentration, and as the 0.46 power of monomer content. Kinetic data suggest that copolymerization takes place in the aqueous phase, and that nuclei for particle growth are formed by precipitation of the initially water-soluble copolymer. The latex is stabilized by sulfonic acid groups of the comonomer, as well as by sulfate end groups from the initiator.  相似文献   

2.
Crosslinked polystyrene microspheres of a diameter of the order of more than 2 μm and a narrow particle diameter distribution were synthesized by emulsifier-free emulsion polymerization. The dependence of various parameters such as an electrolyte (NaCl), an initiator (K2S2O8), the phase volume ratio, the reaction temperature and time on the diameter and the particle size distribution has been discussed.  相似文献   

3.
The polymerization of acrylamide in inverse microemulsions stabilized by Aerosol OT emulsifier and initiated with azobisisobutyronitrile (AIBN) or potassium persulfate (K2S2O8) has been investigated. The inverse polyacrylamide latexes formed are clear and highly stable. A dilatometric technique was used to follow the conversion of monomer at T = 45°C. The rate of polymerization is first order with respect to initial monomer concentration in the presence of AIBN, and is 1.5 order with K2S2O8. An inverse relationship between molecular weight and emulsifier concentration is found which suggests participation of the emulsifier in the initiation reaction. This is confirmed by the independence of the molecular weight of polyacrylamide on the concentration of the initiators. High values of the rate of polymerization are obtained combined with high molecular weights (up to 107). An important and novel feature of this microemulsion process is that each final latex particle consists of one single molecule of polyacrylamide in a collapsed state. This suggests kinetics which do not follow the Smith and Ewart theory but are characterized by continuous particle nucleation.  相似文献   

4.
The polymerization kinetics of monodisperse polystyrene latexes prepared via successive seeding were studied in the region between Smith-Ewart Case 2 (n? = 1/2) and Case 3 (n? ? 1). Potassium persulfate was used as the initiator. The kinetics were measured in a piston/cylinder dilatometer designed for microgravity experiments. A recipe formulation method was developed by which a constant emulsifier (Aerosol-MA) surface coverage was maintained throughout a sequence, beginning with a 0.19 μm polystyrene seed. Monodisperse latexes up to 1 μm in size were prepared using 0.5 mM K2S2O8 with a 4% emulsifier surface coverage. The polymerizations were commenced in Interval III, the particles being swollen with twice their weight in monomer. The kinetics were characterized by the autoacceleration of the gel effect with the overall polymerization rate decreasing with increasing particle size (decreasing Np). The Case 2 to Case 3 kinetic transition was experienced in the first seeding step, however, independence of the rate on the number of particles was not evident even at high values of n? (n? > 10). This was attributed to a dependency of the free radical capture efficiency on the particle size (constant solids). Corroborating indirect evidence was supplied through surface charge analysis and detailed examination of the polymerization kinetics.  相似文献   

5.

Polyurethane containing tertiary nitrogen atoms was synthesized from polyol, diphenylmethane diisoccyanate (MDI) and N‐methyl diethanolamine. The polymer was converted into cationomers by quarternizing with methacrylic acid (MAA) and then dispersed in water. In this reaction, methyl methacrylate (MMA) was used to decrease viscosity; at the same time, it was the monomer in the later reaction. Finally the cationic polyurethane dispersions were further polymerized with an oil‐soluble initiator, azobisisobutyronitrile (AIBN), water‐soluble initiator, K2S2O8 (KPS) and the mixture of AIBN and KPS. The different emulsion particles with shell‐core structure, “invert” shell‐core structure and “irregular” sandwich structure were obtained; the morphological structures were characterized by TEM observation, FT‐IR and particle size analysis.  相似文献   

6.
Monodisperse latex particles with surface amino groups were prepared by a two‐step emulsion polymerization. In the first step, the seeds were synthesized by batch emulsion polymerization of styrene; and in the second step, two different amino‐functionalized monomers [aminoethylmethacrylate hydrochloride (AEMH) and vinylbenzylamine hydrochloride (VBAH)], two different initiator systems (K2S2O8 and K2S2O8/Na2S2O5) and mixtures of emulsifiers sodium dodecylsulfate (SDS) and Tween 21 were used to synthesize the final latexes. To characterize the final latexes, conversions were obtained gravimetrically and particle size distributions and average particle diameters were determined by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The amount of amino groups was determined by the SPDP (N‐succinimidyl 3‐(2‐pyridyldithio)propionate) method. The influence of the different conditions used to synthesize the latexes on the colloidal stability of the particles was evaluated by measuring the diameters of the final latexes dispersed in solutions at different pHs and ionic strengths. The most stable latexes were obtained using the smallest seed, VBAH monomer, and the K2S2O8/Na2S2O5 initiator system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4230–4237, 2000  相似文献   

