Synthèse et caractérisation de copolymères cellulose–poly(méthacrylate de méthyle): Greffage par le système acide de Caro–ion Fe3+

Methyl methacrylate was grafted onto cellulose using Caro's acid-Fe³⁺ system as initiator. The effect of grafting time, ferric ion concentration, and cellulose/monomer ratio, on the per cent grafting, was investigated. From studies of the reaction mechanism with model compounds it was postulated that the grafting did not occur at the 1,2-glycol units or at the hemiacetal unit in the end of the cellulose molecule. Concurrent degradation of the cellulose during the graft copolymerization was examined. A linear relationship between the per cent grafting and the number of cellulosic broken chains by hydrolysis was found, from which it would seem that the structure of the graft copolymer was of block-type. The structure of the graft copolymers was also studied by determination of the molecular weights of the grafted PMMA branches, after hydrolysis of the cellulosic backbone. In all cases, independently of reaction conditions, the molecular weights of the grafted branches were very high and their number low. The number of graft branches per cellulose chain was calculated from the per cent grafting, the molecular weights of the PMMA branches and of the cellulosic backbone. This number was compared with the number of cellulosic bonds broken during grafting.     

Molecular weights of grafted polystyrene onto γ-preirradiated cellulose diacetate

The behavior of molecular weights of grafted polystyrene onto γ-preirradiated cellulose diacetate was studied. The grafting of styrene onto cellulose diacetate was kinetically followed with particular attention paid to the polystyrene molecular weight behavior. The molecular weight was evaluated with the polymer fractions obtained by acid hydrolysis of the grafted copolymer. From the experimental results it appeared that the grafted chain molecular weight is completely controlled by the physical properties of the polymeric matrix either during a “bulk” or a “front” grafting.     

Structure and properties of cellulose graft copolymers. II. Cellulose–styrene graft copolymers synthesized by the ceric ion method

Styrene was graft-copolymerized onto wood cellulose by the ceric ion method of Mino and Kaizerman. The grafting reaction was found to depend strongly on the concentration of ceric ion in the grafting system and maximum grafting occurred in a narrow range of concentration of initiator, 1.0 × 10^?3-1.8 × 10^?3 mol/l, at 58 ± 1°C. A pretreatment technique, developed to enhance the monomer diffusion into cellulose, was found to increase the grafting considerably. The structures of the cellulose-styrene graft copolymers were studied by hydrolyzing away the cellulose backbone to isolate the grafted polystyrene branches. The molecular weight and the molecular weight distributions of the grafted polystyrene were determined using gel permeation chromatography. The number-average molecular weight (M?_n) ranged from 23,000 to 453,000 and the polydispersity ratios (M?_w/M?_n) varied from 2.5 to 8.0. The grafting frequencies calculated from the per cent grafting and molecular weight data were of the order of 0.05–0.4 polystyrene branches per cellulose chain.     

Graft copolymers from thiolated starch and vinyl monomers

Thiol starches of degree of substitution (D.S.) 0.005–0.162 were prepared by displacing starch tosyloxy groups with xanthate and treating the resulting xanthate esters with either sodium hydroxide or sodium borohydride. Acrylonitrile, styrene, acrylamide, acrylic acid, and dimethylaminoethyl methacrylate were grafted onto the thiol starches with hydrogen peroxide as initiator. The peroxide caused both grafting of monomer and coupling of thiol groups to disulfide. Treating graft copolymers with sodium borohydride regenerated thiol groups from disulfide groups so that the grafting sequence could be repeated. By regenerating the thiol groups and repeating the grafting steps, high add-on and high-frequency starch graft copolymers were prepared. During four grafting sequences, acrylonitrile reacted with D.S. 0.162 thiol starch to give graft copolymers that contained increasing amounts of polyacrylonitrile (46.0–66.5%). Grafting frequency increased from 183 to 71 anhydroglucose units (AGU)/graft, while molecular weights of the grafted chains ranged between 20,000 and 25,200. The final product was hydrolyzed with potassium hydroxide solution to a copolymer, which absorbed up to 400 ml water per gram. Styrene was grafted onto thiol starch to give products containing 34.4–69.5% polystyrene with 986–3520 AGU/graft and having molecular weights of grafted chains between 276,000 and 364,000. Graft copolymers containing 48.9% polyacrylamide, 21.2% poly(acrylic acid), and 77.7% poly(2-methacryloyloxyethyldimethylammonium acetate) were obtained under similar conditions.     

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.     

