Radiation-induced graft copolymerization of mixtures of styrene and n-butyl acrylate onto cellulose and cellulose triacetate

Mixtures of styrene and n-butyl acrylate of various compositions were grafted onto cellulose and cellulose triacetate fibers preirradiated with γ-rays at 0°C in air. Monomer reactivity ratios of the grafted copolymers were found to be different from those of the nongrafted copolymers or those of AIBN-initiated copolymers. The active species initiating the graft copolymerization were trapped radicals for cellulose and peroxides for cellulose triacetate. Kinetic investigations of the graft copolymerization of styrene onto preirradiated cellulose triacetate fibers were also carried out, and it was found that the kinetic scheme for radical polymerization is also applicable to graft copolymerization in a heterogeneous system.     

Simulation and optimization of cellulose and styrene graft copolymerization process

Graft polymerization of styrene into cellulose was investigated using Ceric ions redox systems as initiator. A mathematical model with the D-optimal design combined with the least squares method was applied to the system. The variables considered in the model are the reactant variables i.e. monomer and initiator concentrations and the processing variables i.e. reaction time, temperature and agitation rate. The optimal composition and processing conditions were determined using a three dimensional space analysis.     

Ultraviolet-radiation-induced graft copolymerization of styrene and acrylonitrile onto cotton cellulose

Photoinitiated graft copolymerization of the vinyl monomers, styrene and acrylonitrile, onto cotton cellulose was studied using uranyl nitrate and ceric ammonium nitrate as photoinitiators. Uranyl nitrate photoinitiation showed a higher level of grafting for styrene, whereas in the case of acrylonitrile ceric ammonium nitrate was found to be the better photoinitiator. Optimized conditions of grafting, when employed to cotton swollen with sodium hydroxide and zinc chloride, enhanced the graft levels for both monomers. Grafted samples were subjected to thermal analysis, as well as estimation of moisture regain and tenacity. Thermal stability increased, whereas, the moisture regain and tenacity decreased, with the increase in graft add-on in the case of both monomers. Acrylonitrile-grafted cotton showed dyeability with cationic dye that improved with the level of graft add-on. Possible explanations have been given.     

Radiation-induced graft copolymerization of mixtures of styrene and acrylamide onto cellulose acetate. V. Studies on thermal behavior

The thermal behaviors of cellulose acetate, either grafted or ungrafted, were studied. A thermogram of cellulose acetate when grafted with acrylamide is characterized by an endothermic peak at 340°C. If, however, styrene is grafted, the thermogram shows two characteristic exothermic peaks at 330 and 420°C. A thermogram of the mixed graft comprising both acrylamide and styrene, on the other hand, is characterized by only one exothermic peak at 420°C. A consideration of various thermal data indicates that cellulose acetate when grafted is comparatively more stable than when not grafted. Again, styrene is found to be more effective than acrylamide in increasing the stability.     

Radiation-induced reactions with cellulose. III. Kinetics of styrene copolymerization in methanol

The kinetics of the radiation-induced grafting of styrene to cellulose in methanol have been studied in air at dose rates of 0.007, 0.014, and 0.078 Mrad/hr. in ⁶⁰Co and spent fuel element facilities. The variables affecting rate of grafting include monomer concentration, radiation dose rate, and total dose. Grafting reaches a maximum at 60–70% by volume methanol in styrene. The results have been interpreted in terms of possible grafting mechanisms, including charge-transfer intermediates; however, a complete mathematical treatment of the data is not possible at present because of the absence of appropriate swelling data for cellulose in mixtures of styrene and methanol. Poor grafting observed in solutions of up to 10% monomer is attributed to radical scavenging (predominantly from the solvent) by the monomer leading to the formation of scavenged products including homopolymer. Rate of grafting falls off for solutions above 80–90% monomer concentration and radical scavenging by monomer radicals is again postulated to account for the observed behavior.     

New aspects of graft copolymerization of styrene onto cellulose induced by gamma rays

Graft products of styrene onto cellulose prepared by simultaneous gamma-ray irradiation under various conditions were acid-hydrolysed to recover polystyrene produced within the cellulose matrix. The polystyrene was subjected to gel permeation chromatography to determine the molecular weight (M) and further separated with a thin-layer chromatographic (t.l.c.) technique into two components, i.e. the true grafted side-chain polymer and attendant homopolymer. This t.l.c. experiment allowed an estimation of the true percentage grafting (Y). Influences of changing the reaction conditions upon the values of M and Y were thus investigated, and some newer aspects on vinyl polymerization occurring within the cellulose matrix are presented.     

