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.     

Characterization of the collagen–vinyl graft copolymers prepared by the ceric ion method. II. Infrared spectra and electron microscopy

Collagen powder and goat skins were grafted with different vinyl monomers using the ceric ion technique. The graft copolymers were characterized by infrared spectra and electron microscopy. The collagen–vinyl graft copolymers were hydrolyzed by both acid and enzymatic hydrolysis, and the grafted vinyl polymer side chains were isolated. In the grafted poly(methyl methacrylate) (PMMA) side chains isolated by acid hydrolysis, the characteristic amide absorption bands at 1550 and 1660 cm^?1 were not seen prominently. However, in PMMA side chains isolated by enzymatic methods, the amide absorption bands were more prominent as these isolated side chain polymers contained longer fragments of the peptide backbone attached to them. Electron-microscopic observations of grafted collagen fibrils and ultrathin sections of grafted goat skin fibrils did not show any cross-striations. These various evidences indicate that the polymers formed on collagen have penetrated into the fibrils and that they were chemically bound to the collagen molecules.     

Study of radiation-induced graft polymerization of vinyl monomers to cellulose by infrared spectroscopy. II. Cellulose–polystyrene copolymers

Infrared spectral analysis has been applied for the study of cotton-polystyrene copolymers prepared by using the preirradiation method. The degree of grafting was determined from the absorption at 700 cm^?1, which is characteristic of the polystyrene spectrum, with an accuracy of ± 1.5%.     

Fine structure of cellophane–acrylamide graft copolymer by the ceric ion method

The relationship between the grafting yield and the structure of graft copolymer is studied by measuring the branched chain lengths, the number of branches, the crystallinities, and the diffraction intensities of the (101) and (101 ) + (002) planes determined by x-ray diffraction, and the distribution of branched polymers, observed by interferometry. Over a relatively wide range of grafting yield the number of initiating sites is almost constant and about 1–2 per 2 moles of cellulose chain. Therefore, the increase of grafting yield seems to be due mainly to the propagation of branched polymers. Branched polymers are assumed to be formed in cellulose crystallites both on the normal (101) planes and in the amorphous regions of cellulose. It is found that branched polymers grow from the outer layer into the inner part of the film as the grafting yield increases. At more than 250% of grafting yield, however, branched polymers are uniformly formed throughout the layer of film in which the crystalline regions of cellulose are gradually destroyed. This result agrees with the dimensional change of gel film during the reaction. The temperature dependence of tensile strength and elongation and the wet strength of graft copolymer are also investigated. At higher grafting yields, such as 250%, the crystalline structure of cellulose is disturbed by the formation of branched polymer, and no improvement in waterproofness can be expected from grafting; the secondary bonding between branched polymers may be presumed to be same as those among cellulose. In addition, the fine cracking of the film in the burst state is found to appear more easily as the grafting yield increases, in which the aggregating state of cellulose is recognized to be changed by the formation of branched polymer.     

Study of radiation-induced graft polymerization of vinyl monomers to cellulose by infrared spectroscopy. I. Cellulose–polyacrylonitrile copolymers

Infrared spectral analysis has been applied for the study of cotton–polyacrylonitrile copolymers prepared by using the preirradiation method. The degree of grafting was determined from the absorption at 2249 cm.^?1, which is characteristic of the polyacrylonitrile spectrum, with an accuracy of ± 1.5%.     

Oxidation of cellulose by ceric ion

Dissolving pulp was oxidized by ceric ammonium sulfate in sulfuric acid medium under oxygen-free argon. Initial rapid oxidation was followed by first-order consumption of ceric ion. The rate of cellulose oxidation (?R_Ce) which was taken at the beginning of the first order consumption period, levelled off with an increase in the concentration of ceric ion. It was found that the ?R_Ce was dependent on the concentration of cellulose in the second power. The rate of ceric ion consumption was a function of the available surface area of cellulose.     

The preparation and properties of acrylic and methacrylic acid grafted cellulose prepared by ceric ion initiation. II. Water retention properties

Bleached sulfite softwood pulp and the corresponding paper have been grafted with acrylic and methacrylic acids and a number of other monomers. A practical, all aqueous, ceric ion method was used as described in Part I of this series. The water and saline retention values of the grafted pulps were determined. Super water sorbency, up to 48 g/g, were obtained after suitable post treatments. A number of variables were studied including the effects of pH, counterion, crosslinking, drying, and beating. It was gratifying that drying did not affect the effeciency of water or saline water retention. Useful linear functional relationships were found between the saline water retention values and the logarithm of the percent sodium chloride in the water. The two “model” parameters of the plots also correlated well with the water retention values and with the degree of grafting expressed as the ion exchange equivalents of the pulps. The osmotic pressure approach to the water sorption as developed by Grignon and Scallan⁵ coupled with the restraining forces of the grafted polymer itself is used to interpret the process.     

