CONFORMATIONAL FLEXIBILITY OF PARTIALLY HYDROGENATED RINGS IN THE REPEATING UNITS OF RIGID-CHAIN HETEROCYCLIC POLYMERS

The conformational flexibility of partially hydrogenated rings in naph thylimide, naphthalic anhydride, and some of their derivatives used as model compounds for the repeating unit in rigid-chain heterocyclic po lymers, was studied by the semiempirical quantum-chemical AM1 method. The partially hydrogenated rings in all of these compounds possess con formational flexibility. Transition from a planar equilibrium form to a distorted sofa conformation with a torsion angle of +/-20 degrees re sults in an increase in the energy of less than 1 kcal mol(-1). The hi gh flexibility of partially hydrogenated rings, along with other facto rs, can cause finite length of the Kuhn segment in rigid-chain heteroc yclic polymers.