Specific Refractive Index Increment Research Articles

Calculation of the dispersion of specific refractive index increments

Calculation of the dispersion of specific refractive index increments

Characterization of styrene-butadiene copolymers by light scattering

The general theory of Stockmayer and Benoit and their coworkers yields the weight average molecular weight of a binary copolymer and parameters which reflect the heterogeneity of chemical composition of the copolymer, using light scattering data from solutions in at least three solvents with different refractive indices. Although this theory has been applied successfully to block and graft copolymers and to mixtures of homopolymers, it has not seemed to be valid for random copolymers. In this report, molecular weight and heterogeneity parameters of a number of gel-free styrene-butadiene emulsion copolymers were estimated from results of light scattering measurements in toluene, cyclohexane and 1,2-dichloroethane. The calculated heterogeneity parameters contradict expectations from copolymerization theory and appear to be in error. It is suggested that the particular difficulties with statistical copolymers result from a dependence of specific refractive index increment on polymer molecular weight. This dependence varies with different solvents. The effect is illustrated by experimental results for polystyrenes in toluene, cyclohexane and 1,2-dichloroethane. Accurate study of copolymer characteristics requires selection of solvents such that the differences between specific refractive indices of the appropriate homopolymer solutions do not depend strongly on polymer molecular weight in the molecular weight range which corresponds to the sum of homopolymer sequences in the particular copolymers. The apparent inapplicability of the theory to random copolymers appears to be an artifact of the particular systems which were studied.

Specific refractive index increments of polymer systems at four wavelengths

To ascertain whether a low-angle laser scattering photometer under development (76) would give absolute molecular weights for biological macromolecules, it was necessary to obtain specific refractive index increments for light of wavelength 632.8 nm (He-Ne laser). Such data were unavailable for polymers although calibration data have been reported (27) for 589.3 and 632.8 nm for a series of electrolytic solutions. Anderson ( 7 ) also calibrated a commercial differential refractometer resembling that of Brice and Halwer ( 5 ) using the data obtained on salt solutions interferometrically by Kruis (20), and more recently Block ( 4 ) described a technique for using 632.8-nm radiation from a secondary source in differential refractometry. None of these investigators determined specific refractive index increments of polymer systems. We report refractive index increments for a number of polymers determined with the commercially available Brice-Phoenix differential refractometer at four wavelengths from 632.8 to 435.8 nm. Calibration measurements were made at 24.2 f 0.1C by use of potassium chloride and sucrose, followed by studies of polystyrene, bovine serum albumin, D-glyceraldehyde phosphate dehydrogenase, polydimethylsiloxane, amylopectin, and deoxyribonucleic acid (DNA).

Application of specific refractive index increments for determination of partial specific volumes of dissolved macromolecules

Application of specific refractive index increments for determination of partial specific volumes of dissolved macromolecules

The specific refractive index increments of polyisoprenes in various solvents

Specific refractive index increments of polyisoprenes with high cis-1,4 content have been determined in six solvents at 20� and λ 546 nm. A linear relationship was found between the refractive index increment dn/dc = n and the refractive index of the solvent nl : N45620 = 1.687 - 1.105n1 The results are compared with the best values reported for natural rubber which are usually employed for polyisoprene in light scattering measurements.

The intrinsic viscosity‐molecular weight relationship for polypropylene

AbstractMeasurements of intrinsic viscosity in decalin at 135°C and light scattering in α‐chloronaphthalene at 145°C were performed for several polypropylene fractions of molecular weight ranging up to 2.106. The specific refractive index increment at 436 mμ for the α‐chloronaphthalene solution was found to be −0.231 ml/g, which is considerably higher than those reported by CHIANG and others authors. However, no significant disparity is observed between the results of light scattering measurements by CHIANG and the present author. The intrinsic viscosity‐molecular weight relationship obtained is: [η] = 1.15·10−4 M, which is in good agreement with that reported by KINSINGER and HUGHES. This relationship is also compared with those of other authors observed at different conditions of viscosity measurements.