7.
Tables are presented for convenient calculation of the basic parameters of the revised Smith-Ewart theory. For the methyl methacrylate (MMA)/sodium lauryl sulfate (SLS)/K2S2O8, and for the styrene/SLS/K2S2O8 reaction mixtures parameters are presented from which the absolute values of the following quantities can be conveniently calculated for any temperature, soap, and initiator concentration: particle number, particle radius, conversion where particle nucleation stops, rate and molecular weight in interval II, the interval after completion of particle nucleation and before the disappearance of monomer droplets. The theoretical predictions are compared to new experimental data and to those from the literature. The available data confirm the theoretical prediction that particle nucleation stops after a very small amount of polymer is formed, of the order of 0.01 cc. polymer/cc. water in most recipes. The theory and experiments are in good qualitative agreement for the conversion rate prior to completion of particle formation: the conversion rate rises with time and, when particle nucleation stops, it levels off. Excellent quantitative agreement can be obtained between theoretical and experimental particle size values. In the experiments of this laboratory the SLS concentration was varied 60-fold, the K2S2O8 concentration was varied 140-fold and the difference between theoretical and experimental poly(MMA) particle radii was always less than about 20%. Similar good agreement was obtained for polystyrene over the temperature range 30–90°C. Some polystyrene data from the literature with carboxylic soaps give just as good fit as the data with SLS of this laboratory. The predicted proportionality between particle number and the product of 0.6 power of soap concentration and of 0.4 power of initiator concentration was observed for several monomers. The theoretical predictions for the rate and molecular weight obtained in interval II are valid only for relatively low initiator and high soap recipes. For recipes for MMA and styrene the rate data are in good agreement with those calculated from the theory. The theory also correctly predicts the order of magnitude of the experimental molecular weights. For several monomers the rate and molecular weight vary with initiator and soap concentrations in a manner close to theoretical predictions.  相似文献   

8.
Soapless emulsion copolymerization of styrene (S) and n-butyl acrylate (BuA) has been investigated using two types of initiator and different comonomer feed mixtures. When using K2S2O8 as initiator, the particle size and size distribution of the final latexes (500 nm and 1.003, respectively) is not significantly affected by the comonomer feed composition, whereas the molecular weight and surface characteristics were found to sharply change at high butyl acrylate content. Based on the most probable particle nucleation mechanism and type of chain termination in the monomer swollen particles, a tentative explanation of these results has been proposed. Replacing persulfate by a carboxylic initiator (4-4′-azobiscyanopentanoic acid) results in the formation of stable particles as α observed with the persulfate, provided the aqueous phase pH is fixed in between 6 and 7. Results on the initiator residue location as a function of the conversion point out that the particle flocculation mechanism is strongly significant in the preparation of such latexes.  相似文献   

9.
The polymerization of isodecyl acrylate (ISODAC) in vesicles made from an anionic surfactant—sodium di-2-ethylhexyl phosphate (SEHP)—and from water is studied by 1H-NMR, transmission electron microscopy, and quasielastic light scattering. High polymerization rates and high conversion rates are achieved with both water-soluble initiator, K2S2O8 (potassium persulfate), and oil-soluble initiator, AIBN (azoisobisbutyronitrile). ISODAC is probably located inside the vesicle bilayer(s) because of its high hydrophobicity. Particles stable at room temperature with a mean diameter of about 50 nm are obtained. Kinetic orders of ISODAC polymerization are determined and the characterization of the resulting particles during and after polymerization are studied. © 1996 John Wiley & Sons, Inc.  相似文献   

10.
The emulsion polymerization of vinyl acetate using potassium persulfate and cyclohexanone sodium bisulfite as redox pair initiation system was studied. The rate of polymerization, maximum conversion, and the number of polymer particles produced were found to change with redox initiator, monomer and emulsifier concentrations, and temperature variation. The rate of polymerization was found to be dependent on the initiator, the monomer, and the emulsifier concentrations to the 0.88, 0.22, and 0.20 powers, respectively. The K2S2O8–NaHSO3 redox system was found to decrease maximum conversion and doesn't form a stable emulsion. The apparent arrhenius activation energy (Ea) estimated for the polymerization system was 65.6 kJ/mol. The viscosity average molecular weights for some obtained poly(vinyl acetate) were determined.  相似文献   