The graft copolymerization of styrene and lignin. II. Kraft softwood lignin

The radiation-induced graft copolymerization of styrene and various kraft softwood lignins was studied. Expression of the results as the usual “per cent graft” was impossible, because grafting caused the lignin to become extractable in solvents for the styrene homopolymer. However, evaluation of the effects of various solvents on the degree of reaction was made through an indirect, and possibly more characteristic, measure. Grafting was least pronounced under conditions of low lignin accessibility (e.g., when less than 10% methanol was present), but increased with the addition of better lignin solvents or with higher methanol concentrations. The precipitating nature of the latter conditions was also found to contribute to an accelerated rate of grafting. Surprisingly, the graft copolymer was found to degrade at higher doses. Proof of grafting is offered in a fractionation scheme. Measurement of the molecular weight of the polystyrene separated from the lignin backbone allows the estimation of approximately one polystyrene graft per lignin molecule in benzene-extractable copolymers. Two glass transition temperatures could be detected in several fractionated copolymers.     

Synthesis and characterization of graft copolymers of syndiotactic polystyrene with polybutadiene and 4‐methylstyrene

The basic method for synthesizing syndiotactic polystyrene‐g‐polybutadiene graft copolymers was investigated. First, the syndiotactic polystyrene copolymer, poly(styrene‐co‐4‐methylstyrene), was prepared by the copolymerization of styrene and 4‐methylstyrene monomer with a trichloro(pentamethyl cyclopentadienyl) titanium(IV)/modified methylaluminoxane system as a metallocene catalyst at 50°C. Then, the polymerization proceeded in an argon atmosphere at the ambient pressure, and after purification by extraction, the copolymer structure was confirmed with ¹H‐NMR. Lastly, the copolymer was grafted with polybutadiene (a ready‐made commercialized unsaturated elastomer) by anionic grafting reactions with a metallation reagent. In this step, poly(styrene‐co‐4‐methylstyrene) was deprotonated at the methyl group of 4‐methylstyrene by butyl lithium and further reacted with polybutadiene to graft polybutadiene onto the deprotonated methyl of the poly(styrene‐co‐4‐methylstyrene) backbone. After purification of the graft copolymer by Soxhlet extraction, the grafting reaction copolymer structure was confirmed with ¹H‐NMR. These graft copolymers showed high melting temperatures (240–250°C) and were different from normal anionic styrene–butadiene copolymers because of the presence of crystalline syndiotactic polystyrene segments. Usually, highly syndiotactic polystyrene has a glass‐transition temperature of 100°C and behaves like a glassy polymer (possessing brittle mechanical properties) at room temperature. Thus, the graft copolymer can be used as a compatibilizer in syndiotactic polystyrene blends to modify the mechanical properties to compensate for the glassy properties of pure syndiotactic polystyrene at room temperature. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Modification of cellulose acetate reverse osmosis membranes by radiation grafting

Large excesses of a chain transfer agent, carbon tetrachloride, were introduced to a recipe for the mutual radiation grafting of styrene to cellulose acetate film. The effect of the carbon tetrachloride on the molecular characteristics as well as the reverse osmosis and time dependent mechanical properties of resulting graft copolymers was determined. Extremely short side chains were generated as a consequence of the high concentrations of chain transfer agent and the composite results further suggest that the morphology of the grafted films is best described as “destructured” or internally plasticized consequent to grafting in the presence of CCl₄. Reverse osmosis fluxes increased with percent graft; salt rejection was high and unaffected by per cent graft up to 40% graft; and the tensile creep under wet conditions was significantly retarded by the grafting. These effects were shown to accrue from grafting per se by control experiments involving α-methylstyrene which will not propagate to form a polymer under these conditions. These results are compared and contrasted with earlier work on grafting in the absence of CCl₄ where long side chains of polystyrene were generated resulting in a structuring of the polymer involving domains of polystyrene-rich material and domains of cellulose acetate rich polymer.     

