Structure of gum arabic and its configuration in solution

Gum arabic was found to have an osmotic molecular weight of 250,000, in agreement with earlier determinations. A molecular weight of 365,000 was found by light scattering, somewhat higher than obtained earlier by sedimentation equilibrium analysis but lower than light-scattering values reported by other investigators. The M?_w/M _n ratio, 1.46, is quite low in gum arabic. The angular dependence of light scattering exhibited the upward curvature to be expected of a spherical molecule and a radius of gyration of about 100 A. or less, as estimated from a Zimm plot. Fractionation of the original gum arabic was done by precipitation of a 0.5% solution in aqueous 0.5% NaCl with acetone. Comparison of the curves of viscosity versus molecular weight and the estimated radius of gyration shows that the hydrodynamic volume is less than that of branched dextran of similar molecular weight. The electroviscous effects for gum arabic in aqueous solution were shown by reduced viscosity curves at various acidities and in salt. The degree of dissociation was calculated for each pH level. The minimum intrinsic viscosity was found in 0.04N HCl where the degree of dissociation at pH 1.5 was found to be 0.049. When the acidity was increased, further reduction in viscosity was found to be negligible. Routine determination of the viscosity and molecular weight of the fractions was done in 0.35M NaCl at pH 10 to which 0.25% of the sodium salt of ethylenediaminetetraacetic acid was added as a sequestrant. The intrinsic viscosity in this solvent was nearly as low as in 0.04N HCl. Light-scattering dissymmetries in water and in 0.35M NaCl plus EDTA at pH 10 were similar, 1.13 and 1.09, respectively, which showed that actual expansion of the macroion is not the cause of the large increase in viscosity of gum arabic when the ionic strength of the solvent is reduced. Periodate oxidation of the polymer confirmed the existence of a 1–3-linked backbone of galactose. Subsequent treatment of the oxidized polymer with alkali reduced the osmotic molecular weight to 45,000 but failed to remove oxidized side branches. The oxidized polymer was fractionated by gel permeation chromatography and the intrinsie viscosity–molecular weight relation compared with relations for fractions of the unoxidized polymer and for other branched and crosslinked polymers.     

Conformation of poly(methacrylic acid) in alcohol–water mixtures. II. Methanol,ethanol, n-propanol,and 1,2-ethanediol

The intrinsic viscosity of poly(methacrylic acid) has been studied in mixtures of 0.002N HCI and a series of aliphatic alcohols. The behavior found previously with ethanol is shown to apply in the case of admixture with methanol, n-propanol, and 1,2-ethanediol. The intrinsic viscosity first drops to a minimum and then increases sharply to a maximum. With ethanol and n-propanol the maximum is followed by another minimum and maximum. With methanol and 1,2-ethanediol this effect is absent or much smaller. Methanol and 1,2-ethanediol are equivalent, molecule for molecule, in their influence on the intrinsic viscosity. With ethanol and n-propanol there are in addition one and two shoulders, respectively, in the passage from the first minimum to the first maximum. Good correlation of the data is obtained if alcohol concentration is plotted as the mole fraction of carbon atoms per OH group (in the alcohol). The first maximum in particular was shown to correspond to the point where the number of water molecules per alcohol in the solvent mixture equals the number of C atoms per hydroxyl in the alcohol. The shoulders and first minima were found to correspond to other simple ratios. This behavior reflects changes in alcohol–water structure. The maximum in the case of ethanol was found to be the most pronounced and ethanol seems to possess optimal properties from this point of view.     

