Kinetics of radiation-induced grafting reactions. I. Polyethylene–styrene systems

By means of bromine labeling and ESR, the grafting reactions of styrene onto preirradiated polyethylene have been investigated. Not all the radicals produced by irradiations participate in grafting reactions all together, but they are rendered active bit by bit by the swelling of crystalline parts of polyethylene. The growing rates for polystyryl graft chains at 20°C decrease from 4 monomer units/active site/sec to one-fourth the initial value after 100 min. On the contrary, the average lifetimes increase from <10³ sec to >2.6 × 10³ sec. The number-average molecular weight of graft chains also increases with reaction times and rises to 3.5 × 10⁵ after 90 min at 20°C.     

Kinetics of radiation-induced grafting reactions. III. Poly(isobutylene oxide)—styrene systems

Graft polymerization of styrene onto preirradiated poly(isobutylene oxide) was carried out at 25°C. The concentration of active sites for grafting was estimated by means of ESR and by the activation analysis of bromine atoms bound to the chain ends. Kinetic data such as differential amount of active sites (DACT), growth rate (GR), and average lifetime (τ) were obtained to calculate the molecular weight distribution of graft chains by the Monte Carlo simulation method. The number-average molecular weight of the graft chain was calculated from the equation, M _n = 2GRτ (mw), which agreed well with the observed value.     

Kinetic approach to radiation-induced grafting in the polyethylene–styrene system. II

The investigation method reported in the previous paper was applied to four reaction methods: preirradiation method with reaction in liquid monomer, preirradiation method with reaction in monomer vapor, simultaneous irradiation method in liquid, and simultaneous irradiation method in vapor. The increasing patterns and values of the degree of grafting experimentally obtained roughly agreed with those calculated by using the same rate constants. At high monomer concentration, the rate of grafting was small; at low monomer concentration, the rate of grafting was large. Strictly speaking, the data by simultaneous irradiation method were somewhat larger than those by calculation. Two additional factors, as homopolymerization and the grafting from the radicals formed on the grafted polystyrene, were considered and discussed. The rate constants obtained were also discussed.     

Kinetic approach to radiation-induced grafting in the polyethylene–styrene system. III

The method of investigation reported in previous papers was applied to preirradiation methods of reaction in vapor and in liquid. The absorption dose was varied from 2 to 0.1 Mrad. The monomer concentrations during reactions were determined gravimetrically. The patterns of increase of the degree of grafting did not change as the dose was varied in the liquid but changed considerably with dose in the vapor. The monomer concentration during the reaction did not vary with dose in the liquid but did so in the vapor. A model calculation was applied and improved to make the monomer concentration agree with that in the experiment. An attempt was made to describe the mechanism involved. There were some differences between the calculated values and the experimentally obtained ones, but the outline of the reaction mechanism was explained satisfactorily.     

Kinetics and mechanism of grafting of undecylenic acid onto acrylonitrile–butadiene–styrene terpolymer

The graft copolymerization of undecylenic acid onto acrylonitrile–butadiene–styrene terpolymer (ABS) was initiated with benzoyl peroxide (BPO) in a 1,2‐dichloroethane solution. IR spectra confirmed that undecylenic acid was successfully grafted onto the ABS backbone. The influence of the concentrations of undecylenic acid, BPO, and ABS on the graft copolymerization was studied. A reaction mechanism was proposed: the grafting most likely took place through the addition of poly(undecylenic acid) radicals to the double bond of the butadiene region of ABS. A monomer cage effect on the graft reaction was observed to depend on the 1.5 power of the monomer concentration from the experimental results of the initial rate of graft copolymerization. The initial rate of graft copolymerization was written as R_p = 1.77 × 10⁻³[P][I₂][M]^2.5/([P]+2.75[M]^2.5)². © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 486–494, 2001     

Free-radical grafting of monomers to polydienes. II. Kinetics and mechanism of styrene grafting to polybutadiene

A kinetic analysis of the grafting reaction has shown that, provided rubber radicals are not involved in termination reactions, the observed normal kinetics of styrene polymerization are to be expected. An expression relating the graft fraction with the rubber and monomer concentrations has been derived and its validity verified from the results reported in Part I. The observation that the molecular weight of the ungrafted PBD falls during the reaction has been explained on a theoretical basis.     

Reactions in aminosilane–epoxy prepolymer systems I. Kinetics of epoxy–amine reactions

The reactions of an epoxy prepolymer based on bisphenol A diglycidylether (DGEBA) with γ-aminopropyltriethoxysilane (γ-APS) are studied. The results of different techniques are compared: size exclusion chromatography, differential scanning calorimetry, chemical titration, and Fourier Transform Infrared absorption. Epoxy amine reactions are shown to be faster than the crosslinking reactions between alkoxysilane and hydroxy groups, and thus, can be studied seprately. The reactivity of the epoxy group in DGEBA is compared with that of phenylglycidylether (PGE). And the reactivity of the amine group of γ-APS is compared with that of hexylamine. The kinetic constants are calculated with a mechanism which takes into account both the catalytic and noncatalytic reactions. The ratio r = k₂/k₁ of the reactivity of the secondary to the primary amino-hydrogens was also determined. The values of r are 1.4 for hexylamine and 1.2 for γ-APS. The reactivity of the epoxy groups are the same for both PGE and DGEBA.     

