Molar Mass Determination Research Articles

A new mark-Houwink equation for linear poly(ethylene imine)

A new Mark-Houwink equation for linear poly(ethylene imine) has been established in the molar mass range 2 × 10 3 < M w < 3 × 10 4 g mol −1 . The equation, resulting from viscosity measurements combined with weight-average molar mass determinations by light scattering in methanolic solution at 25°C, was found to be: [η] = (1.04 × 10 −2) M 0.95 w . The value of the exponent in the equation indicates the rigid structure of the polymer.

Differential vapour pressure osmometry—I. Description of the method

A differential technique in vapour pressure osmosis is described. It allows accurate determination of thermodynamic parameters over a large concentration range for various temperatures. By measuring the osmotic vapour pressures between two solutions with various concentration differences and using an extrapolation procedure analogous to the Zimm-plot-extrapolation in light-scattering, the differential function of the osmotic pressure is obtained. The applicability of the method is demonstrated with the determination of the number-average molar mass of the polymer and the Flory-Huggins interaction parameters, χ 1 and χ 2, of the system polydimethylsiloxane/cyclohexane.

Measurement of Mass and Surface Stress at One Electrode of a Quartz Oscillator

AbstractThe theory for the calculation of changes of mass and surface stress from frequency measurements at a quartz oscillator subject to different onesided pressures is outlined. The various contributions to apparent changes of the mass are discussed. Experiments refer to the determination of effective molar masses of potassium ions and fluoride ions during electrostatic adsorption and of chemisorbed lead both on polycrystalline gold by a comparison of masses to charges. Effective molar masses of adsorbed species can also be determined by comparison of mass changes to surface concentrations e.g. determined by the radiotracer method as in the example of the adsorption of chloride at the passivating oxide film on iron. The density of very thin films like the passivating oxide film can be obtained by comparing mass changes to thicknesses from optical measurements. In agreement with theoretical expectation, compressive surface stresses were qualitatively found for the underpotential deposition of lead on gold. In the growing oxide film on passive iron very large compressive lateral pressures were observed.

Molecular characterization of gelatin by light scattering

AbstractIn aqueous KSCN solutions the salt is preferentially desorbed from the domain of gelatin molecules, similarly to synthetic polyelectrolytes. Light‐scattering measurements in gelatin solutions in 0,5 M KSCN and in a single solvent (formamide) show that both solvents are suited for the molecular characterization of gelatin at room temperature. Neglecting the effect of selective sorption in salt solutions does not cause any considerable error in the molar mass determination of gelatin.

Effects of 2,4-ionenes of different molar masses on the oxidative coupling of thiol catalyzed by cobaltphthalocyanine

A photometric method is developed for the determination of the molar mass of 2,4-ionene by attaching a chromophoric moiety to its end-groups. Molar mass determination of these polyelectrolytes by acid-base titration of the amine end-groups is also possible, and confirms the photometric method. The effects of molar mass of 2,4-ionenes on the oxidative coupling of 2-mercaptoethanol (ME) was studied in the presence of cobalt(II)phthalocyanine-tetra-sodium-sulphonate (CoTSPc). Monomeric analogues of 2,4-ionene showed no increase of reaction rate as compared with the polymer-free system. However, relatively low molar mass ionene ( M n = 1740 ) showed a dramatic increase of reaction rate. The reactivity showed an optimum around pH = 8. Saturation kinetics (Michaelis-Menten kinetics) were observed. The calculated turnover number was 3200 sec −1 and 3600 sec −1 for M n = 6600 and M n = 1740 , respectively. The stoichiometry of the reaction was disturbed at low thiol concentration.

Molar mass determination of the polysaccharide associated with coccoliths of emiliania huxleyi

Emiliania huxleyi is a marine alga which produces coccoliths, elaborate calcified structures consisting of CaCO 3 and a water-soluble acidic polysaccharide. The polysaccharide was subjected to light scattering measurements to determine the weight-average molar mass ( M w ) and osmometry to assess the number-average molar mass ( M n ). Values of M w of 88,600 ± 3200 g/mol and of M n of 49,100 ± 1500 g/mol were found. These experiments were performed with a polysaccharide mainly in the Na + form. Replacement of Na + by Ca 2+ did not significantly affect the weight-average molar mass or the second virial coefficient. The values of the refractive index increment of these salts were different [(d n/d c)Na + = 0.145 ± 0.004 ml/g; (d n/d c) Ca 2+ = 0.090 ± 0.002 ml/g], indicating a possible conformational change in the molecule.

IR‐und UV‐spektroskopische Eigenschaften einer homologen Reihe von molekulareinheitlichen, 12gliedrige Ringe enthaltenden Leiteroligomeren

AbstractThe reactions of multiple acrylates of oligo[(hydroxyphenylene)methylene] s (2a–2f), strongly diluted in boiling benzene, with 2,2′‐azoisobutyronitrile in a mole ratio of 1:10, were investigated. The elemental analysis and the determination of relative molar masses of the resulting products (3, 4, 5, 6a, 6b, 7a and 7b) demonstrate that their molecules contain two nitrile groups. These data, together with the IR and UV spectra, show that the products are molecularly uniform ladder oligomers with two 1‐cyano‐1‐methylethyl groups on both ends.

