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Summary: Surface modification induced on poly(ethylene terephthalate) (PET) fibers by cold SF6 plasma treatment has been investigated systematically as a function of plasma device parameters. The observed wettability modifications of fibers plasma-treated under different operating conditions were correlated to their dyeability modifications and to the changes in surface chemical composition, determined by X-ray Photoelectron Spectroscopy (XPS), and topography, investigated by atomic force microscopy (AFM). Optical emission spectra from the SF6 plasma at different pressures gave information on its content of fluorine atoms. A striking transition was observed between the increased hydrophilicity and high dyeability, imparted by plasma treatment at low pressure (

Some selective plasma treatments are described, aiming at modifying specific surface properties of textile polymeric materials, such as their hydrorepellence and dyeability. The prevailing plasma–polymer interactions were identified by correlating the physico-chemical modification of treated polymer surfaces to the characteristics of the plasma sources.

The surface chemical and physical modifications of poly(ethylene terephthalate) (PET) fibers induced by radiofrequency air plasma treatments were correlated with the characteristics of the discharge parameters and the chemical composition of the plasma itself, to identify the plasma-induced surface processes prevailing under different operating conditions. Treated polymer surfaces were characterized by water droplet absorption time measurements and XPS analysis, as a function of the aging time in different media, and by AFM analysis. They exhibited a remarkable increase in hydrophilicity, accompanied by extensive etching and by the implantation of both oxygen- and nitrogen-containing polar groups. Etching was mainly a consequence of ion bombardment, yielding low molecular weight, water soluble oxidation products, while surface chemical modifications were mainly due to the action of neutral species on the plasma-activated polymer surface. (C) 2003 Elsevier Science B.V. All rights reserved.

Mixtures of phenanthrene (P) and hydrophenanthrenes (HPs) of increasing hydrogenation degree (H 2 P, H 4 P, H 8 Ps, H 14 Ps) were obtained by hydrogenation of P under kinetic control conditions on Ni catalyst at 292 °C and 315 °C under constant hydrogen pressure (7.1–7.8 MPa) for reaction times up to 96 min. Thermal treatments (400 °C, 60 min) of the final mixtures have permitted to define the roles of individual molecular species (in particular H 2 P and s -H 8 P) in bimolecular reactions of H-exchange and disproportionation and in unimolecular reactions of isomerization and fragmentation connected to the thermal dehydrogenation. H 8 Ps, as overhydrogenated donor species, were further examined with regard to the bimolecular reactions at higher temperature (484 °C) and shorter reaction times (10 min) in the presence of P added as coal model.

H-transfers for upgrading of bridge polyaromatic structures in coal liquids and heavy oil fractions were studied in tetralin (THN) as H-donor model system. Symmetrical hydrogenation of t -stilbene (ΦCHCHΦ), in the presence of diphenyldisulfide (ΦSSΦ), and scission of bibenzyl (BB), as representative of consecutive stages of a same process, were investigated. The results have shown that (1) reduction of t -stilbene to BB, at 350 °C, occurs with stoichiometric yield (100%) when accelerated by addition of diphenyldisulfide as radical generator; (2) scission of BB, at 360–422 °C, takes place for 99.7 to 95.4% according to an unsymmetrical mechanism (formation of benzene) due to H-ipso attack from THN to stronger C ar C al bonds and for the remaining 0.3 to 4.6% with a symmetrical mechanism (formation of toluene) due to weaker C al C al bond homolysis.

Water molecules retained in native cellulose gels obtained from Acetobacter xylinym (AX) were displaced by poly(ethylene glycol)s (PEG) of different molecular weight. The so obtained native cellulose/PEG material, characterized in film form by differential scanning calorimetry, dynamic mechanical thermal analysis and wide angle X-ray scattering, revealed that strong interactions occur between PEG and cellulose and that the polymer mixture is in the rubbery state at ambient temperature. Moreover, it could be dyed in supercritical carbon dioxide by disperse dyes, thus exhibiting typically lipophilic properties and suitability to be employed as a bio-compatible support for lipophilic active species.

Silk samples, treated in an appositely set-up radio frequency SF6 plasma reactor under different operation conditions, were characterized by XPS, EPR, DSC, XRD, ATR analyses and water contact angle measurements, also as a function of storage time after the treatment. Efficient attachment of fluorine atoms on the polymer surface occurred during the plasma treatment, imparting water repellence to it. Also the percentage of surface oxygen increased after the treatment, partially as a consequence of radical scavenging by molecular oxygen and the formation of peroxides. An increase in silk crystallinity during the treatment seems to contribute to ensuring durable water repellence properties.

