| Description |
x, 75 leaves : illustrations ; 28 cm |
| Summary |
"The purpose of this study was to investigate the extent of flow degradation of narrow molecular weight distribution polystyrene samples under the conditions of laminar flow in capillary tubes. In all cases the solvent was toluene at 25°C, the polymer concentration was 0.1 weight percentage, and the calculated shear rate at the wall was in the range of 10⁵ - 10⁶ sec⁻¹. The extent of degradation was obtained by measuring the intrinsic viscosity [eta] of the polystyrene samples before and after flow through capillary tubes having a wide range of length/diameter (L/D) ratios. The polystyrene samples here had molecular weight of 1.80 x 10⁶, 8.6 x 10⁵, 6.33 x 10⁵, 4.11 x 10⁵, 1.6 x 10⁵ and 2 x 10⁴, and molecular weight distributions were such that M[subscript w]/M[subscript n]/ did not exceed 1.10. The experiments showed that the bulk of the polymer degradation occurred after the first pass of the solutions through the capillaries and that [eta] approached an asymptotic value after several passes. The extent of degradation at shear rates of 10⁵ -10⁶ sec⁻¹ was independent of the L/D ratio for L/D of 800 to 1.75. Higher molecular weight samples showed a greater tendency to degrade than lower molecular weight samples down to molecular weights in the range of 1.5 x 10⁵, below which no changes in [eta] were observed. A correlation was not found below the extent of degradation and the molecular weight distribution. For the high molecular weight samples of polystyrene (750,000) k' was found to be 0.34 and increased to 0.44 for the 20,000 molecular weight sample"--Abstract, leaves ii-iii. |
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