ESR study of reactions of cellulose initiated by the ceric ion method

The ESR spectra of microcrystalline cellulose and purified cotton cellulose reacted with ceric ammonium nitrate in nitric acid were determined. The effects of the concentration of ceric ion, atmosphere, temperature, and graft copolymerization with acrylonitrile on the rates of formation and decay of radicals in the cellulose molecule were determined under both static and dynamic conditions. Under static conditions, after the desired conditions of reaction, the samples were frozen at –100 or –160°C., and then the concentration of free radicals was determined. Under dynamic conditions ceric ion solution was continuously flowed through the celluloses while these determinations were being made at 25°C. In the presence of oxygen the rate of decay of free radicals was decreased. On initiation of copolymerization reactions with acrylonitrile, there was an increase in radical concentration, then a decrease. Apparently, during graft copolymerization the radical site initially on the cellulose molecule was retained on the end of the growing polymer chain. Then additional ceric ion coordinated with the hydroxyl groups of the cellulose, leading to the formation of additional radical sites. An Arrhenius interpretation of the effect of temperature on the formation of these additional radical sites gave apparent activation energies for radical formation on cotton cellulose as 34 kcal./mole and on microcrystalline cellulose as 29 kcal./mole.     

Polymerization and graft copolymerization of styrene initiated by ceric ion in acetonitrile/water solution

The polymerization of styrene initiated by a ceric ion/pinacol system and the graft copolymerization of styrene onto microcrystalline cellulose initiated by ceric ion were studied in the mixed solution composed of acetonitrile and water. Although the graft copolymer of polystyrene onto microcrystalline cellulose was not obtained in the acetonitrile solution, addition of water initiated the polymerization, and the grafting ratio was increased with increasing the water added. The rate of polymerization of styrene in the ceric ion/pinacol system increased similarly with increasing the water content in the solution. Acetonitrile is miscible with water, but the solution was separated to two phases by adding styrene into the solution containing above 20% of water; the monomer was dissolved in both acetonitrile and water phases. The polymer was undissolved in this mixed solution. The effects of water on the polymerization in the mixed solvent system are discussed from the standpoint of reaction mechanism.     

Effect of lignin in graft copolymerization of methyl methacrylate on cellulose by ceric ion

The effect of lignin contained in cellulosic materials in graft copolymerization of methyl methacrylate on such materials using ceric ion as initiator was studied. It was found that the percent grafting and the average molecular weight of grafts became lower in samples having a larger lignin content but the number of grafts formed increased proportionally up to lignin content of about 2.5%. Ceric ion reacted at a faster rate with lignin than with cellulose in wood pulp, and the results indicating that the active sites formed on lignin by oxidation with ceric ion accelerate the formation of grafts and increase the number of grafts were obtained. But on the other hand, the active sites participated in the termination reaction of the growing graft polymer radicals to cause lowering of the average molecular weight of grafts.     

Humidity sensing properties of the vinylpyridine–butyl acrylate–styrene copolymers

In this article, the humidity sensors based on the vinylpyridine (VP)–butyl acrylate (BA)–styrene (St) copolymers are developed. The influencing factors of the copolymer's humidity sensing properties, such as the mol percentage of the fed monomers and the quaternization reagent ratio (namely, dibromobutane : butyl bromide ratio), are studied, and the long‐term stability of the copolymers is investigated as well. The results show that as the content of BA increases and the content of St decreases, the copolymer's hysteresis and response time decreases, and with the increasing of the quaternization reagent ratio, the copolymer's hysteresis and response time decreases. Also, the sensors based on the copolymers show 2–3% RH reproducibility under various long‐term test conditions. These results demonstrate an overall excellent performance in the reproducibility and long‐term stability. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1992–1996, 1999     

Synthesis and properties of vinyltrimethoxysilane–EPDM–styrene graft terpolymer

The graft copolymerizations of vinyltrimethoxysilane (VTMO) and styrene (St) onto ethylene–propylene–diene terpolymer (EPDM) were carried out with benzoyl peroxide (BPO) as an initiator in toluene. The effects of EPDM concentration, mole ratio of VTMO to St, reaction time, reaction temperature, and initiator concentration on the graft copolymerizations were examined. The synthesized VTMO–EPDM–St graft terpolymers (VES) were confirmed by infrared and ¹H-NMR spectroscopies. The molecular weight, thermal stability, light resistance, and weatherability of the graft terpolymer were investigated by gel permeation chromatography, thermogravimetric analysis, and Fade-o-Meter. The number-average molecular weight was 109,000. It was found that the heat resistance and light resistance as well as weatherability of VES are considerably better than those of acrylonitrile–butadiene–styrene terpolymer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1345–1352, 1998     