Conformation of poly(methacrylic acid) in alcohol–water mixtures. I. Effect of concentration,temperature, pH,and ionic strength

The reduced specific viscosity of poly(methacrylic acid) has been studied in ethanol–0.002N HCI solvent mixtures as a function of polymer concentration, alcohol concentration, and temperature. In addition, experiments were performed at different HCI concentrations and with KCI instead of HCI. Both intrinsic viscosity and Huggins coefficient were shown to undergo unusually strong variations. Two minima and two maxima could be demonstrated in intrinsic viscosity. The Huggins coefficient seems to show corresponding variations. The first minimum in intrinsic viscosity indicates that the coil volume has collapsed almost to an Einstein sphere. In this region the Huggins coefficient is extremely large (of order 10²) and is controlled by coil association. It was shown that several forms of intramolecular interaction must be assumed to be competing to account for this behavior. The presence of HCI, particularly in the preponderantly aqueous phase, is required to suppress the polyelectrolyte effect. It is found, however, that the behavior of the solutions at relatively high ethanol concentrations is more sensitive to HCI content than is that of highly aqueous solutions. KCI can be used to replace HCI over most of the range. Increase in temperature shifts the turning points of the curves to lower alcohol concentrations. Some evidence has been found that the association constant giving rise to dimers increase with rate of shear. The importance of poly(methacrylic acid) as a chemically simple model substance for various biopolymer effects is stressed.     

Upturn effect in the Non-Newtonian intrinsic viscosity of polymer solutions. II. Polyisobutylene in polybutene oil

With an increasing gradient, the intrinsic viscosity of a high molecular weight polyisobutylene (M?_n = 7 × 10⁶) in polybutene oil L.100 (η_s = 5 poise) first drops to a minimum and then rises again. The minimum occurs at β = M[η]₀η_sG/NkT = 240, which is about ten times the value predicted by the dumbbell model. Such a shift to larger gradient is in good agreement with the more realistic necklace model of macromolecules in a good solvent. The increase of intrinsic viscosity after the minimum is nearly linear with the gradient and continues beyond the value at zero gradient. Experiments with capillaries of different length-to-diameter ratios yield identical flow curves so that one may exclude the possibility that the observed upturn is an artifact caused by end effects or time dependence of viscosity.     

Dilute solution properties of a polyurethane. I. Linear polymers

A linear polyurethane of high molecular weight was prepared in solution by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4-phenyl isocyanate). The polymer was fractionated by using a direct sequential extraction procedure, with a solvent–nonsolvent system consisting of N,N′-dimethylformamide (DMF) and acetone (A). The resulting fractions were characterized by viscosity and lightscattering measurements. The relationship between the intrinsic viscosity and molecular weight was found in DMF at 25°C. to be [η] = 3.64 × 10^?4M^0.71. The unperturbed polymer chain dimensions were determined from intrinsic viscosity measurements carried out under experimentally determined theta conditions.     

Polymerization by oxidative coupling. IV.. Synthesis and properties of poly(2-methyl-6-phenylphenylene ether)

Copper-amine catalyst systems which polymerize 2-methyl-6-phenylphenol to high molecular weight polymer are described. With CuCl and N,N,N ′,N′-tetramethyl-1,3-butanediamine (TMBD), an intrinsic viscosity of 1.56 dl/g was obtained. Faster rates of polymerization resulted with a CuBr-TMBD catalyst. Catalysts from other tertiary amines and mixtures of tertiary amines also produced high polymer. Pyridine and diethylamine catalyst were less active. Samples of polymer were isolated at different stages of the polymerization. Measurements of viscosity, osmotic pressure, light scattering, gel permeation, hydroxyl groups, nitrogen content, and chemical reactivity were made on the samples. Below a molecular weight value of M?_n 60,000, M?_n/M?_w was 2.0. At higher molecular weights, there was a broadening in molecular weight distribution. No major change in the molar concentration of the “;head” endgroups with increasing molecular weight was detected by infrared analysis. However, nitrogen analyses, chemical reactivity studies, and the M?_n/M?_w ratio suggested the chemical nature of the “head” end had changed. The relationships between intrinsic viscosity in chloroform at 25°C and M?_n and M?_w for unfractionated polymer samples are log [η] = ?4.26 + 0.84 log M?_n and log [η] = ?3.86 + 0.70 log M?_w.     

