Graft Copolymerization on to Cellulose Using Binary Mixture of Monomers

The graft copolymerization of acrylonitrile (AN) and ethyl acrylate (EA) comonomers onto cellulose has been carried out using ceric ammonium nitrate (CAN) as an initiator in the presence of nitric acid at 35±0.1°C. The addition of ethyl acrylate as comonomer has shown a significant effect on overall and individual graft copolymerization of acrylonitrile on cellulose. The graft yield (%G_Y) and other grafting parameters viz. true grafting (%G_T), graft conversion (%C_G), cellulose number (Ng) and frequency of grafting (G_F) were evaluated on varying the concentration of comonomers from 6.0–30.0×10^?1 mol dm^?3 and ceric (IV) ions concentration from 2.5–25×10^?3 mol dm^?3 at constant feed composition (f_AN 0.6) and constant concentration of nitric acid (7.5×10^?2 mol dm^?3) in the reaction mixture. The graft yield (%G_Y) and other grafting parameters were optimal at 15×10^?1 mol dm^?3 concentration of comonomers and at 10×10^?3 mol dm^?3 concentration of ceric ammonium nitrate. The graft yield (%G_Y) and composition of grafted chains (F_AN) was optimal at a feed composition (f_AN) of 0.6. The energy of activation (Ea) for graft copolymerization has been found to be 16 kJ mol^?1. The molecular weight (Mw) and molecular weight distribution (Mw/Mn) of grafted chains was determined by GPC and found to be optimum at 15×10^?1 mol dm^?3 concentration of comonomer in the reaction mixture. The composition of grafted chains (F_AN) determined by IR method was used to calculate the reactivity ratios of monomers, which has been found to be 0.62 (r₁) and 1.52 (r₂), respectively for acrylonitrile (AN) and ethyl acrylate (EA) monomers used for graft copolymerization. The energy of activation for decomposition of cellulose and grafted cellulose was determining by using different models based on constant and different rate (β) of heating. Considering experimental observations, the reaction steps for graft copolymerization were proposed.     

<Emphasis Type="Italic">P. psyllium</Emphasis>-<Emphasis Type="Italic">g</Emphasis>-polyacrylonitrile: synthesis and characterization

P. psyllium mucilage, an anionic natural polysaccharide consisting of pentosan and uronic acid obtained from the seeds of Plantago psyllium (Plantago family), was grafted with acrylonitrile (AN). Graft copolymers were prepared by grafting acrylonitrile onto P. psyllium mucilage (PSY) using ceric ion initiated solution polymerization technique for the very first time. The influence of varying concentration of (AN) and ceric ammonium nitrate (CAN) on graft copolymerization was studied. The percent grafting was found to be affected by the concentrations of AN and CAN in the reaction mixture. The prepared copolymers were not soluble in any common solvent or mixture of solvents. The prepared copolymers were characterized by FTIR.     

Effects of carbonyl and aldehyde groups in the graft copolymerization of methyl methacrylate on cellulose with a ceric salt

Graft copolymerization of methyl methacrylate on cellulosic materials of various carbonyl and aldehyde contents with the use of a ceric salt as an initiator was studied. It was found that the concentration of the ceric salt which gives the maximum per cent grafting is in good agreement with the equivalent of total carbonyl content in the cellulosic material, and the number of grafted chains in copolymers is roughly proportional to it. However, the molar ratio of the number of grafted chains to total carbonyl content is quite small, being approximately 1:50, and the graft copolymerization can be explained kinetically on the assumption that the number of radicals produced on cellulose by the ceric salt leading to branching is very much smaller than the number of radicals destroyed by the ceric salt, and growing radicals can be stabilized by the termination reaction with the ceric salt or with a cellulose radical. Although both aldehyde and carbonyl groups contribute to the formation of grafted chains, the former are effective mainly at low concentrations of the ceric salt; both groups participate in the production of graft copolymers showing the maximum per cent grafting.     

