Influence of starch granule swelling on graft copolymer composition. A comparison of monomers

Seven monomers, which varied widely in water solubility and ionic charge, were graft polymerized onto both unswollen starch and starch that had been swollen by heating in water to 60°C. Polymerizations were initiated with ferrous ammonium sulfate hexahydrate–hydrogen peroxide and, where applicable, with ceric ammonium nitrate. Graft copolymers were freed of ungrafted homopolymer by solvent extraction and were characterized by weight percentage of synthetic polymer incorporated in the graft copolymer, molecular weight of grafted branches, and grafting frequency. The influence of starch granule swelling on graft copolymer structure varied with the monomer used and could not be predicted on the basis of water solubility of monomer or its resulting polymer. With acrylonitrile and acrylamide, swollen starch gave higher molecular weight and less frequent grafts than unswollen starch. However, methyl methacrylate, N,N-dimethylaminoethyl methacrylate · HNO₃, N-t-butylaminoethyl methacrylate. HNO₃, and 2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride produced less frequent graft of higher molecular weight when starch was unswollen. With acrylic acid, graft molecular weight was independent of starch granule swelling, although grafting was less frequent when swollen starch was used.     

Graft copolymers of starch. III. Copolymerization of gelatinized wheat starch with acrylonitrile. Influence of chain modifiers on copolymer composition

A study was made of the influence of selected chain modifiers on both the molecular weight of grafted polyacrylonitrile and the grafting frequency of the starch–polyacrylo-nitrile graft copolymer. Gelatinized wheat starch was used with ceric ammonium nitrate as the initiator. The organic chain modifiers investigated were ethyl mercaptan, 1-dodecanethiol, methyl ethyl ketone, acetaldehyde, and chloroform. Sodium chromate, cupric bromide, cupric nitrate, cupric acetate, and cupric chloride were also tested as chain modifiers. In the presence of cupric chloride, there was a tenfold reduction in the molecular weight of grafted polyacrylonitrile; however, fewer chains were grafted to the starch backbone than were observed without cupric chloride.     

Swelling and rheology of saponified starch–g–polyacrylonitrile copolymers. Effect of starch granule pretreatment and grafted chain length

A series of well-characterized starch–g–polyacrylonitrile (PAN) graft copolymers was prepared from corn starch which had been heated in water at temperatures up to 94°C to vary the extent of starch granule swelling and disruption. Graft polymerization onto gelatinized starch gave less frequent grafting of higher molecular weight PAN than comparable graft polymerizations onto ungelatinized starch. A graft copolymer was also prepared from gelatinized starch under high dilution conditions to give lower molecular weight grafted PAN and more frequent grafting. Graft copolymers were then saponified with sodium hydroxide to convert nitrile substituents to a mixture of carboxamide and sodium carboxylate. Saponified graft copolymers were only partially water soluble and consisted largely of highly swollen, insoluble gel, which was separated from solubles for the study of physical properties. Saponification mixtures were also dried to yield highly absorbent polymer films. With the exception of the graft copolymer prepared under high dilution conditions, the physical properties of saponified graft copolymers depended on whether or not the granules of starch were gelatinized before graft polymerization. Compared with saponified graft copolymers derived from ungelatinized starch, those prepared from gelatinized starch gave films that absorbed larger amounts of aqueous fluids. Also, the gel fractions from these saponified gelatinized polymers exhibited higher water swelling, lower shear modulus, and a lower reduced viscosity function (η/cQ). The saponified graft copolymer prepared from gelatinized starch under high dilution conditions more closely resembled those prepared from ungelatinized starch, suggesting that molecular weight of grafted PAN and the grafting frequency rather than starch granule pretreatment might be the most important factor which influences properties.     

Studies in the graft copolymerization of vinyl monomers on cellulosic materials

Graft copolymerization of acrylonitrile, methyl methacrylate, and vinyl acetate on bleached holocellulose initiated by ceric ions in aqueous medium was studied at 29°C. The extent of graft copolymer formation was poly(methyl methacrylate) > polyacrylonitrile > poly(vinyl acetate), indicating the influence of polarity of monomer on graft copolymerization. It was found that, although the molecular weights of the grafted polyacrylonitrile copolymer were lower than the values obtained for poly(methyl methacrylate), the latter was less frequently incorporated on the cellulosic backbone polymer than the polyacrylonitrile grafts. The marked reductions in graft level associated with thiolation of the cellulosic material suggest that hydrogen abstraction reactions from carbon atom carrying hydroxyl groups may not be important in graft copolymer formation.     

