Anionic graft polymerization of methacrylonitrile on potassium starch alkoxide

The anionic graft polymerization of methacrylonitrile on potassium starch alkoxide in dimethyl sulfoxide was studied. Factors affecting the graft polymerization such as monomer and alkoxide concentrations as well as temperature were investigated. The yield of the graft polymers was found to increase with alkoxide concentration, and it was possible to incorporate all the starch into graft polymer. On increasing the monomer concentration the graft polymer yield increased to a flat maximum. At the higher monomer concentrations, the efficiency of monomer in giving graft polymer decreased due to increased homopolymer formation. The composition of the graft polymers varied with increasing monomer concentration, graft polymers having about 40–65% of grafted starch were obtained. With increasing temperature (10 to 60°C), the yield of graft polymer decreased, there was more homopolymerization, but the amount of starch incorporated in the graft remained constant. The structure of the graft polymers was deduced from hydrolysis of the starch backbone of the graft polymers by dilute mineral acid and the determination of the molecular weights of the grafted side chains, and from oxidation by periodic acid, which showed the extent of grafting at the secondary hydroxyl groups. These results have shown that by anionic graft polymerization it is possible to obtain graft polymers having more densely packed grafted side chains of relatively low molecular weights than those obtained previously by free-radical graft polymerization.     

Anionic graft polymerization of methyl methacrylate on starch and dextrin

The anionic graft polymerization of methyl methacrylate on the potassium alkoxide derivative of starch or dextrin in DMSO was studied. The effects of monomer and alkoxide concentrations as well as temperature were investigated. The yield of graft polymer increased with increasing alkoxide concentration. With increasing monomer concentration and with increasing temperature the extent of homopolymer formation increased. The composition of the graft polymers was found to depend on the reaction conditions. Graft polymers having about 10–40% poly(methyl methacrylate) were obtained. There were quantitative differences in yield of isolated graft polymer between starch and dextrin and these were ascribed to differences in the solubility properties of the carbohydrates. Evidence on the structure of the graft polymers and on the mechanism of the graft polymerization was obtained from acid hydrolysis of the graft polymers and determination of the molecular weights of the cleaved side chains.     

Anionic graft polymerization of ethylene oxide on starch. II. Structure of the graft polymers

Starch–poly(ethylene oxide) graft polymers were prepared in DMSO at various monomer and starch alkoxide concentrations. Complimentary and varied information on the structure of the graft polymers was obtained from NMR and periodic acid oxidation of the polymers. From the NMR spectra of the graft polymers in pyridine containing a trace of HCl, which causes shifting of the resonance of the internal ? CH₂O? protons from the terminal ? CH₂OH protons, the polyethylene oxide content, the DP _n of the grafted side chains, and the efficiency of the alkoxides were calculated. With increase of the alkoxide concentration there was a small decrease in ? DP _n, and in the efficiency of the alkoxides in initiating graft polymerization. With increase of monomer concentration, there was only a small increase in ? DP _n but a large increase in the efficiency, indicating the existence of transfer reactions between the growing anions and the free hydroxyl groups on the starch. The results of he periodic acid oxidation showed that with increase of alkoxide concentration there was no significant change in the per cent oxidation of the graft polymers, but with increase of monomer, there was an increase in the participation of the secondary hydroxyl groups in initiation. This supports the NMR evidence for the existence of transfer reactions leading to ? DP _n values much lower than those calculated from [monomer]/[catalyst] ratios.     

Anionic graft polymerization and homopolymerization of phenyl glycidyl ether

Phenyl glycidyl ether was found to react with potassium starch alkoxide in dimethyl sulfoxide (DMSO) to give graft polymers in almost quantitative yields, both the monomer and the starch being incorporated completely into the graft polymer. No transfer reactions to monomer or solvent leading to homopolymerization was found. For this reason this system was used as a model for the study of the rate of the graft polymerization of alkylene oxides on starch and other carbohydrates. Comparison of the rates of the graft polymerization of phenyl glycidyl ether on starch alkoxide with that of the homopolymerization by potassium naphthalene in DMSO under comparable conditions showed that the former reaction was much slower. Rates of the graft polymerizations on dextrin and sucrose under comparable conditions, were similar to those obtained with starch. On the other hand, the rates of polymerization on poly(ethylene oxide) alkoxides of different molecular weights were similar to those obtained in the corresponding homopolymerization by potassium naphthalene, showing that neither the molecular weight of the initiator nor the viscosity of the reaction medium were the governing factors. This suggested that the lower rates obtained by using the carbohydrate alkoxides as initiators were connected with the heterogeneity of these reaction systems, the polymeric alkoxide being insoluble in DMSO. The systematic study carried out on the homopolymerization by potassium naphthalene in DMSO showed that the effective initiator was dimsyl anion obtained by interaction of potassium naphthalene with DMSO. The reaction was bimolecular, being first order to monomer and to initiator. The molecular weights increased with increasing monomer concentration and decreasing catalyst concentration, in accordance with a “living” polymerization system.     