Preparation of poly(N-normalpropyl- acrylamide) gel beads

 The gel beads of N-normal-propylacrylamide are prepared by the radical copolymerization of N-normalpropylacrylamide and N,N′-methylene-bis-acrylamide in water. The optimum reaction conditions to obtain the gel beads are revealed from the phase diagram of the reaction system together with the scanning electron microscopy of the reaction products. The scanning electron microscopy of the reaction products also indicates the formation of the spherical gel beads of sub-micron size ranging from 250 to 500 nm in diameter. The viscosity measurements of the suspension of the gel beads indicate that the concentration dependence of the viscosity of the suspension is well described by Einstein’s theory of the viscosity of colloidal particles. The intrinsic viscosity of the suspension of gel beads is then determined. The density of the gel beads, which was obtained from the intrinsic viscosity of the suspension, indicates that the gel beads are in the swollen state at a temperature of 20 ^°C. Received: 12 September 1997 Accepted: 17 December 1997     

Relaxation characteristics and intrinsic birefringence and viscosity of polystyrene solutions for a wide range of molecular weights

A comparison is made between measurements on polystyrene solutions and the relaxation characteristics and intrinsic birefringence and viscosity given by the theory for the flexible Gaussian chain of variable number of segments and with internal viscosity and internal hydrodynamic interaction. This is done in order to determine the applicability of the theory to polymers over a wide range of molecular weights, including the low molecular weight range in which there may be conflict with the theoretical assumption of chains having a large number of segments. The longest, terminal relaxation time and the number of chain segments are determined from measurements of the frequency dependence of oscillatory flow birefringence while the intrinsic birefringence and viscosity are determined from steady flow measurements. The range of molecular weights studied is from approximately 900 at 10⁶. It is found that the segment weight is approximately 1000 and the number of segments is in direct proportion to the molecular weight for the range from 1 to 1000 segments. The terminal relaxation time has a molecular weight dependence of the type given by the theory but with better agreement for higher molecular weights. While the measured dependences of the intrinsic viscosity and birefringence are in agreement with theory for molecular weights greater than 5 × 10⁴, they deviate significantly for molecular weights below 1 × 10⁴. The ratio of the intrinsic birefringence to intrinsic viscosity, which in theory is a constant independent of molecular weight, is found to change at the lower molecular weights.     

Multichain copoly(α-amino acid). II. Preparation and properties of multi-Nϵ-poly(γ-benzyl-L-glutamyl)copoly(L-lysine γ-methyl-L-glutamate)

A number of multi-N^?-poly(γ-benzyl-L -glutamyl)copoly(L -lysine γ-methyl-L -glutamate)s with branches having various degrees of polymerization and with various intervals of the grafting sites in the core molecule were prepared in N,N-dimethylformamide containing dimethyl sulfoxide by the reaction of N-carboxy anhydride of γ-benzyl L -glutamate with random copoly(L -lysine γ-methyl-L -glutamate)s of different composition with various anhydride-initiator ratios. The relationship between the intrinsic viscosity measured in a coil solvent, dichloroacetic acid (DCA), and the number-average molecular weight determined by osmometry was found to be expressed by the Mark–Houwink–Sakurada equation for the multichain copoly(α-amino acid)s which were made from the same polymeric initiator. The observed α values of the multichain copoly(α-amino acid)s in the equation were lower than that of linear poly(γ-benzyl-L -glutamate). The solvent induced helix–coil transition of the multichain copolymer was investigated in the chloroform?DCA system by the ORD technique. Two kinds of transition regions were clearly distinguished: The α-helices of the core molecules underwent the transition at lower DCA concentration and those of the branch chains at higher DCA concentration. The reduced viscosity of the multichain copoly-(α-amino acid) increased slightly between the two transition regions, in contrast to the large decrease in the reduced viscosity of linear poly(γ-benzyl-L -glutamate) during the helix–coil transition.     