Effect of swelling on radiation-induced grafting of styrene to polyethylene

The radiation-induced grafting of low-density polyethylene in contact with styrene solution was studied. The effect of the degree of swelling of the polymer on the rate of grafting was investigated by diluting the styrene with methanol and with n-octane. For styrene-methanol solution, the rate of grafting was found to increase with degree of swelling, passing through a maximum when the sorbed solvent reaches 6.2 wt-% (70 vol-% methanol in the outside solution) and decreasing therafter. The methanol fraction of the sorbed liquid is far too small to cause precipitation of the grafted chains and inhibition of their termination rate. The dilution of styrene by octane has no effect on the swelling of polyethylene, but it decreases the grafting rate over the entire concentration range. The results are explained in terms of the concentration of sorbed monomer and the viscosity of the amorphous region of the polyethylene swollen by nonpolar liquids. Supporting evidence for the mechanism is presented in the form of grafting kinetic data as a function of dose rate (2.8 × 10²?9.5 × 10⁴ rad/hr), and post-irradiation grafting measurements for polyethylene in methanol-styrene (70/30, v/v). The data indicate that at the maximum grafting rate an optimum is achieved between a high concentration of sorbed monomer and a low viscosity for the poorly swelled polymer matrix.     

Kinetics and mechanism of urethane reactions: Phenyl isocyanate–alcohol systems

Urethane reactions of phenyl isocyanate alcohol systems with toluene as solvent and various aprotic polar solvents (including tertiary amines) as additives were carried out at constant temperature of 10–40°C. Analysis of the variation of the second order rate constants of these systems and those available in the literature indicates that formation of the hydrogen bonding complexes (alcohol with phenyl isocyanate and with aprotic solvent) and electron donor number (DN) of the aprotic solvent are the two factors allowing satisfactory explanation of the catalysis and inhibition effects of the wide range of aprotic solvents (including amines, amides, etc.). Based on these considerations, an ion-pair mechanism and the resulting kinetic equation for the urethane reaction are proposed. Verification on the kinetic equation with experimental results for the systems of phenyl isocyanate with alcohol in toluene (for the self catalysis of the alcohol), with dimethyl formamide and dimethyl sulfoxide in toluene (for the catalysis of the aprotic solvents), and with triethylamine in toluene (for the catalysis of the tertiary amines) shows satisfactory. In the mechanism, the aprotic solvent is considered to solvate the complex of phenyl isocyanate/alcohol at the active hydrogen to form an ion-pair which can undergo the urethane reaction more easily.     

Kinetics of radiation-induced graft copolymerization of styrene with ethyl acrylate

The radiation-induced graft copolymerization of styrene with ethyl acrylate onto preirradiated polyethylene powder was carried out at 20°C. The grafting yield decreased in the following order: ethyl acrylate ? styrene > styrene–ethyl acrylate mixture. On the other hand, the amount of absorption of liquid monomers in polyethylene powder decreased as follows: styrene > styrene–ethyl acrylate mixture > ethyl acrylate. By kinetic analysis of the grafting yield and amount of absorption of monomers it was elucidated that the value K_p/K_t in an ethyl acrylate system (7.7 × 10^?2) was much larger than those in styrene–ethyl acrylate systems and in a styrene system (ca. 1.0 × 10^?2).     

Kinetic approach to radiation–induced grafting in the polyethylene–styrene system

To investigate the mechanism of radiation-induced grafting in this system, the increase of monomer concentration in the polyethylene film in styrene vapor was evaluated by measuring the weight increase and formulated to be V([M_∞] ? [M]). The decay of radical concentration was also measured by ESR and the rate constant of the decay was determined. The alkyl type radical was affected only a little by styrene, while the allyl type radical was much affected by styrene. A new computer investigation method was proposed to clarify the reaction mechanism. The data obtained were substituted into differential equations and used to calculate the pattern of increase of the degree of grafting for the preirradiation method with reaction in the vapor phase. Results of these calculations suggest that only allyl type radicals induce grafting reactions and that the grafting reaction seldom occurs in the region of grafted polystyrene.     

Syntheses and reactions of functional polymers. XLVI. Preparation and reactions of N-benzyloxyisomaleimide–styrene copolymer

Polymerization of N-benzyloxymaleimide(I) was attempted to obtain a polymer with the N-hydroxysuccinimide unit in the chain. In the light of infrared and NMR data the compound reported by Ames as N-benzyloxymaleimide is N-benzyloxyisomaleimide (III). Homopolymerization of III did not give polymer. Copolymerization of III with styrene was carried out in dioxane at 70°C. A strong alternation tendency like that of maleimides was observed. Monomer reactivity ratios and Q-e values were determined. Copolymer having the isoimide structure showed infrared absorptions at 1815 and 1675 cm^?1 in the carbonyl region. The copolymer was isomerized to N-benzyloxymaleimide type copolymer and debenzylated to N-hydroxymaleimide type copolymer. An insoluble copolymer was prepared by using divinylbenzene as a crosslinking agent and was converted to N-acetoxymaleimide type copolymer, which was used as an insoluble acetylating agent.     

