Grafting onto wool,XVII. Graft copolymerization of methyl acrylate and ethyl acrylate by use of VO(acac)2 as initiator. Comparison of monomer reactivities

Graft copolymerization of acceptor monomers methyl acrylate and ethyl acrylate onto Himachali wool fiber has been studied in aqueous medium by using vanadium oxyacetyl acetonate as initiator at 40, 50, 60, and 70°C. Graft copolymerization was carried out for various reaction periods and nitric acid was found to catalyse the reaction. Percentage of grafting and percent efficiency have been determined as functions of concentration of nitric acid, concentration of initiator, concentration of monomer, time, and temperature. Under optimum conditions, methyl acrylate and ethyl acrylate afforded maximum grafting to the extent of 28.4 and 18.5%, respectively. Relative reactivities of methyl acrylate and ethyl acrylate towards grafting have been compared with those of methyl methacrylate, acrylic acid and vinyl acetate reported earlier from this laboratory. Different vinyl monomers showed the following reactivity order: MMA > MA > EA > AAc > VAc. Several grafting experiments were carried out in the presence of various additives which included tert-butylhydroperoxide (TBHP), dimethylsulfoxide, pyridine, and dimethylformamide. Only TBHP was found to enhance grafting to a considerable extent, other additives decrease percent grafting of both methyl acrylate and ethyl acrylate.     

Redox-initiated vinyl graft polymerization onto wool with thiourea as the reductant. I. Grafting of methyl methacrylate with the hydrogen peroxide–thiourea catalyst system

The interaction of methyl methacrylate with wool under the catalytic influence of the hydrogen peroxide–thiourea redox system was studied under a variety of conditions. The degree of grafting depends upon the method empolyed; it is advantageous to first immerse wool in thiourea solution, monomer and hydrogen peroxide being then subsequently applied. Increasing the hydrogen peroxide concentration from 4 to 8 mmole/1. causes a significant enhancement in the graft yield. The latter remains practically unchanged upon further increment in hydrogen peroxide concentration within the range studied, i.e., up to 12 mmole/1. This was also observed with respect to thiourea concentration. On the other hand, increasing monomer concentration is accompanied by a significant increase in the graft yield. The polymerization reaction is temperature dependent; at the three temperatures examined, the graft yields follow the order 80° > 60° > 40°C. The rate of grafting is also dependent on the pH of the reaction medium over the range of 2 to 8, being decreased as the pH increased. Furthermore, the presence of traces of cupric ions in the polymerization system accentuates the graft formation. The alkali solubility as well as the urea bisulfite solubility of wool grafted with poly(methyl methacrylate) are much lower than those of physical mixtures of wool and poly(methyl methacrylate). This demonstrates that grafting of poly(methyl methacrylate) into wool has occurred.     

Grafting onto wool. VII. Ceric ion-initiated graft copolymerization of vinyl monomers. Comparison of monomer reactivities

In an attempt to compare relative reactivities of vinyl monomers toward grafting, methyl methacrylate (MMA) and acrylic acid (AAc) were grafted separately to Himachali wool in aqueous medium by using ceric ammonium nitrate (CAN) as redox initiator. Nitric acid was found to catalyze the reaction. Percent grafting was determined as a function of concentration of nitric acid, concentration of CAN, concentration of monomer, time, and temperature. Optimum conditions for maximum grafting were evaluated for each monomer and were found to depend upon the nature of the monomer. Reactivities of MMA and AAc toward grafting were compared with those of methyl acrylate (MA), ethyl acrylate (EA), and vinyl acetate (VAc) reported earlier from this laboratory and were found to follow the order MA > EA > MMA > VAc > AAc. An explanation for the observed order of reactivity of different vinyl monomers is presented.     

