STUDIES OF THE CONJUGATION LENGTH OF TRANS-(CH)X SEGMENTS IN DIBLOCK COPOLYMERS

We present an optical investigation of diblock copolymers polyacetylen e-polynorbornene in which the polyacetylene sequences have been varied from 10 to 100 double bonds. Based on the precursor route already use d to prepare polyacetylene (Durham procedure), new catalytic systems a llow the preparation of these diblock copolymers in which the non-conj ugated polynorbornene segments are made of almost-equal-to 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 feature s are observed, especially when the number of double bonds is small (1 0 C=C). The Raman bands exhibit narrow profiles, suggesting a very sma ll dispersion of chain length. An analysis of the Raman data in the fr ame of the bimodal distribution model is also presented and results ar e compared to previous ones obtained in the case of triblock copolymer s.