Characterization of products prepared by homogeneous grafting of styrene onto cellulose in a sulfur dioxide–diethylamine–dimethyl sulfoxide medium

Homogeneous graft copolymerization of styrene onto cellulose was carried out using a SO₂–DEA–DMSO cellulose solvent reaction medium and γ-ray mutual irradiation. The yield of grafted side chain polymer and the homopolymer in this reaction system proved to be polysulfone, a styrene–sulfur dioxide copolymer in which the number of sulfur atoms per polymer chain is 3–3.5. Several characterizations of the graft product were attempted. The graft products were extracted with boiling benzene for 24 hr to remove homopolymer, and then the cellulose backbones were hydrolyzed. After hydrolysis, the polysulfone residues were separated by thin-layer chromatography (TLC) into two components, i.e., attendant homopolysulfone and the true side chain polysulfone having some sugar residues at one of the polymer chain ends. The weight fraction of these components for each graft product was determined by a TLC scanner. The molecular weight of the side chain polysulfone remained constant and significantly lower than that of the homopolysulfone throughout the reaction period. By assuming that no scission of cellulose chains occurred throughout the graft reaction, the number of branches per starting cellulose molecule was assessed to be surprisingly large, ranging from 2.4 to 10.6 at a total dose of 1–8 mR of irradiation. It was also found that percent grafting increased with irradiation time because of an increase in the number of branches per cellulose chain. Furthermore, we succeeded in separating the graft product into ungrafted cellulose and the true graft copolymer containing a small amount of attendant hompolysulfone.     

Preparation,characterization, and properties of cellulose–polyacrylamide graft copolymers

Graft copolymers of acrylamide on cellulose materials (α‐cellulose 55.8%, DP 287.3) obtained from Terminalia superba wood meal and its carboxymethylated derivative (DS 0.438) were prepared using a ceric ion initiator and batch polymerization and modified batch polymerization processes. The extent of graft polymer formation was measured in graft level, grafting efficiency, molecular weight of grafted polymer chains, frequency of grafting as a function of the polymerization medium, and initiator and monomer concentrations. It was found that the modified batch polymerization process yielded greater graft polymer formation and that graft copolymerization in aqueous alcohol medium resulted in enhanced levels of grafting and formation of many short grafted polymer chains. Viscosity measurements in aqueous solutions of carboxymethyl cellulose‐g‐polyacrylamide copolymer samples showed that interpositioning of polyacrylamide chains markedly increased the specific viscosity and resistance to biodegradation of the graft copolymers. The flocculation characteristics of the graft copolymers were determined with kaolin suspension. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 913–923, 2003     

Graft polymerization of styrene onto starch by simultaneous cobalt-60 irradiation

Starch-g-polystyrene copolymers have been prepared by the simultaneous ⁶⁰Co-irradiation of starch–styrene mixtures, and copolymers have been characterized with respect to weight per cent polystyrene (% add-on) and also the molecular weight and molecular weight distribution of polystyrene grafts. In a typical polymerization, 4 g each of starch and styrene were blended with 1 ml water and 1.5 ml of an organic solvent; the resulting semisolid paste was irradiated to a total dose of 1 Mrad. With ethylene glycol, acetonitrile, ethanol, methanol, acetone, and dimethylformamide as the organic solvent, values for % add-on ranged from 24% to 29%. The highest % add-on (43%) and the highest conversion of styrene to grafted polymer (76%) were obtained when the organic solvent was omitted, and water alone was used. When water was also omitted, polymerization of styrene was negligible; however, graft copolymer was formed in the absence of water when either ethylene glycol or ethanol was added. Attempts were unsuccessful to achieve a % add-on greater than 43% by doubling the amount of styrene in the polymerization recipe. Mixtures of equal weights of starch and styrene are relatively nonvicious, but these mixtures thicken when either water or ethylene glycol is blended in. Reasons for this thickening action and the possible influence of thickening on the graft polymerization reaction were explored.     

Location of some typical vinyl polymers within radiation-grafted cotton fibers: An electron microscopical survey

Electron microscopical observations of radiation-induced rayon–styrene graft copolymers were published by Kaeppner and Huang in 1965. The present paper reports electron microscopical investigations on the relationship of the structure of vinyl–cotton graft polymers to the original morphology of the cotton fiber and into the distribution of the grafted vinyl polymer in the cotton fiber structure. The grafted vinyl monomers investigated in this study were acrylonitrile, styrene, methyl methacrylate, and vinyl acetate. Two radiation-induced procedures were used: simultaneous irradiation grafting and post-irradiation grafting. Ceric ion grafting of acrylonitrile to cotton was included for purposes of comparison. Distribution of the vinyl polymer within the cotton fiber is illustrated by a series of electron micrographs, selected as typical of the particular grafted species under consideration. Results indicate that the diffusion rate of monomer into the cellulose fiber plays an important role in the final distribution of polyacrylonitrile grafts within the fiber. Uniform distribution of polyacrylonitrile in the fiber was achieved by simultaneous irradiation grafting of acrylonitrile on a highly substituted cyanoethylated cotton. In samples of low degree of cyanoethylation the distribution of graft polymer was non-uniform. In grafting initiated by ceric ion the acrylonitrile graft polymer was evenly distributed. Polystyrene–cotton copolymers from grafts, made by simultaneous irradiation of cotton in methanol solutions of the styrene monomer, were uniform throughout the fiber but showed opening of structure associated with the amount of graft formed. Grafting of methyl methacrylate occurred only in the peripheral regions of the fiber; by contrast, grafting of vinyl acetate was uniform throughout the fiber wall. Important factors governing the successful irradiation grafting in cotton fibers are choice of solvent, ratio of monomer to cellulose, nature of prior chemical modification of the cellulose, and total irradiation dosage.     

