Grafting Kinetics Research Articles

Biocompatible polyphosphazenes by radiation-induced graft copofymerization and heparinization

Investigations were carried out on the radiation-induced graft copolymerization by direct irradiation of dimethylaminoethyl methacrylate on to poly(bis(trifluoroethoxy)phosphazene) and on to poly (bis(phenoxy)phosphazene). Kinetics of grafting were followed with the polyphosphazenes immersed in monomer—methanol mixtures of various composition. The grafted film samples were quaternized with methyl iodide and, to the produced ammonium group, heparin was ionically bonded with high yield. On the grafted and heparinized-grafted film samples an evaluation of hydrophilicity, mechanical properties, biocompatibility and anticoagulating properties was carried out.

Polymerization in nonuniform latex particles. III. Kinetics of grafting in emulsion polymerization

AbstractThe concept of nonuniform distribution of free radicals in polymerizing latex particles has been incorporated into the development of a kinetic model for grafting reactions. This theory permits prediction of grafting efficiency as a function of reaction conditions. It can also be used for evaluation of rate constants for grafting reactions. Experimental data for emulsion polymerization of styrene in the presence of polybutadiene seed latex have been used to assess the proposed grafting theory. The predominant grafting reaction appears to be the attack of growing polystyrene chains on the allyl hydrogen atoms of polybutadiene. The results further reinforce the hypothesis that the entering oligomeric free radicals do not distribute uniformly within the particle volume.

Grafting of unsaturated acids and silanes to ethylene polymers: A kinetic model

AbstractA general kinetic model was developed to simulate the grafting of monomers such as unsaturated carboxylic acids and silanes to ethylene polymers. The polymers considered were ethylene‐co‐vinyl acetate (EVA), ethylene‐co‐butyl acrylate (EBA), and low‐density polyethylene (LDPE). Grafting was assumed to proceed by a free‐radical mechanism involving chain transfer. Organic peroxides having a strong tendency for hydrogen abstraction were selected as the source of primary radicals. The model simulated the grafting reaction as taking place in a single screw extruder. The residence time distribution in the extruder was experimentally determined by tracer analysis, according to which the extruder was a plug‐flow reactor connected to two mixed reactors in parallel. The model is able to predict the extent of grafting in terms of predefined parameters. Comparison of model predictions with available experimental data showed slight deviations, the possible causes of which are discussed. However, the kinetic behavior expected on the basis of the input parameters was observed, and, as such, the model allowed study of the effect of process variables on grafting kinetics and provided insight into the reaction mechanism.

Kinetic studies of grafting of maleic anhydride to hydrocarbon substrates

AbstractThe kinetics of grafting of maleic anhydride to various hydrocarbon substrates has been investigated. Grafting to eicosane and squalane was effected in the pure hydrocarbons and in 1,2‐dichlorobenzene solution, while polyethylene was grafted only in solution. The initiator was 2,5‐dimethyl‐2,5‐di(t‐butylperoxy)‐3‐hexyne which has a half life of about 1 h at a typical reaction temperature of 150°C. At high concentrations of initiator (Ca. 0.02M), the rate of disappearance of maleic anhydride is linear with time. In the pure hydrocarbons the order with respect to initiator is close to 0.5. In squalane, the overall activation energy is 112 kJ mol−1; the average number of maleic anhydride molecules grafted per molecule of peroxide decomposed varies from 8 at high rates of initiation to 57 at low rates of initiation. The results are interpreted in terms of a chain mechanism, including a slow propagation step in which a succinic anhydride radical abstracts hydrogen from the same or a different chain. The same general mechanism is proposed for grafting of maleic anhydride to polyethylene and the hydrocarbons in 1,2‐dichlorobenzene solution.

Post-radiation grafting of acrylamide from acetone solution onto polypropylene films irradiated in vacuum, kinetics of the process and localization of the grafted polymer layer

The post-radiation grafting of acrylamide from acetone solution onto polypropylene films irradiated under vacuum at room temperature, and the kinetics of grafting onto 40–300 μm films at 20–70°C and solution concentrations of 5–20 wt.% are studied. The macrodistribution of the grafted polymer over the film cross-sections at different stages of grafting is studied by IR spectroscopy and optical microscopy.

