Influence of the Polymerization Conditions on the Dilute Solution Properties of Polyacrylonitrile.

Abstract

The light scattering and viscosity measurements were carried out on fractions in N, N′ -dimethylformamide at 20°C. The fractions chosen for this study were polymers prepared by suspension (S) or precipitation (P) polymerization in aqueous or organic (benzene (B) or n-heptane (H)) system with redox (R) or non-redox (nR) catalyst as initiator. Fractions were, in advance, characterized by high resolution nuclear magnetic resonance and infra-red spectra, leading to the conclusion that the degree of microtacticity of polymeric chains is almost constant independent of molecular weight and polymerization conditions. The larger values of refractive increment than those in literatures were obtained for (P-nR) polymer. For fractions polymerized in benzene, the fluorescence had a large effect on the Zimm plot giving the slope with minus sign for c=0 line in the range of small angle of scattering, even if 546mμ as incident light was used. The optical anisotropy of the chain effected little on this kind of distortion appearing in the Zimm plot. Apparent depolarization, of which the magnitude remarkably depended on the conditions of polymerization, decreased with increase of molecular weight. After corrections of fluoresoence, 0.01-0.02 as depolarization factor of scattered light was obtained irrespective of the molecular weight and the preparative procedure.
Relationships between the intrinsic viscosity and molecular weight were determined for polymers except (P-nR (B)): [η] (dl/g) =4.66×10^-4M_w^0.71 and for (P-nR (B)) polymer: [η] (dl/g) =4.29×10^-4M_w^0.71. On the other hand, the identical relationships were obtained between the radius of gyration (SS²) _z^1/2 or second virial coefficient A2 and molecular weight irrespective of the polymerization conditions: (SS²) _z^1/2 (cm) =1.27×10^-9M_w^0.62 and A2 (ml/gg²) =4.94×10^-2M_w^-0.27. The correlationships among the parameters in the above equations were discussed in detail.
Applicability of the Stockmayer-Fixman plot was examined. Flory constant K=3.1×10^-3 for (P-nR (B)) polymer and 3.6×10^-3 for other polymers were determined by egtrapolating the linear portion of the plot to M_w^1/2. From viscosity measurements on the redox polymer in ethylene carbonate-water (85: 15, in weight) system at 44°C for which A₂ vanishes, K=3.5×10^-3 was estimated. The experimental results that the polymerization conditions influenced only the parameter Km in the Mark-Houwink-Sakurada equation [η] =Km Mwa, but not on a and molecular weight dependence fo (SS²) _z^1/2 or A₂ were resonably interpreted by the recent solution theories.
Fluorescence appearing in dimethylformamide solution did not depend on the content in amide, carboxylic acid and it's ester existing in polymer as abnormal structures. Fluorescence of the redox polymer was of ionic and that of (P-nR (B)) polymer was of non-ionic type.