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.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. II. High-energy electrons irradiation

Vapor-phase mutual grafting of methyl acrylate (MA) onto polyethylene (PE) at high dose rates from an electron accelerator yields the same surface graft structure as does the grafting at low dose rates from ⁶⁰Co sources; i.e., a homopolymer layer (consisting of only MA component) is easily formed on the inner graft copolymer layer (consisting of both MA and PE components) as a result of the continuously increasing surface graft composition. To produce the surface layer, 4-MeV electron irradiation with a linear electron accelerator requires only less than 3 min of irradiation time at dose rates of more than 2 Mrad/min, whereas γ irradiation with a ⁶⁰Co source requires at least 1 hr at dose rates of less than 2 × 10³ rad/min. The rate of monomer consumption (or polymerization) in the surface homopolymer layer shows no dependence of irradiation time and a positive dependence of dose rate. It has been suggested that this kinetic feature at the high dose rates shows some contribution of vapor-phase homopolymerization and subsequent deposition (onto the grafting surface) followed by recombination with the grafted side chain radicals, although secondary graft copolymerization from the grafted chain radicals is still the principal process for the growth of the surface homopolymer layer.     

The Radiation-Induced Grafting of Vinyl Monomers to Polyethylene Terephthalate Fibers. Part I. Styrene

Some kinetic features of the mutual radiation grafting of styrene to polyethylene terephthalare fibers have been investigated. The effects of type of swelling agent, monomer concentration, and temperature have been determined. In general a maximum in the grafting rate was found to occur both with the concentration of swelling agent and with temperature. Undrawn fibers were found to graft at higher rates and maximum yield than drawn fibers. These and other features are discussed in terms of a simple grafting scheme coupled with diffusion controlled kinetics.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. I. γ irradiation

Mutual irradiation of polyethylene (PE) in methyl acrylate vapor easily forms a poly(methyl acrylate) (PMA) homopolymer layer on the inner graft copolymer layer consisting of both PE and PMA components as a result of the rapidly increasing surface-graft composition. This growth process of surface grafting has been found to provide some specific kinetic features different from those in other surface-grafting systems. With formation of the surface homopolymer layer, low- and highdensity PE sheets give the same grafting rate, whereas both sheets give different rates in grafting stages or conditions in which the homopolymer layer is not formed. This result indicates that most monomers, penetrating across the surface, are entrapped or consumed in the surface homopolymer layer; accordingly the rate becomes independent of the type of PE sheets that have significantly different diffusion coefficients. The thickness of the inner graft copolymer layer, which is kept constant after homopolymer-layer formation, increases with decreasing dose rate and with increasing monomer vapor pressure and temperature. This behavior can be qualitatively explained according to an equation for the initial steady-state grafting depth.     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—I. Membranes monogreffees carboxyliques ou basiques

We have determined the equilibrium properties (neutralization and swelling and the transport properties: conductivity and dialysis) of hydrophilic membranes obtained by radiation grafting of acrylic acid or 4-vinylpyridine onto thin PTFE films. The presence of strong counter-ion-membrane interaction (PTFE-PAA-K⁺ and PTFE-P4VP-ClO^?₄) has been confirmed in the beginning of neutralization. The grafting ratios of the samples ranged between a few percent and several hundreds percent. The properties have been studied in connection with the average degrees of ionization and the average molalities of the reactive groups throughout the whole thickness of the membrane. The parameters of the synthesis which determine the structure of acid or basic grafted chains also have an influence on the properties of the resulting membranes. For a high dose-rate (> 100 rad min^?1), the properties of carboxylic membranes are related to the degree of cross-linking: for smaller dose rates, the properties are related to the length of the grafted branches and/or to the state of the skeleton of PTFE. For the basic membranes, the properties are controlled by the length of the grafted branches and the importance of the micro-phase-separation between PTFE and the grafted chains; for low dose rates, when the grafted branches are long, separation of hydrophobic and ionizable zones is noticed for grafting ratios higher than 5%. The carboxylic membranes with lower degrees of grafting, prepared with a high dose rate, exhibit very good permselectivity. The pyridinic membranes with a low degree of grafting could be of practical interest, viz. the manufacture of selective electrodes for perchlorate ions.     