Deoxyribonucleate solutions: sedimentation in a density gradient, partial specific volumes, density and refractive index increments, and preferential interactions.

AbstractDensity increments (∂ρ/∂c2)°μ in solutions of NaDNA in NaCl and CsDNA in CsCl were determined over a wide range of salt concentrations; calf thymus DNA, fragmented by sonic irradiation to a molecular weight of 4–6 × 105 was used. The partial specific volume v̄2° of NaDNA at 25°C was found to ho 0.500 ml/g in water, and that of CsDNA 0.440 ml/g. Both values increase with increasing NaCl and CsCl concentration. Refractive index increments under various experimental conditions were also determined. The relevance of the density increments (at constant, chemical potential of diffusible solutes) to equilibrium sedimentation in a density gradient and the evaluation of molecular weights is discussed. Distribution coefficients of diffusible components, sometimes referred to as preferential solvation or net hydration, were derived from the density increments and partial volumes and compared with direct experimental results, whenever available, from membrane distribution and isopiestic distillation. The thermo‐dynamic significance of the distribution coefficients as well as possible interpretations in terms of specific molecular mechanisms are considered.

Solution properties of copolymer of p‐chlorostyrene and methyl methacrylate

AbstractThe monomer reactivity ratios in the free radical copolymerization of methyl methacrylate and p‐chlorostyrene were obtained and an azeotropic copolymer containing the 0.484 mole fraction of methyl methacrylate was prepared. The copolymer was fractionated into nine fractions, which on the basis of their chlorine content and specific refractive index increments, were found to be homogeneous in their chemical composition. The solution behaviour of these fractions was examined by viscosity, osmotic pressure and light‐scattering techniques. The weight‐average molecular weights obtained in dioxane, chloroform and 78:22 v/v mixture of trans‐decalin and trichloro ethylene (Θ solvent at 22.3°C) were found to be identical but those obtained from benzene were as much as 80% higher, depending on the molecular weight. The data were treated by the method of STOCKMAYER and BENOIT and the deviation and square‐deviation of the chemical composition was obtained as zero and proportional to M1.5, respectively. The value of exponent “a” in the KUHN‐HOUWINK equation[η] = KMa obtained by use of the number‐average molecular weight and corrected weight‐average molecular weight, was identical but the apparent weight‐average molecular weights obtained in benzene gave a low value of “a” confirming the applicability of the STOCKMAYER‐BENOIT relationships. The value of the constant K obtained for the copolymer in the theta solvent was 6.4·10−4 compared with 4.9·10−4 and 5.0·10−4 obtained for poly(methyl methacrylate) and poly‐p‐chlorostyrene, respectively, indicating a 10% higher dimension for the copolymer.

Specific refractive index increments of polymer solutions. Part II. Scope and Applications

Specific refractive index increments of polymer solutions. Part II. Scope and Applications

Specific refractive index increments of polymers and copolymers in several solvents

Differential refractometry has been used to obtain accurate values of the specific refractive index increments for the following polymers in several solvents: polystyrene, poly(methyl methacrylate), poly(4-vinyl pyridine), block copolymers of styrene with methyl methacrylate and of styrene with 4-vinyl pyridine. Examples of the application of the d n/d c parameter to determine the composition of copolymers and to detect differences in stereochemical configuration of polymers are also given. The Gladstone—Dale equation is shown to be a convenient method to predict d n/d c from the refractive index of the solvent and values of the refractive index of the polymer and its specific volume.

