Damped Orientational Diffusion Model of Polymer Local, Main Chain Motion. 4. Effects of Probes and Side Chains

The complex damped orientational diffusion model of polymer local, main chain motion in moderately dilute solution is extended to include the effects of attached probes and periodic side chains on the dynamics. In the case of an appended probe attached to the main chain, a prescription is given for extracting the contribution of the probe to the local, main chain dynamics and thereby allows one to determine when the probe essentially exerts a minor influence on the character of the local motions and when it does not. In the case of a polymer containing a periodic array of side chains (as is normally the case), we demonstrate that to an excellent approximation in the context of the complex damped orientational diffusion model, side chains merely modify the effective damping constant of an equivalent polymer lacking any side chains. This is an important conclusion that requires experimental verification. Finally, we demonstrate that the complex damped diffusion model in general remains invariant to the particular kind of short-wavelength cutoff employed (either soft or hard) to represent the fact that the fundamental motional unit is of finite extent. In conjunction with the previous conclusion (Macromolecules 1982,15,1041) that the model is insensitive to the particular form of the long-wavelength cutoff, this implies a certain robustness of the basic orientational diffusion picture of polymer local motion.