Chemically induced graft copolymerization of acrylic acid onto polyester fabrics. I. Kinetic investigation of grafting

AbstractThe kinetics of grafting of acrylic acid onto poly(ethylene terephthalate) fabrics initiated by benzoyl peroxide has been studied. Extent of grafting depended upon time, concentration of the initiator and the monomer, as well as the presence of the activator used. From the temperature dependence of the initial rate of grafting the overall activation energy for grafting was found to be 90 kJ/mol. The results of the monomer and temperature dependence found in this study are consistent with the rate expression derived from a normal kinetic scheme for grafting.

KINETICS OF GRAFTING IN SOLUTION POLYMERIZATION

A mechanistic kinetic model, which includes several elementary reactions occurring simultaneously, is developed for the kinetics of grafting in solution polymerization. This model allows prediction of the rate of polymerization and grafting efficiency under various reaction conditions. It also permits evaluation of grafting reaction rate constants. Experimental data available in the literature are used to test the model. Very good agreement is observed between the data and model predictions.

Mechanism and kinetics of grafting of polypropylene by water-soluble monomers in emulsion

Oxidized isotactic polypropylene powder was grafted at 30 °C in aqueous emulsion with water-soluble monomers such as acrylic acid and acrylamide. The decomposition of the polypropylene -O-O- groups, initiating the graft polymerization, proceeds due mainly to the effect of the activator used, viz. a chelate of iron(II), and is favoured by the monomer and the necessarily present water-insoluble liquid phase. The grafting reaction order with respect to the concentration of the water-soluble monomer is 2 and higher. A mechanism and kinetics are suggested for the polypropylene grafting by these water-soluble monomers, involving the concept of presence of long-living radicals bonded to the solid polypropylene phase.

A study of the kinetics of radiational graft polymerization of acrylic monomers on a butadiene-styrene thermoelastomer

1. The kinetics of radiochemical grafting of acrylonitrile and acrylic acid to a butadiene-styrene thermoelastomer have been studied by irradiating a material impregnated with the monomer; it has been shown that kinetic chain rupture in such systems is a monomolecular process. 2. The rate constant for propagation of the graft polyacrylonitrile chain and the activation energy for grafting have been calculated, the values obtained being close to those for homogeneous acrylonitrile polymerization.

Grafting of polymeric side chains to gelatin

AbstractKinetics of grafting of poly(butyl acrylate) onto gelatin was studied with H2O2—ascorbic acid redox systm. Percent grafting, grafting efficiency, Rg, and Rh were determined as a function of time, temperature, initiator, monomer, and backbone concentration. It was found that Rg depends on first power of monomer concentration and 0.5 power to the initiator concentrations. A detailed kinetic scheme is proposed to explain these results.

Radiation graft-copolymerization kinetics of poly(ethylene terephthalate) fibres

A theoretical analysis of radiation grafting kinetics has been made in terms of the quantitative interrelationship between the degree of grafting ( G f ), the grafting periods ( t) grafting temperature ( T) and the monomer content in the polymeric system (M). Poly(ethylene terephthalate) fibres and a number of hydrophilic monomers have been employed for these experiments. The grafting reactions were initiated by trapped radicals produced by irradiation of the polymeric system under vacuum at room temperature. Experimental results showed that the monomer content in the fibres obeyed the Arrhenius relationship. The overall activation energy of the grafting reaction has been calculated. Grafting reactions can proceed only if ΔE t > ΔE p + ΔE M. This termination activation energy ΔE t is a function of the state of polymeric system.

Mechanism and kinetics of grafting of macrodiisocyanate on to carboxyl‐containing acrylonitrile copolymers

AbstractThe reaction of a carboxyl‐containing acrylonitrile copolymer with a macrodiisocyanate based on polypropylene oxide (Mn = 2000) in dimethylformamide (DMFA) and dimethylsulfoxide (DMSO) solutions was studied. The mechanism and main kinetic regularities of the grafting reaction were investigated. The reaction proceeds through formation of a mixed anhydride with its subsequent decomposition leading to liberation of CO2 and formation of graft copolymers. Carboxyl and nitrile groups of the copolymer take part in the reaction. A side reaction involving interaction of isocyanate groups of macrodiisocyanate with DMFA proceeds during synthesis of graft copolymers in DMFA solutions. The dependence of graft polymer yield on temperature, macrodiisocyanate concentration and on the catalyst/NCO ratio was determined. The activation energy of the grafting reaction is 22.9 kcal/mole. The specific viscosity of graft copolymers in DMFA solutions increases with the number of grafted chains.

