Radiation-induced grafting of styrene vapor to polyethylene

The radiation-induced grafting of styrene vapor to low-density polyethylene film of 0.063 mm thickness was studied at 23°C at a dose rate of 1.98 × 10⁴ rad/hr. The concentration C of monomer in the film was measured as a function of pre-irradiation exposure time to monomer vapor. The concentration-dependent diffusion coefficient of styrene in polyethylene was calculated to be 4.9 × 10^?9 exp {2.0C/C₀} cm²/sec, where C₀ is the saturation concentration of styrene in the film, and a linear boundary diffusion coefficient for styrene vapor into polyethylene film was found to be 2.0 × 10^?7 cm/sec. The rate of grafting was determined as a function of the concentration of styrene absorbed in the film. The maximum graft yield was obtained with an initial styrene concentration in the film of 4 wt-%. Under conditions of low initial monomer concentration, the grafting rate increases with irradiation time. The results are compared with previously published data on grafting of polyethylene from methanol–styrene solutions. They are explained in terms of the viscosity of the amorphous region as a function of styrene content and the resistance to the diffusion of monomer at the film–vapor interface.     

Radiation-induced grafting of diallyldimethylammonium chloride onto acrylic acid grafted polyethylene

Diallyldimethylammonium chloride (DADMAC) was grafted onto polyethylene (PE) films by a double grafting procedure. The PE film was initially modified by grafting acrylic acid (AA), through a mutual irradiation method. AA-g-PE film, thus obtained was subjected to subsequent radiation grafting reaction of DADMAC, to give a DADMAC-g-AA-g-PE film having a comb-type structure. The influence of different conditions, such as the extent of AA grafting, DADMAC concentration, absorbed dose and dose rate, on the grafting yield of DADMAC was investigated. A maximum DADMAC grafting of 30% was achieved. The equilibrium degree of swelling (EDS) of the grafted films were gravimetrically determined. TGA and FT-IR techniques were employed to characterize the grafted PE films.     

Radiation-induced copolymerization of hexafluoroacetone with 2-methyl-1-pentene

Copolymerization of hexafluoroacetone (HFA) with 2-methyl-1-pentene (2MP) in trichlorotrifluoroethane (R-113) was carried out by γ-ray irradiation in a low-temperature region of ?100 to 0°C. Though HFA does not homopolymerize and 2MP scarcely does, the copolymerization took place at various monomer compositions. The copolymerization rate and the molecular weight in the low-temperature region were much higher than those at 0°C. Above room temperature the copolymerization did not take place and only the adduct of monomers was formed. The copolymerization was inhibited to some extent by cation scavengers, but not by radical or electron scavengers. Elemental analysis and nuclear magnetic resonance (NMR) spectra show that the copolymer consists of almost equimolar monomer units and has two types of structure, head to tail and head to head or tail to tail. It has been concluded that copolymerization probably proceeds via a cationic mechanism to form an alternating copolymer.     

Radiation-induced grafting of sensitive polymers

Films of PP and PTFE were modified by gamma-radiation grafting of pH and thermo sensitive monomers (two step method) by using both the preirradiation and the direct methods. The effects of the absorbed dose, monomer concentration and reaction time were investigated. The surface chemistry of grafted samples was analyzed by FTIR-ATR spectroscopy, while their thermal properties were analyzed by TGA and DSC. The stimuli-responsive behavior was studied by swelling and contact angle in water, as well as by DSC. Sensitive films presented a critical pH and LCST.     

Radiation-induced grafting of acrylic acid to nylon-6 in solution

The mutal irradiation technique has been employed to graft acrylic acid to nylon-6 in solution. Homogeneity of reactants and products was achieved by the use of the mixed solvent, o-chlorophenol-methanol (55·6/44·4 vol). The process resembled the heterogeneous grafting to nylon film rather than the homopolymerization of acrylic acid in solution. Some evidence is presented for a micellar growth of the graft copolymer.     