Interpretation of spin relaxation in polyisobutylene in terms of specific motions

Porton and carbon spin-lattice relaxation times T₁ and nuclear Overhauser enhancements are interpreted in terms of motions likely in linear polyisobutylene. Most of the interpretation is based on relaxation data in the literature, but some additional ¹H and ¹³C pulse Fourier transform experiments were conducted to resolve a disagreement in the literature concerning cross relaxation between the two types of protons present in polyisobutylene. Spin relaxation in solution and the bulk is accounted for by three specific motions considered as independent sources of motional modulation of the dipole–dipole interaction. The first motion is overall isotropic rotatory diffusion which has a known dependence on molecular weight, intrinsic viscosity, and solvent viscosity for polymers in solution, and a known dependence on molecular weight and viscosity for bulk polymers. The effects of overall tumbling account for a decrease of T₁ for the methylene and methyl carbons with increasing molecular weight in solution and increase of T₁ of methylene carbons with molecular weight in bulk. The second motion considered is backbone rearrangements caused by the three-bond jump. This motion dominates relaxation of the methylene carbons either in solution or in the bulk allowing for the determination of the associated correlation time. The correlation time characterizing the occurrence of the three-bond jump in a 5% (wt/vol) solution in CCI₄ at 45°C is 58 psec, and in the bulk at 45°C it is 11 nsec. The last motion included in the model is methyl-group rotation about the threefold symmetry axis. The methyl-group rotational correlation time is 0.20 nsec in a 5% (wt/vol) solution in CCI₄ at 45°C and 0.33 nsec in the bulk at 45°C. The concentration dependence of the backbone motion contrasts strongly with the corresponding dependence of methyl-group rotation.     

Conformational transition of the copolymer of maleic acid and styrene in aqueous solution

The pH-induced conformational transition of maleic acid–styrene copolymer in aqueous NaCl solutions has been investigated by potentiometric titration, viscosimetry, and dilatometry. The dependence of the intrinsic viscosity on the degree of neutralization of the primary carboxyl group indicates that the transition is from a compact to a loosely coiled form. From titration data, the standard free energy change ΔG° per monomole, for the transition from the uncharged compact from to the hypothetical uncharged loosely coiled one is estimated to be about 370–280 cal/monomole for concentrations ranging from 0.0092 to 0.2739N in NaCl. The value of ΔG° decreases slightly with increasing temperature in the temperature range from 15 to 30°C. The volume change associated with the transition was found to be ?0.6 ml in 0.01N NaCl and ?0.9 ml in 0.09N NaCl per monomole, respectively. From viscosity data, changes of molecular dimensions and the long-range interaction parameter through the transition region have been discussed.     

Association of polyacrylonitrile prepared by low-temperature,solution polymerization with an organometallic catalyst

The weight-average molecular weights of polymers of acrylonitrile prepared by a free-radical initiator and an organometallic catalyst have been determined by lightscattering measurements in N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide at 25°C. and in dimethyl sulfoxide at 140°C. The apparent molecular weights of the polymers prepared with the NaAlEt₃S(i-Pr) catalyst in DMF at ?78°C. (referred to as high-melting polymers) changed from 54,800, 82,700, and 480,000 when measured in DMF at 25°C. to 36,000, 41,600, and 225,000 when measured in DMSO at 140°C., whereas the molecular weights of the free-radical polymers remained unchanged. Furthermore, from results obtained in DMSO at 140°C., The intrinsic viscosity–molecular-weight relationships were found to be identical for the high-melting and the free-radical polymer and in substantial agreement with an equation reported by Cleland and Stockmayer. The apparent decrease in molecular weight of the high-melting polymer from 25 to 140°C. indicates rather clearly that the high-melting polymers are associated in DMF at 25°C. The “aggregates,” even though present only at low concentrations, raised the weight-average molecular weight markedly but affected the number-average molecular weight only slightly, thus giving a high M?_w/M?_n ratio. It appears likely that when temperature and solvent are such that association does not occur, linear PAN's will have approximately the same intrinsic viscosity–molecular weight relationship (subject of course to slight change by polydispersity). The often reported abnormal molecular weight of samples prepared by solution polymerization especially at low temperatures, may be attributed to branching, or to an association, as reported here. The nature of association of PAN in dilute solution is also discussed.     