Radiation‐induced grafting polymerization by the anionic mechanism

AbstractThe radiation‐induced grafting polymerization of phenylacetylene and 2‐methyl‐5‐vinylpyridine (2M‐5VPy) onto low‐density polyethylene has been investigated under strict identical conditions, using crude and thoroughly dried monomers. In the case of thoroughly dried monomers, the radiation‐induced grafting is performed by the combined (radical + anionic) mechanism. The kinetics of radical and anionic grafting of 2M‐5VPy are investigated in detail. The activation energies are 4.8 ± 0.3 and −2.7 ± 0.3 kcal/mole for the radical and anionic grafting, respectively. The initial rate of grafting is approximately proportional to the dose rate to the 0.47 ± 0.03 and 0.92 ± 0.03 power for the radical and anionic grafting, respectively. The initial rate of grafting is approximately proportional to monomer concentration to the 1.55 ± 0.05 and 2.1 ± 0.05 power for the radical and anionic grafting, respectively. These data conform to the contribution of the anionic mechanism in a thoroughly dried system. The mechanism of radiation‐induced anionic grafting is discussed.

Grafting onto polyester fibers. II. Kinetics of grafting of acrylic acid, acrylonitrile, and vinyl acetate onto polyester fibers

AbstractThe kinetics of grafting of acrylonitrile, acrylic acid, and vinyl acetate onto polyester fiber by catalytic initiation and radiation were studied. The energy of activation determined for acrylic acid grafting by the catalytic method was 10.7 kcal/mole and that for vinyl acetate grafting by the radiation method, 11.7 kcal/mole. In the case of acrylonitrile grafting by the catalytic method, the rate of grafting decreased with increase in temperature of grafting, showing the differential behavior of the precipitating type of polymer from that of homogeneous polymerization.

Greffage radiochimique de l'acetate de vinyle et du styrene sur la nitrocellulose—I. Partie Cinetique

Vinyl acetate and styrene were grafted onto nitrocellulose using the direct radiation grafting technique. Four vinyl acetate, the reaction proceeds homogeneously. The kinetics are dominated by degradative chain transfer to the nitrocellulose. The polymerization of vinyl acetate was examined in the presence of isoamyl nitrate, a model for nitrocellulose; the transfer constant was determined and the results are treated semi-quantitatively. For styrene, grafting occurs in a swollen film irradiated in the presence of excess monomer. The diffusion of styrene into nitrocellulose is extremely slow; methanol was added to the reaction mixture to favour diffusion which was found to obey Fick's law. The diffusion constant and activation energy of diffusion are evaluated. The grafting kinetics are controlled by monomer diffusion, accounting for the increase of dose-rate exponent with temperature. A spontaneous grafting process occurs in the absence of irradiation. It is initiated by macroradicals arising from thermal decomposition of nitrocellulose.

Reaction Kinetics of the Radiation-Induced Grafting of Styrene on Polyethylene Film

Abstract Based on rate data obtained previously, an analysis has been made of the reaction kinetics of the radiation-induced grafting of styrene on polyethylene film by using various concentrations of methanol in the styrene. A new feature of the work involves the use of internal film concentrations of styrene and methanol computed from the Flory theory of polymer /solvent interaction, which possibly improves the accuracy of calculations of termination rate constant kt at various methanol concentrations. A graphical plot of kt dependence on internal film viscosity is computed from an equation of Smoluchowski. Techniques are defined which may lead to improved accuracy in the computation of rate constants.

The post-radiation grafting of styrene to polyethylene films crystallized under different conditions

A kinetic study was made of the gas phase radiation graft copolymerization of styrene to films of high and low density PE (PELD, PEHD). The PE films were crystallized under conditions of rapid (∼2000 deg/min) and slow (∼2 deg/min) cooling from the melt. Slow cooling from the melt resulted in a 1·3 to twofold increase in the radiation yield of radicals that are quasi-stable in PE at 20°. Data are given whereby the structure and thickness of PE films are related to grafting kinetics and to the degrees of grafting. It was found that with thicknesses ranging from 60 to 100 μ the degree of grafting for the films prepared under slow cooling conditions is double that observed for the annealed films. For the latter films it was found that grafting distribution in the volume of a film was uniform over a wide range of film thickness (200 to 800 μ for PELD and 60 to 200 μ for PEHD). Data were obtained on the extent to which the kinetics of grafting are influenced by film thickness, film structure and the radiation dose. Relationships between degrees of grafting and the radiation dose were found to be of an extremal type. The experimental results provided a basis for a phenomenological model accounting for regularities of the radiation grafting process.

