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.     

Graft copolymerization of cellulose initiated by ceric salts: Effect of reaction conditions on the consumption of ceric ion

A soluble monomer [methyl acrylate (MA)] and an insoluble monomer [butyl methacrylate (BMA)] were grafted onto cellulose by three types of ceric salts under both oxygen-free conditions and in the presence of oxygen. For comparison, Ce(IV) consumption during cellulose oxidation was also determined under similar reaction conditions. Slightly more Ce(IV) was consumed during cellulose oxidation in the presence of oxygen. During graft copolymerization of MA under oxygen-free conditions, the consumption of Ce(IV) was much lower than during cellulose oxidation regardless of the type of ceric salt employed. The opposite was observed in the presence of oxygen: much more Ce(IV) was consumed during grafting than during cellulose oxidation. The consumption of Ce(IV) in the graft copolymerization of BMA by ceric sulfate was nearly independent of reaction conditions and it was approximately the same as in cellulose oxidation. In the reaction initiated by ceric ammonium nitrate under oxygen-free conditions, less Ce(IV) was once again used up during grafting than during cellulose oxidation. However, the difference was much smaller than in the case of MA.     

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.     

Highly branched acrylamide graft copolymer

Acrylamide graft copolymerization onto poly(3-O-methacryloyl D -glucose) (PMG) as a backbone was performed by the ceric ion method. The number of polyacrylamide (PAM) chains grafted was dependent upon the concentration ratio of the redox catalyst system at constant acid concentration and increased in proportion to the ceric ion concentration. A maximum number of grafts obtained, for example, was 29 onto PMG (DP = 244) under the conditions [Ce⁴⁺]/[PMG] = 1/5, [H⁺] = 1.0 × 10^?2 mole/l. In other words, the graft frequency was 12 per 100 monomer units of PMG. Such a high frequency of the grafts was, however, greatly decreased when the acid concentration was increased. Characteristics of the highly branched structure were revealed by the relationship between intrinsic viscosity and graft frequency, which showed a downward curvature with the increasing graft frequency. Influences of acid and ceric ion concentrations on the copolymerization were kinetically evaluated. The rate of polymerization was found to be first-order with respect to ceric ion and proportional to the square of the reciprocal acid concentration. The result suggests that the graft frequency is dependent upon the rate of polymerization.     

Relationship between reduction of ceric ion with poly(vinyl alcohol) and graft copolymerization

Various poly(vinyl alcohol) samples were preliminarily subjected to oxidation treatment with sodium hypochlorite, and the reduction of ceric ion and subsequently initiation in the graft copolymerization in the system containing methyl methacrylate were investigated. The reduction behavior of ceric ion could be subdivided into three parts, each of different reaction rate. In the initial stage of the reaction, there was observed rapid cleavage of the backbone chain of poly(vinyl alcohol) with ceric salts. The amount A of cleavage was proportional to the amount of ceric ion reduced at the initial fastest rate for various samples of different extents of oxidation; cleavage of 1 mole required ca. 10 moles of reduction of ceric ion. Higher carbonyl contents of the sample caused increased A. Graft polymerization was carried out in the same system with the addition of the monomer. The amounts of grafted chains produced were determined, and approximately one mole of grafted chains was obtained for per mole of cleavage. The copolymer is concluded to be blocklike in structure. The contribution of the carbonyl groups in poly(vinyl alcohol) sample to the initiation of the polymerization should be emphasized.     

Synthesis and Characterization of Water-Soluble Graft Copolymers from 2, 3-Dihydroxypropylcellulose and Acrylamide

Water-soluble 2,3-dihydroxypropylcellulose-polyacrylamide graft copolymers (DHPC-g-PAM) were prepared by Ce⁴⁺ ion-initiated graft copolymerization of acrylamide (AM) onto 2,3-dihydroxypropylcellulose (DHPC) dissolved in dilute nitric acid at room temperature under argon. The ratios of the concentration of Ce⁴⁺ ion to the concentration of DHPC were shown to affect the number and the length of the polyacrylamide grafts. The average number of grafts per chain was determined by acid-catalyzed degradation of the cellulose backbone and was found to be consistent with the presence or absence of free DHPC in the polymerization product prior to hydrolysis. The average number of grafts per DHPC molecule was found to be 2.7 or less depending on the reaction conditions.     