11.
Abstract

The kinetics of phase-transfer-agent-assisted free-radical polymerization of methyl methacrylate using K2S2O8 as the water-soluble initiator and triethylbenzylammonium chloride (TEBA) as the phase-transfer catalyst (PTC) was investigated in toluene-water biphase media at 60°C. The effect of varying [MMA], [K2S2O8], [TEBA], [H+], the ionic strength of the medium, and the temperature on the rate of polymerization (R p) was studied. R p was found to be proportional to [MMA]2, [K2S2O8]1, and [TEBA]0.5. Based on the kinetic results, a mechanism involving initiation of polymerization by phase-transferred S2O8 2- and termination by Q+ (quaternary ammonium ion) is proposed.  相似文献   

12.
The polymerization of methylated β‐cyclodextrin (m‐β‐CD) 1 : 1 host‐guest compounds of methyl methacrylate (MMA) ( 1 ) or styrene ( 2 ) is described. The polymerization of complexes 1 a and 2 a was carried out in water with potassium peroxodisulfate (K2S2O8)/sodium hydrogensulfite (NaHSO3) as radical redox initiator at 60°C. Unthreading of m‐β‐CD during the polymerization led to water‐insoluble poly(methyl methacrylate) (PMMA) ( 3 ) and polystyrene ( 4 ). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in ethanol as organic solvent with 2,2′‐azoisobutyronitrile (AIBN) as radical initiator showed significantly lower molecular weights and were obtained in lower yields in all cases. Polymerization of m‐β‐CD complexed MMA in water, initiated with 2,2′‐azobis(N,N ′‐dimethyleneisobutyroamidine) dihydrochloride, occurred much faster than the polymerization of uncomplexed MMA in methanol under similar conditions. Furthermore, it was shown, that the precipitation polymerization of complexed MMA from homogeneous aqueous solution can be described by equations (Pn–1 ∝ lsqb;Irsqb;0.5) similar to those for classical polymerization in solution.  相似文献   

13.
Reversible addition fragmentation chain transfer (RAFT) polymerizations of N‐isopropylacrylamide (NIPAM), and acrylamide (AM) were successfully performed in aqueous media at ambient temperature using a redox initiator, potassium persulfate (K2S2O8), and sodium thiosulfate (Na2S2O3). The molecular weight of the polymers obtained increases linearly with monomer conversion, molecular weight distribution is narrow even at high conversion (>90%), and a linear relationship exists between ln([M]0/[M]) and polymerization time. Moreover, self‐chain extension reaction also proceeded successfully. All the results demonstrate that K2S2O8–Na2S2O3 is a very efficient initiating system for the RAFT polymerizations of NIPAM and AM in aqueous media at room temperature.

  相似文献   


14.
Two methods for the polymerization of acrolein are proposed: suspension polymerization in water with the redox system K2S2O8:AgNO3 = 1:0.1 with respect to the monomer and a static method with the system K2S2O8:PA–SO2 adduct. The dependencies of yield, molecular weight, and structure of polyacrolein under investigation on the following factors: the amount and the ratio of the initiator components, the pH of the medium, and the monomer:solvent ratio were investigated. The structure of polyacrolein was studied by infrared spectroscopy, thermogravimetric analysis, and chemical functional analysis. The molecular weight distribution of samples of static and suspension polyacroleins modified under identical conditions was determined by gel permeation chromatography.  相似文献   

15.
Polymer colloids based on 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D ‐glucofuranose (3‐MDG) and butyl acrylate (BA) were prepared via free radical mini‐emulsion polymerization. The kinetic and colloidal features of the copolymerization were investigated. The final particle size (D) of the sugar latexes is inversely proportional to the concentration of the anionic emulsifier (sodium dodecyl sulphate, SDS) and the non‐ionic one (alkyl polyglucoside, APG). It was also found that D is independent of the concentration of either the water‐soluble initiator (potassium persulfate, KPS), or the oil‐soluble initiator (2,2′‐azobisisobutyronitrile, AIBN). The rate of mini‐emulsion polymerization is lower in comparison with the conventional emulsion polymerization under the same conditions. The polymerization rate (Rp) and the total number of particles (Np) are proportional to the 0.72th and 0.93th power of the SDS, and to the 1.40th and 2.22th of the APG concentration. Following reaction orders, 0.79/0.06 were obtained for Rp/Np versus the concentration of KPS, and 0.22/?0.01 for AIBN, respectively. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

