Crystal structures of odd and even trans polyalkenamers

Abstract

The odd trans polyalkenamers (CHCH(CH 2) 2 n+1 crystallize in orthorhombic unit cells, the equatorial dimensions of which are very similar to those found for orthorhombic polyethylene. The space group is the same (P nam) for odd trans polyalkenamers or for orthorhombic polyethylene and the packing of the macromolecules is nearly identical for all these polymers. A three dimensional least squares refinement was carried out for trans polypentenamer and for trans polyheptenamer. The “full matrix” methods and the weighing scheme by Cruickshank were employed. An overall temperature factor was used in the refinement. The standard deviations of the final atomic co-ordinates of the C atoms range between 0·01 and 0·02 Å for both polymers. The even trans polyalkenamers (CHCH(CH 2) 2 n ) p can crystallize either in a monoclinic unit cell or in a triclinic unit cell. The α and b axes of the monoclinic unit cells have the same value for all the trans polyalkenamers examined; the same is verified also for the triclinic unit cells. A three dimensional least squares refinement was carried out for the monoclinic forms of trans polydecenamer and of trans polydodecenamer. The standard deviations of the final atomic co-ordinates of the C atoms range between 0·02 and 0·03 Å for both polymers. The triclinic form of even trans polyalkenamers may be in some way connected to the triclinic form shown by cold-worked polyethylene. The triclinic structure of trans polyoctenamer and of trans polydecenamer have been checked by a three-dimensional Fourier analysis. The standard deviations of the atomic co-ordinates range from 0·02 to 0·04 Å for the C atoms of both polymers.