Concentration dependence of local chain motions of polymers

Abstract

The chain dynamics of an alternating 1,4-trans-butadiene-propene copolymer has been investigated by high resolution 13C NMR spectroscopy in a broad range of concentrations in solution and in the melt. While in semidilute solution all main chain carbon atoms have the same activation energy of motion it is found that, above a concentration of 20 wt%, the activation energy of the aliphatic carbon atoms increases faster with concentration than the activation energy of the olefinic carbon atoms. It is concluded that in dilute and in semidilute solution all carbon atoms are relaxed by localized transitions about methine-methylene bonds, i. e. the bonds with the lowest energy barrier, whereas in concentrated solution and in the melt the relaxation of aliphatic and olefinic carbon atoms is controlled by independent localized transitions about methylene-methylene and methine-methylene bonds, respectively.