Copolymers of Wheat Starch and Polyacrylonitrile. Effect of Aqueous-Organic Solvent Systems on Copolymer Composition

Starch-polyacrylonitrile graft copolymers prepared in a number of aqueous-organic solvent systems with ceric ammonium nitrate as the initiator had more grafted chains than those prepared in water alone, and these were of lower molecular weight. Substitution of methanol for 80% of the water produced grafted chains with a molecular weight of 15,700 and a grafting frequency of 253 anhydroglucose units per graft. The influence of catalyst concentration, increased reaction temperature, and sodium sulfate on the composition of the copolymer were investigated for the methanol-water system.     

Graft polymerization of vinyl monomers onto starch by use of tetravalent cerium

Grafting of acrylonitrile onto starch showed slightly higher yields when using soluble rather than insoluble starch, for reaction times < 1.5 hr. Beyond this time, the rate of grafting onto the soluble starch levels off, while that for grafting onto the insoluble starch proceeds leading to prograssive increase in the grafting yield. Momomer reactivity was in the following order: acrylonitrile > ethyl acrylate? methyl methacrylate. For the first two monomers, the order of reactivity is the reverse of that found for grafting onto cellulose; extremely low grafting yields resulted from grafting of ethyl acrylate rather than acrylonitrile onto starch. This result was attributed to the jelly nature of the polyethyl acrylate grafted starch, preventing diffusion of the monomer into the starch granules. This view was supported by the higher consumption of ceric ions at the start of the reaction, on grafting ethyl acrylate instead of acrylonitrile. As the reaction proceeds, the reverse takes place. Increase of ceric salt concentration, as well as the liquor to starch ratio, led to increased grafting yields.     

Graft Copolymerization of Monomer Mixtures Acrylonitrile/Ethyl Acrylate and Acrylonitrile/Methyl Methacrylate on Carboxymethyl Cellulose

Abstract

Graft copolymerizations of acrylonitrile/ethyl methacrylate and acrylonitrile/methyl methacrylate monomer mixtures on carboxy methyl cellulose (d.s. 0.4–0.5) were studied in aqueous medium at 30°C using ceric ion as initiator. The amounts of the polymer grafted were measured as a function of the mole fraction of acrylonitrite in the feed. The compositions of the copolymer samples were obtained from their nitrogen contents. It was found that the presence of acrylonitilte in the polymerization system was associated with reductions (of up to 80%) in the amounts of polymer grafted; and that disproportionately low amounts of acrylonitrile monomeric units were incorporated into the graft copolymer even at relatively high acrylonitrile content of the feed.     

Polymers from renewable resources. II. A study in the radio chemical grafting of poly(styrene‐alt‐maleic anhydride) onto cellulose extracted from pine needles

A binary mixture of styrene and maleic anhydride has been graft copolymerized onto cellulose extracted from Pinus roxburghii needles. The reaction was initiated with gamma rays in air by the simultaneous irradiation method. Graft copolymerization was studied under optimum conditions of total dose of radiation, amount of water, and molar concentration previously worked out for grafting styrene onto cellulose. Percentage of total conversion (Pg), grafting efficiency (%), percentage of grafting (Pg), and rates of polymerization (R_p), grafting (R_g), and homopolymerization (R_h) have been determined as a function of maleic anhydride concentration. The high degree of kinetic regularity and the linear dependence of the rate of polymerization on maleic anhydride concentration, along with the low and nearly constant rate of homopolymerization suggest that the monomers first form a complexomer which then polymerizes to form grafted chains with an alternating sequence. Grafting parameters and reaction rates achieve maximum values when the molar ratio of styrene to maleic anhydride is 1 : 1. Further evidence for the alternating monomer sequence is obtained from quantitatively evaluating the composition of the grafted chains from the FT‐IR spectra, in which the ratio of anhydride absorbance to aromatic (CC) absorbance for the stretching bands assigned to the grafted monomers remained constant and independent of the feed ratio of maleic anhydride to styrene. Thermal behaviour of the graft copolymers revealed that all graft copolymers exhibit single stage decomposition with characteristic transitions at 161–165°C and 290–300°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1763–1769, 1999     

Studies of the graft copolymerization of methyl methacrylate by means of the photochemical reduction of ceric ion adsorbed on cellulosic materials

