Effect of the chemical nature of the sorbate on the sorption capacity of crystalline polymers

Abstract

IN AN earlier study of the sorptive capacity of isotactic polypropylene in a wide temperature range above and below the melting point of its crystals, we used n-dodeeane as the adsorbate [1]. The results showed that the nature of the sorption varied considerably with temperature due, apparently, to changes in the structure of the polymer on rising temperature, I t was suggested that to some extent the structural changes taking place in the polymer must also be due to interaction between the polypropylene and n-dodecane. If this is correct, then if a low molecular weight compound of another kind is used as the sorbate and it is inert with regard to polypropylene, it would be right to expect that the magnitude of the sorption and the structural changes of the polymer with rising temperature would be different from the case of n-dodecane. I t seems that the lower alcohols, methanol, ethanol, are just such inert media in relation to isotactic polypropylene. But they cannot be used for our purposes, due to their low boiling points. We must therefore use a high-boiling alcohol, in which case the long hydrocarbon chain may interact with the polymer. For sorption experiments on isotactie poljrpropylene in a wide temperature range from 80 to 200 °, we used n-nonylic alcohol as the sorption material; it has a boiling point of 213.59 which is higher than of the polymer, 160 °. The isotactic polypropylene was the residue after the polymer had been extracted in ether and heptane. Its molecular weight measured in decalin at 135 ° was 120,000. I t was established on a polarization microscope that the specimen melted in the range 160-170 ° , which is consistent with published figures.