Graft copolymerisation of vinyl monomers on modified cottons. VII. Grafting by chain transfer

Grafting of methyl methacrylate on cellulosic materials by chain transfer under the catalytic influence of azobisisobutyronitrile (AIBN) was extensively studied. The graft yield is influenced by reaction time, temperature, monomer and initiator concentration, reaction medium and nature of the substrate. In general, the grafting reaction shows an induction period after which the polymerisation proceeds rapidly. The graft yield increases and the induction period decreases by rising the reaction temperature from 50 to 70°C. This is also the case when the monomer concentration was increased from 2 to 6%. Increasing the AIBN concentration up to 0.01 M causes a significant enhancement in grafting while further increase brings about a marked fall in the graft yield. Among the reaction media studied, a water/solvent mixture containing 25% of either methanol, ethanol, propanol, butanol or acetone seems to constitute a reaction medium where the monomer and initiator are completely miscible and the swelling of cellulose by water is not hindered by the presence of these solvents. Increasing the solvent ratio in the water/solvent mixture causes a considerable decrease in the graft yield. The polymer content of the cellulosic materials, i. e. the graft yield, follows the order: partially carboxymethylated cotton > cotton treated with 12N sodium hydroxide > cyanoethylated cotton > cotton treated with 0.5 N sodium hydroxide > purified cotton. In addition, proof of grafting was provided by the fractional precipitation method.     

Redox-initiated vinyl graft copolymerisation onto wool with thiourea as the reductant. II. Fe3+-thiourea co-catalyst induced graft copolymerisation of methyl methacrylate on wool and modified wool fibres.

The capability of Fe³⁺-thiourea redox system to induce graft polymerisation of methyl methacrylate onto wool fibres was investigated under various conditions. Variables studied include sequence of addition of reagents, acidity of the reaction medium, temperature, monomer concentration and nature of the substrate. In addition, alkali solubility of wool before and after grafting was examined. Allowing the ferric ion to be absorbed first on wool before addition of the thiourea and monomer leads not only to higher grafting but to greater grafting efficiency and total conversion than when all the reagents were present together. The graft yield increases significantly by increasing reaction time in the initial stages of the reaction but it does slow down on prolonging the duration of grafting. The effect of increasing monomer concentration is to bring about a significant enhancement in the graft yield. The same holds true for acidity of the reaction medium and temperature. The graft yields are considerably influenced by chemical modification prior to grafting. For instance, wool reduced via treatment with thioglycolic acid is more amenable to grafting than untreated wool. The opposite holds true for esterified and dinitrophenylated wools. The alkali solubility of wool decreases significantly by increasing the graft yield; a graft yield of ca. 95% makes wool practically unimpaired with aqueous sodium hydroxide.     

Graft copolymerization of vinyl monomers on modified cottons. VI. Vinyl graft copolymerization initiated by manganese (IV)

The ability of potassium permanganate in the presence of different acids to induce grafting of methyl methacrylate and acrylonitrile onto sodium hydroxide-treated cotton, partially carboxymethylated cotton, partially cyanoethylated cotton, and partially acetylated cotton was investigated. The copolymerization reaction was carried out under a variety of conditions. The graft yields are greatly enhanced by increasing concentration of monomer, reaction time, and temperature. The opposite holds true for initiator at higher concentrations. The effectiveness of the acids was: nitric acid > sulfuric acid > perchloric acid > hydrochloric acid. The change in the physical and/or chemical structure of cellulose by its modification via etherification reaction or esterification reaction had a significant effect on the susceptibility of cellulose toward grafting. While partial carboxymethylation or partial cyanoethylation of cellulose prior to grafting increased the graft yield, partial acetylation caused a decrease.     

Pentavalent vanadium ion–cellulose thiocarbonate redox-system induced grafting of methyl methacrylate and other vinyl monomers onto cotton fabric

Cellulose thiocarbonate was prepared by reacting cotton cellulose fabric with carbon disulphide in the presence of sodium hydroxide. The treated fabric formed, with pentavalent vanadium ion, an effective redox system capable of initiating grafting of methyl methacrylate (MMA) and other monomers no+o the cotton fabric. The dependence of grafting on vanadium concentration, pH of the polymerization medium, temperature and duration of grafting, nature and concentration of monomer, and solvent/water ratio was studied. The results indicated that increasing the pentavalent vanadium (V^v) concentration up to 60 mmol/L was accompanied by enhancement in the rate of grafting; the latter was not affected by further increase in V^v concentration. Maximum grafting yield was achieved at pH 2; grafting fell greatly at higher pH. The rate of grafting followed the order: 70° > 60° > 50°C. The graft yield increased significantly by increasing the MMA concentration from 0.5 to 5%. Of the solvents studied, n-propanol and isopropanol enhanced the grafting rate provided that a solvent/water ratio of 5 : 95 was used; a higher solvent ratio decreased the magnitude of grafting. Other solvents, namely, methanol, ethanol, n-butanol, and acetone, in any proportion, decreased the rate of grafting. With the monomer used, the graft yield followed the order: methyl methacrylate > methyl acrylate > methacrylic acid > ethyl methacrylate > acrylic acid. Also reported was a tentative mechanism for vinyl-graft copolymerization onto cotton fabric using cellulose thiocarbonate-V^v. © 1993 John Wiley & Sons, Inc.     