Compression molded wood pulp biocomposites: a study of hemicellulose influence on cellulose supramolecular structure and material properties

In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young’s modulus as the composite based on paper grade kraft pulp, 11–12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS ¹³C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.     

GRAFTING OF ACRYLAMIDE ONTO SURFACE OF COPOLYMERS CONTAINING P-TOLYLCARBAMOYL PENDANT GROUP INITIATED WITH CERIC SALT

Two copolymers containing p-tolylcarbamoyl pendant group poly (MAMT-co-VAc) and poly(MAMT-co-MA) were synthesized f and the graft copolymerization of AAM onto these two func-tional copolymers films initiated with ceric salt were carried out in aqueous solution for variousperiods at 30℃. The formation of graft copolymer was verified by water absorption, ESCA andSEM photographs. Based on the results of the study of the initiation mechanism of model com-pounds and ceric salt systems, the reaction mechanism of the graft copolymerization initiated withceric salt was proposed.     

The role of ceric ion in vinyl polymerization and graft copolymerization

Six kinds of new ceric ion redox initiation systems for vinyl radical polymerization and two kinds of macromolecule graft copolymerization by ceric ion have been briefly reviewed in this paper. The initiators include ceric ion/acetanilide, ceric ion/alkyl phenylcarbamate, ceric ion/4-methoxysuccinyltoluidine, ceric ion/aliphatic aldehyde, ceric ion/aromatic aldehyde, ceric ion/diketone systems. Macromolecules such as poly(ether-urethane) and macromolecules having active pendant groups were selected for graft copolymerization with acrylamide initiated by ceric ion.     

Coordinated radical polymerization and redox polymerization of acrylamide by ceric ammonium nitrate

The ceric salt-initiated polymerization on acrylamide and graft copolymerization of acrylamide onto cellulose were studied. The mechanism of the ceric salt-initiated polymerization of acrylamide in the homopolymerization system can be explained by a radical mechanism based upon Ce⁴⁺-coordinated acrylamide, and the mechanism of the ceric salt-initiated graft copolymerization of acrylamide onto cellulose can be explained in two ways: a free-radical mechanism with the ceric—cerous redox system, and a radical mechanism based upon Ce⁴⁺-coordinated acrylamide. The velocities of initiation, propagation, and termination in the redox mechanism are quite different from those in the coordinated radical mechanism. From the infrared absorption and nuclear magnetic resonance spectra measurements it is concluded that the structure of the ceric-coordinated acrylamide is the π-complex.     

CERIC ION INITIATED GRAFTING ON CELLULOSE FROM BINARY MIXTURE OF ACRYLONITRILE AND METHYLACRYLATE

The Ce(IV)-ion induced grafting on cellulose from the binary mixture of acrylonitrile-methylacrylate has been investigated in heterogeneous and acidic conditions at 25 ± 0. 1°C. Various grafting parameters were evaluated as a function of molarity, feed composition, reaction time, and concentration of ceric ion at constant concentration of nitric acid in the feed. The higher fraction of acrylonitrile in the grafted chains than the feed has indicated the synergistic effect of methylacrylate taken in the feed along with acrylonitrile. IR and elemental analysis for nitrogen contents in the synthesized copolymers were used to determine the composition of the grafted copolymers. The reactivity ratios of acrylonitrile and methylacrylate have been determined by the Mayo and Lewis method and are found to be 1.45 and 0.9, respectively. The grafting parameters have shown increasing trends on varying feed composition (f_AN) from 0.25 to 0.80 and varying monomer concentration from 0. 6 to 5 4 mol dm^?3. The number of grafted moles of synthetic polymer (N_g) on cellulose were found to be dependent on molarity, feed composition, and ceric ion concentration. The experimental results have clearly indicated that maximum fraction of the feed was consumed in the formation of grafted copolymer chains in comparison to the homocopolymers and homopolymers. Estimation of ceric ion disappearance as a function of reaction time has clearly suggested that grafting on cellulose is initiated by the reactive sites generated through hydrogen ion abstraction by single electron transfer process.     

