Abstract
Polyacetylene prepared by the Durham precursor route can be obtained in a disordered form by thermal conversion of a solution-cast film of the precursor polymer, or in a highly oriented form by stretching the precursor film during the transformation reaction. The oriented films show the properties that are characteristic of long straight-chain sequences, but the unstretched films show evidence for very short straight-chain lengths, of no more than 20 or 30 carbon atoms. The authors discuss the dispersion of the resonantly-enhanced Raman modes with excitation energy and show that within the amplitude-mode formalism of Horovitz the defects that terminate the straight sequences in unstretched material do not impose a preferred sense of bond alternation on the chain.