Azobisisobutyronitrile-induced vinyl graft polymerization onto nylon 66

The presence of nylon 66 during polymerization of methyl methacrylate (MMA) under the influence of azobisisobutyronitrile (AIBN) produces a nylon-PMMA graft copolymer. The copolymerization reaction is greatly influenced by the reaction medium, temperature and time of the reaction, concentration of MMA, and addition of metallic ions. Polymerization in pure organic solvents brings about little or no grafting. Incorporation of water into the polymerization system enhances grafting significantly. A reaction medium of a water/solvent mixture in a ratio of 75:25 constitutes the most favorable medium for the grafting reaction in question. Of the solvents examined, methanol, ethanol, propanol, isopropanol, and acetone work extremely well. Increase in reaction time is accompanied by an increase in the graft yield. The same holds true for the reaction temperature; the graft yield is much higher at 70 than at 50°C and follows the order 70°C > 60°C > 50°C. Increasing MMA concentration also causes considerable enhancement of the graft yield. The presence of 0.01M cupric sulfate in the polymerization system brings about an eightfold increase in the graft yield, whereas the presence of ferric sulfate at the same concentration causes a sixfold increase. The mode of initiation of grafting seems to be different in the presence of metallic ions than in their absence. A mechanism for the reactions involved in the both cases has been proposed.     

Pentavalent vanadium ion-induced grafting of methyl methacrylate onto cotton cellulose

Graft polymerization of methyl methacrylate (MMA) onto cotton cellulose using vanadium pentanitrate as initiator was studied under a variety of conditions. The graft yield increased with increasing initiator concentration up to 8 mmole/l. and then decreased upon further increase in initiator concentration. Increasing MMA concentration from 1 to 5% was accompanied by a significant increase in the degree of grafting. The latter was also affected by the kind and concentration of the acid incorporated in the polymerization medium. Based on graft yields, the efficiency of the acids follows the order H₂SO₄ > HNO₃ > HClO₄. Replacement of the acid with isopropyl alcohol was also examined. An isopropyl alcohol concentration of 10% constitutes the optimal concentration for grafting. Maximum graft yield depends upon the polymerization temperature; it follows the order 50°C ≥ 60°C > 40°C > 30°C > 70°C. Reaction mechanisms for grafting in the presence of acid as well as in the presence of isopropyl alcohol are proposed.     

A novel method for vinyl grafting onto cotton fabric using ceric-cellulose thiocarbonate redox system

Treatment of cotton fabric with carbon disulphide in presence of NaOH resulted in cellulose thiocarbonate. The latter formed a complex when treated with ceric ammonium nitrate (CAN). After being thoroughly washed, the Ce^IV cellulose thiocarbonate was capable of initiating vinyl graft polymerization onto cotton fabric without homopolymer formation. The graft yield obtained with methyl methacrylate was found to increase by increasing CAN from zero to 50 mmol/l at temperatures from 60 to 80°C. Grafting was greatly favoured at pH 2; alkaline pH offset grafting. Incorporation of up to 7% of methanol, ethanol, or isopropanol in the aqueous polymerization medium enhanced grafting significantly with the certainty that the highest graft yield was obtained with isopropanol; using higher alcohol percentages decreased grafting. The rate of grafting showed an initial fast rate followed by a slower rate; 60 minutes reaction time proved appropriate for grafting irrespective of the condition used. In addition to methyl methacrylate the ability of Ce^IV-cellulose thiocarbonate to induce grafting of acrylonitrile and acrylamide was also examined. The rate of grafting followed the order methyl methacrylate > acrylonitrile > acrylamide.     

