Helical conformations, internal motion, and helix sense reversal in polyisocyanates and the preferred helix sense of an optically active polyisocyanate

Abstract

Empirical force field studies of poly(alkyl isocyanates) are presented. A barrier of 12.5 kcal/mol for cis-trans isomerization of the polymer-backbone's conjugated partial double bonds makes the calculated energy of helix sense reversal agree best with corresponding experimental results. The alternating cis and trans torsion angles are found to be distorted, to about 170° and -55° for right-handed helices, by strong repulsions between the α-carbon of each alkylside chain and the neighboring backbone atoms of four consecutive monomer units