Radiation-induced crystallinity changes in linear polyethylene

Two kinds of ultrahigh-molecular-weight linear polyethylene (UHMW PE), together with conventional high-density polyethylene (HDPE), were subjected to β irradiation, and changes in their properties were monitored. Elastic modulus increased steadily with dose for all materials, as did the yield stress. A dramatic rise of density with dose was observed in the UHMW PE specimens accompanied by a corresponding increase in heat of fusion, x-ray crystallinity, and peak melting temperature. The magnitude of such changes in HDPE was much smaller. In UHMW PE specimens, the x-ray long period simultaneously decreased but crystal thickness remained constant. No changes in long period occurred in HDPE. The effects are attributed to the scission of tie molecules in UHMW PE followed by a growth in the perfection of the crystal lamellae, and suggest a method for assessing the tie-molecule content of such materials.     

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 crosslinking and grafting of two polyphosphazene elastomers

The radiation-induced crosslinking and grafting of two aryloxy-substituted elastomeric polyphosphazenes have been carried out by both gamma and electron beam irradiation. The classic Charlesby–Pinner [1] plus a simpler approach were used to determine the G(X) values for the crosslinked elastomeric polymers. The apparent G(X) value for the same polymer depended on whether the gamma-ray or the E-beam results were used. The presence of 8.5% repeat units with allylic groups in the side chain increased the G(X) value by an order of magnitude when the irradiation was performed under vacuum with the gamma source. The extent of acrylic acid grafting was also higher for the polymer containing the allylic group. Nearly all the grafted polyphosphazene films were insoluble in THF, a good solvent for the ungrafted samples.     

Radiation-induced grafting of styrene onto ultra-high molecular weight polyethylene powder and subsequent film fabrication for application as polymer electrolyte membranes: I. Influence of grafting conditions

Ultra-high molecular weight polyethylene (UHMWPE) powder was irradiated by gamma rays using a ⁶⁰Co source. Simultaneous and pre-irradiation grafting was performed in air and in inert atmosphere at room temperature. The monomer selected for grafting was styrene, since the styrene-grafted UHMWPE could be readily post-sulfonated to afford proton exchange membranes (PEMs). The effect of absorbed radiation dose and monomer concentration in methanol on the degree of grafting (DG) is discussed. It was found that the DG increases linearly with increase in the absorbed dose, grafting time and monomer concentration, reaching a maximum at a certain level. The order of rate dependence of grafting on monomer concentration was found to be 2.32. Furthermore, the apparent activation energy, calculated by plotting the Arrhenius curve, was 11.5 kJ/mole. Lower activation energy and high rate dependence on monomer concentration shows the facilitation of grafting onto powder substrate compared with film. The particle size of UHMWPE powder was measured before and after grafting and found to increase linearly with increase in level of grafting. FTIR-ATR analysis confirmed the styrene grafting. The grafted UHMWPE powder was then fabricated into film and post-sulfonated using chlorosulfonic acid for the purposes of evaluating the products as inexpensive PEM materials for fuel cells. The relationship of DG with degree of substitution (DS) of styrene per UHMWPE repeat unit and ion exchange capacity (IEC) is also presented.     

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.     

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.     

Radiation-induced changes in the microdestruction mechanisms in high-density polyethylene

High–density polyethylene (HDPE) samples irradiated by Co⁶⁰ gamma source have been investigated. The integration between the macromolecular structural units building the supermolecular structural organization is changed and different microdestruction mechanisms are achieved in the irradiation interval (0–20 Mrad). These microdestruction mechanisms are a result of specific radiation-induced crosslinking for the different irradiation doses. The crosslinking unites the primary structural units into macromolecular networks and lattices, which have a different effect upon the micro- and macrocharacteristics of the polymer, i.e., local micro-Brownian mobility, elongation at break, etc. © 1996 John Wiley & Sons, Inc.     

