SORPTION BEHAVIOR OF POLY (4-VINYLPYRIDINE) AT TEMPERATURES ENCOMPASSING THE GLASS TRANSITION POINT

Abstract

Adsorption behavior of organic compounds on poly (4-vinylpyridine) (P-4-VP) was studied by the inverse gas chromatography at temperatures encompassing the glass transition point (Tg) of the polymer.Using P-4-VP as a stationary phase in the GC column, retention data were obtained for a series of polar organic probes (good solvents): n-propanol, n-butanol, n-amylalcohol and n-hexanol, and a nonpolar hydrocarbon (nonsolvent): n-dodecane.At temperatures well above Tg, the specific retention volume (Vg) increased linearly with increasing peak area (S), whereas at temperatures below Tg, two distinct regions in the Vg and S relation were observed. At the low probe concentrations, Vg increased with decreasing S markedly in a curvilinear fashion, while at the high concentrations, Vg increased with increasing S linearly. In the low concentration region, plots of 1/Vg against √S for all systems were represented by straight lines. The limiting specific retention volumes (V0g ) were estimated in both regions by extrapolating the respective relations to S=0.Values of In V0g were plotted against the reciprocal of thermodynamic temperature. Each plot showed a Z shaped curve characteristic of the system in which a thermal transition occurred in the temperature region concerned. From the plots, Tg of P-4-VP was estimated as 126°C.Heats of adsorption at the infinite dilution of the solute in the stationary phase were determined from the temperature dependence of Vg. Values of 19-21 and 13-15kcal/mol were obtained, respectively, at the low and high concentrations.In the present system, plot of log V0g vs. boiling point was represented not by a straight line, which is observed generally for systems of n-alcohol and polymer, but by a curve with a minimum. This may indicate that n-alcohols of the lower boiling point have the stronger affinity for P-4-VP.From these results, it is considered that adsorption of the probe on the surface of the stationary phase dominated at temperatures below Tg and that penetration of the probe into the bulk occurred at temperatures above Tg.