Radiation-induced graft copolymerization of mixtures of styrene and acrylamide onto cellulose acetate. VI. Permeability of sodium chloride and sodium sulfate

Acrylamide, styrene, and mixtures of acrylamide and styrene were grafted onto cellulose acetate film. The permeabilities of sodium chloride and sodium sulfate through the ungrafted and grafted cellulose acetate films were studied. Permeability increases with the increase in the extent of grafting of acrylamide; whereas it decreases with the increase in the extent of grafting of styrene onto cellulose acetate. The same trend in permeability was observed when cellulose acetate was grafted with the binary monomer mixture. Permeability is also found to depend on the nature of the solute dissolved in water. The results were discussed in terms of free volume concept of the water-swollen films.     

Radiation-induced graft copolymerization of butadiene to polyethylene and polypropylene

Polyethylene and polypropylene films were irradiated by γ-irradiation from a Co⁶⁰ source in butadiene gas flow and in liquid butaidne. Irradiating in the butadiene gas flow is particularly convenient because the gas state monomer is available directly and little homopolymer is produced. In this case, there is a retardative effect on the grafting near the surface of the film and the grafting rate shows the maximum values at 50–60°C. for high-density PE (PEH) and PP. Irradiating in the liquid butadiene decreases the retardative effect near the surface. The effect of dose rate I on the grafting rate Rp is represented by R_p ∞ I^1/4 in this case. The grafting rate is always higher in PEH than in low-density PE (PEL). Results of x-ray diffractometry and electron microscopy indicate that the grafting reaction occurs predominantly near the surface of the crystallite (lamella) of PE and the grafting rate is not affected by the overall crystallinity of the trunk polymer but by the configurational structure, such as the degree of branching or side-chain length.     

Structure and properties of cellulose graft copolymers. I. Radiation-induced rayon–styrene graft copolymer

Rayon–styrene graft copolymers were prepared by the direct radiation method, with the use of the preswelling technique, by irradiation with γ-rays from ⁶⁰Co. The grafting was carried out in bulk styrene and in styrene–solvent mixtures, such as styrene–methanol and styrene–acetone, to study their effect on the graft copolymerization reaction and the structure of the resulting graft copolymer. The effects of carbon tetrachloride, a chain-transfer agent, was also investigated. Three different types of rayon yarn were used; Fortisan, a modifier-type high wet-modulus rayon, and a high-tenacity tire yarn, in order to study the effect of rayon microstructure on the grafting reaction. The molecular structure of the rayon–styrene graft copolymers was studied by hydrolyzing away the cellulose backbone and measuring the molecular weights of the grafted polystyrene branches. For grafting in bulk styrene, the molecular weights of the grafted polystyrene ranged from 400,000 to 1,000,000, while those of the polystyrene homopolymer formed in the outside solution were of the order of 30,000–50,000. The molecular weights of the grafted polystyrene branches tended to increase with per cent grafting in the graft copolymer. For grafting in styrene–methanol and styrene–acetone mixtures, the molecular weights of the polystyrene branches decreased with increasing solvent content. The addition of carbon tetrachloride to bulk styrene resulted in a sharp decrease in the molecular weights of the grafted branches. The grafting frequency or number of polystyrene branches per cellulose chain was calculated from the per cent grafting and the molecular weights of the polystyrene branches. The morphology of the rayon–styrene graft copolymers and some of their physical properties are discussed.     

Radiation-induced copolymerization of vinylphosphonic dichloride with methyl methacrylate and styrene

The γ-ray-induced copolymerization of vinylphosphonic dichloride (VPDC) with methyl methacrylate (MMA) and styrene (St) was studied at 25°C (liquid phase) and ?78°C (Solid phase). The reaction mechanisms are discussed. The reactivity ratios for the copolymerization of the VPDC–MMA system were determined as follows: The difference between the reactivity between the liquid-phase (25°C) and solid-phase (?78°C) copolymerization is mainly attributable to the r₂ value. The behavior of the liquid-phase copolymerization of the VPDC–St system was anomalous, the r₁ value being negative in the range from 0 to 80 mole-% of VPDC monomer. In the solid-phase (?78°C) copolymerization for the VPDC–St system, the reactivity ratios r₁ and r₂ were 0.097 and 1.6, respectively. The rate of copolymerization (R_p) at 25°C, for both the VPDC–MMA and VPDC–St systems, passes a maximum point at a certain monomer concentration, suggesting that the composition of copolymer is considerably affected by R_p. This phenomenon was interpreted by the assumption that an energy transfer reaction from VPDC monomer to the other vinyl compound can easily occur.     

