Poly internal polymer motions

Heijboer [28] has reported the dynamic mechanical properties of poly(nethacrylate)s with different size of the saturated ring as side chain. The y relaxation in these polymers is attributed to a conformational transition in the saturated ring. In the case of poly(cyclohexyl methacrylate), the transition is between the two chair conformations in the cyclohexyl ring. However, this type of internal motion in hindered by rather high intramolecular barriers, which can reach about 11 kcal mol-1. 

The invariance of relaxation frequency with molecular wei t may not be apparent at finite concentrations of polymer, because cofl — c< interactions can effect the relaxation of internal modes as well as the first order, rotational mode. There have been a number of studies of the concentration dependence of dielectric loss processes some of which show weU the continuous trend in behawour from dilute solution to the bulk state. Temperature variation can provide useful information on the enthalpies of activation of local mode motions. Finally, since such local modes are very structure sensitive, differences in chain tacticity would be expected, and do cause changes in loss behaviour. This prediction has been authenticated for such polymers as poly(methyl methacrylate) and poly(ethyl acrylate). ... 

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