Grafting of poly(ethylene oxide) on poly(methyl methacrylate) by transesterification

The grafting of the potassium alkoxide derivative of poly(ethylene oxide) on poly(methyl methacrylate) in homogeneous solution in toluene was studied. The alkoxide was prepared by reaction with potassium metal with methanolic potassium methoxide, or with potassium naphthalene. The last was the most suitable for the systematic investigation of the grafting process. Soluble graft polymers were formed, and essentially the initial poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) participated in the production of graft polymer. The composition of the graft polymers and the frequency of grafting of the side chains were determined by NMR. The solubility of the graft polymers in methanol and water increased with increasing PEO contents, while the melting ranges decreased. Fractionation of the crude graft polymers showed that the grafting reaction was random, and graft polymers containing one PEO side chain per about 10–170 MMA units were obtained.     

Grafting of Preformed Polyethylene Oxide on Dialdehyde Starch by Acetal Formation

The acid-catalyzed reaction of dialdehyde starch with diethylene glycol and polyethylene oxide-400 under anhydrous conditions was studied as a new approach to the preparation of graft polymers of polyalkylene oxides on starch, the attachment of the side chains being through acetal linkages. The reaction was carried out in DMF in the presence of p-toluene sulfonic acid. It was found that increasing the reaction temperature, the diol concentration, or the reaction time led to an increase in the degree of grafting, as seen from the decrease in the dicarbonyl content of the products. Fusible graft polymers, soluble in water and in organic solvents, were obtained.     

Amphiphilic graft copolymers - preparation and interfacial properties

Amphiphilic graft copolymers containing poly(ethylene oxide) (PEO) grafts have been prepared by various methods, for example, by coupling of reactive hydrophobic backbone polymers with end-functionalised PEO, by macromonomer copolymerisation, and by anionic graft polymerisation of EO onto polymer backbones carrying functional groups as initiator precursors. The graft copolymers are amphiphilic and were shown to accumulate at surfaces and interfaces in solution and in the solid state. Amphiphilic starch derivatives were prepared by reaction of amylose and starch with aliphatic α-epoxides.     

Synthesis and Some Properties of Graft Copolymers with Uniform Polyoxyethylene Side Chains

Abstract

Graft copolymers with uniform polyoxyethylene (PEO) side chains were synthesized by transesterification of poly(methyl, ferf-butyl fumarate) (PMtBF) or poly(methyl, tert-butyl fumarate-co-styrene) poly-(MtBF-co-St) with potassium alkoxide of PEO monoether. The grafting efficiency increased with enhanced alkoxide reactivity, but the main factor in the ester exchange proved to be the structure of the backbone. This effect was ascribed to the thermodynamic incompatibility between fumaric polymers and PEO. The polymers were characterized by spectral methods, GPC, and DSC. In THF the graft copolymers comprising a polyfumarate backbone with PEO side chains eluted at higher elution volumes than did the backbone homopolymers. In benzene their intrinsic viscosities were lower than those of the backbones. In aqueous eluents, micelles were detected, and their aggregation number depended on the composition of the copolymer and the eluent.     

Preparation and properties of alkylated poly(styrene-graft-ethylene oxide)

Poly(styrene-graft-ethylene oxide), having alkyl chains (C₁₂ or C₁₈) on the polystyrene main chain or on the poly(ethylene oxide) (PEO) side chains, were synthesized. The main chain was alkylated by first ionizing amide groups in a styrene/acrylamide copolymer with tert-butoxide, and then using the amide anions as sites for reactions with 1-bromoalkanes. An excess of amide anions was used in the reaction, and the remaining anions were subsequently utilized as initiator sites for the anionic polymerization of ethylene oxide (EO). Synthesis of poly(styrene-graft-ethylene oxide) with alkylated side chains was accomplished by polymerization of EO onto the ionized styrene/acrylamide copolymer, followed by an alkylation of the terminal alkoxide anions with 1-bromoalkanes. The alkylated graft copolymers were structurally characterized by using elemental analysis, ¹H NMR, GPC, and IR spectroscopy. DSC analysis showed that only graft copolymers with PEO contents exceeding about 50 wt % and side chain crystallinities comparable to those of homo-PEO. Main chain alkylated graft copolymers generally had higher crystalinities, as compared to nonalkylated and side chain alkylated samples. The graft copolymers absorbed water corresponding to one water molecule per EO unit at low PEO contents. The water absorption increased progressively at PEO contents above 30 wt % for main chain alkylated samples and above 50 wt % for non-alkylated samples. © 1995 John Wiley & Sons, Inc.     

