AbstractThe most stable conformations of typical isotactic helical polymers, polypropylene (PP), poly‐4‐methyl‐1‐pentene (P4MP), poly‐3‐methyl‐1‐butene (P3MB), polyacetaldehyde (PAA), and poly(methyl methacrylate) (PMMA), were analyzed without fixing the fiber identity period by taking into account the intramolecular potential energy due to the internal rotation barriers, and van der Waals and electrostatic interactions. According to the results of the calculations, the number of chemical units per turnNin the stable conformations is 2.91 for PP (value determined by x‐ray diffraction: 3.0), 3.52 for P4MP (3.5), 4.17 for P3MB (4.0), and 3.94 for PAA (4.0). This indicates that the molecular conformations of these four polymers are governed primarily by intramolecular interactions, i.e., steric hindrance of side chains, and are additionally modified by the intermolecular interactions in the crystal. For PMMA, the lowest minimum in the potential map corresponds toN= 12, but the energy difference between the minima ofN= 12 andN= 5 (corresponding to the actual one) is only 3 kcal/mole of monomer unit. The (5/1) helix of PMMA may be reasonably interpreted in terms of the intermolecular interactions mainly due to the polar and bulky side groups. The intermolecular interaction energy of isotactic PAA in the crystal lattice is also calcula