Graft copolymerization of vinyl monomers on modified cottons XV. Initiation by decomposition of aryl diazonium groups

Cellulose bearing aromatic amino groups was prepared by reacting cellulose with 2,4-dichloro-6-(p-nitroaniline)-s-triazine in presence of alkali followed by subsequent reduction of the nitro groups to amino groups. The latter were diazotized and grafting was achieved without homopolymer contamination through decomposition of the cellulose diazonium salt under the effect of metal ions. The dependence of grafting on the nature of the monomers was governed by the pH of the polymerization medium, reaction temperature and concentration of emulsifier. Using a large liquor ratio decreased the graft yield. The cellulose macroradical formed via decomposition of the diazo group was found very effective in inducting methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, isopentyl methacrylate, acrylamide and 2-methyl-5-vinyl pyridine.     

Graft copolymerization of vinyl monomers on modified cottons. III. Grafting of acrylonitrile and methyl methacrylate on cyanoethylated cotton by the ceric ion method

The interaction of acrylonitrile and methyl methacrylate with cyanoethylated cotton in the presence of ceric ion has been studied under a variety of conditions. Increasing the reaction time, the monomer concentration, and the temperature favorably influences the degree of grafting. The same holds true for initiator concentration up to a certain limit, after which a decrease in the graft yield was obtained. On the other hand, ceric consumption during grafting and oxidation increases by increasing the magnitudes of all these factors. However, the consumption during grafting is always higher than that during oxidation. The graft yields obtained with cyanoethylated cotton are greater than those of the control, being increased by increasing the degree of substitution (D.S.) of the cyanoethylated cotton, suggesting that the cyanoethyl groups afford additional sites of grafting. On the other hand, the ceric consumption during oxidation of cyano-ethylated cotton was much lower than that of the control, being increased also by increasing the D.S., indicating perhaps that ceric ion attacks the cyanoethylated cotton exclusively at the cyanoethyl groups. Based on these findings, a scheme for the mechanism of reaction of a vinyl monomer with cyanoethylated cotton was proposed.     

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.     

Graft copolymerization of vinyl monomers onto modified cottons. XII. Grafting of 1,1-dihydroperfluoroheptyl acrylate onto cellulose carbamate using hydrogen peroxide as initiator

Cellulose carbamate having 1.4% N was grafted with 1,1-dihydroperfluoroheptyl acrylate (DHPFHA) using H₂O₂ as initiator under a variety of conditions. The technique used involved padding the fabric in H₂O₂ solution at room temperature followed by impregnating it in an aqueous emulsion of DHPFHA. The graft yield, expressed as fluorine percent, was found to depend upon monomer and initiator concentration, temperature, and reaction time and pH of the polymerization medium as well as upon the carbamate content of the modified cotton. Increasing the monomer concentration up to 5% caused a considerable enhancement in grafting. The same holds true for initiator concentration up to a certain limit after which the grafting decreases. Raising the reaction temperature up to 100°C was accompanied by an increment in the magnitude of grafting reaction. The latter was characterized by an initial fast rate followed by a slower rate. Slightly acidic media (pH 5–6) proved to be the best for performing grafting. The graft yields were quite poor when grafting was carried out in acidic (pH 2–4) or alkaline (pH 8–12) media. The presence of a relatively smaller amount of carbamate groups in the cellulose molecules decreases its susceptibility to grafting. The opposite holds true for larger amounts. Incorporation of FeSO₄ at low concentration in the monomer emulsion had no effect on the graft yield. However, the latter decreases at higher FeSO₄ concentration. Grafted cellulose carbamate having ca. 15% fluorine showed very good oil and water repellency. The grafted product retained ca. 85% of the strength of cellulose carbamate.     