This research concerns the development of a SF6 RF discharge at low pressure in a small reactor for industrial applications. The plasma is produced in the pressure range 0.05-1 mbar by a RF supply. The pumping system sustains a flowrate of about 50 cm s-1, with residence time in the discharge of about 0.2 s at a pressure of 0.1 mbar. The discharge parameters were measured at a low operation power. Measurements were performed by means of movable electrostatic probes and a photodiode. Particular care in the analysis of the data proved to be necessary due to the presence of a substantial amount of negative ions. The reactor has been employed for textile treatment in order to modify the surface properties of the fibres. Favourable operating conditions leading to an improved hydrophobicity of the textiles were achieved.

Poly(ethylene terephthalate) (PET) and cotton fibres, treated in an appositely set up RF SF6 plasma reactor under different operating conditions, were characterised by XPS, EPR, DSC, XRD, ATR analyses, water contact angle and water droplet roll-off angle measurements. The ageing of plasma-treated samples was also investigated under different post-treatment conditions. Plasma treatment led to efficient implantation of fluorine atoms on the surface of both polymers; this resulted in water repellence without altering the bulk properties of the polymers. The radical species formed in the plasma-activated polymer surface were involved in its fluorination and in the subsequent uptake of atmospheric oxygen. Surface reorganisation of polymer segments, tending to reduce the interfacial energy between the polymer and the phase in contact with it, induced the surface modifications observed under ageing and in samples plasma-treated several times. An increase in the depth of the fluorinated layer, leading to outstanding stable hydrorepellence, was achieved by repeated SF6 plasma treatments, followed by surface rearrangements favoured by swelling.

The decolorization and mineralization of some azo and anthraquinone dyes by photoactivated hydrogen peroxide has been studied. The degradation process seems to occur according to a similar mechanism for all the selected dyes. Decolorization is complete in a relatively short time and follows apparent first order kinetics, whereas mineralization requires longer irradiation times. Initially fluorescent intermediates are generated in all cases by hydroxylation of the studied compounds. A simple kinetic model, describing adequately the process, has been proposed; pH does not influence significantly the process in the range going from 3 to 9.

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.

Melted blends of polypropylene and polyamide 6 compatibilized with a poly(propylene)/maleic anhydride copolymer were extruded and stretched to give filaments. The polypropylenic fibers obtained by this method were found to be easily dyeable in an aqueous dyebath. The wet-washing at 40, 60, and 90°C and the light and dry-cleaning fastnesses of the new material appeared quite satisfactory.

To improve the physical picture of the polymeric glassy state, the influence of morphological changes achieved by different thermal treatments of an amorphous glassy poly(alkylene terephthalate) film on the oxygen transport properties has been studied. Annealing treatments were performed on films in constraint imposed giving samples of different crystallinity contents and morphology. The dependence of the oxygen permeability and diffusion as the free volume from crystallinity content was investigated at sub-Tg temperatures within the range of 303–348 K. The investigations reveal that on crystallized samples, permeability and solubility coefficients decrease at higher crystallization temperature, while annealed samples showed an opposite trend despite higher crystallinities. Further, annealed films showed higher free volume content. The trend of results suggests that different parameters are likely to play a significant role in determining apparent permeability coefficients. The presence of microvoids in annealed samples may be supposed. Zum besseren Verstandnis des glasigen Zustandes von Polymeren wurde der Einflus auf die Sauerstofftransportfahigkeit untersucht, den die morphologischen Veranderungen infolge verschiedener thermischer Behandlungen in Poly(alkylenterephthalat-Filmen ausuben. Zur Herstellung von Proben unterschiedlicher Kristallinitat und Morphologie wurden die Filme unter Schrumpfungsverhinderung unterschiedlich thermisch behandelt (Abschrecken, Kristallisieren). Die Abhangigkeit der Sauerstoffdurchlassigkeit und -diffusion vom Kristallinitatsgrad sowie der Inhalt an freiem Volumen im Inneren des Polymeren wurden unterhalb der Glastemperaturen, im Bereich von 303 bis 348 K, untersucht. Die Ergebnisse zeigen eine Abnahme der Durchlassigkeits- und Loslichkeitskoeffizienten mit zunehmender Kristallisationstemperatur. Im Falle eines uber 0,37 liegenden kristallinen Anteils zeigen die abgeschreckten Filme jedoch, trotz ihrer hoheren Kristallinitat, ein umgekehrtes Verhalten. Aus den durchgefuhrten Untersuchungen scheint hervorzugehen, das verschiedene Parameter eine wichtige Rolle bei der experimentellen Bestimmung der Durchlassigkeitskoeffizienten spielen. Bei den abgeschreckten Filmen wurden auserdem hohere Werte des freien Volumens (fa) festgestellt, was auf die Anwesenheit von Mikrohohlraumen im Polymeren hindeutet.

