The polyoxyethylene chain—on the origin of its conformational flexibility

Abstract

Polyoxyethylene (POE) is known to be highly flexible, a variety of spatial configurations being permitted. Like many other conventional polymers, the conformation of the POE chain can be treated within the framework of the rotational isomeric state (RIS) approximation using a limited number of RIS parameters. An unambiguous assignment of numerical values to statistical weights such as σ and ω has not been achieved for the chain occurring under various conditions: σ for the rotation around the C—C bond and ω for the so-called second-order interaction taking place between the methylene group and the oxygen atom separated by four bonds. In this work, we have attempted to demonstrate the role of these two parameters in determining the conformation-dependent properties of the POE chain. Various RIS parameter sets reported in literature have been compared with a model calculation, in which σ and ω are varied over a wide range, the other parameters being kept invariant. A comprehensive analysis provides a rational explanation for the long lasting question why so many RIS parameter sets effectively reproduce the conformational characteristics of the identical polymer molecule. Finally, it is emphasised that a critical assessment of ω and/or σ is required to establish an unambiguous RIS description of the POE chain.