Radiation-induced polymerization of isobutylene oxide

In the absence of oxygen, liquid isobutylene oxide is polymerized by high energy radiation. The resultant polyethers may possess the same gross structures as those prepared by Lewis acid catalysis: The reaction is characterized by (1) a small, apparent activation energy (2.7 kcal/mole), (2) a polymerization rate proportional to the first power of the dose rate, (3) inhibition by Lewis bases, and (4) moderate inhibition by free-radical scavengers. The molecular weights of the polymers increase with decreasing temperatures of polymerizations. These results will be discussed in terms of a cationic propagation mechanism.     

Radiation-induced polymerization of tetraoxane in the solid state

The radiation-induced polymerization of tetraoxane in the solid state has been investigated in air and in vacuo. The polymerization rate was higher in air than in vacuo, whereas the molecular weight of the polymer obtained at high conversion in air was considerably lower than in vacuo. A large decrease in the molecular weight with increasing polymer yield observed in air may be explained mainly by degradation during polymerization.     

Radiation-induced polymerization of 1,1,2-trichlorobutadiene in the solid state

Changes in the polymerization and in the structure of the polymer formed during the course of polymerization of 1,1,2-trichlorobutadiene in the solid state were studied. We observed that the rate of polymerization and the molecular weight of the polymers formed increasing conversion. The content of 1,4 units in the polymer also increases with increasing conversion.     

Radiation-induced polymerization of cyclohexene sulfide in the solid state

Radiation-induced solid-state polymerization of cyclohexene sulfide has been investigated. Differential thermal analysis shows that this compound has a phase transition point at ?74°C and behaves as a plastic crystal in the temperature range from ?74 to ?20°C (melting point). By rapid cooling, this plastic crystal was easily supercooled, and below ?166°C a glassy crystal, i.e., a supercooled nonequilibrium state of plastic crystal, was obtained. In-source polymerization proceeded in the plastic crystalline state. Postpolymerization of glassy crystalline monomer irradiated at ?196°C occurred above ?166°C (glass transition point) during subsequent heating.     

Anionic polymerization of 1,2-butylene oxide

Anionic polymerizations of 1,2-butylene oxide were carried out in vacuum-sealed dilatometers in the range of 30–60°C. Potassium terbutoxide and dimsyl sodium were used as initiators; dimethyl sulfoxide (DMSO) and mixtures of DMSO with tetrahydrofuran were solvents. The polymer products were analyzed by gel permeation chromatography and infrared spectroscopy. The object of the investigation was to obtain information on the mechanism of the reaction and to elucidate some of its kinetic aspects. It has been shown that the polymerizations occur by two different processes, depending on the choice of experimental conditions. One of the processes involves free ions and ion-pairs, the other, ion-pairs alone. In the first case, where dimethyl sulfoxide is used as solvent, the order of the reaction with respect to the initiator concentration far exceeds unity (～1.8), while in the second case, involving mixed solvents, the order of the reaction, for all practical purposes, is one.     

Triphenylmethyl hexafluoroarsinate-initiated polymerization of 1,2-butylene oxide

The polymerization of 1,2-butylene oxide initiated with triphenylmethyl hexafluoroarsinate in the ?20 to +25°C temperature range with 1,2-dichloroethane as solvent is characterized by a rapid nonstationary initial stage. This is followed by a second slower stage, during which the disappearance of monomer is first-order with respect to its concentration. The conversion of monomer at the end of the first stage is related to the initial catalyst concentration but not to the initial monomer concentration. Invoking the hypothesis of an instantaneous initiation reaction, the experimental results lead to the conclusion of the existence of a unimolecular termination step. Propagation-to-termination rate constant ratios yield a propagation–termination activation energy difference of 5.9 kcal/mole. The termination step proposed is thought to involve the formation of stable macrocyclic oxonium ions. These, in turn, can reactivate the polymerization by an intramolecular reaction leading to the formation of new active centers. An energy of activation of 8.7 kcal/mole was calculated for this reactivation. GPC analyses of the reaction products recovered at the end of the first stage revealed the presence of large proportions of oligomers. Based on kinetic data, the formation of oligomers is explained by a backbiting process similar to the reactivation reaction suggested for the initiation of the second stage.     

Radiation-induced polymerization of 3-octylthiophene

In order to develop a new synthetic method and to study mechanism of oxidative polymerization of conducting polymers, polymerization of 3-octylthiophene in several organic solvents by γ-irradiation was examined. Polymers bimodal distribution with molecular weights at 500–1000 and 2000–3000 were generated by the irradiation of chloroform solutions. The values of monomer conversion (G(?M)) decreased from 445 to 10 with doses from 0.99 kGy to 594 kGy. The large G(?M) values and dose dependence of G(?M) cannot be explained with widely accepted mechanism for electrochemical polymerization or chemical oxidative polymerization. Another mechanism, which proceeds through chain reactions, is proposed. This mechanism explains the large G(?M) and the dependence on the dose.     