N-benzoylimine of hexafluoroacetone

Conclusions The N-benzoylimine of hexafluoroacetone is considerably more active than the imine of hexafluoroacetone in reaction with nucleophilic reagents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2046–2048, November 1965     

Radiation-induced grafting of perfluorinated vinyl ether into fluorinated polymer films

We report herein the first successful grafting of perfluorinated vinyl ether monomer into base polymer films by simultaneous radiation method. 2-Bromotetrafluoroethyl trifluorovinyl ether (BrTFF) could be grafted into poly(ethylene-co-tetrafluoroethylene) (ETFE) films by γ-rays irradiation at room temperature. The grafting yield increased linearly with an increase in the dose up to 1400 kGy. The required dose for a satisfactory grafting yield, such as 20%, was as high as ca. 400 kGy probably due to low polymerization reactivity of fluorinated monomers. However, the solvent and catalyst had no positive influence for improving the grafting yield. FTIR spectra and SEM-EDS testified that BrTFF was successfully grafted into ETFE films homogeneously in the perpendicular direction. The thermal analysis of the grafted films further indicated no phase separation between poly(BrTFF) grafts and ETFE films, probably owing to high compatibility of the fluorinated grafts and base polymers.     

Pre-irradiation grafting of span 60-IAH onto polyethylene to improve dripping properties of water on polyethylene films

A reactive type dripping anti-condensation agent, Span 60-IAH, was grafted onto linear low density polyethylene (LLDPE) by β-ray pre-irradiation and reactive extrusion. Effects of total dose, monomer concentration and extrusion temperature and rate on the degree of grafting were studied in detail. It was shown that the optimum conditions for grafting were the extrusion temperature of 130–220°C, screw run speed of 90 rpm and total β-ray dose of 12.5 kGy. The structure of the LLDPE-g-(Span 60-IAH) (LS) was characterized by Fourier-transform infrared spectroscopy (FT-IR). The tensile properties and light transmission properties of extruded films were determined. The thermal behavior of the LS was investigated by using differential scanning calorimetry (DSC). Compared with pure LLDPE, the crystallization temperature (T_c) of LS increased about 3°C. Accelerated dripping properties of film samples were investigated. The dripping duration of the LS film and a commercial anti-fog dripping film at 60°C were 45 days and 17 days, respectively, indicating a significant improvement.     

The addition of methyl radicals to hexafluoroacetone

The reaction of methyl radicals (Me) with hexafluoroacetone (HFA), generated from ditertiary butyl peroxide (dtBP), was studied over the temperature range of 402–433 K and the pressure range of 38–111 torr. The reaction resulted in the following displacement process taking place: where TFA refers to trifluoroacetone. The trifluoromethyl radicals that were generated abstract a hydrogen atom from the peroxide: such that k_6a is given by: where θ = 2.303RT kcal/mol. The interaction of methyl and trifluoromethyl radicals results in the following steps: Product analysis shows that k₁₇/kk = 2.0 ± 0.2 such that k₁₇ = 10^10.4±0.5M^?1 · s^?1. The rate constant k₅ is given by: It is concluded that the preexponential factor for the addition of methyl radicals to ketones is lower than that for the addition of methyl radicals to olefins.     

Radical grafting on lignin. Part I. Radiation-induced grafting of styrene onto hydrochloric acid lignin

By irradiation with gamma rays styrene was grafted onto hydrochloric acid lignin. When the graft polymers were subjected to nitrobenzene oxidation, the vanillin yields indicated two kinds of reaction occurring in the grafting. Polystyrene branches were separated from the graft polymers, and their M?_n were determined osmometrically. At grafting ratios of up to 100 the vanillin yields diminished proportionately with increasing grafting, and the M?_n of the branches, 5000, was unchanged. At grafting ratios of more than 100 the vanillin yields were constant, independent of the ratios, but the M?_n values of the branches increased with grafting. Paper chromatography of the aromatic acids obtained by oxidation of methylated lignin and the graft polymer indicated that isohemipic and metahemipic acids were more abundant in the acid fraction of the graft polymer than in the lignin itself. A qualitative mass analysis of the gaseous products evolving from the irradiated lignin showed the presence of hydrogen molecules only. Gamma-ray radiation brought about no change in the yields of vanillin. It was therefore concluded that radiation grafting on lignin at grafting ratios of less than 100 proceeded through the addition of the styrene polymer radicals to the aromatic nuclei of the lignin and that then branches propagated from the aliphatic part of the lignin, where C? H bond scission had been caused by the irradiation. The grafting sites of lignin would be C-5 and C-6 of the guaiacyl nucleus and, probably the β and γ carbon atoms of the aliphatic side chain of the lignin.