Chain Conformations in Polymers

Abstract

A polymer molecule can take many different shapes (conformations) primarily due its degree of freedom for rotation about σ bonds. Studies of the heat capacity of ethane (CH₃—CH₃) indicate that the bond linking the carbon atoms is neither completely rigid nor completely free to rotate. Figure 2.1 shows the different rotational positions of ethane as viewed along the C—C bond. The hydrogen atoms repel each other, causing energy maxima in the eclipsed position and energy minima in the stable staggered position. The torsion angle may be defined as in Fig. 2.1, Ø = 0 for the eclipsed position and Ø > 0 for clockwise rotation round the further carbon atom. Some authors set Ø = 0 for the staggered position. In both cases, the value of Ø is independent of the viewing direction (turning the whole molecule round).