Anionic polymerization of β‐nitrostyrenes

AbstractThe rate of polymerization of β‐nitrostyrene initiated by sodium alkoxide was setudied gravimetrically. The rate was found to be first order with respect to monomer concentration and first order with respect to initiator concentration. Rate constants in the order of 0,25 dm3 · mol−1 · s−1 were obtained at 15°C, 20°C, and 25°C for the polymerization of β‐nitrostyrene, p‐methoxy‐β‐nitrostyrene, and p‐methyl‐β‐nitrostyrene initiated by sodium methoxide and by sodium ethoxide. The activation energy of polymerizations initiated by sodium methoxide and by sodium ethoxide was ∼24 kJ · mol−1 and ∼ 16 kJ · mol−1, respectively. The number average degree of polymerization of poly(β‐nitrostyrene)s was determined by polymerization of the monomer in the pressence of 14C‐alkanol. This is the first time that accurate number average molar masses of poly(β‐nitrostyrene)s have been reported since conventional methods of molar mass determination cannot be used owing to the insolubility of these polymers in most common organic solvents.

Absolute determination of molar masses of standard polystyrenes by means of sedimentation‐diffusion measurements in cyclohexane

AbstractAccurate measurements of the sedimentation coefficients at unit pressure and zero‐concentration s, the diffusion coefficients at zero concentration D0, and the intrinsic viscosities [η] were conducted at theta‐conditions (cyclohexane, 34,5°C) on 11 polystryrene standard samples with narrow molar mass distribution. These samples with nominal mass‐average molar masses (5 · 104 &lt; Mw &lt; 2 · 106 g · mol−1), provided by three manufacturers for the use as calibration standards, were the same as in the previous paper of this series summarizing our measurements in toluene. Logarithmic correlations between s, D0 and [η] are linear with deviations lower than ± 3% and indicate good consistency of all three independent sets of measured quantities. The molar masses MsD as determined from s and D0 by means of the Svedberg equation are in very good accordance with those previously determined in toluene, but for most samples the MsD are lower than the nominal values Mw as given by the manufacturers. For some standards the deviations amount to 15−35% and cannot be explained by experimental errors or by the polydispersity of the samples. On the other hand, two pairs of standards exhibit the same values of s, D0 and [η] in both solvents, although the nominal molar masses differ by 20%. These results lead to the conclusion that the experimentally determined MsD values are more reliable characteristics of the standard samples than the nominal Mw values and that the sedimentation‐diffusion technique is a powerful, though laborious, tool for an absolute determination of the molar mass.

Allowance for polymolecularity in polymer structure‐property relationships

AbstractRelations between molar mass M and molar mass dependent properties E of polymers are mostly strictly valid only for monomolecular samples i: For polymolecular polymer samples the corresponding averages Mav and Eav must be applied: Provided the kind of average (number‐, weight‐ or any general average) of e.g. Mav is known, the corresponding average Eav is given by. Eqs. (1a, b). This is demonstrated for the relationships of van't Hoff and Mark‐Houwink, frequently used for the determination of molar masses of polymers. It is also shown that the four different relations for the expansion factor α by Flory‐Stockmayer, Fixman, Ptitsyn, and by Yamakawa‐Tanaka can be applied to polymolecular polymer samples (i.e. without fractionation), provided the corresponding averages[η]av and Mav from the Mark‐Houwink relationship are taken for the evaluation of the parameters KΘ and B′.

Determination of the Average Molar Mass of the Vapour Above Molten Sodium Chloride by the Transpiration Method.

Determination of the Average Molar Mass of the Vapour Above Molten Sodium Chloride by the Transpiration Method.

Fluorinated alkoxides. 14. Template synthesis of some large-ring iminoalkoxy complexes of nickel(2+). Structure of a dinuclear square-planar nickel(II) complex

The template condensation of 5,5,5-trifluoro-4-hydroxy-4-(trifluoromethyl)-2-pentanone, (CF3)2C(OH)CH2COCH3, with an apdiamine NH2(CH2)nNH2 (n = 2, 3, 4, 5, 6, 8, or 12) in the presence of a metal ion (Cu, Ni2+) leads to a series of stable, neutral, iminoalkoxy metal complexes. An X-ray structural elucidation of the Ni complex with n = 6 has been completed, showing it to have a dinuclear composition. Crystals are monoclinic, space group C2/c, with unit cell dimensions a = 28.867 (9, A, b = 9.982 (2) A. c = 17.276 (3) A, and p = 105.49 (1)'. Full-matrix least-squares refinement on F converged with a conventional agreement factor of 0.046. Each Ni atom is coordinated in square-planar geometry to trans N202 donor atoms in two ligand molecules whose -(CHJ- chains link the two metal coordination planes at an angle of 55'; there is no direct Ni-Ni interaction. Molar mass determinations (acetonitrile solution) on the nickel complexes (which are all red and diamagnetic) show a change from mononuclear to dinuclear aggregation at n 2 4; evidence from the formation of five-coordinate adducts with pyridine suggests that the complexes with n = 5, 8, or 12 are similar in structure to the n = 6 complex but a different arrangement, tentatively assigned to a cis dinuclear geometry, is present for n = 4. The copper complexes appear to be exclusively mononuclear in solution. Reaction pathways by which such condensation products could arise are discussed.