The aging of bacterial polyester poly(D(—)3-hydroxybutyrate) has been studied by coloring it with 4-diethylamino-4′-methoxyazobenzene and determining the reduction in isomerization rate of the dye with aging, such a reduction being a measure of the loss in polymer sequential mobility that is responsible for the considered phenomenon. A preliminary test carried out on poly(ethylene terephthalate) colored with 4-diethylaminoazobenzene proved the isomerization of the dispersed dye to be a sound probe for determining the aging process. In the case of the bacterial polyester, the aging process appeared even above the polymer Tg value measured by calorimetric analysis. The kinetics and rate coefficients of aging were determined at 30°C for the examined polymers. Aging in the copolymer poly(hydroxybutyrate-hydroxyvalerate) was also investigated. © 1995 John Wiley & Sons, Inc.

Conventional direct dyeing techniques have limited use for the coloration of polypropylene fibers. In this paper, blends of isotactic polypropylene (iPP) with hydrogenated oligocyclopentadiene (HOCP), a glassy amorphous resin, have been used for the preparation of fibers dyeable in an aqueous dyebath. These fibers show better light, wet-washing and cleaning fastness properties than iPP while retaining similar statical mechanical properties.

Atactic poly(epichlorohydrin) (PECH) was blended in a wide range of ratios with poly(D(−)3-hydroxybutyrate) (PHB) isolated from Alcaligenes eutrophus cultures. The crystallization and thermal behaviour of PHB/PECH blends were analysed by d.s.c. and microscopy. All blends show a single glass transition temperature, whose value is dependent on composition, in good agreement with the theoretical values calculated by the Fox equation. The influence of blend composition on the overall crystallization rate and on the spherulite growth rate suggests that the two components form a miscible blend in the amorphous phase. The equilibrium melting temperature decreases with blending; the negative value of the χ12 parameter of the PHB/PECH system suggests that the two components can form a miscible mixture which is thermodynamically stable above the equilibrium melting temperature. The reorganization phenomenon of PHB crystals after first melting was also observed.

Oxygen permeation through films of pure poly(propylene) (iPP) and iPP blended with a fully saturated alicyclic hydrocarbon resin (IST), obtained by oligomerization of indonaphthene, α-methylstyrene and vinyltoluene, was studied as a function of temperature and weight fraction of the two components. Increasing IST content lowers oxygen permeability and increases the glass transition temperature of the polymer blends. Annealing for 2 min at 375 K was shown to transform completely the smectic phase in the α crystalline form, while annealing for 10 min at 393 or 403 K induces a marked increase in crystallinity and in effective oxygen permeability per unit of amorphous component, Pa. This experimental behaviour may be explained by the formation of microvoids; the increase in microporosity modifies the mechanism of the permeation process.

The thermal cis-trans isomerization of some 4-diethylaminoazobenzenes was studied kinetically as a function of temperature in various polymeric matrices. Blends of isotactic polypropylene mixed with various weight fractions of hydrogenated oligocyclopentadiene or oligo-β-pinene were used. Kinetics experiments confirmed that the isomerization reaction is a sound probe for characterizing the transition from rubbery to glassy state of the medium with the appearance of a multiplicity of first-order reactions. The isomerization rates were found to be dependent on the position of the substituents, but no marked influence of the composition of the polymeric blend was detected, even in the presence of considerable changes in the glass transition temperature or in the crystallinity of the samples. This behavior confirms that the isomerization reaction takes place essentially in the amorphous regions which appear to be quite similar for the various blends examined.

Films obtained from native cellulose synthesized by Acetobacter xylinum and from cellulose obtained from cuproammoniacal solutions (cellulose II) were morphologically characterized by studying the cis-trans isomerization of azo dye Chrysophenine dispersed in their amorphous region. The kinetic measurements of the reaction showed that both films behave as glassy polymers in the temperature range explored (36–66°C). In going from native cellulose to cuproammoniacal cellulose, an increase of the isomerization rate was observed, revealing a more homogeneous distribution and likely larger extent of free volume in the amorphous phase of cellulose II.