Grafting acrylonitrile and methyl methacrylate on holocellulosic materials

Graft copolymers of acrylonitrile and methyl methacrylate on bleached holocellulose and thiolated holocellulose were obtained by the use of ceric ions in aqueous medium at 29°C. The level and efficiency of grafting on the bleached holocellulose were significantly higher than on the thiolated holocellulse, but the molecular weights and number of grafted copolymer chains on both the unmodified and thiolated holocellulose were similar. The graft level and molecular weight of acrylonitrile graft copolymer were significantly lower than those for methyl methacrylate at comparable ceric ion and monomer concentrations. These results indicate the significance of the influence of the polarity of monomer on the extent of graft copolymer formation and lead to the suggestion that graft copolymerization may not result entirely from radicals generated on the cellulose substrate.     

Effects of SPORL and Dilute Acid Pretreatment on Substrate Morphology, Cell Physical and Chemical Wall Structures, and Subsequent Enzymatic Hydrolysis of Lodgepole Pine

The effects of pretreatment by dilute acid and sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) on substrate morphology, cell wall physical and chemical structures, along with the subsequent enzymatic hydrolysis of lodgepole pine substrate were investigated. FE-SEM and TEM images of substrate structural morphological changes showed that SPORL pretreatment resulted in fiber separation, where SPORL high pH (4.2) pretreatment exhibited better fiber separation than SPORL low pH (1.9) pretreatment. Dilute acid pretreatment produced very poor fiber separation, consisting mostly of fiber bundles. The removal of almost all hemicelluloses in the dilute acid pretreated substrate did not overcome recalcitrance to achieve a high cellulose conversion when lignin removal was limited. SPORL high pH pretreatment removed more lignin but less hemicellulose, while SPORL low pH pretreatment removed about the same amount of lignin and hemicelluloses in lodgepole pine substrates when compared with dilute acid pretreatment. Substrates pretreated with either SPORL process had a much higher cellulose conversion than those produced with dilute acid pretreatment. Lignin removal in addition to removal of hemicellulose in SPORL pretreatment plays an important role in improving the cellulose hydrolysis of the substrate.     

Graft Copolymerization of 4-Vinylpyridine Onto Modified Cellulosic Fibers. the Ceric Ion Concentration Effect

The graft copolymerization of 4-vinylpyridine was carried out on mercerized cellulose and partially carboxymethylated cellulose (PCMC) using eerie ammonium nitrate (CAN) as the initiator. the grafting parameters (grafting efficiency (GE), graft yield (G), and total conversion (C¹)) were studied as a function of CAN concentration. It was shown that by increasing the CAN concentration, G and C, reached a maximum. the graft yields for PCMC were significantly higher than those for mercerized cellulose. the largest GE values appeared for PCMC and mercerized cellulose at low and high CAN concentrations, respectively. the Ce(IV) consumption during grafting increased with rising concentration of CAN, and it was greater in the case of PCMC than of mercerized cellulose. After acid hydrolysis of the polysaccharide backbone, the average molecular weight of grafts was determined viscometrically. Molecular weight decreased with initiator concentration. Graft frequency (GF), on the other hand, increased with CAN concentration. GF for PCMC was higher than that for mercerized cellulose. Ce(IV) consumption increased with CAN concentration and it was lower for mercerized cellulose than that consumed during grafting on PCMC. After that, the effect of CAN concentration on the graft copolymerization onto PCMC was examined while the total nitrate ion concentration was maintained constant at 1.59 M by addition of sodium nitrate. Maximum G, C¹ and Ce(IV) consumption were higher than in the previous case.     