Graft copolymerization of vinyl monomers on modified cottons. XVIII. Grafting of methyl methacrylate and acrylonitrile on cotton treated with N-methylol crosslinking agents using tetravalent cerium as initiator

Ce^IV-induced grafting of methyl methacrylate and acrylonitrile on cotton fibers crosslinked with dimethylol ethylene urea, dimethylol dihydroxyethylene urea, and dimethylol carbamate was investigated. The graft yields obtained with crosslinked cotton were signifcantly lower than the untreated cotton, irrespective of the crosslinking agent and the monomer used. However, the extent and rate of grafting depended upon the degree of crosslinking and the nature of monomer. Based on the magnitude of grafting and Ce^IV consumption during grafting and oxidation of the untreated and crosslinked cottons, the different reactions occurring during grafting of vinyl monomers on these modified cottons were elucidated.     

Graft copolymerization of vinyl monomers with modified cotton. II. Grafting of acrylonitrile and methyl methacrylate on acetylated cotton

Ce(IV)-induced polymerization of acrylonitrile and methyl methacrylate with acetylated cotton having different acetyl contents was investigated. The extent of interaction between the cotton and monomer is dependent upon the acetyl content of the former as well as on the reaction conditions. Increasing the acetyl content caused a significant decrease in the graft yield. Increasing the acrylonitrile concentration was accompanied by a substantial increase in the graft yields. The same effect was found with the initiator up to a certain concentration, but beyond it there was a reversal. The rate of grafting increased by rising the temperature and follow the order 60° > 40° > 30°C. The Ce(IV) consumption during grafting is greater than that consumed during oxidation. The consumption of Ce(IV) by the cellulosic materials was favorably influenced by the concentrations of monomer and initiator, time, and temperature. Rates of grafting and Ce(IV) consumption during oxidation of acetylated cottons having different acetyl contents strongly support the postulated mechanism of grafting using the Ce(IV)–cellulose redox system. Ce(IV) oxidation had practically no effect on the acetyl groups (expressed as per cent combined acetic acid) of the modified cotton.     

Graft copolymerization of vinyl monomers on modified cotton. IV. Ceric-induced grafting on vinyl monomers on cellulose bearing different substituents

The influence of introducing various functional groups into the cellulose molecule on its susceptibility toward grafting with vinyl monomers such as acrylonitrile and methyl methacrylate using the Ce(IV)–cellulose redox system was studied. While cellulose bearing either cyanoethyl or carboxymethyl groups showed higher graft yields, cellulose bearing both groups showed lower yields. Presence of acrylamidomethyl groups in the cellulose molecule reduced its reactivity to grafting. The same holds true for cellulose bearing acrylamidomethyl groups along with carboxymethyl groups. On the other hand, introducing carbamoylethyl groups in the cellulose molecule enhances significantly the susceptibility of cellulose toward grafting. This is also observed with cellulose bearing cyanoethyl and carboxyethyl groups. Treating cellulose with N-methylolacrylamide in alkaline medium seems to produce a crosslinked cellulose with lower reactivity to grafting. The results obtained with the different substrates were discussed on the basis of the change in the physical and/or chemical structure of cellulose brought about during its modification as well as on the nature of the substituent groups introduced. The mode of Ce(IV) attack on cellulose was also clarified.     

Grafting vinyl monomers onto silk fibers,VII. Graft copolymerization of methyl methacrylate onto silk using peroxydiphosphate as initiator

Graft copolymerization of methyl methacrylate onto silk was investigated in aqueous solution using potassium peroxydiphosphate as initiator. The rate of grafting was determined by varying monomer, peroxydiphosphate ion, temperature, and solvent. The graft yield increased with increasing peroxydiphosphate ion upto 8 × 10^?3 mol/1 and with further increase of peroxydiphosphate ion the graft yield decreased. The graft yield increased with increasing monomer concentration upto 9 wt.-% and with further increase of monomer the graft yield decreased. The rate of grafting increased with the increase of temperature. The effect of acid and water soluble solvents and salts on graft yield was investigated and a suitable rate expression was derived.     