Gamma ray‐induced graft copolymerization of acrylamide and acrylic acid to nylon 6 fabric

AbstractKinetics of radiation‐induced grafting of acrylamide (Aam) and acrylic acid (Aa) to nylon 6 fabric were investigated employing a mutual radiation technique. Copper sulfate was used as the radical scavenger to reduce homopolymer formation. Formic acid was used for swelling, and its effect on grafting was studied. Maximum amount of grafting was doubled when formic acid was used for swelling nylon prior to, but not during, irradiation. The rate of grafting was not significantly affected if it was carried out in an atmosphere of air instead of nitrogen. The effect of monomer concentration, dose rate, and total dose on grafting has been studied. Rate of grafting was significantly higher when lower dose rates and monomer concentrations were used. Saturation grafting was proportional to monomer concentration up to 2.1M. Initial rate of grafting was proportional to monomer concentration. The rate of grafting of Aam was proportional to the dose rate to the power 0.25–1.0. A synergestic effect was noticed during grafting with mixtures of Aam and Aa (80:20; 20:80). Grafted fabrics showed considerable increase in moisture regain. Dyeability and tensile properties of the grafted fabrics were not significantly affected by grafting. Aa‐grafted fabrics did not melt up to 320°C, whereas untreated nylon melts at 215°C.

Radiation-induced grafting polymerization by the ionic mechanism

A technique of radiation-induced grafting under conditions of extreme drying of monomers has been developed. Under such conditions, radiation-induced grafting polymerization of isobutylene, α-methylstyrene, vinyl-n-butyl ether, styrene, acrylonitrile, and 4-vinylpyridine by the ionic mechanism at room temperature has been performed. The grafted copolymers of polyethylene, Teflon and polyvinyl chloride with monomers polymerized only ionically (isobutylene, α-methylstyrene, vinyl-n-butyl ether) have been obtained for the first time. The kinetics of the radiation-induced grafting of vinyl-n-butyl ether on to polyethylene have been studied; the ionic mechanism has been confirmed. It has been found that the rates of the radiation-induced ionic grafting of styrene, acrylonitrile, and 4-vinylpyridine are much greater than those for radical grafting. The highest grafting rates are observed for 4-vinylpyridine. The mechanism of radiation-induced ionic grafting polymerization has been discussed; generalized kinetic equations have been derived to account for the contributions from radical and ionic processes.

Contribution to the kinetics of grafting of natural rubber with acrylonitrile

A study was made of the kinetics of grafting of natural rubber with AN and the dependence of the process on concentration of —O—O— groups formed during cold mastication, temperature of grafting, and the composition of the mixtures. The grafting has a characteristic course: after the initial non-stationary state, caused by the consumption of —O—O— groups, the rates reach a constant value (when all the —O—O— groups are practically decomposed) which depends on the initial concentration of —O—O— groups in rubber. It is caused by the “trapped” radicals present in the system. Grafting takes place in a heterogeneous phase since rubber swells only to a limited range in AN; the resulting interpolymer is still crosslinked at small conversion and the content of —O—O— groups is relatively small. The amount of the formed homopolymer is relatively small (about 20 per cent of the total amount of reacted AN) mainly due to the transfer of HO' and P' radicals to rubber. A formal mathematical equation for the grafting was derived : (1) R p = a k d [ p ] e − k d t + ( c − b k d e − k d t ) [ p ] 2 where a, b, c are empirical constants and k d is the rate constant of decomposition of —O—O— groups under the given conditions; at 120° the values are: a = 4·2 × 10 3, b = 2·4 × 10 6 kg/mol, c = 71·23 kg/mol, k d = 1·8 × 10 −4 sec −1. From the suggested reaction scheme, the relation for the rate of polymerization of AN in presence of rubber was derived; on the assumption that c = 2 b. k d, the relationship is identical with a formal mathematical equation so leading to an understanding of the physical significance of the empirical constants.