ESR studies of the photodegradation of cellulose graft copolymers

Ultraviolet light induced free radicals in cellulose and cellulose graft copolymers were studied by means of ESR spectroscopy. At least six kinds of free radicals were formed in cellulose when the polymer was irradiated with ultraviolet light. Polystyrene and poly(methyl methacrylate) are more resistant to ultraviolet light than cellulose; however, the cellulose graft copolymers of polystyrene and poly(methyl methacrylate) were degraded by ultraviolet light. ESR studies revealed that photoinduced free radicals in cellulose graft copolymers were formed at the grafting branches of the copolymers rather than the cellulose backbone. The mechanisms of light stabilization and energy transfer reactions of cellulose and cellulose graft copolymers are discussed.     

Graft copolymers of starch with mineral acid salts of dimethylaminoethyl methacrylate. Preparation and testing as flocculating agents

Mineral acid salts of dimethylaminoethyl methacrylate (DMAEMA) have been graft polymerized onto starch with ferrous ammonium sulfate–hydrogen peroxide initiation. The nitric acid salt was used in most reactions, and graft polymerizations were run in both water and aqueous–organic solvent systems. Increased monomer concentration in water led to an increase in both the percentage of poly(DMAEMA · HNO₃) in the graft copolymer (percent add-on) and the molecular weight of grafted branches. Variations in initiator concentration altered the percent add-on only slightly but affected the molecular weight of grafted polymer significantly. When swollen starch, in contrast with unswollen starch was used in graft polymerization reactions run in water, the product had a higher per cent add-on and a larger number of grafted branches of lower molecular weight. The efficiency of starch–poly(DMAEMA · HNO₃) graft copolymers as flocculants for diatomaceous silica increased with per cent add-on; however, variations in grafting frequency and graft molecular weight had less effect on the behavior of these materials as flocculants.     

Behavior of cellulose graft copolymer towards persulphate oxidation. III. Poly(acrylonitrile) graft copolymers

Cotton cellulose was graft copolymerized with poly(acrylonitrile) to different levels. The copolymers so obtained together with the nongrafted cellulose were oxidized at different pH's (4–10) and temperatures (50–70°C) with potassium persulphate. The oxidation reaction was studied with respect to oxygen consumption, mass loss, and changes in copper number and carboxyl content of the cellulosic materials. It was found that the rates of oxidation at pH 4 for the copolymers are substantially higher than that of the nongrafted cellulose and the rate of oxidation is higher the higher the level of grafting. The reverse is the case at pH 10. The mass loss increases as the oxygen consumption increases irrespective of the substrate used and the pH employed. The magnitude of the mass loss is substantially lower in the case of grafted cellulose than in the case of nongrafted cellulose. The cellulosic copolymers with higher graft levels show lower mass loss than those having lower graft levels. However, the copper number and carboxyl content of the oxidized grafted cellulose are higher than those of the nongrafted cellulose at the same oxygen consumption. It is believed that the presence of poly(acrylonitrile) graft in the molecular structure of cellulose impedes cellulosic chain scission without necessarily preventing oxidation of cellulose hydroxyls.     

Physical properties of model graft copolymers and their use as blend compatibilizers

The present investigation pertains to the structure–property relationships of highly structured graft copolymers. The specific model graft copolymers are based on an elastomeric backbone, i.e., poly(ethyl acrylate), and monodisperse thermoplastic grafts, i.e., polystyrene. The synthesis of these graft copolymers is based on the free-radical polymerization of ethyl acrylate and an anionically polymerized polystyrene macromonomer. It is clearly demonstrated that grafts significantly enhance tensile properties. The level of improvement is directly related to the graft level, i.e., number of grafts/chain, and graft molecular weight. In addition, blending these graft copolymers into their respective homopolymer mixture results in a mechanical performance strikingly dependent on the molecular characteristics of the graft copolymer. For example, tensile strength is maximized at a level between one and two grafts per chain. This result parallels observations noted in blend compatibilization using diblock and triblock copolymers. It is also demonstrated that using mutually grafted copolymers produces an interesting variety of compatibilized ternary (or higher) component blends. © 1994 John Wiley & Sons, Inc.     