It was observed that the rate of reduction of ceric ion adsorbed on cellulose was remarkably accelerated by irradiation with ultraviolet light, and this behavior depended upon the kind of cellulose. When the graft copolymerization of methyl methacrylate on cellulose with adsorbed ceric ion was carried out by irradiation with ultraviolet light, the percent grafting decreased for softwood, bleached sulfite pulp and increased for hardwood semichemical pulp. The average molecular weight of the grafts was observed generally to decrease. If it is assumed that the ceric ions, which are reduced at an accelerated rate in the early stages of reaction with SCP, do not participate in the graft formation, a relation is observed between the modified amount of reduced ceric ion and the number of grafted chains formed, and the molar ratios of these quantities are 12:1 without irradiation and 75:1 to 100:1 with irradiation. Even when the rate of reduction of ceric ion is accelerated, the increase in the number of grafted chains is found to be very small.     

Structure and properties of cellulose graft copolymers. III. Cellulose–methyl methacrylate graft copolymers synthesized by the ceric ion method

The ceric ion-initiated graft copolymerization of methyl methacrylate onto wood cellulose was found to depend on the concentrations of initiator, monomer, and cellulose. The structure of cellulose—methyl methacrylate graft copolymers was studied by hydrolyzing away the cellulose backbone to isolate the grafted poly(methyl methacrylate) branches. The molecular weights and molecular weight distributions of the grafted poly(methyl methacrylate) were determined by using gel-permeation chromatography. The number-average (M?_n) molecular weights ranged from 36 000 to 160 000 and the polydispersity ratios (M?_w/M?_n) varied from 4.0 to 7.0. The grafting frequency or the number of poly(methyl methacrylate) branches per cellulose chain calculated from the per cent grafting and molecular weight data varied from 0.38 to 3.2. The structure of cellulose—methyl methacrylate graft copolymers and the effect of stepwise addition of initiator on the structure are discussed.     

Copolymers of Starch and Polyacrylonitrile. Influence of Granule Swelling on Copolymer Composition under Various Reaction Conditions

Molecular weights and grafting frequencies of graft copolymers prepared with ferrous ammonium sulfate-hydrogen peroxide initiation showed a dependence on granule swelling similar to that found with ceric ammonium nitrate (increased swelling of starch granules decreased the number of grafted polyacrylonitrile chains and increased their average molecular weight). As with unswollen starch, the composition of the copolymer prepared from swollen starch was not influenced by granule size. Molecular weights of polyacrylonitrile branches grafted to swollen and unswollen starch were independent of reaction time; however, grafting frequencies with swollen and unswollen starch tended to converge toward a common value with increased reaction time and increased dilution. Data suggest that the influence of granule swelling on copolymer composition is due to a faster termination rate for growing polyacrylonitrile chains in unswollen starch.     

Controlled grafting of MMA onto cellulose and cellulose acetate

Homogeneous graft copolymerization of methyl methacrylate onto cellulose and cellulose acetate was carried out in various solvents and solvent systems taking ceric ammonium nitrate, tin (II) 2-ethyl hexanoate [Sn(Oct)₂] and benzoyl peroxide as initiators. The effect of solvents, initiators, initiator and monomer concentration, on graft yield, grafting efficiency and total conversion of monomer to polymer were studied. Formation of Ce³⁺ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights and polydispersity indices of the grafted PMMA were found out by gel permeation chromatography. The products were characterized by FTIR and ¹H-NMR analyses and possible reaction mechanisms were deduced. Finally, thermal degradation of the grafted products was also studied by thermo-gravimetric and differential thermo-gravimetric analyses.     

Grafting onto wool. I. Ceric ion-initiated grafting of poly(methyl acrylate) onto wool

Poly(methyl acrylate) has been grafted onto wool by using ceric ion as redox initiator in an aqueous medium. Initiation by ceric ammonium nitrate (CAN) was carried out in the presence of nitric acid of varying concentration at 35, 45, and 50°C for a period of 1.5 or 3 hr. Percent grafting was found to be dependent on concentrations of acid and monomer, reaction time, and temperature. Above 45°C, a considerable amount of homopolymer was formed; at 35°C, very little grafting of poly(methyl acrylate) was observed. Nitric acid catalyzed the reaction and a concentration of 0.17–0.19M HNO₃ was found suitable.     