16.
Various crown ethers were used as phase-transfer catalysts for free radical polymerizations of some water-insoluble vinyl monomers such as acrylonitrile, methylmethacrylate and styrene with persulfate as initiator. The catalytic abilities of these crown ethers for free radical polymerization of acrylonitrile with S2O82?ion as an initiator were in the order: 18-crown-6 > 15-crown-4 > 12-crown-4 > benzo-15-crown-5 > dibenzo-18-crown-6. Among various persulfates such as Na2S2O8 K2S2O8 and (NH4)2S2O8, ammonium persulfate was the optimum initiator for the polymerization of acrylonitrile catalyzed by 18-crown-6 or 15-crown-5. Among the organic solvents used, chloroform seems to be the best solvent for the catalytic polymerization of acrylonitrile. An apparent activation energy of 72.9 kJ mol?1 was observed for the polymerization of acrylonitrile. The catalytic reaction rates of free radical polymerization for these hydrophobic vinyl monomers were in the order: acrylonitrile > methylmethacrylate > styrene > isoprene. Effects of concentrations of crown ether, initiator, and nitrogen on the polymerization of these vinyl monomers were investigated.  相似文献   

17.
<正> Suen等采用氯酸盐-亚硫酸盐氧化还原引发体系在不同的pH条件下进行丙烯酰胺溶液聚合,结果表明,起始聚合速度与([ClO_3][H_2SO_3])~(1/2)成正比,井本用K_2S_2O_8为引发剂研究了pH对丙烯酰胺聚合的影响,认为pH在3—8范围内,起始聚合速度几乎不受pH影响,当pH达到9以上时,则急剧下降,我们采用过硫酸盐-亚硫酸盐、过硫  相似文献   

18.
Fe_3O_4/Polystyrene(PSt) magnetic particles with core/shell structure have been prepared in thepresence of Fe_3O_4 magnetic fluid in ethanol/water medium by dispersion polymeriation of styrene. A Fe_3O_4particle formation mechanism was proposed. According to this mechanism, the size of particle nuclei isdetermined by the extent of aggregation of Fe_3O_4 /oligomer. Magnetic particles with diameter ranging from 5to 200 μm were prepared under different reaction conditions. Some polymerization parameters such as theconcentration of monomer, stabilizer, initiator, and ethanol which affect particle size and size distribution arediscussed and their effect on particle formation are explained by the proposed mechanism.  相似文献   

19.
In order to improve stability and reduce droplet size, the PEG-modified urethane acrylates were synthesized by the reaction of polyethylene glycol (PEG) with residual isocyanate groups of urethane acrylate to incorporate hydrophilic groups into the molecular ends. The droplet sizes of the PEG-modified urethane acrylate emulsions were much smaller than those of unmodified urethane acrylate emulsions at the same surfactant composition, and the droplet sizes of these emulsions were significantly effected not by surfactant compositions and types, but by the reaction molar ratio of PEG, because the urethane acrylate containing polyoxyethylene groups as terminal groups aided the interfacial activity of surfactant molecules and acted as a polymeric surfactant. The actions of PEG-modified urethane acrylate were confirmed by the investigation of adsorption of urethane acrylate in a water/benzene interface.For polymerization of emulsions, the stability of emulsion in the process of emulsion polymerization was changed by the type of surfactant or initiator. In the case of emulsion polymerization with a water soluble initiator (K2S2O8), the emulsions prepared using TWEEN 60 were broken in the process of polymerization. However, polymerization of these emulsions could be carried out using an oil soluble initiator (AIBN). The conversion of emulsion polymerization changed with the type of urethane acrylates, that is, the reaction molar ratio of PEG to 2-HEMA.  相似文献   

20.
Miniemulsion polymerization of styrene (St) in the presence of a hydrophobe (hexadecane:HD) using a cationic polymerizable surfactant (N,N-dimethyl-N-n-dodecyl-N-2-methacryloyloxyethylammonium bromide:C(12)Br) and a cationic initiator (2,2'-azobis(2-amidinopropane) dihydrochloride:V50), called St/C(12)Br/V50 hereafter, proceeded efficiently compared with that using sodium dodecyl sulfate (SDS) and potassium persulfate (KPS), i.e., St/SDS/KPS, providing monodisperse polystyrene latex particles with a narrower particle size distribution. In St/C(12)Br/AIBN, where an oil-soluble initiator, i.e., 2,2'-azobisisobutyronitrile (AIBN), was used in place of V50, little changes in polymerization kinetics or in particle size distribution were observed, while a significant drop in polymerization rate and a broad particle size distribution were observed with St/SDS/AIBN. A polymerizable pyrene derivative (1-pyrenylmethyl methacrylate: PyMMA) was quantitatively incorporated into monodisperse latex particles in St/PyMMA/C(12)Br/V50 compared to pyrene (Py) in St/Py/C(12)Br/V50. Contrary to our expectation, however, increased excimer emission was observed with St/PyMMA/C(12)Br/V50 particles, indicating less evenly distributed pyrene chromophores in the particles. The fluorescence lifetime of pyrene chromophores in St/Py/C(12)Br/V50 particles was determined to be 286 ns, which was 17 times longer than that of pyrene in THF solution.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号