Specific refractive index increments of polymer solutions. Part II. Scope and applications

AbstractThe data of Part I are examined in the light of accepted theories. The specific refractive index increment ñ of most polymer solutions lies between −0.2 and +0.2 ml./g., although larger values can obtain in circumstances wherein the scattering unit is unusually large, e.g., solutions of partially neutralized polyacids the units of which contain the gegenions. ñ depends on the indices of solvent n1 and polymer n2. Among common solvents, water and 1‐bromonaphthalene are capable of affording high positive and negative values, respectively, for n. The Gladstone‐Dale rule applies rigorously to pure and mixed solvents, but the Lorenz‐Lorentz expression is preferable for evaluating n2. Results of current theories applied to mixed solvents and copolymers are summarized. In the former, the true molecular weight M is determined by using ñ and the variation of solvent index with composition. For a copolymer of monomers A and B, M as well as Ma and Mb are obtainable by using ñ, ña, and ñb. Dispersion is expressed as (ñ)λ = (ñ)436[D′ + D″/λ2] at a wavelength λ, and dispersive constants D′ and D″ are evaluated for some solutions. ∂ñ/∂T is generally 3.2 (±2.3) × 10–4 ml./g./°C. and changes very little with λ. When ñ increases with M, the limiting characteristic value is derived (at 1/M = 0) from a plot of ñ versus 1/M. ñ can be determined to a maximum accuracy of 1% by using n2 calculated from the Lorenz‐Lorentz equation and the experimental partial specific volume.

Specific refractive index increments of polymer solutions. Part I. Literature values

AbstractThe specific refractive index increments of 158 natural and synthetic polymers and copolymers in pure and mixed solvents have been collated. Wherever possible the temperature and wavelength (generally 436 and/or 546mμ) are quoted.

The physical properties of a glycoprotein from bovine cortical bone (bone sialoprotein)

Physicochemical studies have been made of two different preparations of bone sialoprotein, a glycoprotein from bovine cortical bone, which contains a high proportion of sialic acid groups. Determinations have been made of s 0 20, w , diffusion coefficient, molecular weight, sedimentation coefficient distribution, optical rotatory dispersion curves, mobility during free boundary electrophoresis, partial specific volume and refractive index increment. The two preparations differed slightly in molecular weight, but both are small molecules, polydisperse but homogeneous with respect to centrifugation and electrophoresis. Their frictional coefficients are higher than that expected for globular molecules and they have little or no helical content. The results are discussed in the light of available analytical and structural information.

Interference refractometry of polymer solutions

AbstractThe specific refractive index increments of a number of polymer/solvent systems have been measured by means of an interference refractometer. The technique described permits rapid and precise evaluation of dn/dc, as well as eliminating the difficulties normally associated with interferometric measurements in organic solvents.

The temperature dependence of the specific refractive index increment of polyethylene in various solvents

AbstractThe specific refractive index increment, dn/dc, of polyethylene in α‐chloronaphthalene, tetralin, and n‐decane bas been determined as a function of temperature in the range of 50–80°C. The value of dn/dc was found to be a linear function of the refractive index of the solvent. The temperature coefficient of dn/dc of polyethylene in α‐chloronaphthalene, tetralin, and n‐decane was found to be approximately 0.1 × 10−4, 0.96 × 10−4, and 2.43 × 10−4 cc./g. °C, respectively. There results are interpreted on the basis of the Gladstone‐Dale equation. A simple modification of the Brice‐Phoenix differential refractometer for use at moderately high temperatures is described.

Sedimentation analysis of styrene–butadiene copolymer rubber

AbstractMethyl n‐propyl ketone (MNPK) at 21°C. and methyl isobutyl ketone (MIBK) at 46°C. are found to be theta conditions for a styrene–butadiene copolymer rubber commercially designated as SBR‐1500. Data for specific refractive index increment and density indicate that these solvents are appropriate for ultracentrifugation of this polymer by the method of schlieren optics. Sedimentation measurements are made on one whole polymer and six fractions in MNPK at 21°C. It is demonstrated that in this theta solvent the distribution of sedimentation coefficient s (at the limit of zero concentration) of a given SBR‐1500 can be determined, with a good accuracy, from a single sedimentation run at one nonzero concentration below 0.4 g./dl. A relation between s and molecular weight M necessary to convert this distribution of s to the distribution of M is derived by making use of the theory of Flory which correlates s limiting viscosity number, and M. It is believed that the theta conditions and the procedure of analysis presented in this paper are readily utilized for heterogeneity studies on this particular type of synthetic rubber SBR‐1500.