Room-temperature polycondensation of β-amino acid derivatives. V. Synthesis of hydrophilic polyamide by the polycondensation of β-amino acid derivatives

N-(Hydroxyalkyl) β-alanine ester which was obtained from amino alcohol and acrylate yielded polyamide at room temperature in the presence of a basic catalyst. Alkali and alkali earth metal alkoxides had a strong catalytic effect on the room-temperature polycondensation of N-(hydroxyethyl)-β-alanine esters. The catalytic activity of metal alkoxides decreased in the order: Li > Na > K > Cs and Ca > Zn > Mg. Aluminum and titanium alkoxide had a weak catalytic effect, while boron (III), tin (IV), antimony (V), and tellurium (VI) alkoxides did not show any catalytic activity for the polycondensation. It was also found that solvent had an effect on the course of the polycondensation of N-(hydroxyethyl)-β-alanine esters, and the highest molecular weight polymer was formed only in methanol solution. The solid-phase polycondensation of the low molecular weight prepolymer resulted in a high molecular weight polymer with an inherent viscosity of 1.0 in the presence of a catalytic amount of phosphoric acid. The polymer obtained is hydrophilic and its moisture absorption is more than twice that of nylon 6.     

Flow birefringence and optical anisotropy of poly(N-vinylpyrrolidone) molecules

Concentration dependences of flow birefringence and viscosity of poly(N-vinylpyrrolidone) solutions in water and benzyl alcohol are investigated. The intrinsic anisotropy for a poly(N-vinylpyrrolidone) macromolecular segment, (α₁ ? α₂) = ?(82 ± 8) × 10^?25 cm³, is determined from the results of birefringence measurements in benzyl alcohol. For aqueous solutions, a strong concentration dependence of the specific anisotropy of solution is obtained, a result that may be explained by the heterogeneity of coils. A model allowing for this heterogeneity is suggested. It makes it possible to fit the concentration dependence to a hyperbolic function, to separate contributions of heterogeneity anisotropy and form anisotropy to the birefringence of a solution, and to estimate the segment asymmetry parameter as p = 3.0 ± 0.5.     

Polymerization of N-vinylcarbazole by chlorides and oxychlorides of some group V elements. II. Kinetics and mechanism of the polymerization initiated by arsenic trichloride

The polymerization of N-vinylcarbazole (NVC) initiated by AsCl₃ in benzene and nitrobenzene solvents was studied at 33°C. R_p is proportional to the first power of the initiator concentration. R_p varies in a first-order manner with NVC concentration up to a certain optimum concentration of the latter, after which it falls and ultimately levels off. The rate and the molecular weight are depressed by the addition of various amines, preformed poly-NVC, and water. HCl does not have any cocatalytic effect on the system. Rate and the molecular weight are increased in nitrobenzene. The degree of polymerization stays independent of the initiator and NVC concentration and also of increasing conversion. These results suggest a conventional cationic mechanism, and overrule the possibility of a cation radical initiation. A suitable kinetic scheme has been proposed in conformity with the findings.     

