1,720,983 research outputs found
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
Photodecomposition of substituted 4-diethylaminoazobenzenes under visible light irradiation in different solvents
No full textThe visible light-induced decomposition of two series of 4-diethylaminoazobenzenes has been studied in solvents of different polarity, in the presence and absence of O-2, in order to clarify the reaction mechanism. Two different paths have been recognised, whose importance depends on the nature of the solvent; both involve the formation of organic free radicals. Decomposition is much faster in acetone than in the other solvents. A strong inhibiting effect of molecular oxygen has been observed in all cases. (C) 2002 Elsevier Science B.V. All rights reserved
Surface modifications of silk by cold SF6 plasma treatment
No full textSilk samples treated in an appositely set-up radio frequency SF6 plasma reactor under different operation conditions, were characterized by XPS, EPR, DSC, XRD, and ATR analyses and water contact angle measurements, and also as a function of storage time after the treatment. Efficient attachment of F atoms on the polymer surface occurred during the plasma treatment, imparting water repellency to it. Also the percentage of surface oxygen increased after the treatment, partially as a consequence of radical scavenging by mol. oxygen and the formation of peroxides. An increase in silk crystallinity during the treatment seems to contribute to ensuring durable water repellency properties
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
A simple device for quality control of polymer films, using measurements of permeation and diffusion coefficients
No full textA simple device for the rapid determination of transport characteristics of vapors, gases or gaseous mixtures through polymer films has been constructed. This device may be useful either for routine quality control or for precise research work. It consists of two coupled permeation cells: the difference between the permeation rates of a tested specimen with respect to a standard film is measured and the resulting signal interpreted in terms of diffusion and permeation coefficients. The two coupled cells are of a differential type: the gas permeating through the film is collected by a flowing stream of an inert gas and carried to the analytical system (gas-chromatographic determinations have been used in this study). Such a system allows high pressure measurements without imposing mechanical stresses on the film and determination of transport coefficients of any gaseous mixture. A theoretical analysis of the transient signal in terms of transport parameters is reported together with some experimental results on commercial polycaprolactam films
Photosynthetic membranes. A model study of the influence of photoinitiated grafting and graft polymerization of 1,6-hexanediol diacrylate and 4-(N-ethyl,N-2-acryloxyethyl)amino-4′-nitro-azobenzene, as co-monomers, onto polypropylene ribbon, on permeation and diffusion coefficients of oxygen and nitrogen
No full textPhotoinitiated grafting and graft polymerization of 1,6-hexanediol diacrylate (I) and 4-(N-ethyl,N-2-acryloxyethyl)amino-4′-nitro-azobenzene (II) as co-monomers with a fixed molar ratio I:II equal to 10, in the presence of 1,2-diphenyl-2,2-dimethoxyethanone (III) as photoinitiator with a ratio R of its molar concentration of 0.005-0.38 with respect to the sum of molar concentrations of I and II, were studied using a polypropylene ribbon as a model system of a macroporous substrate. By polychromatic irradiation at 45°C with energy inputs of 90 mW cm-2, ultrathin layers of co-polymer, able to function as asymmetric membranes, could thus be obtained. Mean polychromatic quantum yields of grafting and graft polymerization, as a function of R, were also measured. Membrane specimens with constant values of grafted (200±20) and graft polymerized (500±80) molecules of monomer units in co-polymer per unit apparent surface (Å2) have been subjected to measurements of permeabilities (P) and diffusivities (D) at 25°C for oxygen and nitrogen, as a function of R. Results show that only an optimum R minimizes P and D, and a narrow range of R-values allows a normal membrane behaviour
MODEL STUDY FOR RELEASE OF PLASTICIZERS FROM POLYMER FILMS THROUGH VAPOR PHASE
No full textA model has been applied to release of plasticizers from polymer films through vapor phase, for which the overall rate of release may be generally determined by evaporation of the plasticizer from the surface of the film, and/or by migration to the surface at below saturation in the polymer. The experimental system employed made use of n-butyl formate, diethylphthalate, di-n-butylphathalate, and N,n-butylbenzenesulfonamide in polycaprolactam films. Experimental measurements were made (at 298-333 K) by investigating in a suitable cell the permeation of plasticizers both at concentrations below and above the saturation limit. Rate of evaporation of plasticizers from the membrane surface above the saturation limit, measured in this cell, were found to coincide satisfactorily with those calculated by application of the mass transfer theory to evaporation from a stationary liquid into a stirred gas, at a known velocity of gas flowing past the surface. In the light of the theoretical model a correlation was found between activation energies of H and evaporation enthalpies of the model molecules
PHOTORESPONSIVE MEMBRANES INCORPORATING 6-SUBSTITUTED 1',3',3'-TRIMETHYLSPIRO-(2H-1-BENZOPYRAN-2,2'-INDOLINES)
No full textPhotoresponsive membranes incorporating 6-X-1',3',3'-trimethylspiro-(2H-1-benzopyran-2,2'-indolines) (6-X-BIPS), with X equals H, OH, Br, NO2 and 1',3',3'-trimethylspiro-(2H-1-naphthopyran-2,2'-indoline) (NIPS), supported by cellulose 2,4-diacetate, have been prepared. Membrane potentials, while irradiated by visible and UV light alternatively, in a pH range between 0. 5 and 10, were found to depend not only on the photochemical equilibrium between 'closed' and 'open' forms of 6-X-BIPS, but also on pH. Isoelectric points of membranes, which substantially coincide with zero point charge of 6-X-BIPS, were found to be independent of X substituents
Photostability of substituted 4-diethylaminoazobenzenes
No full textThe stability to visible light of five 4-diethylaminoazobenzenes was investigated in different solvents under Various experimental conditions, as well as in solid crystalline form and on dyed poly(ethyleneterephthalate). Though generally exhibiting relatively high photostability, all investigated dyes underwent photodegradation in acetone solution. Two different reaction paths were recognised in this solvent, depending on the nature and position of the substituting groups on the second aromatic ring, both involving the formation and subsequent fragmentation of organic free radicals, as suggested by the strong inhibiting effect of molecular oxygen on the photodegradation rate. (C) 2001 Elsevier Science Ltd. All rights reserved
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