Haloaldehyde Polymers. XIV. Endgroups in Polychloral

Chloral polymers prepared by anionic polymerization have alkoxide endgroups as terminal ends at the end of this polymerization. The initiating anion has, as expected, no influence on the type of terminal group formed. Polychloral with terminal alkoxide ends degrades easily thermally to monomeric chloral. Alkoxide endgroups in polychloral do not readily react with alkylating or acylating agents, although partial stabilization has been observed when alkoxide-terminated polymers were allowed to stand for periods of time; the endgroups seem to react either with impurities or with excess chloral in side reactions. With protic acids, alkoxide-terminated polychloral is transformed into hydroxyl-terminated polymer of higher thermal stability. Studies of the initiation step of the chloral polymerization revealed that above the ceiling temperature of polymerization, strong nucleophiles, such as soluble tertiary butoxide, initiate quantitatively, but polymerization does not proceed until the mixture is cooled. When chloral is initiated with weaker nucleophiles such as chloride or carboxylates, the initiation equilibrium is not on the side of the initiated species, although it shifts effectively as polymerization proceeds; with carboxylates as initiators the ester group has been found incorporated as the initial endgroup in polychloral. With sufficient amounts of lithium tertiary butoxide as anionic initiator, polychloral of low molecular weight was prepared. This polymer does not react with end-capping reagents (other than PCl₅) as does high molecular weight polychloral; in spite of considerable effort it was not possible to prepare low molecular weight soluble polychloral or oligomeric polychloral. Polychloral prepared with cationic initiators is thermally more stable than unstabilized anionically initiated polychloral but is generally crumbly and incoherent. The end-groups of such polymers are usually hydroxyl endgroups. Identification of endgroups of the polymers has been done where possible by IR spectroscopy, for the initiation reaction by NMR spectroscopy, but for high molecular weight insoluble polymers almost exclusively by comparative thermal polymer degradation.     

Synthesis and characterization of poly(ethylene oxide) star polymers possessing a tertiary amino group at each arm end by organized polymerization using macromonomers

Functional poly(ethylene oxide) star polymers possessing a tertiary amino group at each arm end were prepared by free-radical copolymerization of poly(ethylene oxide) macromonomers with divinylbenzene (DVB) in water or ethanol. The poly(ethylene oxide) arm was prepared by anionic polymerization using 2-[2-(N,N-dimethylamino)ethoxy]ethanol potassium alkoxide as the initiator. The star polymers had narrow molecular weight distribution. The arm number was controlled by varying the feed ratio [DVB]/[M], the initial concentration of macromonomer [M], and solvent media. The branching factor g' in methanol ([eta]S/[eta]L are the intrinsic viscosities of the star and linear molecules, respectively) exhibited a power-law dependence on the arm number, f, with a negative exponent. This means that the dimensions of a star were in agreement with the Daoud-Cotton scaling model.     

Copolymers of modified starches with polyacrylonitrile

A study was made of the ceric ammonium nitrate-initiated graft polymerization of acrylonitrile (AN) onto a number of modified starches that had been reduced in molecular weight by either acid, hypochlorite, or enzyme treatment. With highly soluble starches, much of the starting material was recovered as ungrafted carbohydrate, and the reaction product was largely dimethylformamide-soluble polymer with a high polyacrylonitrile (PAN) content. The molecular weight of grafted PAN was lower when the modified starches existed as granules in water dispersion; however, heating (60°C) an aqueous slurry of an acid-modified corn starch (with intact granules) before the reaction had relatively little effect on the composition of the copolymer. Decreasing the concentrations in water of modified starch and AN resulted in more frequent and lower molecular weight grafts of PAN. Aqueous methanol as a reaction medium for an acid-modified starch with intact granules led to more frequent grafting of lower molecular weight PAN than when water alone was used. The number of grafted chains, however, was fewer than found with unmodified wheat starch under comparable conditions. A modified starch with the granule structure completely broken down gave no detectable reaction in aqueous methanol.     

