The potential curve of the 1,4-polymn. of diacetylene to prepare polybutatrienes and further polydiacetylenes was studied based on the topochem. model and the quantum-chem. method of EHCO-ASED. The transformation of the frontier orbital symmetry along the reaction coordinates was analyzed. The problem about the Woodward-Hoffmann's orbital symmetry conservation of such reactions in the literatures was solved., and then the reasons why these reactions might be thermally allowed were presented.

Key words: REACTION MECHANISM, REACTION KINETICS, POLYMERIZATION, POTENTIAL ENERGY, ACETYLENE P, TOPOLOGY, CONSERVATION OF SYMMETRY OF MOLECULAR ORBITAL