Photochemical 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.

The geometrical photoisomerization reaction of the title molecule ( trans -I) has been studied in methanol/water 90/10 wt.% mixtures containing sulphuric or hydrochloric acid. Quantum yields of the process, measured under acidic conditions in the range 0.095 N + ] trans -I as a function of pH, experimental quantum yields have been interpreted in the light of prototropic equilibria in the excited state. Mechanistic models are proposed which are able to fit results obtained in the investigated experimental conditions.

The quantum yields for the trans-cis (Φ 1 ) and cis-trans (Φ 2 ) photoisomerization reaction of 4'-X-4-diethylaminoazobenzenes (X=H, OCH 3 , CN, NO 2 ) have been measured in cyclohexane, N,N-dimethylformamide and diethyleneglycol dimethyl ether by irradiation at 415 nm. The corresponding visible absorption spectra of the cis isomers have been determined. The sum of Φ 1 and Φ 2 is equal to unity, within the limits of experimental error, for all the investigated dyes in all solvents. Electron-withdrawing 4'-substituents increase Φ 1 . The same effect is brought about by increasing solvent polarity. The experimental data suggest that photoisomerization proceeds in the singlet manifold along an inversion path.

Two polycaprolactam films were prepared characterized by different crystallinity degrees, the free volume model being prevalent in the former and the pore model in the latter. They were colored with azo dyes XC6H4NNC6H4N(C2H5)2 (where X is H and COOH), the latter of which gives specific interactions with the polymer. The kinetics of the thermal cis–trans isomerization of these dyes has been studied below and above the glass transition temperature of the polymer (Tg) in the range 20–80°C. In every case, the isomerization process was found to be the result of a multiplicity of first-order reactions and the dependence on temperature exhibited a break at the Tg value. Lightfastness of the dyes in the polymer matrices has been also investigated. The isomerization and fading kinetics are discussed in terms of polymer structural features as well as of the nature of the dye.

Surface modification of poly(ethylene terephthalate) (PET) fabrics induced by air radiofrequency (RF) plasma treatment has been investigated systematically as a function of plasma device parameters, to identify the plasma-polymer surface interactions prevailing under different operating conditions and leading to an increased color depth upon dyeing. Some tests have also been performed employing chemically inert argon as a feedstock gas. The dyeing properties of plasma-treated fibers were correlated to their topographical characteristics, determined by AFM analysis, and to their chemical surface composition, determined by XPS analysis, while the plasma-originated UV radiation was found to have no relevant effects in PET surface modification. The relative importance of plasma-induced surface processes, such as etching and grafting of polar species, is discussed in relation to their role in modifying PET dyeing properties. (c) 2005 Elsevier B.V. All rights reserved.

The visible light-induced decomposition of two series of 4-diethylaminoazobenzenes has been studied in solvents of different polarity, in the presence and absence of O2, 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.

The 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.

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 °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 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.

The solvent dependence of the kinetics of the geometrical isomerization of trans -3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3 H )-one and the subsequent intramolecular acylation of the cis substrate was studied. Even if the quantum yields Φ 1 and Φ 2 of the two processes increase on increasing the polarity of the methanol solutions, addition of water is found to quench dramatically Φ 1 and Φ 2 . 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.

Equilibrium pressures of hydrogen chloride and water vapour over solid or liquid barium chloride have been measured between 1173 K and 1473 K. All other gases were excluded from the system. The corresponding equilibria were represented by the following reactions: BaCl2(s) + H2O(g) ⇄ BaO(s) + 2 HCl(g), between 1173 K and 1235 K; BaCl2(1) + H20(g) ⇄ BaO(s) + 2 HCl(g), between 1235 K and 1473 K; 32 BaCl2(1)(saturated with BaO) + H2O(g) ai 12 (BaCl2 2BaO)(s) + 2 HCl(g), between 1173 K and 1268 K; and 43 BaCl2(1) (saturated with BaO) + H2O(g) ⇄ 13 (BaCl2. 3BaO)(s) + 2 HCl(g), between 1268 K and 1473 K. The equilibrium constants Kp fit satisfactorily a linear plot of In Kp versus reciprocal absolute temperature. Mean enthalpy and entropy values of the reactions studied in the temperature range investigated were obtained from the plot and compared to literature data and to the phase diagram of the barium chloride — barium oxide system. The reactions involved and the thermodynamics of reactivity of barium chloride with water are critically examined.