Grafting onto wool. XIV. Graft copolymerization of vinyl monomers by use of Mn(AcAc)3 as an initiator

Ethyl acrylate (EA), butyl acrylate (BA), and vinyl acetate (VAc) have been graft copolymerized onto Himachali wool fiber in an aqueous medium by using Mn(AcAc)₃ as an initiator. Graft copolymerization was studied at 45°, 55°, 65° and 75°C for various reaction periods. Percentage of grafting and percent efficiency were determined as functions of concentration of monomer, concentation of initiator, concentration of nitric acid, time, and temperature. Several grafting experiments were carried out in the presence of various additives which included: (i) pyridine and (ii) Et₃ N. EA, BA, and VAc were found to differ in reactivity towards grafting and followed the order: EA > BA > VAc.     

Polymerization of methyl methacrylate by tri-n-butylborane in the presence of amino acid esters

The polymerization of methyl methacrylate by tri-n-butylborane in the presence of amino acid esters was investigated. The binary systems of tri-n-butylborane and amino esters were found to be more effective for initiating the polymerization than tri-n-butylborane alone. Co-catalytic effects of amino acid esters were in the order: tyrosinate > glutamate > aspartate ? phenyl alaninate > serinate > glycinate. The rate of polymerization in a mixture of dimethylsulphoxide and toluene was proportional to the square root of the concentration of the initiator system, to the monomer concentration, and to the concentration of dimethylsulphoxide in the solvent. The overall energy of activation was estimated to be 4.6 kcal/mol for the tri-n-butylborane/methyl tyrosinate system. Copolymerization curves gave a typical free-radical character.     

Studies on the grafting of methyl methacrylate onto polyacrylonitrile

Grafting of methyl methacrylate onto polyacrylonitrile was carried out using benzoyl peroxide as initiator and dimethylformamide as solvent. The occurrence of grafting was confirmed by IR spectroscopy and SEM analysis. Effects of various parameters such as reaction time, reaction temperature, initiator concentration, and monomer concentration on rate of polymerization, percentage grafting, and grafting efficiency were studied. The graft copolymers were found to have the similar thermal and structural properties like virgin polyacrylonitrile. Decreasing extent of swelling was observed for the polymers of higher percentage graft in polar solvents. © 1993 John Wiley & Sons, Inc.     

Grafting vinyl monomers onto wool fibers. I. Graft copolymerization of methyl methacrylate onto wool using V5+–thiourea redox system

The graft copolymerization of methyl methacrylate in wool fibers was investigated in aqueous solution using V⁵⁺—thiourea redox system. The rate of grafting was determined by varying monomer, thiourea, acidity of the medium, temperature, nature of wool, different acrylic monomers, and reaction medium. The graft yield increases significantly by increasing reaction time in the initial stages of the reaction but it does slow down on prolonging the duration of grafting. The effect of increasing monomer concentration brings about a significant enhancement in the graft yield. The graft yield increases with increasing thiourea concentration, but beyond 0.0075M, the percentage graft yield decreases. The graft yields are considerably influenced by chemical modification prior to grafting. Wool reduced with thioglycolic acid is more susceptible to grafting than untreated wool; the opposite effect is noted in the case of trinitrophenylated and esterified wools. A suitable kinetic scheme has been proposed and the rate equation has been evaluated.     

Grafting vinyl monomers onto wool fibers,IX. Graft copolymerization of methyl methacrylate onto wool using peroxydiphosphate-cysteine redox system

The graft copolymerization of methyl methacrylate onto wool was studied at 50°C using peroxydiphosphate-cysteine redox system as initiator. The rate of grafting was determined by varying monomer, initiator, cysteine, acid and temperature. The grafting is considerably influenced by chemical modification prior to grafting. A suitable kinetic path has been pictured and a rate expression has been derived.     

