Perfectly alternating ethylene–carbon monoxide copolymer crystallized epitaxially on alkali halides. 2. Energy calculation

As reported in our previous papers, edge-on lamellar crystals of poly(3-oxotrimethylene) (POK) can be epitaxially grown from solution on alkali halides, and the crystal orientation depends on the type of substrate utilized: The chain-stems on the (001) surface of NaCl orient in the 〈110〉 directions of the substrate, while those on the (001) surface of KI orient in the 〈100〉 directions of the substrate. In order to explain this experimental evidence, calculations of the interaction energy between one rigid POK chain-segment of planar–zigzag conformation and a given substrate (the (001) surface of NaCl or KI) were carried out: in the calculations, the Lennard–Jones 6–12, the Coulomb and the induced-dipolar potentials were utilized. The calculation results were in good agreement with the experimental facts. Particularly in the calculation for POK on KI, the Coulomb energy was found to be the most important of the three to explain the the 〈100〉 orientation of the chain-segment. It was concluded that the interaction energy between the oxygen atoms in the POK chain-segment and the positive ions in a given alkali halide is an important factor to determine the orientation of the chain-stem in epitaxial crystallization of POK on these alkali halides.