Effect of stirring on cellulose graft copolymerization

Dissolving pulp was grafted with several monomers ranging from hydrophilic (dimethylaminoethyl methacrylate) to hydrophobic (styrene). The conversion of these monomers to polymer and copolymer was investigated in dependence on the number of revolutions of the agitator. The formation of grafted copolymer was found to be strongly influenced by stirring. For all the monomers employed, almost no copolymer was formed above 400 rpm. The formation of homopolymer was also severely reduced at higher stirring speeds. For some monomers, a maximum was obtained at about 200–300 rpm with both copolymer and homopolymer yields dropping off sharply at both lower and higher stirring speeds. The position of this maximum was affected by the size of the reactor. The behavior displayed by the xanthate? Fe²⁺–H₂O₂, Fe²⁺–H₂O₂, and ceric ion initiation systems was very similar. Also, monomer solubility in water seemed to have little importance in determining the general behavior.     

Homogeneous graft copolymerization of styrene onto cellulose in a sulfur dioxide–diethylamine–dimethyl sulfoxide cellulose solvent

Graft copolymerization of styrene onto cellulose was studied in a homogeneous system (SO₂–DEA–DMSO medium) by γ-ray mutual irradiation technique. At the same time, homopolymerization of styrene was also examined separately in DMSO, SO₂–DMSO, DEA–DMSO, and SO₂–DEA–DMSO media by the same technique. Polymerization of styrene hardly occurs on concentrations above 10 mole SO₂–DEA complex per mole glucose unit. Maximum percent grafting was obtained in concentrations of 4 mole, after which it decreased rapidly. Total conversion and percent grafting increased with the irradiation time. The value (=0.55) of the slope of the total conversion rate plotted against the dose was only a little higher than the 1/2 which was expected from normal kinetics. No retardation in homopolymerization of styrene in DMSO, SO₂–DMSO, and DEA–DMSO was evident, while the retardation of homopolymerization in the SO₂–DEA–DMSO medium was measurable. Sulfur atoms were detected in the polymers obtained in both of SO₂–DMSO and SO₂–DEA–DMSO solutions. All of the molecular weights of polymers obtained in the present experiment were very low (3.9 × 10³?1.75 × 10⁴).     

苯乙烯-异戊二烯-丁二烯橡胶接枝苯乙烯聚合动力学

以自制的4种苯乙烯-异戊二烯-丁二烯橡胶(SIBR)为增韧组分,采用本体聚合工艺,以过氧化苯甲酰为引发剂进行苯乙烯接枝聚合以制备高抗冲聚苯乙烯,考察了用量、相对分子质量及分子链结构不同的SIBR对苯乙烯聚合速率的影响,并比较了用不同橡胶改性聚苯乙烯时的聚合动力学行为。结果表明,SIBR的用量越大聚合速率越小,相对分子质量越大则聚合速率越大;按SIBR分子链序列结构的不同聚合速率还呈现出从大到小依次为线型嵌段SIBR、线型无规SIBR、星形嵌段SIBR及星形无规SIBR的规律。用不同橡胶增韧聚苯乙烯时的聚合速率从大到小依次为SIBR、丁苯橡胶及顺丁橡胶。苯乙烯的表观接枝率随着SIBR用量或其相对分子质量的增大而减小,且远大于使用顺丁橡胶。     

Radiation-induced graft copolymerization of butadiene on polyethylene by trapped radicals

The low-temperature grafting of butadiene on polyethylene (PE) preirradiated in air is compared with that on PE preirradiated in vacuo for the effect of several factors on the grafting. Little fundamental difference between the two cases was observed. In both cases the graft conversion curve is trapped radical type and the overall activation energies are 9.7 and 8.4 kcal/mol for 0.947-density PE and 0.916-density PE, respectively. Percent grafting is proportional to the square root of the dose rate (= total dose). The retarding effect of oxygen at irradiation or storage after irradiation on the grafting scarcely appears when the irradiation temperature or storage temperature is below 15°C. For thinner film and lower density of PE this effect appears clearly at the higher temperature. Therefore, it may be concluded that the low-temperature grafting of butadiene onto PE preirradiated in air is initiated predominantly by nonoxidized radical (allyl radical) trapped in PE and that the grafting reaction occurs in the semicrystalline part of PE.     