Radiation grafting kinetics of HEMADGDA onto silastic in different atmospheres

The radiation grafting kinetics of HEMA, as well as that of the mixture monomers of HEMA and DGDA have been researched. The effects of radiation dose, dose rate, and temperature on grafting are systematically researched in different atmospheres. It has been found that grafting is different in different atmospheres. The findings show that the depth distribution of HEMA/ DGDA monomer units in grafting layer is nonuniform. At first, HEMA grafting is superior, in the later stage of grafting, however, DGDA grafting is increased. The temperature effect on grafting is great at the beginning, it is less in the later stage of grafting.     

Radiation grafting of methyl methacrylate on radiation crosslinked natural rubber film

Summary Grafting ofmethyl methacrylate (MMA) on radiation crosslinked natural rubber (NR) film has been investigated by mutual radiation grafting. The effect of experimental parameters like radiation dose, dose-rate, additives like acids and inorganic salts, solvents, monomer concentration, cross-linking density of the natural rubber film on the grafting extent has been studied.From the kinetic studies, a kinetic equation showing almost parabolic and linear dependence of grafting on concentration and dose rate, respectively, was deduced.Preliminary thermal stability studies of grafted films indicated that grafting of MMA does not enhance the thermal stability of NR.     

Graft polymerization of vinyl monomers onto cellulose in presence of soda lime glass. II

In the sodium bisulfite–soda lime glass initiating system, crude and true grafting yields increased with increasing ratio of methyl methacrylate to cellulose up to a limit; beyond this limiting value, grafting yields decreased due to the increase of the rate of sodium bisulfite-monomer addition over that of polymerization. Limitation was also achieved on increasing the glass to cellulose ratio through increased termination rates by coupling and disproportionation reactions, as the free radicals are increased. In addition, a limiting value was reached with increasing sodium bisulfite concentration; this may be related to the formation of a nonfunctioning disulfite ion at the expense of bisulfite radicals at high concentrations of sodium bisulfite. The temperature plays a role in this initiating system. Maximum rates of conversion and grafting were achieved at the ceiling temperature. Dissociation of the sodium bisulfite, which decreases with temperature, also has an effect.     

Grafting vinyl monomers on silk fibres—I. Graft copolymerization of methyl methacrylate on silk by tetravalent cerium ion

The use of tetravalent cerium to initiate graft copolymerization of methyl methacrylate on to silk fibres has been investigated. The extent of grafting was determined while varying Ce(IV) and monomer concentrations, temperature and nature of the fibre. The graft yield increased on increasing Ce(IV) concentration up to 0.015 M and monomer concentration up to 0.469 M; thereafter it decreased. The effect of an inorganic salt (copper sulphate) on grafting has also been studied. Chemical modification of the silk prior to grafting noticeably affected graft yield.     

Kinetics of radiation-induced grafting reactions. II. Cellulose acetate–styrene systems

Kinetics of grafting reactions of styrene to preirradiated cellulose acetate have been studied by labeling the active sites with bromine atoms. The dilution of styrene monomer with methanol affected grafting reactions remarkedly: e.g., as the concentration of methanol in monomer solutions increased, the growth rates of individual graft radicals decreased while the average lifetimes increased. The integrated amounts of active sites which participated in grafting reactions were also affected by the constitution of monomer solutions and varied roughly in proportion to the extents of swelling of cellulose acetate. Grafting yields for styrene/methanol = 1/1 were higher than for 3/1 and 1/3 throughout the duration of grafting reactions, which is due not only to the high molecular weight of graft chains but also to the large number of graft chains for the 1/1 system compared to the other systems.     

Gamma radiation induced graft copolymerization of vinyl monomers onto poly(vinyl alcohol)

In an attempt to modify water-soluble synthetic polymers, graft Copolymerization of methylmethacrylate (MMA) and ethyl acrylate (EA) onto poly(vinyl alcohol), PVA, has been studied by using gamma irradiation from a Co⁶⁰ source as initiator. The graft copolymerization was carried out in an aqueous medium by the mutual method in air. The effect of total dose and concentration of vinyl monomers on percentage of grafting has been determined. Water plays a significant role in the enhancement of graft copolymerization and the optimum amount of water to afford maximum grafting has been evaluated. The effect of CH₃OH on aqueous grafting of MMA and EA by radiation method has been studied. The graft copolymer has been characterized by IR spectroscopic and thermogravimetric methods.     