Water-Soluble Copolymers. II. Synthesis and Characterization of Model Dextran-g-Acrylamides by Ce(lV)/HNO3-lnduced Initiation

In order to develop polymers useful as mobility control agents in enhanced oil recovery processes, water-soluble acrylamide grafted polysaccharide copolymers have been synthesized in water at 25° C using a ceric ammonium nitrate/nitric acid system. The effects of varying concentrations of ceric ion, monomer, and substrate on conversion, graft length, and molecular structure of the reaction products have been examined. The crude reaction products were purified by fractional precipitation and then were analyzed for nitrogen content using a micro-Kjeldahl method. The chemical structures of the graft copolymers were studied by selective hydrolysis of the carbohydrate backbones. Intrinsic viscosity and grafting length data were used to predict solution behavior of the graft copolymers prepared under controlled conditions. Aqueous size exclusion and viscosity studies showed direct correlations between hydrodynamic volume and length of the polyacrylamide side-chain grafts.     

Characterization and Evaluation of Thermal,Morphological, and Physicochemical Properties of Chemically Modified Lignocellulosic Biomass

A novel redox system, ascorbic acid-hydrogen peroxide, was employed to initiate graft copolymerization of ethyl acrylate and methyl methacrylate binary monomer mixtures onto Abelmoschus esculentus fibers at a temperature of 45°C for 90 min in an aqueous medium. Factors affecting grafting such as feed molarity and comonomer composition were investigated. Contrary to the lower affinity of methyl methacrylate for grafting on Abelmoschus fibers, a synergistic effect of ethyl acrylate on methyl methacrylate was observed when graft copolymers were prepared using different feed compositions (f_MMA). The percentage of grafting increased from 40.2% to 89.74% at 0.4 mole fraction of f_MMA. The graft copolymers were characterized by FT-IR, TGA, and SEM techniques.     

The Preparation and Properties of Acrylic and Methacrylic Acid Grafted Cellulose Prepared by Ceric Ion Initiation. Part I. Preparation of the Grafted Cellulose

The ceric ion method has been used to graft acrylic acid directly onto cellulose with a minimum amount of homopolymer. The method utilizes the pretreatment of the cellulose with ceric ammonium nitrate followed by washing out any excess of the catalyst. Oxygen can be present with the pretreatment step, but must be excluded during the grafting reaction itself. The process, which is entirely aqueous in nature, would appear to be quite practical on a large scale. Wet strengthened papers which are essential for the use of the grafted products as ion-exchange media can also be grafted but with adequate but lower yields than with the untreated paper. Apart from ion exchange, the products are of considerable potential value as water sorbing agents. Methacrylic acid gave lower grafting yields than acrylic acid, but these were much improved at higher temperatures.     

Cellulose-Monomer Interaction and a Revised Mechanism for Graft Copolymerization

Graft copolymerization of electron acceptor acrylic monomers on cellulose involves cellulose-monomer complexation. Cellulose acts as a matrix promoting high localized concentrations of donor-acceptor complexes in which uncomplexed monomer, normally an electron acceptor, behaves as a donor relative to the complexed monomer which has been converted to a stronger acceptor. The cellulose-monomer complexation influences both homopolymerizability and grafting efficiency, e. g. acrylonitrile (AN) and methacrylonitrile (MAN) in the presence of a catalyst and methyl methacrylate (MMA) in the absence of a catalyst. The presence of water, cupric ion, aldehydes, and CCU influence the course of the uncatalyzed reaction. When a donor monomer is present, equimolar alternating rather than random, grafted and ungrafted copolymers are produced, e. g., styrene or butadiene with MMA, MAN, or AN, as a result of the formation of an ordered array of donor-acceptor complexes on the cellulose. The revised mechanism of polymerization involves the homopolymerization of the donor-acceptor complexes, irrespective of the nature of the initiator, and grafting results from termination of the propagating chains by coupling with radicals on the cellulose.     