Dehydrochlorination reactions in polymers. Part III. Vinylidene chloride–styrene copolymers

A systematic study of the effect of styrene units on the thermal stability of vinylidene chloride copolymers was made. In general, the copolymers were more easily dehydrochlorinated than the homopolymer. The copolymers eliminate HCl at rates that could only be interpreted in terms of styrene group activation. However, the elimination rate fell too rapidly with reaction extent to be accounted for by concentration changes or weak links and was consistent with retardation by the reaction products. The elimination was a radical process and accompanied by chain scission and crosslinking in competition.     

Preparation and characterization of some cellulose graft copolymers. Part IV. Some properties of isolated cellulose acetate–styrene graft copolymers

A series of purified graft copolymers of cellulose acetate and polystyrene, which were prepared and characterized during the course of an earlier investigation, have been used for some initial property studies. Grafts with high molecular weight backbones and low molecular weight side chains and vice versa, and with both side chains and backbones of high and low molecular weights, were prepared. The graft polymers were found to be insoluble in most solvents but soluble in dimethylformamide and pyridine and in mixtures of solvents for each component. Films cast from mixtures of the grafts and homopolymers showed that the grafts were compatible with the homopolymer of the component with a higher molecular weight. A graft copolymer with high molecular weight backbone and side chains was found to be compatible with both homopolymers separately and with a mixture of both across a wide range of compositions. A blend of the high and low molecular weight grafts was also found to be highly compatible with both homopolymers. The permeability, diffusion, and sorption of gases and water vapor in the grafts and in the corresponding homopolymers was also studied. In the case of water vapor, the sorption in cellulose acetate was much higher than in polystyrene whereas the diffusion was much lower. It was found that the graft polymers showed both diffusion and solution behavior closer to that of cellulose acetate, whereas the permeability constants were more intermediate between those of the two homopolymers. The gas permeability and diffusion constants were found to be intermediate between the values obtained with the two homopolymers.     

Effect of amines on vinyl polymerization initiated by chromous acetate–alkyl halide systems

The radical polymerization of vinyl monomers initiated by Cr²⁺–RX in the presence of various amines was studied in DMF at 30°C. Polyamines able to form the chelate complex with Cr²⁺ accelerated the rate of polymerization of styrene in the following order: ethanolamine > triethylenetetramine > diethylenetriamine > ethylenediamine. However, aliphatic monoamine, hexamethylenediamine, and aromatic diamine did not have any effect on the polymerization. These results suggest that the effect of multidentate ligands may be associated with chelating effects which affect the electron transfer ability of the metal complex. An apparent activation energy of 8.2 kcal/mole for the polymerization of styrene was obtained in the presence of ethanolamine. With the Cr²⁺–CHCl₃ system, on addition of ethanolamine, the polymerization of methyl methacrylate was accelerated, and acrylonitrile and vinyl chloride, could be polymerized.     

Kinetics of radiation-induced graft polymerization of styrene onto poly(ethylene oxide)

The graft polymerization of styrene onto preirradiated poly(ethylene oxide) was studied. From the measurement of swelling of the polymer in various solvents the solubility parameter of poly(ethylene oxide) was estimated as 9.3. The kinetic analysis of the reaction indicated that the graft polymerization was diffusion controlled. Kinetic parameters of the reaction such as \documentclass{article}\pagestyle{empty}\begin{document}$\int_0^t {R_i} dt,k_{p,} k_{tr}$\end{document}, and k_t were obtained in poly(ethylene oxide)-styrene system and compared with those in poly(isobutylene oxide)-styrene system.     

Photocrosslinking of elastomer systems. II. Ultraviolet light-induced reactions in an EPDM modified by grafting of benzoin derivatives

Photocrosslinking experiments were performed on elastomeric polymer films (EPDM) previously modified by grafting a photosensitive initiator (benzoin derivative) onto the macromolecular backbone. This modification was performed by a series of Friedel–Crafts reactions and the resulting materials were characterized by infrared (IR) spectroscopy in conjunction with model reactions. After ultraviolet (UV) irradiation the photocrosslinked samples were studied by IR spectroscopy in conjunction with the measurement of physical properties. It apperared that grafting the photosensitizer onto the elastomer considerably enhances the crosslinking reaction even with a limited quantity of grafted benzoin derivative. Moreover, the results obtained suggest that the structure of the resulting networks is strongly dependent on the crosslinking process used; that is, curing the elastomer with peroxide or UV irradiation either of a blend of elastomer and photosensitizer or of the same elastomer modified by grafting the chromophore.