Copolymers of starch and polyacrylonitrile: The dilution effect

In the ceric ammonium nitrate-initiated graft polymerization of acrylonitrile (AN) with starch, grafting frequencies and molecular weights of grafted polyacrylonitrile changed from 600 anhydroglucose units (AGU)/graft and 120000 to 280 AGU/graft and 36000 when concentrations of starch and AN were varied from 0.27 and 1.20 to 0.023 and 0.235 moles/l. of water, respectively. The influence of variety of starch, size of the starch granules, and reaction time was studied, and possible reasons for the influence of reactant concentration on the composition of the copolymer are considered.     

Graft copolymers from thiolated starch and vinyl monomers

Thiol starches of degree of substitution (D.S.) 0.005–0.162 were prepared by displacing starch tosyloxy groups with xanthate and treating the resulting xanthate esters with either sodium hydroxide or sodium borohydride. Acrylonitrile, styrene, acrylamide, acrylic acid, and dimethylaminoethyl methacrylate were grafted onto the thiol starches with hydrogen peroxide as initiator. The peroxide caused both grafting of monomer and coupling of thiol groups to disulfide. Treating graft copolymers with sodium borohydride regenerated thiol groups from disulfide groups so that the grafting sequence could be repeated. By regenerating the thiol groups and repeating the grafting steps, high add-on and high-frequency starch graft copolymers were prepared. During four grafting sequences, acrylonitrile reacted with D.S. 0.162 thiol starch to give graft copolymers that contained increasing amounts of polyacrylonitrile (46.0–66.5%). Grafting frequency increased from 183 to 71 anhydroglucose units (AGU)/graft, while molecular weights of the grafted chains ranged between 20,000 and 25,200. The final product was hydrolyzed with potassium hydroxide solution to a copolymer, which absorbed up to 400 ml water per gram. Styrene was grafted onto thiol starch to give products containing 34.4–69.5% polystyrene with 986–3520 AGU/graft and having molecular weights of grafted chains between 276,000 and 364,000. Graft copolymers containing 48.9% polyacrylamide, 21.2% poly(acrylic acid), and 77.7% poly(2-methacryloyloxyethyldimethylammonium acetate) were obtained under similar conditions.     

Graft polymerization of vinyl acetate onto starch. Saponification to starch–g–poly(vinyl alcohol)

Graft polymerizations of vinyl acetate onto granular corn starch were initiated by cobalt-60 irradiation of starch-monomer-water mixtures, and ungrafted poly(vinylacetate) was separated from the graft copolymer by benzene extraction. Conversions of monomer to polymer were quantitative at a radiation dose of 1.0 Mrad. However, over half of the polymer was present as ungrafted poly-(vinyl acetate) (grafting efficiency less than 50%), and the graft copolymer contained only 34% grafted synthetic polymer (34% add-on). Lower irradiation doses produced lower conversions of monomer to polymer and gave graft copolymers with lower % add-on. Addition of minor amounts of acrylamide, methyl acrylate, and methacrylic acid as comonomers produced only small increases in % add-on and grafting efficiency. However, grafting efficiency was increased to 70% when a monomer mixture containing about 10% methyl methacrylate was used. Grafting efficiency could be increased to over 90% if the graft polymerization of vinyl acetate-methyl methacrylate was carried out near 0°C, although conversion of monomers to polymer was low and grafted polymer contained 40-50% poly(methyl methacrylate). Selected graft copolymers were treated with methanolic sodium hydroxide to convert starch–g–poly(vinyl acetate) to starch–g–poly(vinyl alcohol). The molecular weight of the poly(vinyl alcohol) moiety was about 30,000. The solubility of starch–g–poly(vinyl alcohol) in hot water was less than 50%; however, solubility could be increased by substituting either acid-modified or hypochlorite-oxidized starch for unmodified starch in the graft polymerization reaction. Vinyl acetate was also graft polymerized onto acid-modified starch which had been dispersed and partially solubilized by heating in water. A total irradiation dose of either 1.0 or 0.5 Mrad gave starch–g–poly(vinyl acetate) with about 35% add-on, and a grafting efficiency of about 40% was obtained. A film cast from a starch–g–poly(vinyl alcohol) copolymer in which homopolymer was not removed exhibited a higher ultimate tensile strength than a comparable physical mixture of starch and poly(vinyl alcohol).     