Effect of aging on synthesis of graft copolymer of EPDM and styrene (EPDM‐g‐PS)

The effect of aging on synthesis by the graft copolymerization of styrene onto random ethylene–propylene–diene monomer with benzoyl peroxide (BPO) as the initiator is described. Results showed that yields of graft copolymer are increased in the first 10 min. After 10 min, the total polymer produced has a maximum at about 25 min. However, the portion of the graft copolymer is decreased and the portion of the pure polystyrene is increased. In addition, the influence factors, such as reaction time, temperature, BPO concentrations and styrene concentrations, effect of solvents on the extent of graft copolymerization were discussed. The extent of grafted copolymerization was verified by hexane and acetone Soxhlet (solvent extraction). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4809–4813, 2006     

Modification of Tefzel film through graft copolymerization

The graft copolymerization of styrene (st) and methacrylonitrile (MAN) onto Tefzel film in aqueous media by the preirradiation method has been studied. In order to follow the effect of preswelling of the backbone polymer, grafting was attempted onto preirradiated Tefzel film and monomer preswollen, preirradiated Tefzel film. Optimum conditions pertaining to maximum percentage of grafting of st and MAN have been evaluated. Grafting onto preswollen, preirradiated Tefzel film displayed better results. The effect of different alcohols of increasing chain length on the percentage of grafting of st and MAN was also studied. Graft copolymerization of st showed an increase, while grafting with MAN exhibited a decrease, in the percentage of grafting in the presence of alcohols as compared to that obtained in the aqueous medium. Characterization of the graft copolymers was made by IR and thermogravimetric studies. Tefzel‐graft‐polystyrene showed improved thermal stability while the MAN grafted onto preswollen, preirradiated Tefzel film produced graft copolymer with poor thermal stability. Copyright © 2004 Society of Chemical Industry     

Preparation and characterization of block and graft copolymers using macroazoinitiators having siloxane units

α,ω-Amine terminated organofunctional polydimethylsiloxane (PDMS) was condensed with 4,4′-azobis-4-cyanopentanoyl chloride (ACPC) to prepare macroazoinitiators containing siloxane units. Interfacial polycondensation reaction at room temperature was applied: ACPC was slightly dissolved in carbon tetrachloride and it was poured on aqueous NaOH solution of PDMS. Block copolymers containing PDMS as a block segment combined with polystyrene (PS) have been derived by the polymerization of styrene monomer initiated by these macroazoinitiators. PS-b-PDMS block copolymers were characterized by using nuclear magnetic resonance and infrared spectroscopy. Thermal and mechanical properties of the block copolymers were studied by using thermogravimetric analysis, differential scanning calorimetry, and a Tensilon stress-strain instrument. The morphology of block copolymers was investigated by scanning electron microscopy. PDMS-g-polybutadiene (PBd) graft copolymers were also prepared by reaction of PBd with the above macroazo-initiator. Increase in the amount of macroazoinitiator in the mixture of PBd (52% w/w) leads to the formation of crosslinked graft copolymers. Molecular weights of soluble graft copolymer samples were between 450 and 600 K with a polydispersity of 2.0–2.3. © 1996 John Wiley & Sons, Inc.     

Graft copolymerizations of modified cellulose,grafting of acrylonitrile,and methyl methacrylate on carboxy methyl cellulose

Graft copolymers of acrylonitrile (ACN), methyl methacrylate (MMA), and their mixtures on carboxy methyl cellulose (d.S 0.4–0.5) were prepared by the use of ceric ion initiator in aqueous medium. The graft copolymers were characterized by IR spectroscopy. The extent of graft copolymerization of ACN and MMA was measured in terms of graft level, molecular weight of grafted polymer chains, and the frequency of grafting as functions of ceric ion concentration. It was found that at comparable reaction conditions, the molecular weight of the grafted polymer chains and the frequency of grafting were not of the same order of magnitude. For the monomer mixtures, the copolymer compositions obtained from the total nitrogen contents of the copolymer samples showed that a disproportionately low amount of ACN monomeric units were incorporated into the graft copolymer, even at high ACN content of the feed. © 1996 John Wiley & Sons, Inc.