Radiation-induced polymerization of 1,1,2-trichlorobutadiene

The γ-ray-induced polymerization of 1,1,2-trichlorobutadiene, m.p. ?48.5°C., was investigated in the temperature range from +55 to ?196°C. In the liquid state, the following results were obtained: (1) the rate decreases with decrease of temperature (E_a = 8.0 kcal./mole); (2) the dose rate dependences of rate and of molecular weight are 0.49 and ?0.25, respectively; (3) the reaction is inhibited by DPPH; (4) the structure of the polymer is predominantly 1,4 units. It was concluded that the liquid-state polymerization proceeds by a radical mechanism, and the radical yield was found to be 19.7. In the solid state, the following results were obtained: (1) the rate is considerably higher than in the liquid state immediately above the melting point and gradually decreases with decrease of temperature (E_a = 0.34 kcal./mole); (2) the dependence of the rate on dose rate is unity while the molecular weight is independent of the dose rate; (3) the reaction rate is unaffected by DPPH and accelerated by dimethylformamide; (4) the structure of the polymer, 3,4 units, is completely different from that of the polymer obtained in the liquid-state polymerization. The solid-state polymerization is probably of a different nature and is not well elucidated.     

Radiation-induced bulk polymerization of maleimide

Radiation-induced bulk polymerization of maleimide in both solid and liquid states was studied. Benzoquinone inhibited the liquid-state polymerization and retarded solid-state polymerization. The results of ESR study showed that solid monomer irradiated at 61°C. gave a spectrum, the concentration of which slowly decreased without changing the shape at 61°C. The radical detected at 61°C. was shown not to be the main propagating species. Overall rate polymerizations in the liquid and solid states were expressed, respectively, by first-order and zero-order rate equations with respect to the concentration of monomer. The overall rate constants in liquid and solid states were proportional to I^0.9 and I^1.0, respectively.     

Mass spectrometry in structural and stereochemical problems—CLXXVIII: The electron-impact promoted fragmentation of 1,2-cyclohexene oxide

The mass spectra of 1,2-cyclohexene oxide and three deuterium labeled analogs are discussed and mechanistic rationalizations are given for the major fragmentation processes observed. Multiple mechanisms are required to explain the indicated peak shifts in the labeled analogs for many of these ions, thus demonstrating again the care that needs to be exercised in the interpretation of the mass spectra of relatively simple molecules.     

Radiation-induced degradation and crosslinking of poly(ethylene oxide) in solid state

The effects of g-irradiation on solid poly(ethylene oxide) (PEO) of an initial weight-average molecular weight of 6.3^.10⁵ Da were investigated by gel permeation chromatography and viscometry. The parameters studied were changes in number- and weight-average molecular weight, molecular weight distribution and viscosity of PEO in aqueous solution. Irradiation of poly(ethylene oxide) powder in the presence of oxygen leads to the dominance of chain scission reactions. Their high radiation-chemical yield [G(scission) » 2.5^.10^-6 mol/J] indicates the occurrence of effective chain reactions. Upon irradiation in vacuum, crosslinking and scission occur side-by-side and the changes in molecular weight are less pronounced in the studied dose range (up to 20 kGy). Scission dominates for doses up to ca. 15 kGy, while for higher doses intermolecular crosslinking gains in importance. The competition between these processes seems to depend not only on the applied dose but also to be influenced by the inhomogenity of the material (molecular weight and/or possibly the crystallinity). Parallel occurrence of scission and crosslinking leads to the broadening of the molecular weight distribution.     

Photoinduced ionic polymerization. VII. Cationic polymerization of cyclohexene oxide in solid state

Photopolymerization of cyclohexene oxide in the presence of electron acceptors was studied in a bulk system (in liquid as well as in solid states). The polymerization was proved to proceed by a cationic mechanism in both states by the effect of inhibitors. In a liquid phase the light intensity dependence of the rate of polymerization and the molecular weight distribution showed a contribution of a free ionic polymerization. Any discontinuous phenomenon in the rate as well as in the molecular weight was not discerned between liquid(above ?36°C) and plastic crystal (between ?36 and ?81°C) phases. A quantum yield of monomer consumption as high as 8 × 10³ was observed in the plastic crystal phase. Below ?81°C in the normal crystal phase the rate as well as the molecular weight was remarkably suppressed.     

