Studies have been made of the crystal and molecular structure of isotactic poly-5-methyl-1hexene, poly-(S)-5-methyl-l-heptene and poly-(S), (R)-5-methyl-l-heptene, using X-ray diffraction spectra of drawn fibres. The unit cell parameters are: ra = 17-62 A; b = 10.17 A; c = 6.33 .& (fibre axis) poly-5-methyl-l-hexene -{~ = 90Β°; space group P21 ~.Z = 6 (C,H~4); d~ = 0.86 g/cm 3 (dob~ = 0"84 g/cm 3) ~'a = 18"40 ./~; b = 10.62 A; c = 6-36 A (fibre axis) poly-(S)-5-methyl-l-heptene 413 = 90:; probable space group P2~ (2" = 6 (CsH,6); dx = 0.89 g/cm 3 (dob, = 0"86 g/cm 3) ~'a = b = 20.00 A; c = 38"76 .& (fibre axis) poly-(S), (R)-5-methyl-l-heptene .{probable space group Pg [Z = 76 (CnHt6); d, = 0-91 g/cm a (doo,= 0'88 g/cm 3)
The main chain conformation for poly-5-methyl-l-hexene and poly-(S)-5-methyl-l-heptene is S(3/1)1.
Anticlined helices of only one sense of spiralization are packed together in the crystals of the two polymers; in the optically active one, only left-handed helices are present, showing that in the solid state the correlation between absolute configuration of the asymmetric carbon atom of the side chain and sense of screw of the helix is the same as in solution.
The main chain conformation of poly-(S), (R)-5-methyl-l-heptene is of the S(M/N)I type in which the ratio MINis not integral (M = 19; N = 6); chains of both sense of spiralization are present in the unit cell of this polymer.