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 36 Cl-labelled 0.25 M NaCl solutions at 25°C, 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.

Five polypropylene films were prepared having different crystallinity and morphology, the latter having been modified by stretching. They were colored with azo dyes XC6H4NNC6H4N(C2H5)2 (where XH, OCH3, CN, and NO2). The kinetics of the thermal cis-trans isomerization of these dyes has been studied in the range 21–41°C, much above the glass transition temperature of the polymer. The isomerization process was found to be strictly first-order; the kinetic parameter values have been correlated with the free volume extent in the amorphous regions of the matrix. Lightfastness of the dyes in the polymer matrices has been also investigated: It appeared to be more important for the unoriented samples with respect to the stretched ones and substantially independent on the crystalinity degree.

A 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, diethyl-phthalate, di-n-butylphthalate, and N,n-butylbenzenesulfonamide as model molecules in polycaprolactam films, both with the aims of studying undesirable loss of plasticizers, and of simulating a model able to envisage releasing, at a constant rate, of any desired additive, with relatively high solubility and vapor pressure, to the content of packaging 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. From these latter rates and solubilities, the mass transfer coefficients H for evaporation could be obtained, as well as from experimental time lags the diffusivities Dp through the polymer membrane. In the light of the theoretical model a correlation was found between activation energies of H and evaporation enthalpies of the model molecules.

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 ± 2°C. Irradiation was carried out polychromatically, with impinging photoenergy from 2.1 × 10−8 to 20.5 × 10−8 einstein s−1 cm−2; in some of the runs the ultraviolet radiation was filtered. The ratio R between the molar concentration of photoinitiator and the sum of concentrations of dye and diacrylate varied between 0.005 and 0.095; the ratio M between the molar concentration of dye and diacrylate varied between 0.005 and 0.046. The moles of dye and diacrylate n initially deposited per unit apparent polymeric surface S varied between 2 and 74 μmol cm−2. 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 < R < 0.095), by diacrylate or dye concentrations, or by the kind of polymer substrate. This parameter, on the contrary, clearly depended on n/S, and linearly up to n/S ≅ 30 μmol cm−2. Quantum efficiencies for the two consecutive kinetic processes of grafting and graft polymerization (Φ1 and Φ2, respectively) were evaluated. The dependency of Φ1 on R, as well as of Φ2 on n/S, are critically discussed on the basis of the proposed mechanism involving grafting of an oligomeric chain (Φ1 values up to the order of 102) followed by a step-by-step graft polymerization (Φ2 limiting values of the order of unity). The sensitizing effect of acryloxy-substituted aromatic diazenes on both Φ1 and Φ2 is evidenced.

Asymmetric membranes were prepared by photochemical grafting of 28.1 μmol cm−2 of 1,6-hexanediol diacrylate onto cellulose in the form of filter paper, in the presence of 1,2-diphenyl-2,2-dimethoxyethanone as a photoinitiator, the molar ratio of photoinitiator to acrylated monomer being fixed at 0.086. A fixed polychromatic irradiation flux of 20.2×10−8 einsteins s−1 cm−2 was used. After 10 min irradiation, a nearly quantitative graft yield was reached. By multiple internal reflection IR analysis, a structure with one pendant acrylate group per monomer unit was assigned to the grafted polymer; at longer irradiation times, a further decrease in unsaturation resulting from photo-cross-linking between pendant acrylate groups was observed. Permeabilities P and diffusivities D at 25 °C for hydrogen and carbon monoxide were measured for membrane specimens obtained at different irradiation times. An increase in P reflects a decrease in unsaturation, while the D are independent of irradiation time. The selectivity of them embranes is not influenced by photo-cross-linking.

Photoinitiated 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 (A2) 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.

Thermal cis–trans-isomerization of some 4′-substituted 4-diethylaminoazobenzenes has been studied. Substitution in the 4′-position leads invariably to an acceleration of the reaction regardless of the nature of the substituent. Logarithms of kinetic constants in various solvents were found to be satisfactorily correlated by the π* scale of solvent polarities both for 4′-nitro-4-diethylaminoazobenzene (I) and for 4′-methoxy-4-diethylaminoazobenzene (II), excluding amphiprotic solvents. Activation parameters (ΔH‡ and ΔS‡) were also measured in NN-dimethylformamide. The results support an inversion mechanism rather than a rotational one; in the case of (I), the highly dipolar nature of the transition state can be justified by its stabilization through coplanar resonance structures (impossible in pure rotation).