Grafting polymerization on cellulose based textiles: A C solid state NMR characterization

Grafting of methyl methacrylate and ethyl acrylate onto cellulose chains of textiles with oxidized sites has been carried out. To this aim, carboxyl and carbonyl groups have been introduced by oxidation of the cellulose and used as photosensitive agents, allowing the formation of radical sites. The copolymerization has been started irradiating the substrate with ultraviolet light for a short time. With the grafting of acrylic monomers the mechanical strength and the thermal stability of cellulose based textiles may be improved, as well as the resistance to chemical and biological agents. The method has been successfully tested performing the grafting on a naturally aged cotton sample. It is worth to note that the grafting does not affect the aspect of the material.All samples have been characterized with ¹³C solid state NMR spectroscopy. A semi-quantitative evaluation of the grafting has been performed either studying the cross-polarization dynamic process, or by direct integration of resonances in ¹³C single pulse excitation spectra.     

Grafting of acrylic acid onto radiation-peroxidized polypropylene film in the presence of ferrous ion

Acrylic acid has been grafted from aqueous solution onto 70 μ isotactic polypropylene-film previously peroxidized by irradiating in air with both 400 keV electrons and γ-radiation from a ⁶⁰Co source. Ferrous ion has been used to induce the redox decomposition of the macromolecular peroxy species at temperatures between 0 and 40°C. It has been shown that the effect of low [Fe²⁺] is to increase grafting rates, but that at [Fe²⁺] > 8 × 10^?4 molal the retarding effect of the reducing ion becomes increasingly important. At constant [Fe²⁺] a pronounced maximum in rate is observed at around 50 wt-% of acrylic acid; this may be related to increased swelling of the polymer matrix at this point. The initial rate of grafting increases as the square root of the preirradiation dose and, in the preirradiation dose rate range, 1.6–8.0 Mrad/sec, is independent of the dose rate. The grafting rate during the later stages of the reaction, however, increases as the preirradiation dose rate decreases. In the temperature range 0–40°C, the overall activation energy is 19 kcal/mole; from this value, the activation energy of initiation has been estimated to be around 20 kcal/mole.     

Radiation-Induced Copolymerization of Styrene and Cellulose at Low Dose Rates

A study has been made of the radiation-induced grafting of styrene to cellulose in the presence of cobalt 40 gamma irradiation at low total doses and dose rates. For copolymerization, What mans 41 filter paper was immersed in solutions of styrene in methanol at various monomer concentrations. The dose rates were varied from 140 to 3100 rads/hr while the total dose varied from lo³ to 2 × 10⁵ rads.

In the presence of oxygen the grafting results showed considerable scatter, but a statistical analysis revealed that at all concentrations a linear relationship existed between total dose and graft %. Three factors contributing to the variance about the regression line were examined. Residual oxygen in the solution, while not important at high dose rates, was shown markedly to contribute to the variance in the range examined. A linear dose-rate effect involving a decrease in graft with increasing dose rate was demonstrated. A LET effect also contributed to the over-all variance. Preliminary results indicate the presence of a maximum which may be a Trommsdorff effect.     

Comparison of pre-irradiation and mutual grafting of 2-chloroacrylonitrile on cellulose by gamma-irradiation

Radiation-induced graft polymerization is one of the best methods for obtaining materials with new properties. In this work, radiation grafting of 2-chloroacrylonitrile to cellulose by mutual and pre-irradiation grafting methods was investigated. The grafting yield was enhanced by applying the emulsion grafting method. The grafting yield determined in the above systems was observed as 27% at highest and 6% at lowest. The effects of concentration of monomer, reaction time and reaction temperature on grafting yield were studied. Evidence of grafting has been based on the comparative studies of cellulose and grafted cellulose by infrared spectroscopy, thermal analysis and contact angle measurement. Grafting enhances thermal stability of cellulose backbone.     

Grafting polymerization of acrylic acid onto preirradiated polypropylene fabric

Acrylic acid (AAc) was grafted onto polypropylene (PP) fabric by a preirradiation method using a Co-60 gamma ray. The effect of absorbed dose, AAc concentration, reaction temperature, reaction time, storage time, as well as the effect of ferrous ion and sulfuric acid on the degree of grafting were determined. It has been shown that the synergistic effect of sulfuric acid with the ferrous sulfate can not only increase the grafting yield, but also decrease the apparent activation energy for the grafting. It leads to the possibility of getting a particular grafting yield at a lower absorbed dose. In this experiment, It has also been shown that the grafting activity of preirradiated PP fabric in AAc aqueous solution could be well kept at room temperature for a long period.     