Triblock and Radial Star-Block Copolymers Comprised of Poly(ethoxyethyl glycidyl ether), Polyglycidol,Poly(propylene oxide) and Polystyrene Obtained by Anionic Polymerization Initiated by Cs Initiators

The anionic polymerization of ethoxyethyl glycidyl ether (EEGE) initiated by cesium alkoxide was studied. The ring-opening polymerization of EEGE in the presence of cesium alkoxide of 1-methoxy-2-ethanol does not involve any side reactions. The presence of an additional alcohol leads to a significant increase of the initiator efficiency. Aqueous solutions of poly (ethoxyethyl glycidyl ether) (PEEGE) exhibit lower critical solution temperature (LCST), and the polymer solubility in water is extremely sensitive to its MW. Two novel types of block copolymers based on PEEGE were synthesized: triblock-copolymers of ABA (A′:BA′) structure, where A is the PEEGE block, A′ polyglycidol (PG) and B the polypropylene oxide (PPO) block, and A₂S (A′₂S) and A₄S (A′₄S) heteroarm stars, where S is the polystyrene block. The synthesis of the ABA block was performed by polymerization of EEGE initiated by bi-functional PPO/Cesium alkoxide macroinitiator. The PEEGE blocks were converted into PG blocks by successful cleavage of the ethoxyethyl group. Polystyrene/PEEGE and polystyrene/PG three- and five- heteroarm star copolymers were synthesized by a coupling reaction between well-defined chain-end-functionalized polystyrenes carying dendritic benzyl bromide moieties with living anionic polymers of PEEGE with one cesium alkoxide terminal group. The coupling reaction proceeds quantitatively without any side reactions, and thus series of star-branched polymers can be systematically synthesized. Polystyrenes with two or four PG arms have been obtained after the cleavage of the protecting group. The compact structure of these multi-arm star polymers and their amphiphilic character leads to the formation of nanoparticles in aqueous solution with rather uniform size distribution and a mean diameter of 15 nm.     

Novel water-soluble photosensitizer based on starch and containing porphyrin

Novel water-soluble polymeric photosensitizers (SPO) based on starch and containing porphyrin chromophores were synthesized and studied. The polymers were soluble in water and in dimethyl sulfoxide. Photophysical studies and solubilization of molecular probes proved the formation of hydrophobic, rigid microdomains in an aqueous solution of SPO; they were created due to the clustering of porphyrin chromophores attached to the polymer chain. SPO polymers absorbed light from the UV-visible spectral region. The polymers could sensitize photochemical reactions mediated by electron transfer, energy transfer or both, from the singlet-excited state of porphyrin chromophores to the molecules of organic compounds solubilized in the hydrophobic microdomains or residing in the water phase.     

Chromatography of amphiphilic graft copolymers

Amphiphilic comb polymers were prepared through grafting poly(ethylene glycol) methyl ether (MPEG 2000) onto acrylic and methacrylic copolymers. The graft copolymers were purified from unreacted MPEG by partition chromatography on methanol pretreated fibrous cellulose using ethyl acetate and methanol as eluents. The separation was found to depend on the water contents of the cellulose and the eluents. It is proposed that one parameter of importance for the chromatographic separation is the formation of hydrated inverted micelles. The amphiphilic comb polymers were shown by gel chromatography on Sepharose to form high molecular weight aggregates in water. On addition of sodium lauryl sulphate or inorganic salts to the eluent at low ionic strengths these aggregates dissociated and were fractionated by the gel. It was also shown that on GPC in THF solution on Styragel columns the polymers exhibited apparent molecular weights equal or smaller than those of the corresponding backbones. This effect may be a consequence of the graft copolymers having relatively small hydrodynamic volumes, and this idea is supported by the fact that their intrinsic viscosities generally were lower than those of the backbones. However, adsorption on the Styragel columns also may be of importance.     