Radiation-induced polymerization of glass-forming systems. VII. Polymerization in supercooled state under high pressure

Radiation-induced polymerization of glass-forming monomers such as 2-hydroxyethyl methacrylate and glycidyl methacrylate under high pressure was studied. The glass transition temperature of these monomers was heightened by increased pressure. The temperature dependence of polymerizability showed a characteristic relation; similar to those in supercooled-phase polymerization under normal pressure, that had a maximum at T_v which shifted to higher levels of temperature as well as to T_g under high pressure. Polymerizability in the supercooled state also increased under increased pressure.     

Radiation-induced homogeneous polymerization of ethylene in cyclohexane

The radiation-induced polymerization of ethylene in cyclohexane was carried out in a reactor of 100 ml capacity under a range of temperature of 25–150°C, dose rate of 4.1 × 10⁴–2.9 × 10⁵ rad/hr, pressure of 200 kg/cm², and amount of cyclohexane of 20–90 ml. The polymerization was found to proceed at a steady state from the beginning. The polymerization rate is maximum at ca. 50 ml of cyclohexane. The dose rate exponent of the polymerization rate was 0.6 at every temperature from 25 to 150°C. The polymer molecular weight is in the range of 10³–10⁴, independent of dose rate, and decreases with increasing amount of cyclohexane. The molecular weight distribution is unimodal and narrow. Kinetic analysis of these results indicates that the polymerization proceeds via a simple scheme of homogeneous polymerization and the polymer molecular weight was determined by the chain transfer reaction which takes place mostly with cyclohexane. The unimodal and narrow molecular weight distribution is also consistent with the homogeneous polymerization scheme.     

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, -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, -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.     

Radiation-induced grafting polymerization by the anionic mechanism

The 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.     

Radiation-induced graft polymerization of metal-containing monomers

Graft polymerization of acrylates and acrylamide complexes of Mn(II), Cr(III), Fe(III), Co(II), Ni(II), and Cu(II) from alcohol solutions onto a polyethylene powder preirradiated in air up to total doses of 10–300 kJ/kg was studied. Graft copolymers with a metal content of as high as 1.7 mass% were obtained. The addition of a σ- or a coordinate-bound metal atom to the monomer molecule (acrylic acid, acrylamide) was shown to decelerate the process of thermal homopolymerization by 4 to 8 times, significantly reduce the reaction order in respect with monomer concentration in solution, and in most cases produce no effect on the polymer chain termination mechanism. The grafting of metal-containing monomers was found not to alter the structure of the monomer unit, valent state, and coordination of the metal atom, either. The graft polymerization of the monomers from solution is distinguished by a weak effect of the radical reaction inhibitors. The effective activation energies for the grafting of the metal-containing monomers lie within 42–60 kJ/mol.     

Radiation-induced crosslinking and cyclization in 1,2-polybutadiene

In order to get information on the radiolytic changes in 1,2-polybutadiene (1,2-PB) the sol and gel fractions, the conversion of double bonds, the structure and concentration of radicals, the formation of dienes and the formation of gaseous products were measured. In addition, the dose rate dependence and temperature dependence for the conversion of double bonds were determined. G values for double bond conversion depend on molecular weight and range from 20 to 200. G values for crosslinking are about 10. A mechanism for the double bond conversion is proposed which involves initiation by a transformation of the primary radical ion in the vinyl group into a carbonium ion and a radical. This is supported by ESR measurement. Reaction of the carbonium ion with a vinyl group in the same chain gives rise to cyclization, whereas reaction with a vinyl group in a neighboring chain results in crosslinking. A comparison of the G values for conversion of double bonds with the G values for crosslinking shows that the formation of cyclic rings exceeds the formation of crosslinks by a factor of about 10. The corresponding values in 1,4-cis- and 1,4-trans-polybutadiene are much smaller [G(cl) ? 2; G(db) ? 7]. The pendent vinyl groups in 1,2-polybutadiene therefore are more reactive than the vinylidene groups in 1,4-polybutadienes.     

Radiation-induced polymerization for the immobilization of penicillin acylase

The immobilization ofEscherichia coli penicillin acylase (EC 3.5.1.11) was investigated by radiation-induced polymerization of 2-hydroxyethyl methacrylate at low temperature. A leak-proof composite that does not swell in water was obtained by adding the crosslinking agent trimethylolpropane trimethacrylate to the monomer-aqueous enzyme mixture. Penicillin acylase, which was immobilized with greater than 70% yield, possessed a higherK _m value toward the substrate 6-nitro-3-phenylacetamidobenzoic acid than the free enzyme form (K _m = 1.7 × 10⁻⁵ and 1 × 10⁻⁵M, respectively). The structural stability of immobilized penicillin acylase, as assessed by heat, guanidinium chloride, and pH denaturation profiles, was very similar to that of the free-enzyme form, thus suggesting that penicillin acylase was entrapped in its native state into aqueous free spaces of the polymer matrix.