Local orientational motions in flexible polymeric chains

Effects of chain connectivity, viscous resistance of the environment, and internal barriers to conformational transitions are studied in relation to local orientational motions in flexible chains. Calculations are performed according to the dynamic rotational isomeric states scheme. Only a single transition over a bond at a time is assumed. That such single bond rotations are indeed possible in a sequence of 20 bonds without significant distortion of the tails is shown by the present analysis. The increase in the frictional resistance to motion with the size of the mobile sequence is investigated for polyethylene at 300 K. The latter, referred to as the size effect, is included in the treatment through consideration of the total path traveled by each of the moving atoms. Orientational autocorrelation functions for a bond at the end of an N bond mobile sequence are evaluated in the presence and absence of the size effect. Two different correlation times, emphasizing short and long time motions, are defined. Dependence of the correlation times on the length of the mobile sequence is evaluated.