PHOTOCHEMICAL GRAFTING OF ACRYLATED AZO DYES ONTO POLYMERIC SURFACES .7. KINETICS AND MECHANISM OF DYE-SENSITIZED PHOTOINITIATION OF SOME DIACRYLATES

Photoinitiated 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 study of photoinitiated grafting of diallyl oxydiethylene dicarbonate onto cellulose

Photochemical grafting of diallyl oxydiethylene dicarbonate onto cellulose (in the form of filter paper) was investigated kinetically at 20 \ub1 2 \ub0C with 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator. Irradiations were carried out polychromatically with an incident radiation flux of (1.25 \ub1 0.07) 7 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 \u3bcmol cm-2. Two consecutive rate processes were shown by the kinetic curves, with quantum yields differing by about two orders of magnitude. Quantum yields \u3a61 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

PHOTORESPONSIVE MEMBRANES INCORPORATING 6-SUBSTITUTED 1',3',3'-TRIMETHYLSPIRO-(2H-1-BENZOPYRAN-2,2'-INDOLINES)

Photoresponsive 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

Thermodynamic study of solvent and substituent effects on 4-substituted aminoazobenzenes

Proton dissociation equilibria of various 4-substituted aminoazobenzenes have heen studied as a function of temperature. The corresponding thermodynamic functions \u394Go, \u394Ho, and \u394So have been calculated. Azonium-ammonium tautomeric equilibria of the monoprotonated dyes have also been investigated. The experimental data have been interpreted in terms of linear free energy relationships. Analysis of the solvatochromism of these dyes has led to the determination of some specific interactions with solvents, which, together with electronic factors, can well rationalize many aspects of the behaviour of these molecules

Electrolyte permeation through photo-cured acrylic polymers on steel as related to corrosion of the substrate

The effect of 1,2-diphenyl, 2,2-dimethoxy, ethanone as photoinitiator in some ultraviolet radiation-cured acrylated acrylic formulations on steel was studied. Correlation between corrosion rates, measured with ASTM D610 standardized method, and electrolyte permeation through coatings, measured with 36Cl-labelled 0.25 M NaCl solutions at 25\ub0C, was systematically investigated. The length of time necessary for the complete failure of the coatings, as observed by the extension of corrosion products over the entire surface, was evaluated by visual inspection of corrosion or by the breakthrough curve of permeation, and found to be a function of photoinitiator concentration. The slight difference between failure time obtained by the two methods may well be due to a time lag between the activation of corrosion cells over the whole surface and onset of visible corrosion products everywhere. This time lag may be correlated to the protective value of the coating, and to its permeation properties, particularly

Kinetic approach to the release of vinyl chloride monomer from polymer films, as related to diffusional theories

Monomer-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 \ub0C. 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 \ub1 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

Surface modifications of silk by cold SF6 plasma treatment

Silk 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 study on the sunlight-induced degradation of acid azo dyes on silk

The effects of solar irradiation on the two azo dyes CI Acid Red 1 and CI Acid Orange 8 were investigated both on dyed silk and in aqueous solution at pH 2-4.5. When absorbed on silk, the dyes were more photoreactive, both undergoing photodegradation, though at different rates, and displaying a protective action towards the fibre substrate, as evidenced by viscosimetric analysis. In aqueous solution CI Acid Orange 8 underwent photodegradation, with a quantum yield around 10(-3) mol einstein(-1), while the predominant reaction occurring from CI Acid Red 1 was photocyclization, especially at low pH

Influence of the solvent and excited state prototropic equilibria on photochemical intramolecular acylatio of trans-3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one

The solvent dependence of the kinetics of the geometrical isomerization of trans-3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one and the subsequent intramolecular acylation of the cis substrate was studied. Even if the quantum yields \u3a61 and \u3a62 of the two processes increase on increasing the polarity of the methanol solutions, addition of water is found to quench dramatically \u3a61 and \u3a62. This behaviour is interpreted in terms of the proton exchange equilibria of the excited singlet state. A detailed analysis of the dependence of the fluorescence on the pH was carried out and a mechanistic model which is able to describe satisfactorily the experimental results is proposed