Grafting onto poly(vinyl alcohol). II. Graft copolymerization of methyl acrylate and vinyl acetate and their binary mixture using γ-rays as initiator

Methyl acrylate (MA), vinyl acetate (VAc) and their binary mixture (MA + VAc) have been graft copolymerized onto poly(vinyl alcohol) using γ-rays as initiator by mutual radiation method in aqueous medium. The optimum conditions for affording maximum grafting have been evaluated. The percentage of grafting has been determined as a function of total dose, concentrations of poly(vinyl alcohol), MA, VAc, and their binary mixture. Rate of grafting (R_p) and induction period (I_p) have been determined as a function of total initial mixed monomer concentration and concentration of poly(vinyl alcohol). The graft copolymer has been characterized by thermogravimetric method. The effect of donor monomer (vinyl acetate) on percent grafting of acceptor monomer (methyl acrylate) has been explained.     

纳米SiO_2锚固光敏基团引发MMA光接枝聚合研究

对纳米SiO2进行了锚固光引发剂的表面修饰,进而引发甲基丙烯酸甲脂(MMA)光接枝聚合制备有机/无机复合粒子.纳米SiO2粒子首先用氯化亚砜进行表面氯化,再与光引发剂2-羟基-4-(2-羟基乙氧基)-2-甲基苯丙酮(Irgacure2959)反应从而锚固上光引发剂.通过紫外光引发MMA在经过修饰过的纳米SiO2表面上进行表面光接枝聚合.采用IR、TGA和TEM等方法表征了接枝前后纳米粒子的变化,证明了表面接枝物的存在,并研究了不同反应条件对单体转化率、接枝率和接枝效率的影响.研究结果表明,搅拌对接枝过程的影响比较显著.TGA结果显示未搅拌聚合时接枝率只能达到比较小的程度,而在搅拌条件下180min内MMA的接枝率可达到110%.     

In situ studies of the adsorption kinetics of 4-nitrobenzenediazonium salt on gold

Self-assembled organic layers are an important tool for modifying surfaces in a range of applications in materials science. Covalent modification of metal surfaces with aryldiazonium cations has attracted much attention primarily because this reaction offers a route for spontaneously grafting a variety of aromatic moieties from solution with high yield. We have investigated the kinetics of this process by performing real-time, in situ nanogravimetric measurements. The spontaneous grafting of 4-nitrobenzene diazonium salts onto gold electrodes was studied via quartz crystal microbalance (QCM) from aqueous solutions of the salt at varying concentrations. The concentration dependence of the grafting rate within the first 10 min is best modeled by assuming a reversible adsorption process with free energy comparable to that reported for arylthiols self-assembled on gold. Multilayer formation was observed after extended grafting times and was found to be favored by increasing bulk concentrations of the diazonium salt. Modified gold surfaces were characterized ex situ with cyclic voltammetry, infrared reflection absorbance spectroscopy, and X-ray photoemission spectroscopy. Based on the experimentally determined free energy of adsorption and on the observed grafting rates, we discuss a proposed mechanism for aryldiazonium chemisorption.     

Functional polymers. XIV. Grafting of 2(2-hydroxy-5-vinylphenyl)2H-benzotriazole onto polymers with aliphatic groups

Successful grafting of 2(2-hydroxy-5-vinylphenyl)2H-benzotriazole onto saturated aliphatic C? H groups of polymers has been accomplished. When the grafting reaction was carried out in chlorobenzene at 150–160°C with di-tertiary butylperoxide as the grafting initiator, grafts as high as 20–30% at grafting efficiencies of 50 and 80% have readily been obtained. It was very important to carry out the grafting reaction in tubes sealed under high vacuum since trace amounts of oxygen cause complete inhibition of the grafting reaction by the phenolic monomer. Grafting reactions were carried out on a variety of different polymers including atactic polypropylene, ethylene/vinyl acetate copolymer, poly(methyl methacrylate), poly(butyl acrylate), and polycarbonate.