The intensity of depolarized components of light scatered by polymer solutions has been measured in solvents of different refractive indexes. It has been found that the dependence of the Rayleigh ratio (RHv/c) on the solvent refractive index (n0) for polymer solutions significantly differs from the corresponding dependence (RHv/c) = f (n0) for solutions of low molecular weight compounds. The interpretation of the observed relations (RHv/c) = f (n0) is given and the equation relating RHv/c with the polarizability tensor anisotropy 〈γ2〉 of dissolved macromolecules proposed. The equation differs from the corresponding equation applicable to low molecular weight compounds by the use of Λ in a medium. Values of 〈γ2〉 for atactic polystyrene determined by the equation given are compared with calculation reported by Flory and co‐workers. The difference between the statistical segment principal polarizabilities calculated from the anisotropic light scattering data has been also compared with that determined from birefringence data. All the results obtained are in agreement with the equation proposed. It is shown that the intensity of the anisotropic light scattering by block copolymer solutions is sensitive to disturbances in the regular block structure and, hence, the anisotropic scattering method can be used to characterize the alternating of monomer units in copolymer chains.
Branching in isoprene polymers with cis‐1,4 content of ∼85% obtained by polymerization in the presence of a complex catalyst and under the action of lithium was determined by studying intrinsic viscosity of polymer fractions in an ideal solvent. It was established that macromolecules of polyisoprenes obtained with a complex catalyst under polymerization conditions commonly used are essentially linear. At the same time, in the polymers studied, there is a fraction (∼10% of the polymer weight) consisting of colloidal size particles formed by highly crosslinked polymer molecules. A rubber sample of the above type prepared with uncontrolled dosage of catalyst components and at elevated temperature proved to be a highly branched polymer. The discovered features in hydrodynamic behavior of macromolecules in benzene solutions suggest that trans units in the macromolecules of polyisoprenes obtained in the presence of the complex catalyst are not randomly distributed along the chain but form comparatively long blocks. The intrinsic viscosity—molecular weight relation in benzene solutions was determined for both types of polymers studied.
The physical motivations, present status, main results in study of cosmic rays and in the field 1
In an investigation of three different synthetic rubbers, methods of fractionation were examined and measurements were made of the molecular-weight distribution by analysis of fractions. The following conclusions may be drawn. (1) The method of equivalent Gaussian distributions correctly reproduces the distribution within each fraction and makes it possible to distinguish the broadening of the sedimentation curve attributable to diffusion and that attributable to polydispersion. (2) The method of accounting for the final concentration of the solution under investigation introduced by us result in correct values of molecular weights of fractions and correct values of standard deviations. (3) Comparison of a series (about 10) of fractions of a given polymer makes it possible to transpose the sedimentation constant distributions into the distribution of molecular weights in a simple and natural way. An investigation of the three rubbers demonstrates two facts. (1) Fractionation of rubbers by precipitation from solutions gives true fractions, i.e., mode values of molecular weights and sedimentation constants do not overlap but form continuous series. By this means fractionation of K-1 and K-3 resulted in very homogeneous fractions of Gaussian shape having dispersion coefficients smaller than 0.33. Fractionation of K-2 resulted in less homogeneous fractions of somewhat asymmetric shape; however, in this case, the broadness and asymmetry of fractions, as it is easy to show, does not exceed the limits predicted by the theory of fractionation. (2) The method of determination of molecular-weight distributions by tracing the steplike curve of precipitation, with subsequent smoothing by graphic differentiation, gives a correct picture of the distribution function of polymers for molecular weights; however, the finer details of distribution can be distorted and lost in tracing the steplike curve. The molecular-weight distributions of synthetic rubbers by the ultracentrifuge method must be closely related to the process of genesis of a polymer, i.e., with the mechanism of the polymerization reaction. Thus, with proper experimental technique our method can be applied to the investigation of various mechanisms of polymerization and polycondensation.
By changing the sol-gel ratio and the structure of the gel fraction it is possible to obtain various grades of synthetic cis-poly(isoprene) which show promise for different applications in the tire and mechanical rubber goods industries. The processability of commercial SKI-3 rubber (at a given average molecular weight of sol) depends mainly on the structure of the gel fraction. Thus, for example, inferior processing properties of rubber compounds is associated primarily with the presence of tight gel. The content and structure of the gel fraction also significantly affect plasto-elastic properties of raw rubbers, e.g. a low plasticity of raw rubbers owes to the increased content of gel fraction. The reduced green strength of compounds based on SKI—3 rubber is accounted for by its chemical structure. Conventional methods used to change the properties of rubbers (including the variation in molecular weight, molecular weight distribution, branching degree, and variation in the content and structure of gel fraction) cannot be considered to be adequate to tackle the problem of the green strength of SKI—3 black stocks. The way to solve the problem appears to be the introduction of functional groups into the polymer chain at the stage of synthesis or processing. These functional groups should be active as to the formation of labile rubber—carbon black—rubber and/or rubber—rubber bonds. High purity of microstructure is necessary but not sufficient for obtaining the required level of green strength of compounded SKI—3. The gel fractions of SKI—3 rubber yield vulcanizates with a more dense network than the corresponding sol vulcanizates. The temperature dependence of the tensile strength is controlled by the network density of vulcanizates from high cis-1,4 poly(isoprene).
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