Hexavalent-chromium-initiated graft copolymerization of methyl methacrylate onto cellulose

Graft copolymerization of methyl methacrylate (MMA) onto cotton–cellulose has been carried out using hexavalent chromium Cr(VI) as initiator. Aqueous-methanolic solution of perchloric acid has been chosen as the reaction medium. The effect of monomer, initiator, acid, reaction medium, and temperature on the graft percentage has been found out. The reactions have also been carried out in the presence of polymerization, inhibitors, and retarders, such as hydroquinone and transition metal salts like CuSO₄, FeCl₃, etc. The grafted samples, after exhaustive separation of homopolymers and purification, were subjected to various chemical, mechanical, and thermal testings. The results of various analyses have been compared with the reference, and the improvement in the graft has been evaluated. A suitable mechanism for the grafting processes has been suggested, in accordance with the experimental results.     

Radiation-induced graft copolymerization of mixtures of styrene and acrylamide onto cellulose acetate. IV. Studies on some physical properties and structural characterization by means of scanning electron microscopy

Binary mixtures of monomers, e.g., styrene and acrylamide in 1:1 methanol:water solution, were grafted onto cellulose acetate film by taking recourse to preirradiation grafting procedure. The surface modification of the films due to grafting was examined by means of scanning electron microscopy. The mechanical properties, e.g., tensile strength elongation at break, and elasticity as well as water vapor permeability of the grafted films, were investigated. In the case of ungrafted films or when acrylamide was grafted to a low extent, the film surfaces were smooth and hence were not modified to any significant extent. But when acrylamide was grafted appreciably, or when styrene was grafted singly or in binary mixture with acrylamide, the surfaces were found to be covered with fibrils. The pattern of the surface modification also changes with the increase of the extent of grafting. The observed properties of the grafted films were explained on the basis of the electron microscopic results.     

Photoinitiated graft copolymerization of hydroxyethyl methacrylate onto cotton cellulose

The photoinitiated graft copolymerization of hydroxyethyl methacrylate (HEMA) onto cotton cellulose was studied using uranyl nitrate (UN) and ceric ammonium nitrate (CAN) photoinitiators. Optimization of various parameters of the graft-copolymerization reaction viz., time, temperature, initiator, and monomer concentration, was carried out. The optimized conditions of grafting were employed to cotton samples swollen in zinc chloride as well as sodium hydroxide. Graft add-on was found to be dependent on the nature of substrate and the concentrations of monomer and photoinitiator. UN was found to be the better photoinitiator, giving higher grafting with HEMA. The grafted samples showed initially decrease and then marginal increase in the moisture regain with increase in graft add-on. The dye uptake of both direct and reactive dyes decreased with increase in graft add-on.     

Gamma radiation-induced graft copolymerization of divinylbenzene onto cellulose fabric

The extent of DVB grafting onto cellulose fabric increases with total gamma radiation dose up to 10–15 kGy while it decreases with the radiation dose rate. A quantitative analysis of DVB grafting has been attempted by means of IR spectroscopy using the baseline method. Characteristic bands were selected in the spectra of copolymers, namely, the cellulose band at 1160 cm^?1 and DVB band at 798 cm^?1. The former band decreased and the latter increased with the degree of copolymerization, and the values were in accordance with the calibration straight line. An attempt to graft DVB onto cotton fabric previously grafted with styrene showed greater extent of copolymerization than with pure fabric.     

Radical formation and graft copolymerization on photo-irradiated aldehyde cellulose

The relationship between the activity to initiate graft copolymerization under photo-irradiation and the photo-induced radicals of periodic acid-oxidized cellulose (aldehyde cellulose) was investigated. Aldehyde cellulose proved to have a high activity to initiate graft copolymerization under photo-irradiation, and the effect was profound, especially for hydrophilic vinyl monomers such as acrylic acid and acrylamide. By studying the ESR spectrum of photo-irradiated aldehyde cellulose, the formation of a radical giving a singlet spectrum with linewidth of 14–15 G and a g value of 2.001 was observed. This was assigned to an acyl radical orginating in the aldehyde group of the sample. Employing low molecular weight aldehydes, it was confirmed that an acyl radical formed on aldehyde compounds by photo-irradiation has a function sufficient to initiate the graft copolymerization of vinyl monomers. It was concluded that the high activity needed to induce the graft copolymerization of aldehyde cellulose under photo-irradiation was based on an acyl radical which originated in the aldehyde group of the sample.