Studies on polymer blends. II. Butadiene–styrene copolymers and polybutadiene–polystyrene blends

The properties of butadiene–styrene copolymers and of polybutadiene–polystyrene blends were compared. Polybutadiene, polystyrene, and four copolymers having styrene contents of 20, 40, 60, and 80% were prepared. The copolymers were compared with blends having various styrene contents and prepared by means of latex blending and roll blending. Vulcanizates were prepared by three different curing methods, i.e., sulfur cure, peroxide cure, and radiation cure. The results of the benzene extraction of three vulcanizates showed that the polystyrene blended was not cured by any of the curing methods used. The properties of the vulcanizates of the copolymers were markedly different from those of the blends, i.e., in the case of the blends the properties showed a linear relationship with their blending ratio, while in the copolymers the properties showed a curvilinear relationship which had an inflection point at a styrene content of about 60%. From this phenomenon of the copolymers, it was proposed that the second-order transition point of styrene is the cause of the properties showing this peculiar point. From the results, it was found that the behavior of styrene in copolymers is essentially different from that in blends.     

Poly(methyl methacrylate)–cellulose nitrate copolymers. II. Physical and mechanical properties

Poly(methyl methacrylate)–cellulose nitrate copolymers were prepared by bulk polymerization using benzoyl peroxide as initiator. Cellulose nitrates of two different nitrogen contents (11.4 and 12.2%) were used. The prepared copolymers were γ-irradiated for specified periods of up to 11.83 Mrad. Their physical and mechanical properties were measured before and after irradiation. The title copolymers showed lower modulus, tensile strength, and elongation at break than poly(methyl methacrylate) itself, but they showed better hardness and abrasion. Irradiation to up to 6.57 Mrad improved the modulus of the copolymers. Hardness and abrasion were improved by increasing cellulose nitrate content. The prepared copolymers that contained cellulose nitrate of 11.4% nitrogen showed secondary transition points. The increase of cellulose nitrate concentration shifted both first and second transition points to relatively higher values.     

Grafting of acrylonitrile onto cellulose initiated by ceric ion

Acrylonitrile was grafted onto cellulose with the use of ceric salt as initiator and the grafting was found to be maximum at 0.6N acid concentration. The effect of monomer and initiator concentration on the extent of grafting was studied. A new method for quantitative estimation of extent of grafting on cellulose was developed and its validity was established. The grafted samples with 20% increase in weight were found to be highly resistant to microorganisms.     

Permeation of gases through modified polymer films. I. Polyethylene–styrene graft copolymers

The permeabilities of nitrogen, oxygen, and carbon dioxide through polyethylene–styrene graft copolymer films were measured by means of a gas permeability apparatus based on a modification of Barrer's high vacuum technique. Polyethylene–styrene grafts were prepared by mutual γ-ray irradiation of low-density polyethylene films in styrene–methanol solution. Densities and thicknesses of the graft copolymer films were determined. It was observed that the gas permeability constants decreased with increasing grafting to minimum values at 20–30% styrene grafting and increased again above 30% grafting. These results are explained in terms of a decrease in the free volume of the amorphous regions of the polyethylene by a “filling in” effect of the grafted polystyrene chains. Above 30% grafting, disruption of the crystallites may occur resulting in increased gas permeation. Activation energies for gas permeation through polyethylene–styrene graft copolymer films were calculated and found to decrease with increasing per cent styrene grafting. For nitrogen permeation, the activation energy decreased from 11.7 kcal/mole for unirradiated polyethylene to 9.5 kcal/mole for a 50.5% graft. Corresponding values for oxygen and carbon dioxide were 10.2–8.2 kcal/mole for a 48.7% graft and 8.4–6.5 kcal/mole for a 50.5% graft.     

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).     

Relationships between rheological properties,morphological characteristics,and composition of bitumen–styrene butadiene styrene copolymers mixes. II. A thermodynamical interpretation

The variations of the dynamic mechanical properties (at 5 Hz) of bitumen–SBS mixes in the function of their composition (polymer content, bitumen composition) have been established. The relationships between the viscoelastic measurements and the morphological characteristics, previously determined, have been used to interprete these variations in terms of change of morphological characteristics (phase composition, phase content in the blends). Finally, a theoretical approach based on the thermodynamics of mixing is proposed to explain the relationships between the composition and the morphological characteristics. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1609–1618, 1997