Conformational and packing analysis of the alternating copolymer of ethylene and tetrafluoroethylene

Potential energy calculations have been made for the conformation and packing of chains of the alternating copolymer of ethylene and tetrafluoroethylene. Although the copolymer composition is similar to that of poly(vinylidene fluoride), the conformation and packing of the copolymer are quite different. The calculations indicate that for an isolated chain, a 3, helical conformation is lower in energy than the all-trans planar zigzag. Examination of the potential energy maps indicated that half of the available bond rotations are required to be nearly trans, making the copolymer chains considerably less flexible than poly(vinylidene fluoride) chains. Calculations of the energies for packing the copolymer chains into a crystalline array indicate three possible packing modes. Packing similar to polyethylene packing, poly(vinylidene fluoride) phase I packing, and a third structure proposed by Wilson and Starkweather have been found to have very similar energies. These three packing modes also seem to agree equally well with the experimental data available.