Graft copolymers composed of high molecular weight poly(ethylene oxide) backbone and poly(N-isopropylacrlylamide) side chains and their thermoassociating properties

Novel, water-soluble thermoassociative graft copolymers based on high molecular weight (HMW) poly(ethylene oxide-co-glycidol) backbone and relatively short grafts of poly-N-isopropyl acrylamide (NIPAAm) were prepared. The copolymer precursors with two architectures (block and graft) were synthesized using Ca-amide-alkoxide initiators. The OH groups in the copolymer precursors have been utilized for grafting NIPAAm using ceric ion (Ce⁴⁺) redox initiation. The idea was to imprint the “smart” properties of PNIPAAm grafts into common HMW poly(ethylene oxide). The sensitive moieties undergo reversible association transitions by changing the temperature of dilute and semidilute aqueous solutions of the copolymers. Associative properties were studied by viscosity and rheology measurements. Two types of interactions, induced by heating, depending on the copolymer concentration namely intra- and intermolecular association were observed.     

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 to Vinylpyrrolidone Polymers and Copolymers by the Ceric lon Method

Polymers and copolymers of vinylpyrrolidone were investigated as grafting substrates for methyl methacrylate using the ceric ion method. Ceric ion readily initiates methyl methacrylate grafting to commercial poly (vinylpyrrolidone) (PVP) of 360,000 nominal molecular weight. The resulting graft copolymer was surprisingly found to be an ABA triblock system with PVP in the center block. This conclusion is supported by three key pieces of evidence: first, selective degradation of the PVP/MMA graft copolymer showed two PMMA grafts per PVP chain: second, blocking of what are apparently hydroxylic or glycolic PVP end groups by reaction with phenyl isocyanate rendered the PVP unreactive to ceric ion grafting; third, if the PVP is prepared by methods which preclude formation of hydroxylic end groups, the PVP is unreactive to ceric ion grafting.

Vinylpyrrolidone polymers can be made graftable via ceric ion if N-methacryloyl-D-glucosamine (NMAG) is incorporated as a comonomer in the PVP backbone. Regardless of the method of preparation, incorporation of NMAG provides grafting sites which are highly reactive to ceric ion. At copolymer compositions up to 10 mole % NMAG, the methyl methacrylate graft copolymers are soluble in organic solvents. Above 10 mole % NMAG, the grafting reaction leads to cross-linking and formation of intractable gels.     

Effects of solvent in photo-induced graft copolymerization of vinyl monomers on cellulose

The effects of swelling of the sample and polymerization solvents were studied for photo-induced graft copolymerization of vinyl monomers on cellulose. The graft copolymerization of methyl methacrylate (MMA) was activated by swelling of the sample or organic solvent-water solutions within a certain range of their concentrations. Though each organic solvent gave a maximum in per cent grafting and the number of grafts at about 25 vol-% concentration, the initiation reaction scarcely took place at 100% concentration; thus, the solvent itself is considered to have a negative effect. The solvents used in the experiments were all hydrophilic, such as methanol, acetone, and dioxane. The average molecular weight of the grafted PMMA differed in each solvent, indicating a different characteristic effect of solvent on the growing grafted polymer radicals. The presence of ferric ion as a sensitizer stimulated further the contributions of the sample swelling and the organic solvents to the copolymerization reaction. A similar effect was observed for styrene as for MMA, but not for acrylic acid and methacrylic acid.     

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.     

Graft copolymerization of methyl methacrylate to poly(vinyl alcohol) initiated by ferric ion-hydrogen peroxide system

The reaction occurring on treatment of samples of poly(vinyl alcohol) previously oxidized by sodium hypochlorite with ferric ion and hydrogen peroxide was studied. The graft copolymerization taking place on adding methyl methacrylate to the above system was also studied. Early in the reaction there was a period during which hydrogen peroxide was greatly reduced by the poly(vinyl alcohol), and this corresponded with a rapid cleavage reaction of the main chain of the polymer. Moreover, it was found that the reaction was quantitatively proportional to the formation of carbonyl groups in the sample. On the other hand, very few grafts were scarcely formed during this period; they formed by a mild reaction which took place immediately after this period. It seems that this behavior is quite different from that observed with the ceric ion initiating system. It is presumed that the formation of grafts is due to radicals formed by the cleavage of the main chain, and that the structure of the copolymer so formed is something like a block polymer.