Graft polymerization of styrene onto starch by simultaneous cobalt-60 irradiation

Starch-g-polystyrene copolymers have been prepared by the simultaneous ⁶⁰Co-irradiation of starch–styrene mixtures, and copolymers have been characterized with respect to weight per cent polystyrene (% add-on) and also the molecular weight and molecular weight distribution of polystyrene grafts. In a typical polymerization, 4 g each of starch and styrene were blended with 1 ml water and 1.5 ml of an organic solvent; the resulting semisolid paste was irradiated to a total dose of 1 Mrad. With ethylene glycol, acetonitrile, ethanol, methanol, acetone, and dimethylformamide as the organic solvent, values for % add-on ranged from 24% to 29%. The highest % add-on (43%) and the highest conversion of styrene to grafted polymer (76%) were obtained when the organic solvent was omitted, and water alone was used. When water was also omitted, polymerization of styrene was negligible; however, graft copolymer was formed in the absence of water when either ethylene glycol or ethanol was added. Attempts were unsuccessful to achieve a % add-on greater than 43% by doubling the amount of styrene in the polymerization recipe. Mixtures of equal weights of starch and styrene are relatively nonvicious, but these mixtures thicken when either water or ethylene glycol is blended in. Reasons for this thickening action and the possible influence of thickening on the graft polymerization reaction were explored.     

Graft copolymers of starch with mineral acid salts of dimethylaminoethyl methacrylate. Preparation and testing as flocculating agents

Mineral acid salts of dimethylaminoethyl methacrylate (DMAEMA) have been graft polymerized onto starch with ferrous ammonium sulfate–hydrogen peroxide initiation. The nitric acid salt was used in most reactions, and graft polymerizations were run in both water and aqueous–organic solvent systems. Increased monomer concentration in water led to an increase in both the percentage of poly(DMAEMA · HNO₃) in the graft copolymer (percent add-on) and the molecular weight of grafted branches. Variations in initiator concentration altered the percent add-on only slightly but affected the molecular weight of grafted polymer significantly. When swollen starch, in contrast with unswollen starch was used in graft polymerization reactions run in water, the product had a higher per cent add-on and a larger number of grafted branches of lower molecular weight. The efficiency of starch–poly(DMAEMA · HNO₃) graft copolymers as flocculants for diatomaceous silica increased with per cent add-on; however, variations in grafting frequency and graft molecular weight had less effect on the behavior of these materials as flocculants.     

Graft copolymerization onto starch. IV. Grafting of methyl methacrylate to granular native potato starch by manganic pyrophosphate initiation

A study has been made of graft copolymerization of methyl methacrylate onto native potato starch in aqueous slurry at 30°C. As Mn³⁺ concentration was increased from 0.15 X 10^-3M to 1.0 X 10^-3M, conversion of monomer to polymer and add-on of polymer to starch increased and frequency of grafts (anhydroglucose units per grafted chain) decreased sharply. The average molecular weights of the PMMA grafts also decreased in this range. At Mn³⁺ concentrations from 1.0 X 10^-3M to 3.0 X 10^-3M, only minor changes in grafting parameters were observed. When the amount of starch charged per batch was increased threefold, the add-on decreased sharply, the molecular weight increased slightly, and the conversion of MMA monomer to polymer remained almost constant. The increase in frequency of grafts (AGU/chain) was almost directly proportional to the increase in the amount of starch charged. In all cases the average molecular weights of grafts were of the order of 10⁶ and the grafting efficiencies high, normally greater than 85%. These results were compared with those previously obtained for grafting of acrylonitrile onto starch. They were interpreted in terms of initial (Mn³⁺)/(AGU) ratio, total number of radicals initiating grafting, and compatibility of methyl methacrylate monomer with poly(methyl methacrylate) chains.     

