1,721,014 research outputs found
Photopolymerization of multifunctional monomers: Kinetic aspects
No full textA review with 160 refs. on the kinetics and mechanism of photopolymn. of multifunctional monomers
Photochemical production of composite materials and membranes: Mechanistic aspects and applications
No full textThe title review with 67 refs. focuses on characterization of radicals trapped during the photopolymn. of multifunctional monomers and related phenomena, as well as specific photochem. processes for prodn. of composite membranes and their applications
Photochemical grafting of acrylated azo dyes onto polymeric surfaces. V. Grafting of some acryloxy-substituted aromatic diazenes as model molecules onto polypropylene, polycaprolactam, and poly(ethylene terephthalate) films
No full textPhotochemical induced grafting (1) and graft polymerization (2) from N,N-dimethylformamide solutions of four acryloxy-substituted aromatic diazenes, chosen as model molecules of acryloxy azo dyes, were investigated kinetically at 25°C onto polypropylene, polycaprolactam, and poly(ethylene terephtalate) films, by polychromatic irradaition. Quantum efficiencies at zero concentration of dyes and lifetimes of excited states for processes (1) and (2) were evaluated from experimental data by Stern-Volmer plots. The surface density of grafted molecules at the end of process (1) was not affected by the concentration of dyes in solution, but varied sensibly with the chemical nature of polymers and dyes. The relevant parameters are discussed on the basis of the proposed mechanism
Kinetic study of photoinitiated grafting of diallyl oxydiethylene dicarbonate onto cellulose
No full textPhotochemical grafting of diallyl oxydiethylene dicarbonate onto cellulose (in the form of filter paper) was investigated kinetically at 20 ± 2 °C with 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator. Irradiations were carried out polychromatically with an incident radiation flux of (1.25 ± 0.07) × 10-7 einstein s-1 cm-2. The ratio R between the molar concentrations of photoinitiator and monomer was varied in the range 0.032-0.150 and the n/S value (n moles of monomer adsorbed per unit apparent surface S) was varied in the range 8.40-43.8 μmol cm-2. Two consecutive rate processes were shown by the kinetic curves, with quantum yields differing by about two orders of magnitude. Quantum yields Φ1 for the first, almost constant, rate period were measured as a function of R and n/S. Kinetic features of the grafting process of diallylic monomer are discussed in the light of a general mechanism proposed for grafting of diacrylates and the photochemical reactivity of the allylic vs. the acrylic function
PHOTOCHEMICAL GRAFTING OF ACRYLATED AZO DYES ONTO POLYMERIC SURFACES .7. KINETICS AND MECHANISM OF DYE-SENSITIZED PHOTOINITIATION OF SOME DIACRYLATES
No full textPhotoinitiated grafting and graft polymerization of liquid mixtures, adsorbed onto polypropylene, polycaprolactam, and poly(ethylene terephthalate) films, containing one of four acryloxy-substituted aromatic diazenes and one of four diacrylate comonomers, in the presence of 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator, were investigated kinetically at 30 plus or minus 2 degree C. Irradiation was carried out polychromatically, with impinging photoenergy from 2. 1 multiplied by 10** minus 8 to 20. 5 multiplied by 10** minus 8 einstein s** minus 1 cm** minus 2; in some of the runs the ultraviolet radiation was filtered. No selective effect was shown by the presence of dyes in the comonomer mixture. The surface density of grafted molecules at the end of the grafting process was not affected by the photoinitiator concentration (for 0. 030 less than R less than 0. 095), by diacrylate or dye concentrations, or by the kind of polymer substrate
Kinetic modeling of pilot plant photomineralization of aqueous Cibacron CR as model molecule of industrial azo dyes on titanium dioxide-immobilizing membranes
No full textThe kinetics of photobleaching by spectrophotometric analysis and of photomineralization by total organic carbon (TOC) analysis of Cibacron CR in aqueous solutions were studied using titanium dioxide-immobilizing membranes. The experiments were carried out in a pilot plant under monochromatic irradiation. From the rate data as a function of initial concentration, the kinetic parameter k and the pseudo-thermodynamic parameter K for photobleaching were evaluated by complying with the Langmuir-Hinshelwood equation. These parameters were employed to optimize a kinetic model, which considered the mineralization of substrate S to CO2 through one single intermediate I, as being able to represent and mediate the behaviour of all the intermediates effectively formed, both S and I acting as competitive apparent adsorption agents on the immobilized semiconductor surface. By this way, the two couples of constants -k1 and K1 as well as k 2 and K2 - were obtained. With these two couples of parameters the calculated curves fitted very well to the experimental ones, both for photobleaching and photomineralization, whereas the formal Langmuir model was unable to predict rates other than those at the beginning of the bleaching process. Therefore, the Langmuir model alone is unsuitable to infer temporal disappearance of TOC during the photomineralization process. The influence of the membrane's position within the annular photoreactor at several distances from the irradiating lamp was systematically studied with optical paths varying from 2.5 to 12.8 cm. The optimum pH value in order to reach the maximum degradation was around 6, whereas at lower and higher values, a monotonous decrease in rate occurred
Photochemical grafting of acrylated azo dyes onto polymeric surfaces. VI. Effect of 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator on the grafting of some acryloxy-substituted aromatic diazenes onto poly(propylene) and poly(caprolactam) fibres
No full textPhotochemical grafting of acrylated azo dyes onto polymeric surfaces. VI. Effect of 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator on the grafting of some acryloxy-substituted aromatic diazenes onto polypropylene and polycaprolactam fibres
No full textWith the wide variety of vinyl and other monomers available today, photochemical grafting may become an established technical method to impart desired surface characteristics: from antistatic behavior to thermal stability, from adhesion to bacteriocidal properties, from water repellency to hygroscopicity, from soil resistance to flame retardant properties, from optical imaging to dyeability and so on. Photochemistry may consequently play a very important role in this field, by promoting knowledge, by studying applications, as well as optimizing conditions of industrial processes, potentially capable of being developed. This presentation focuses attention on some photochemical processes for textile treatments, and for textile printing, particularly
Kinetic approach to the release of vinyl chloride monomer from polymer films, as related to diffusional theories
No full textMonomer-release kinetics from polyvinyl chloride films, previously saturated by equilibration with monomer solutions in n-hexane, ethylene glycol monomethylether, methanol, and water, were measured by extraction with these model solvents, at 10-50 °C. Solute desorption rate data fitted a linear plot of total amount of solute released vs. the square root of time. Their analysis, in terms of diffusional release theory of a dissolved solute from a polymer matrix with initial solute loading given by the solubility limit, allowed one to obtain diffusivities of vinyl chloride in the polymer as a function of temperature, from which an activation energy of 11.9 ± 0.9 Kcal/mol could be calculated. Release kinetics were practically controlled by the low diffusivities, without any resistance to solute transport due to external mass transfer coefficients. The accelerating influence of solvents, relative to solvent-free experiments reported in the literature, may be compared to a plasticizing penetrant effect, which, however, does not appear to be susceptible, as to its bearing on diffusivities, to the chemical nature of the solvent used
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