Poly(1-Butene) Chain Flexibility from Sorption Data

Abstract

A previous investigation of the sorption properties of polyethylene over a wide range of temperatures, above and below the melting point, showed that this polymer, the simplest member of the polyolefin series, has chains of quite high flexibility, a factor which also governs its extent of crystallization. The present work is devoted to the study of the sorption properties of crystalline polybutene to obtain data on chain flexibility. This polymer is of considerable interest, since it exhibits elastomeric properties as well as crystalline structure. A polybutene sample with an intrinsic viscosity of 1.14 (determined in decalin at 90°) was used in the study. Observation in a polarization microscope showed that the sample melted in the temperature range 94.3° to 104.8°. Isotherms for sorption of n-octane by polybutene at 50°–115° (Figure 1) were obtained by means of a spring balance placed in a high temperature air thermostat. As Figure 1 shows, sorption increases regularly with temperature up to a relative adsorbate vapor pressure of 0.45, with the exception of the isotherm obtained at 50°, which lies above the isotherm at 60°. This somewhat unexpected result is possibly associated with the less dense packing of the chains at 50°, a factor which also results in higher sorption. At higher relative vapor pressures, when chain flexibility increases as a result of the plasticizing effect of the solvent, the density of molecular packing increases, and sorption becomes lower than at 60°.