Synthesis and absorbency of a superabsorbent from sodium starch sulfate‐g‐polyacrylonitrile

A sodium starch sulfate–based superabsorbent was synthesized to improve water and saline absorbencies. A sodium starch sulfate with high degree of substitution was synthesized by the reaction of starch gelatinized with dimethyl acetamide (DMAc)/lithium chloride (LiCl) and a dimethyl formamide–sulfur trioxide (DMF–SO₃) complex. The sodium starch sulfate was then graft‐polymerized with acrylonitrile and the nitrile groups of the sodium starch sulfate‐g‐polyacrylonitrile were converted to a mixture of hydrophilic carboxamide and carboxylate groups by alkaline hydrolysis. The hydrolyzed sodium starch sulfate‐g‐polyacrylonitrile copolymer exhibited improved water and saline absorbencies compared with that of existing starch‐based superabsorbents, resulting from the presence of sulfate groups. The maximum water and saline absorbencies of the sodium starch sulfate–based superabsorbent were 1510 and 126.4 g/g, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1423–1430, 2001     

A new biodegradable plastic made from starch graft poly(methyl acrylate) copolymer

A starch graft poly(methyl acrylate) copolymer was developed having grafted side chains with molecular weight of less than 500,000. This material can be easily extruded into a film which shows excellent initial tensile strength and elongation. Tensile strength, however, falls off rapidly after 70 hr of water immersion at 25°C. Starch graft poly(methyl acrylate) films show excellent susceptibility to fungal growth, some samples losing more than 40% of their weight after 22 days of incubation with Aspergillus niger. Tensile tests and scanning electron micrographs of the incubated samples, after being freed of mycelium, indicate substantial biodegradation of the starch portion of the copolymer. This material may have application as a biodegradable plastic mulch.     

Separation and characterization of the vinyl side chains from grafted polyacrylonitrile–cotton copolymers

A method of separation of polyvinyl side chains from grafted polyacrylonitrile–cotton copolymers was developed in order to study the effect of length of side chain on copolymer properties. The method consists of dispersion of the copolymer (1 g.) containing 20% polyacrylonitrile in 75% aq. ZnCl₂ (100 ml.), addition of 6N HCl (100 ml.), heating for 1 hr. at 100°C., and precipitation and purification of the resulting vinyl polymer. The effect of hydrolysis on the intrinsic viscosity, the nitrogen content, and the infrared absorption spectra of the polyacrylonitrile polymers was investigated. It was concluded that this method of separation of the grafted polymers permitted a comparison of samples grafted by various techniques. A series of grafted copolymers was hydrolyzed, and the molecular weights of the isolated products were determined by measurements of intrinsic viscosity. Copolymer samples prepared by a post-irradiation grafting technique had the longest polyacrylonitrile side chains (molecular weight, 1 × 10⁶). Samples grafted by a simultaneous irradiation technique varied in side-chain length, depending upon the monomer-solvent system used in the preparation of the copolymer (molecular weight, 3 × 10⁴?5 × 10⁵). Chemically initiated grafting to cotton resulted in a copolymer containing relatively short side chains (molecular weight, 9 × 10⁴).     

Graft copolymerization onto starch. II. Grafting of acrylonitrile to granular native potato starch by manganic pyrophosphate initiation. Effect of reaction conditions on grafting parameters

The effect of reaction conditions on the composition of native potato starch–polyacrylonitrile graft copolymers initiated by manganic pyrophosphate onto starch slurries at 30°C has been examined. In general, when the Mn³⁺ ion concentration was increased from 0.15 × 10^?3M to 3.0 × 10^?3M (other conditions kept constant), an increase in conversion of monomer to polymer and % add-on was observed, whereas frequency of grafts (anhydroglucose units, AGU, per grafted chain) decreased. Also, the average molecular weights of grafts showed a decrease from 2.2 × 10⁵ to 1.5 × 10⁵. Increasing the concentration ratio of starch to monomer during polymerization by a factor of 3 produced an increase in the conversion of monomer to polymer, whereas an increase in frequency of grafts (AGU/chain) was obtained. Values of % add-on and average molecular weights of the grafts showed, however, a decreasing tendency. It was observed that grafting onto starch took place readily even at acid additions as low as 10 × 10^?3M H₂SO₄ (pH ?1.8). Selective solvent extraction of homopolymer and extremely low conversions of monomer to polymer (0.1%–1.5%) in duplicate runs without addition of starch indicated that grafting efficiencies were high in all cases. An attempt has been made to interpret the results in terms of variations in factors such as initial ratio of (Mn³⁺)/(AGU), termination rate of acrylonitrile chain radicals by oxidation by Mn³⁺ ions, oxidation rate of radicals formed on anhydroglucose units by Mn³⁺ ions, and physical factors such as diffusion rate of Mn³⁺ ions through the polyacrylonitrile-grafted starch granules for terminating the radicals.     