Functional graft poly(N-isopropyl acrylamide)s using reversible addition-fragmentation chain transfer (RAFT) polymerisation

A series of NIPAM/4-vinyl benzyl chloride copolymers were substituted with 4(5)-imidazole dithioic acid or N-pyrrole dithioic acid to form multi-functional linear dithioate-functional polymers, which can be used as macromolecular transfer agents in a controlled radical polymerisation (RAFT) process. The presence of imidazole dithioate or N-pyrrole dithioate units along the NIPAM copolymer was determined by (1)H NMR, which showed broad CH-imidazole or CH-N-pyrrole resonances. Subsequent reaction of these multi-branch point polymers to produce graft polymers was achieved by reaction with NIPAM in the presence of AIBN. The graft polymers are produced as mixtures containing the desired product and linear polymer. The linear polymer is produced following transfer to the pendant dithioate group. Some of the branched polymers formed from the imidazole dithioate polymers were insoluble in water whilst others were found to be water soluble only in the presence of copper(II) ions. The use of N-pyrrole dithioate groups was found to substantially increase the solubility of the branched polymers in conventional solvents.     

Synthesis and characterization of model block-graft copolymers via anionic polymerization: Introduction of poly(isoprene) and poly(ethylene oxide) as graft chains

New architectural graft copolymers were prepared, that is, the graft chains were situated in terminal or center position of the backbone chain. These graft copolymers were termed block-graft copolymers. Two different block-graft copolymers were prepared from a “grafting onto” process and a “grafting from” process via living anionic polymerization. These backbone chains are poly(styrene), and the graft chains are poly(isoprene) and poly(ethylene oxide). The polymers were characterized by GPC measurements, osmometry, and ultracentrifugation. The block-graft copolymers formed fine microphase separation structures. It was a morphological feature that an apparent volume fraction of the graft to the backbone might be higher than the real volume fraction.     

Starch and amylose degradation by 60Co γ-irradiation

The effects of γ-irradiation (0.02–4.0 Mrad absorbed dose and 1.2 Mrad/hr dose rate) on depolymerization and selected physical properties of corn starch and amylose (both dry solid and solution forms) were investigated under conditions used to make graft polymers. Radiation introduces an alkali-sensitive structure, most likely β-alkoxycarbonyl, having a G value of 2.8. A dimethyl sulfoxide (DMSO)-acetic acid-water solvent for intrinsic viscosity was developed that degraded irradiated amylose less than did aqueous 90% DMSO. The G (scission) value of 1.3 for solid amylose irradiated at 0°C under nitrogen is lower than most literature values for either amylose or other polysaccharides. The protection of amylose against irradiation degradation in water by additions of DMSO is noteworthy. The G (scission) for amylose irradiated in 99.8% DMSO is 2.3; whereas, in water it is 30.     

Grafting of living poly(ethylene oxide) onto polystyrene via aromatic nucleophilic displacement of activated nitro groups

Polystyrene of M?_ω = 2.2 × 10⁴ was alkylated with 4-nitrophthalimidomethyl groups as grafting sites. Several backbone polymers with various degrees of grafting sites (G = 2–100%) were prepared and characterized by elemental analysis, IR, ¹H- and ¹³C-NMR, and viscosity measurements. “Living” poly(ethylene oxide) with narrow molecular-weight distribution was prepared in the presence of 15-crown-5, and grafted onto the 4-nitrophthalimidomethylated polystyrene. The nitro displacement reaction was fast and the grafting yield was quantitative (100%). The graft copolymers are highly soluble in water and in organic solvents. The intrinsic viscosities of the graft copolymers are higher than those of the backbone polymers. The intrinsic viscosities show an initial increase followed by a decrease as the degree of grafting increase.     

Distribution of Methoxyl Groups in the Methylation of Starch Alkoxides Obtained by Metallation with Alkali Metal Naphthalene

Abstract

The distribution of the alkoxide groups obtained in the metallation of starch in dimethyl sulfoxide solution by alkali metal naphthalenes was studied. The starch alkoxide was reacted with methyl iodide, and the methylated starch was hydrolyzed and analyzed for glucose and O-methyl glucose derivatives. The metallation reaction was found to be random, as seen from the fact that at low alkoxide concentration (D.S = 0.6), 2,3,6-tri-O-methyl glucose was formed, while at relatively high alkoxide concentration (D.S. = 1.5) unreacted glucose was still present. At low alkoxide concentration (D.S. ? 0.6) there was, to a certain extent, preferential metallation at the C₂ hydroxyl groups, and to a lesser extent at the C₆ hydroxyl groups, as seen from the relative molar ratios of about 10:4:1 of the 2-, 6-, and 3-O-methyl glucose derivatives obtained, respectively. An increase in the metallation at the C₃ hydroxyl occurred with increasing alkoxide concentration. The distribution of the methoxyl groups with the three alkali metals potassium, sodium, and lithium was similar; there were differences only in the ease of metallation of the starch by the various alkali metal naphthalenes and in the efficiency of the coupling reaction with methyl iodide.