ISSN:0959-8103    

DOI:10.1002/pi.4990300402

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWater vapour diffusionD, solubilitySand permeabilityPcoefficients have been determined for films obtained from carboxylated styrene‐butadiene (SB) copolymer latexes. The experimental method is water vapour sorption performed in the range 30–60d̀C. Using the small angle neutron scattering (SANS) method and a selective labelling with D2O vapour, it has been shown that water molecules mainly diffuse in the films through the particle‐particle interfaces, which consist of a polar carboxyl‐rich copolymer. It has been shown that the degree of cross‐linking of the particles does not significantly affect the values ofDandS.Moreover, the effect of neutralization conditions, regarding both the pH value of the initial latex and the nature of the neutralizing agent, has also been investigated. It has been found thatDdoes not depend on these parameters, whereasSappears to be very sensitive to them. The results have been interpreted on the basis of the structural modifications of the films induced by neutralization. Finally, the hydrophilicity (or hydrophobicity) of the neutralizing agent has been identified as one of the key features for controlling the affinity of the latex film for water vapour and hence its permeability

ISSN:0959-8103    

DOI:10.1002/pi.4990300403

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractIn this paper, the change of vapour pressure in the emulsion copolymerization of vinylidene chloride (VDC) was determined. It was observed that the vapour pressure drops at conversion about 60% when VDC/comonomer = 90/10 (wt). The types of emulsifier, concentrations of emulsifier and initiator, temperature do not effect these conversion values significantly. According to the principle of phase equilibrium, that the critical conversion at the end of Interval 2 in the emulsion copolymerization of VDC is about 60% was suggested. The effects of types of emulsifier, concentrations of emulsifier and initiator, temperature, types and concentrations of comonomer on rate of copolymerization were also studied. It was found that the different types of comonomer will have no great effect on the copolymerization rate and intrinsic viscosity of a VDC copolymer. And a common route and recipe can be adopted for producing different grades of PVDC latex.

ISSN:0959-8103    

DOI:10.1002/pi.4990300404

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe particle size distribution of a blend of two polymer latex monodisperse standards, 86 and 238 nm, has been measured by capillary hydrodynamic fractionation (CHDF). The particle size distributions obtained agreed well with the expected particle diameters. The relative amounts of the two standards in the blends were accurately measured at different blend ratios. The particle size distribution of a parenteral lipid sample was successfully measured. A soluble species was fractionated from latex standards smaller than 100nm. This soluble species appears to be excess surfactant used in the preparation of small size monodisperse latexes. The amount of excess surfactant increases as the particle diameter of the standard decreases.

ISSN:0959-8103    

DOI:10.1002/pi.4990300405

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractPhotoacoustic and photothermal spectroscopy methods can be effectively applied to the characterization of single microparticles. As the optical beam deflection method, in which a thermal wave generated by non‐radiative transition is detected by deflection of a probe beam, is sensitive for a single microparticle, and is a remote‐measurement method without using a cell, it is suitable for nondestructive characterization of microparticles. This method was applied to determination of chemical species adsorbed on a single microparticle, and spectral differences between leukemia and normal white blood corpuscles could be obtained. A more violent photothermal conversion phenomenon of a particle, laser breakdown and accompanying plasma and acoustic emission, was applied to individual detection and analysis of ultrafine particles in liquids. Laser‐like nonlinear emission from the plasma was obs

ISSN:0959-8103    

DOI:10.1002/pi.4990300406

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA method to determine the minimum time monomer addition policy for composition control in emulsion polymerization systems when technical grade monomers are used is presented. The method involves a series of semicontinuous emulsion copolymerizations carried out under semistarved conditions. The values of the propagation rate constants, reactivity ratios and monomer partition coefficients are required to use the approach. The method is model‐independent and does not require extremely accurate measurements of the particle size. The method was checked in the methyl methacrylate‐ethyl acrylate seeded emulsion copolymerization. The monomers contained 4‐methoxyphenol as inhibitor. It was found that the iterative approach converged ra