Grafting copolymerization of styrene and maleic anhydride binary monomer systems induced by UV irradiation

Photografting copolymerization of maleic anhydride (MAH) and styrene (St) onto LDPE film was investigated by using a one-step method, and further thermally induced grafting copolymerization of them was carried out by using a two-step method. Regarding the photografting copolymerization of MAH/St binary monomer system, both conversion percentage (CP) and grafting efficiency (GE) increased with raising the content of MAH in the monomer feed. In addition, the content of MAH in the grafted copolymers also increased with increasing the fraction of MAH in the monomer feed. The formation of LDPE-g-P(MAH-co-St) grafted film was identified by FTIR and ESCA spectroscopy. In the case of grafting copolymerization of MAH/St by the two-step method, grafting copolymerization proceeded slowly compared with the non-grafting copolymerization. The apparent activation energy (E_a) for the non-grafting copolymerization in the solution and the grafting copolymerization on LDPE film was 24 and 82 kJ/mol, respectively, which were noticeably lower than those of MAH/vinyl acetate (MAH/VAC) binary monomer system under the similar grafting conditions. These data of E_a explained why the grafting copolymerization of styrene/MAH took place faster than that of MAH/VAC binary monomer system. The composition of the grafted copolymer chains was largely affected by the composition of the monomer feeds; however, the composition of the non-grafted copolymers nearly remained at 1/1 even in systems with largely different MAH/styrene ratios in monomer feeds. It is indicated that the non-grafting copolymerization proceeded predominantly following alternating copolymerization, but the grafting copolymerization performed random copolymerization.     

Synthesis and Characterization of Chitosan‐graft‐Poly(3‐(trimethoxysilyl)propyl methacrylate) Initiated by Ceric (IV) Ion

The grafting of 3‐(trimethoxysilyl)propyl methacrylate (TMSPM) onto chitosan by ceric ion initiation was studied under homogeneous conditions in 2% acetic acid solution. The grafted polymer was characterized by FT‐IR, ¹H‐NMR, TGA and XRD and swelling studies. TGA results showed that the incorporation of TMSPM to the chitosan chains decreased the thermal stability of the grafted chitosan. Due to the grafting of TMSPM, the crystallinity of chitosan derivatives was found to be destroyed. The solubility of the grafted chitosan in water was improved. The effects of reaction conditions such as initiator concentration, monomer concentration, reaction temperature and reaction time were studied by determining the grafting parameters such as grafting and grafting efficiency. Under optimum conditions, the grafting parameters were achieved as 1440 and 97%, respectively.     

Characterization of the collagen–vinyl graft copolymers prepared by the ceric ion method. I. Solution properties

Graft copolymerization of vinyl monomers on to collagen was carried out by the ceric ion method. The grafted vinyl polymer chains were isolated by both acid and enzymatic hydrolysis of the collagen backbone in order to characterize the graft copolymers. Proof of grafting was obtained through the detection of amino acid endgroups in the grafts isolated by both the methods. The grafts isolated gave the characteristic blue color normally associated with the presence of amino acids. The presence of amino acid endgroups was further confirmed by dinitrophenylation of the isolated grafts. The absorption spectra of the dinitrophenylated(DNP) grafts showed absorption maximum in the ultraviolet region of 340–360 mμ, characteristic of DNP-amino acids. Soluble collagen grafted with polyacrylamide(PAA) formed fibrils on heating to 37°C at neutral pH but, unlike the native collagen, these fibrils did not redissolve on cooling at 2°C. These results show that the redispersion property of soluble collagen was impaired, probably by attachment of the PAA side chains to the collagen molecule. The turbidimetric titration behavior of the grafts, their general behavior of swelling in different solvents, and the intrinsic viscosity of the copolymers in mixed solvents also provided additional proof of grafting.     

Ceric Ion Initiated Graft Polymerization onto Poly(vinyl Alcohol)

This paper describes the kinetics of the ceric ion-initiated graft co-polymerization of vinyl acetate-acrylonitrile to poly(vinyl alcohol). The graft copolymerization rate R_p was found to be first order with respect to the total concentration of the comonomer mixture [M], the concentration of vinyl alcohol repeating units [PVA], and the mole fraction of vinyl acetate in the comonomer feed mixture. R_p was independent of cerous ion. The grafting rate was independent of ceric ion above a ceric concentration of 0.0020 M but first order in ceric ion below that concentration. Rp initially increased rapidly with [H⁺] to a maximum and then decreased and levelled off at hgher [H⁺]. The rate of ceric ion disappearance was first order in [PVA], independent of [MI, and increased with increasing [H⁺] with a leveling off at high [H⁺]. A reaction mechanism.