Graft copolymerization of vinyl monomers onto modified cottons. VIII. Dimethylaniline–benzyl chloride-induced grafting of methyl methacrylate onto partially carboxymethylated cotton

The feasibility of dimethylaniline (DMA)–benzyl chloride (BC) mixture to initiate graft polymerization of methyl methacrylate (MMA) onto partially carboxymethylated cotton was examined. The graft yield depends on the nature of the solvent used along with water; ethanol proved to be the best at a water;ethanol ratio of 90:10. Considerable grafting occurred in the presence of acetic acid at a concentration of 200 mmol/l. Higher concentrations of this acid decrease grafting significantly. The graft yield obtained in the presence of formic acid was much lower than that obtained in the presence of acetic acid. Inclusion of hydrochloric or sulfuric acid in the graft polymerization system prevent grafting. A DMA–BC mixture at a concentration of 0.08:0.087 mole/l. constitutes the optimal concentration for grafting. This contrasts with 0.32:0.35 mole/l. for total conversion. The rate of grafting increases by raising the polymerization temperature; it follows the order 50°>60°>65°>70°>75°C. Furthermore, increasing the monomer concentration caused a significant enhancement in the graft yield and total conversion.     

Graft copolymerization of vinyl monomers on modified cottons,part XVII. Continuous and semi continuous methods for grafting of partially carboxymethylated cotton with acrylamide

Semi continuous and continuous methods were described for grafting of acrylamide to partially carboxymethylated cotton (PCMC). In essence, PCMC previously treated with ferrous sulphate was padded in a solution containing acrylamide and H₂O₂ followed by drying and baking. Incorporation of N-methylol finishing agent to the polymerization solution brought about easy care cotton with improved strength properties and good fabric performancy as measured by crease recovery.     

Grafting vinyl monomers onto cellulose. IV. Graft copolymerization of methyl methacrylate onto modified cellulose using peroxydiphosphate as the initiator

The graft copolymerization of methyl methacrylate onto modified cellulose was studied at 60° causing peroxydiphosphate as the initiator. The rate of grafting in case of different modified cellulose was determined by varying peroxydiphosphate, monomer, nature of substrate, and temperature. The molecular weight of the isolated polymer has been determined, and the mechanism of grafting is discussed.     

Graft copolymerization of vinyl monomers on modified cottons,XXI. Cu++/hydrazine hydrate redox system induced grafting of methyl methacrylate on periodate oxidized cellulose

Periodate oxidized cellulose was grafted with methyl methacrylate using hydrazine hydrate in presence and absence of Cu⁺⁺. The grafting reaction was favoured in presence of Cu⁺⁺ and it was advantageous to treat first the cellulose material with copper sulphate solution rather than to incorporate it in the polymerization system. The graft yields depended upon the concentrations of copper sulphate and hydrazine hydrate, pH, temperature, and time of polymerization as well as degree of oxidation of cellulose. There were optimal concentrations of copper sulphate (6–8 mmol/l) and hydrazine hydrate (2 mmol/l). A polymerization medium of pH 6 and a temperature of 60°C constituted to optimal pH and temperature for grafting. Oxidized cellulose proved to be more amenable to grafting as compared with unoxidized cellulose and the magnitude of grafting relied on the degree of oxidation. A tentative mechanism was also suggested for grafting of cellulose substrates with a vinyl monomer using a Cu⁺⁺-hydrazine hydrate redox system.     

Electroinitiated emulsion polymerisation of vinyl monomers. III. Homopolymerisation and copolymerisation with vinyl acetate

Of the monomers studied, vinyl acetate and vinyl n-caproate are the only ones capable of electroinitiated homopolymerisation in aqueous acidic emulsion. Water solubility does not appear to be the overriding consideration. Activity of the radical would seem to be most important. Copolymerisation with monomers not undergoing homopolymerisation in this system produces good yields of copolymers low in vinyl acetate concentration.     