Thermal behavior of graft copolymers of cotton cellulose and acrylate monomers

Cotton cellulose yarn was grafted with methyl acrylate, ethyl acrylate, n-butyl acrylate, and methyl methacrylate at various percentages of grafting. The effects of concentration of the initiator, concentration of the acid, and of temperature on grafting was studied and the mechanism discussed. The effect of reactivity of the monomer on the percentage graft-on is pointed out. Thermal behavior of natural and grafted cotton yarn was studied using dynamic thermogravimetry in air at a heating rate of 6°C/min up to a temperature of 500°C. The thermal stabilities of the samples grafted with various acrylate monomers to various percentages of grafting were computed from their primary thermograms by calculating the values of IDT, IPDT, and E^*. The results show that the thermal stability increases with increase in graft-on per cent, and the thermal stabilities of natural cotton and cotton grafted with different monomers are in the order ethyl > methyl > natural cellulose > methyl methacrylate > n-butyl acrylate.     

Grafting of nylon 66 with methyl methacrylate using dimethylaniline–benzyl chloride–acetic acid initiating system

Grafting of nylon 66 with methyl methacrylate (MMA) under the initiating influence of dimethylaniline (DMA)–benzyl chloride (BC)–acetic acid (AC) mixture was studied to discover optimal conditions for grafting. Results of this investigation showed that a mixture of water/ethanol at a ratio of 90:10 constitutes the most favorable medium for the grafting reaction. Optimal grafting occurred when a concentration of 0.16 mole/l. DMA plus 0.17 mole/l. BC plus 0.2 mole/l. AC was used. Using lower or higher concentrations of this initiator led to lower grafting. On the other hand, increasing MMA concentration brings about a significant increase in the graft yield. The same holds true for reaction time and temperature, though an induction period was observed at a lower temperature (65°C) and when lower monomer concentration (2%) was used.     

Grafting vinyl monomers onto wool fibers. V. Graft copolymerization of methyl methacrylate onto wool using peroxydiphosphate as initiator

Graft copolymerization of methyl methacrylate onto wool was investigated in aqueous solution using potassium peroxydiphosphate as initiator. The rate of grafting was determined by varying monomer, peroxydiphosphate ion, temperature, solvent, and nature of wool. The graft yield increases with increase in monomer concentration. The graft yield increases significantly by increasing peroxydiphosphate ion up to 80 × 10^?4mole/l.; with further increase of peroxydiphosphate ion the graft yield decreases. The rate of grafting increases with increase in temperature. The effect of acid-and water-soluble solvents on the rate of grafting was investigated and a suitable rate expression has been derived.     

Graft copolymerization of methyl methacrylate onto wool using thallium (III) ions as initiator

The graft copolymerization of methyl methacrylate onto wool initiated by thallium (III) perchloric was investigated in aqueous perchloric acid medium. The rate of grafting was evaluated varying the concentrations of the monomer, initiator, acid, and temperature. The rate of grafting was found to increase with the increase of the monomer and the initiator concentration. The graft yield was found to decrease upon increasing the acid concentration. Increase of temperature was accompanied with the increase of the graft yield. From the Arrhenius plot the overall activation energy was calculated to be 4.7 kcal/mol. The effect of inhibitors, various solvents, cationic and anionic surfactants, and different inorganic salts on the graft yield was studied. The grafting was considerably influenced by chemical modification of wool prior to grafting. A suitable kinetic scheme has been proposed, and a rate equation has been derived.     

Graft copolymerization of benzyl methacrylate onto wool fibers

Benzyl methacrylate (BzMA) was graft copolymerized onto wool fibers by using ammonium peroxydisulphate as the initiator. Grafted samples with different polymer add ons (from 7 to 180%) were obtained by varying the monomer concentration in the reaction system. Following grafting with BzMA, the X-ray diffraction peak at 20.2° slightly moved towards higher spacing values. Birefringence decreased, indicating a lower degree of molecular orientation of grafted wool fibers. The equilibrium regain values of grafted wool decreased with increasing add on. Tensile strength increased in the range 45–77% add on, while elongation at break decreased. Differential scanning calorimetry (DSC) and thermogravimetry (TG) measurements showed a higher thermal stability for grafted wool. Following grafting, the drop of dynamic storage modulus (E′) shifted to a lower temperature. Accordingly, the intensity of the loss modulus (E′) peak decreased, indicating that the thermally induced molecular motion was enhanced by grafting. Thermomechanical analysis (TMA) confirmed the increase in chain mobility for the grafted wool fibers. Above 35–40% add on, the presence of homopolymer on the surface of the wool fibers was identified by scanning electron microscopy. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 343–350, 1997