Studies of the conjugation length of trans-(CH) xsegments in diblock copolymers

Abstract

We present an optical investigation of diblock copolymers polyacetylene-polynorbornene in which the polyacetylene sequences have been varied from 10 to 100 double bonds. Based on the precursor route already used to prepare polyacetylene (Durham procedure), new catalytic systems allow the preparation of these diblock copolymers in which the non-conjugated polynorbornene segments are made of ≈400 units. An extensive study of the Raman spectra of the A-B copolymers has been carried out as a function of the excitation wavelength from the near U.V. range (351.1 nm) to the red range (647.1 nm). Interesting features are observed, especially when the number of double bonds is small (10 CC). The Raman bands exhibit narrow profiles, suggesting a very small dispersion of chain length. An analysis of the Raman data in the frame of the bimodal distribution model is also presented and results are compared to previous ones obtained in the case of triblock copolymers.