Grafting of vinyl monomers by the xanthate method

The removal of oxygen from swollen pulp is very difficult. At least 1–2 h of purging with oxygen-free nitrogen or argon is required as well as efficient mixing and a low concentration of pulp (not higher than 1%). During the grafting reaction, in which the xanthate cellulose is a part of the redox system, the concentration of oxygen falls to zero and stabilizes at this level even if air is purged through the system or a higher rate of stirring is applied. Primary sulfur radicals created in the reaction of the xanthated groups with H₂O₂ are further oxidized by H₂O₂ or by particles of oxygen dissolved in the reaction mixture. The observed increase in reaction caused by an increase in stirring speed is due to the higher rate of diffusion of hydrophobic monomers as well as the diffusion of oxygen to active centers at high stirring speed. The low rate of grafting at lower agitation speeds is caused by agglomeration of monomer molecules to bigger particles and, as a result, decreased diffusion of monomer to active centers. Above 300 rpm, the effect of monomer diffusion diminishes and further increase in conversion is caused only by a higher rate of oxygen diffusion to active centers from reaction mixture or passing gas. However, above a certain level of oxygen, the effect of termination by oxygen prevails and the rate of reaction decreases. Additives increase the conversion in the lower range of agitation speed only. The application of additives and agitation are two equivalent methods, both of which lead to an increase in conversion in the lower range of stirring speed.     

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.     

Grafting onto wool. XX. Graft copolymerization of vinyl monomers by use of redox initiators. Comparison of monomer reactivities

Methyl methacrylate (MMA) and ethylacrylate (EA) have been graft copolymerized onto Himachali wool in aqueous medium by using a ferrous ammonium sulfate–hydrogen peroxide (FAS? H₂O₂) system as redox initiator. Percentage of grafting has been determined as functions of concentration of monomer, molar ratio of [FAS]/[H₂O₂], time and temperature. Percentage of grafting is found to depend upon the molar ratio of [FAS]/[H₂O₂]. An attempt has been made to compare the reactivities of the acceptor monomer (MMA and EA) with that of the donor monomer (VAc) toward grafting onto wool.     

Grafting vinyl monomers onto silk fibers. II. Graft copolymerization of methyl methacrylate onto silk by hexavalent chromium ion

The feasibility of chromium(VI) to induce graft polymerization of methyl methacrylate onto silk was investigated. The rate of grafting was determined by varying monomer concentration, chromium(VI) concentration, temperature, acidity of the medium, nature of the silk, reaction medium, and redox system. The graft yield increased with increasing monomer concentration up to 0.65M, and with further increase of monomer the graft yield decreased. The graft yield increased with increasing chromium(VI) concentration. The grafting is considerably influenced by chemical modification of silk prior to grafting. The graft yield is influenced by thiourea concentration, decreasing with increasing thiourea concentration. The effect of certain inorganic salts and anionic surfactants on the rate of grafting was investigated.     

Graft copolymerization of vinyl monomers on cellulosic materials

Graft copolymers of acrylonitrile, ethyl acrylate, methyl acrylate, ethyl methacrylate and methyl methacrylate and of acrylonitrile/ethyl methacrylate and acrylonitrile/methyl methacrylate monomer mixtures on carboxymethylcellulose (degree of substitution 0.4–0.5) were prepared by use of ceric ion initiator in aqueous medium. The extent of graft polymer formation was measured in terms of graft level, molecular weight of grafted polymer chains and frequency of grafting as function of ceric ion concentration. It was found that at comparable reaction conditions, the molecular weight and frequency of grafting were not of the same order of magnitude. For the monomer mixtures, the copolymer compositions obtained from the total nitrogen content of the acrylonitrile/alkyl methacrylate copolymer samples showed that a relativity low amount of the acrylonitrile monomeric units were incorporated into the graft copolymer even at high acrylonitrile content of the feed.