Structure and molecular properties of saponified starch–graft-polyacrylonitrile

The Mn3+ initiation system has been used to prepare starch-g-polyacrylonitrile copolymers. Both granular native starch and water-swollen gelatinized starch have been used as substrate. Conversion of monomer, graiting ratio, and percent add-on tend to increase with increasing amounts of monomer charged. The amount of homopolymer formed is extremely low, a p proximately 1%. The efficiency, measured as conversion, is consistently higher with gelatinized starch as Substrate. The molecular weight of the grafta on gelatinized starch is approximately eight times higher than those on granular starch. Granular starch has a correspondingly higher frequency of grafta. Solubility measurements of starch, polyacrylonitrile, and grafted starch were carried out in dimethylsulfoxide (DMSO) at 348 K. Starch and polyacrylonitrile were totally soluble in DMSO under the chosen conditions. The solubilities of grafted samples were independent of the state of the substrate before grafting and of molecular weights of the grafted chains, but were found to be correlated to percent add-on. Starch-g-polyacrylonitrile samples, with gelatinized starch as substrate, were saponified in aqueous sodium hydroxide eolution. The water retention value increased linearly with increasing add-on. The saponified polyacrylonitrile, branches alone had a water retention value that was three times higher than that of the original copolymer.     

Graft copolymers of starch with mixtures of acrylamide and the nitric acid salt of dimethylaminoethyl methacrylate

Mixtures of acrylamide and the nitric acid salt of dimethylaminoethyl methacrylate (DMAEMA·HNO₃) have been graft polymerized onto unmodified wheat starch with ferrous ammonium sulfate–hydrogen peroxide initiation. Graft polymerizations were carried out with both unswollen starch granules and granules that had been swollen by heating in water to 60°C. Ungrafted synthetic polymers were removed from graft copolymers by cold-water extraction and were characterized by their M?_n and DMAEMA·HNO₃ content. Graft copolymers were characterized with respect to per cent add-on, M?_n and DMAEMA·HNO₃ content of grafted polymer, and grafting frequency. Ungrafted synthetic polymers contained a mole percentage of DMAEMA·HNO₃ equal to or greater than that present in the initial monomer mixtures; whereas in most grafted polymers the mole-% DMAEMA·HNO₃ in the grafted branches was less than that in the starting monomers. At all monomer ratios examined, polymer grafted to swollen starch granules contained a higher percentage of DMAEMA·HNO₃ then polymer grafted to unswollen starch. The influence of starch granule swelling on the molecular weight and frequency of grafted branches was correlated with the composition of the initial monomer mixture. It was determined that the effect of granule swelling on graft copolymer structure would be minimal when 25–30 mole-% DMAEMA·HNO₃ was used. In an acetonitrile–water solvent system, reactions with 20 and 50 mole-% DMAEMA·HNO₃ produced graft copolymers with less DMAEMA·HNO₃ in grafted branches than corresponding graft polymerizations run in water. The flocculation of 3% aqueous suspensions of diatomaceous silica was examined with selected starch graft copolymers.     

Graft copolymerization of methoxypoly(ethylene glycohol) methacrylate onto polyacrylonitrile and evaluation of nonthrombogenicity of the copolymer

Methoxypoly(ethylene glycohol) methacrylate was grafted onto polyacrylonitrile in dimethylsulfoxide solution via thioamide formation, where ammonium peroxydisulfate was used as an initiator. Optimum conditions for the graft copolymerization, such as degree of thioamidation of the trunk polymer, feeding concentration of the acrylate and the trunk polymer, and temperature were examined. Also the rate of graft polymerization was found to be proportional to concentrations of the acrylate and the trunk polymer. An increase of the degree of the grafting increased water content of the graft copolymer and decreased interfacial free energy between the copolymer and water. In vivo tests showed that the graft copolymer obtained was highly nonthrombogenic.     

淀粉接枝共聚物微球的合成研究

用V(环己烷)∶V(淀粉溶液)=4∶1构成反相悬浮体系,m(Span60)∶m(Tween60)=2∶1复配为分散剂,在60℃下以K2S2O8-NaHSO3引发N,N’-亚甲基双丙烯酰胺(MBAA)与淀粉的接枝共聚,制备了淀粉接枝共聚物微球。正交实验表明,合成共聚微球的较优工艺条件为:淀粉液浓度20%,引发剂用量0.2 g,MBAA用量0.4 g,油水比为3∶1,乳化剂用量1.0 g。用SEM和粒度分析仪对微球形貌和粒度分布进行了研究,用FT-IR对其结构进行了表征,用XRD,TGA对其物性进行了分析。结果显示,共聚物微球形态圆整,平均粒径50.2μm,微球中存在酰氨基结构,与淀粉颗粒相比,结晶度降低,热稳定性提高。     

Molecular weight distribution of the graft copolymer comprising mixtures of styrene and acrylamiae on cellulose acetate film by means of gel permeation chromatography

Styrene portion of the radiation-induced graft copolymer comprising styrene and acrylamide was separated by acid hydrolysis and the effects of various grafting parameters (e.g., reaction time, reaction temperature, solvents, monomer composition, etc.) on molecular weight distribution were evaluated by means of gel permeation chromatography. When a single monomer or mixture of two monomers are grafted, the molecular weights is found to increase, but polymer dispersity decreases with the increase of reaction time or reaction temperature except at a higher reaction time due to the continuous enlargment of the growing chain through increased swelling and molecular motion of the trapped radicals. At higher reaction time the degradation of the graft chains lead to lower molecular weight and higher polymer dispersity. Effects of solvents (e.g., methanol, ethanol, and t-butanol) on the molecular weight and molecular weight distribution were discussed on the basis of swelling property and chain transfer constants of the solvents. Styrene-type graft radical being long lived compared to acrylamide type, gave long-chain styrene graft with the increase of styrene content in the reaction mixture. A comparison of the effect of one-and two-component systems on a molecular weight distribution is also discussed.     

Preparation of soapless latexes by sonification of starch-based poly(isoprene–co–acrylonitrile) graft reaction mixtures

Graft copolymerization of isoprene (IP) and acrylonitrile (AN) onto gelatinized starch (S) and cationic starch having quaternary amine functionality through cerium(IV) initiation gave grafted side chains of poly(IP–co–AN). Grafts of various compositions are obtained by controlling the amounts and ratios of monomers added to starch. IP alone does not homograft onto gelatinized starch at 25° or 50°C by cerium(IV) initiation and requires the presence of an “initiator–monomer” such as AN to obtain copolymer side chains. Although cografting of IP and AN onto starch depends on AN to initiate radical chains, the ratio employed of the two monomers is critical for graft polymerization to occur. For example, at a molar ratio of IP to AN of 1 or greater, little polymer was produced; at molar ratios in the range of 0.4 to 0.67, considerable amounts of polymer were produced; and at a molar ratio of 0.13 or less, polymerization of AN was greatly retarded. Concentration of HNO₃ in the cerium(IV) reagent and reaction temperature also influence the grafting reaction. Lower HNO₃ concentrations favor grafting at 50°C, while higher acid concentrations favor grafting at 25°C. Starch graft reaction mixtures were sonified at 20 kHz to form latexes that air dry to clear pliable films. Poly(IP–co–AN) obtained by acid hydrolysis of the starch portion of the grafts failed to dissolve in either dimethylformamide or benzene, thus indicating presence of crosslinks. S–g–poly(IP–co–AN), having about one third starch and grafted side chains averaging about 2 parts polymerized IP per part of polymerized AN, was masticated on steel rolls at 100°C to a tough pliable film which was subsequently vulcanized to a rubber.