Three poly(ethylene terephthalate) films were prepared having the same crystallinity but different morphology. They were colored with azo dyes XC6H4N = NC6H4N(C2H5)2 (where X is H, OCH3, CN, and COOC2H5). The kinetics of the thermal cis-trans isomerization of these dyes has been studied below the glass transition temperature in the range 25–56°C. The isomerization process was found to be the result of a multiplicity of first-order reactions. The kinetic parameters have been correlated with the order degree at molecular level of the polymer. Lightfastness of the dyes in the polymer matrices has been also investigated: it appeared to be in relation with the supermolecular structure of the film.

The thermal cis-trans isomerization of 3'-nitro-4-diethylaminoazobenzene in various solvents and in poly (ethyleneglycol methylethers) of different molecular weights has been studied kinetically as a function of temperature. The dependence of the experimental data on medium polarity, using both alcohols and aprotic solvents, and on polymer viscosity is discussed and compared with the behaviour of other similar dyes. An inversion mechanism, passing through an sp-hybridized linear transition state, appears to be the general path for all 4-diethylaminoazobenzenes. No viscosity effect could be observed. The possibility of using this reaction as a probe of the dynamic behaviour of bulk polymer molecules is discussed.

Photochemical grafting of 1,6-hexanediol diacrylate, diethylene glycol diacrylate and tetraethylene glycol diacrylate onto cellulose in the form of filter paper was investigated kinetically at 30 ± 2 °C with 1,2-diphenyl-2,2-dimethoxyethanone as a photoinitiator, under experimental conditions suitable for the preparation of membrane systems. Irradiations were carried out polychromatically, with incident radiation of flux (2.5 × 10−8)−(22.6 × 10−8) einsteins s−1 cm−2. The ratio R between the molar concentrations of photoinitiator and monomer were varied between 0.005 and 0.095, while the n/S value (n, moles of diacrylate monomer deposited per unit apparent surface S) was varied between 7.61 and 75.0 μmol cm−2. Two consecutive constant-rate processes were indicated by the kinetic curves. The quantum yields Φ1 and Φ2 for the first and second constant-rate periods were calculated. They are almost insensitive to the difference in diacrylate monomer structure; the Φ1 show a linear dependence on R, while the Φ2 show an inverse dependence on n/S. The relevance of photochemical parameters in the proposed reaction mechanism is discussed.

The thermal cis-trans isomerization of azo dyes XC6H4N=NC6H4N(C2H5)2 (where X is H, OCH3, CN, and NO2) in poly(ethylene terephthalate) matrices, below the glass transition temperature, and in dibutylphthalate solutions has been studied kinetically in the temperature range 20–60°C. Kinetic behavior in the polymer is characterized by two or three simultaneous first-order processes with similar activation enthalpies. These processes reflect an unequal distribution of “tie-molecules,” “folds,” and “cilia” in the amorphous region of the polymer. Lightfastness of the dyes in poly(ethylene terephthalate) films has been investigated. Polymer morphology strongly affected the photofading, but no significant influence was observed in the kinetic experiments.

Proton dissociation equilibria of various 4-substituted aminoazobenzenes have heen studied as a function of temperature. The corresponding thermodynamic functions Δ G o , Δ H o , and Δ S o 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.

Auto-oxidation–reduction of substituted nitrosobenzenes RC6H4NO (R = H, p-NMe2, p-OMe, p-Cl, m-NO2, and p-NO2) has been studied kinetically at 70–100° in cyclohexane solution. Experimental data and the influence of substituents are discussed on the basis of an equilibrium between monomer (M) and dimer (D), and of the reaction 2M → D being the rate-determining step.

Acid-catalysed intramolecular acylation of trans-3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3H)-one was studied kinetically in 5–11.5M-HCl, 2–8.8M-HBr, and 5-18M-H2SO4 solutions at 70–105, 70–120, and 80° respectively. The rate dependence on acidity is discussed on the basis of hydration parameter treatments. A kinetic scheme is proposed, visualizing the transition state as leading from the protonated substrate through its cis-form to the products. This scheme is consistent with the hydration parameters and acyl– or alkyl–oxygen fission concerted with acylation, the second being the operative mechanism in halogen acid solutions.