Intrinsic viscosity and axial extension ratio of random-coiling macromolecules in a hydrodynamic shear field

The shear dependence of the intrinsic viscosity and the conformation of high molecular weight polyisobutylene in dilute solutions of decahydronaphthalene under shear were determined simultaneously. Experimental variables investigated were the shear rate (0 to 2 × 10³ sec^?1), the molecular weight (1.0 × 10⁷ to 1.7 × 10⁷) and the polymer concentration (1.8 × 10^?4 to 8.4 × 10^?4 g/cc). Correlations allowing concentration and shear rate normalization for any one sample are described. Conformational extention ratios along the orientation direction of the deformed molecule to 1.42 and intrinsic viscosity ratios (sheared to zero shear) to 0.5 were observed.     

Corresponding state relations for the Newtonian viscosity of polymer solutions. II. Further systems and concentrated solutions

In earlier work we have indicated a superposition principle for moderately concentrated mixtures (c ? 2/[η]) in good and poor solvents. By an examination of data on a number of vinyl polymers and cellulose derivatives in good as well as poor solvents, the validity of this principle is extended to concentrated solutions (c ? 50%). The characteristic concentration factor γ is proportional to M over the whole concentration range, with 0.47 ≤ a₁ ≤ 1.10 being larger for good than for poor solvents, the result obtained earlier. Significant deviations from this relationship are noted in good solvents for those low molecular weights at which deviations from the usual intrinsic viscosity relationship occur. This may be related to the expansion factor of the polymer coil. On the basis of these results, the concentration and molecular weight dependence of the viscosity in the concentrated solution can be related to each other in terms of the parameter a₁ and thus to thermodynamic characteristics. In this manner a bridge between the relatively dilute and concentrated regions is established. Currently used semiempirical expressions are analyzed in terms of these results. For the polystyrene–cyclohexane systems and θ ? 9 ≦ T ≦ θ + 3, γ can be identified with the critical concentration for phase separation. Provided an “entanglement” concentration c_e exists, in the neighbourhood of which the concentration dependence of the viscosity changes reapidly, γ can alternatively be shown to be proportional to c_e, or c_e ∝ M. The temperature reduction scheme suggested earlier remains to be investigated.     

Solution properties and chain conformation characteristics of cellulose tricarbanilate

Fractions of two cellulose tricarbanilate samples were characterized by light-scattering (weight-average molecular weight, second virial coefficient, mean-square radius of gyration), gel permeation chromatography (polydispersity index), and viscometry (intrinsic viscosity) in tetrahydrofuran and acetone. The intrinsic viscosity data were analyzed in terms of the theory developed for the continuous wormlike cylinder model, and the chain parameters (Kuhn statistical segment length λ^?1, chain diameter d, and shift factor M_L) were evaluated. The molecular-weight dependence of the mean-square radius of gyration in tetrahydrofuran was calculated for the Kratky—Porod chain model and compared with the experimental results. Data on the intrinsic viscosity and radii of gyration for other solvents at temperatures from 0 to 100°C were analyzed in the same way, and the effects of solvent and temperature on the statistical segment length were evaluated. Polymer—solvent interaction parameters were estimated from the second virial coefficients.     

Generalized correlations for molecular weight and concentration dependence of zero-shear viscosity of high polymer solutions

Data are presented to show that two correlations of viscosity–concentration data are useful representations for data over wide ranges of molecular weight and up to at least moderately high concentrations for both good and fair solvents. Low molecular weight polymer solutions (below the critical entanglement molecular weight M_c) generally have higher viscosities than predicted by the correlations. One correlation is η_sp/c[η] versus k′[η], where η_sp is specific viscosity, c is polymer concentration, [η] is intrinsic viscosity, and k′ is the Huggins constant. A standard curve for good solvent systems has been defined up to k′[η]c ≈? 3. It can also be used for fair solvents up to k′[η]c ≈? 1.25· low estimates are obtained at higher values. A simpler and more useful correlation is η_R versus c[η], where η_R is relative viscosity. Fair solvent viscosities can be predicted from the good solvent curve up to c[η] ≈? 3, above which estimates are low. Poor solvent data can also be correlated as η_R versus c[η] for molecular weights below 1 to 2 × 10⁵.