ISSN:0959-8103    

DOI:10.1002/pi.4990300407

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractFor systems of emulsifier‐free emulsion polymerization having particle diameter (Dp) greater than 0.15–0.2μm, a shell‐growth mechanism for particle growth was proposed. According to the mechanism, the polymeric radicals can propagate only within the shell region having a thickness about equal to the most probable end‐to‐end distance of the terminated polymer. This mechanism was considered to result from anchoring of hydrophilic ends of the growing radicals on the particle surface and from a high average number of radicals per particle. The occurrence of limiting conversion for such large particles was attributed to the consequence of shell‐region polymerization characteristic of large emulsion particles and a monomer‐diffusion‐controlled polymerization mechanism within the particles during the high c

ISSN:0959-8103    

DOI:10.1002/pi.4990300408

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractMonodisperse polystyrene particles (6.6 μm diameter) were produced by seeded polymerization utilizing the dynamic swelling method with cooling process as follows. Monodisperse polystyrene seed particles (1.8 μm diameter) were dispersed in ethanol/water (3/4 w/w) medium containing styrene monomer, benzoyl peroxide as initiator and poly(vinyl alcohol) as stabilizer at 65d̀C. By lowering the temperature to −5d̀C at a speed of −1d̀C/min the polystyrene seed particles were swollen from 1.8 to 7.7 μm by the absorption of styrene monomer, keeping the high monodispersity. An appropriate amount of water was then added to the dispersion at −5d̀C to depress the redissolution of styrene from the swollen particles into the medium. By elevating the temperature the seeded polymerization was carried out at 70d̀C. The production of submicron‐size polystyrene new particles as a by‐product was depressed by the addition of N

ISSN:0959-8103    

DOI:10.1002/pi.4990300409

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractIn the soapfree emulsion polymerization of a methyl methacrylate‐K2S2O8‐CaSO3‐H2O system, the polymerization rate, average molecular weight of polymer, particle size and particle concentration would vary with the concentration of CaSO3.It was shown that when the concentration of CaSO3was well below the saturation concentration (3 × 10−4mol/litre H2O), the polymerization rate was higher than that of the system not containing CaSO3. On the other hand, when the concentration of CaSO3was above the saturation concentration, the polymerization rate at the latter stage was lower than that of the system not containing CaSO3within our experimental conditions.The molecular weight of polymer was measured by Gel Permeation Chromatography (GPC). It decreased initially and then increased due to the gel effect over the entire course of polymerization. The size of the polymer particles was measured by both photo correlation spectroscopy (PCS) and transmission electron microscopy (TEM), The reaction mechanism was studied according to the above observation. The mechanical property of poly(methyl methacrylate)‐CaSO3composite obtained from soapfree emulsion polymerization was tested and compared with that obtained from mechanica

ISSN:0959-8103    

DOI:10.1002/pi.4990300410

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractCharacteristic features of particle nucleation and growth in the emulsion copolymerization of styrene and multifunctional monomers such as ethylene glycol dimethacrylate and divinylbenzene were investigated. It was found that in these emulsion copolymerization systems the rate of polymerization per particle decreased drastically with an increase in the content of the multifunctional monomer in the initial monomer feed, and the number of polymer particles produced, on the other hand, increased corresponding to the decrease in the rate of polymerization per particle. The increase in the number of polymer particles produced was explained on the basis of Smith‐Ewart theory, which predicts that the number of polymer particles produced would increase inversely proportional to the 0.4 power of the volumetric growth rate per particle, that is the rate of polymerization per particle during the interval of particle formation (Interval I). It was pointed out that the decrease in the rate of polymerization per particle in Interval I would be due mainly to a decrease in the monomer concentration in the polymer particles which was caused by crosslinking networks of the resultant polyme

ISSN:0959-8103    

DOI:10.1002/pi.4990300411

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY