research papers
Two points of general interest in structural refinement of polymers based on internal coordinates are discussed: the chain orientation and the chain continuity. Using a proprietary computer program, based on revised approaches to these questions, the structure of polyisobutene has been reconsidered, using new X-ray diffraction measurements (Fuji image plate) and performing a structure refinement based on internal coordinates. Three refinement schemes, with a decreasing number of degrees of freedom, have been considered, with the conclusion that the distortion from the 83 regular helix, claimed by Tadokoro [(1979). Structure of Crystalline Polymers, p. 136. New York: Wiley-Interscience], is confirmed, though lower than supposed. The new procedures implemented for chain orientation and chain continuity work excellently.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889806044955/db5009sup1.cif |
CCDC reference: 660871
Computing details top
(yill) top
Crystal data top
? | β = 90° |
Mr = ? | γ = 90° |
?, &unitsp; | V = ? Å3 |
a = 6.880 Å | Z = ? |
b = 11.910 Å | ? radiation, λ = ? Å |
c = 18.600 Å | × × mm |
α = 90° |
Crystal data top
? | β = 90° |
Mr = ? | γ = 90° |
?, &unitsp; | V = ? Å3 |
a = 6.880 Å | Z = ? |
b = 11.910 Å | ? radiation, λ = ? Å |
c = 18.600 Å | × × mm |
α = 90° |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Biso*/Beq | ||
C1 | 0.3421 | 0.0540 | 0.0442 | ||
C2 | 0.3256 | 0.0372 | 0.1261 | ||
C3 | 0.1453 | 0.0277 | 0.1748 | ||
C4 | 0.2067 | 0.0307 | 0.2544 | ||
C5 | 0.3640 | −0.0362 | 0.2948 | ||
C6 | 0.3271 | −0.0305 | 0.3764 | ||
C7 | 0.2834 | 0.0706 | 0.4254 | ||
C8 | 0.2837 | 0.0335 | 0.5047 | ||
C9 | 0.2716 | 0.1728 | 0.0246 | ||
c10 | 0.5557 | 0.0398 | 0.0212 | ||
C11 | 0.0401 | −0.0837 | 0.1591 | ||
C12 | 0.0074 | 0.1267 | 0.1593 | ||
C13 | 0.5651 | 0.0141 | 0.2780 | ||
C14 | 0.3580 | −0.1596 | 0.2702 | ||
C15 | 0.0825 | 0.1190 | 0.4062 | ||
C16 | 0.4403 | 0.1612 | 0.4141 | ||
H17 | 0.3962 | 0.0995 | 0.1458 | ||
H18 | 0.3951 | −0.0314 | 0.1348 | ||
H19 | 0.0892 | 0.0136 | 0.2799 | ||
H20 | 0.2423 | 0.1077 | 0.2623 | ||
H21 | 0.4419 | −0.0631 | 0.3970 | ||
H22 | 0.2180 | −0.0795 | 0.3836 | ||
H23 | 0.2608 | 0.1018 | 0.5307 | ||
H24 | 0.4144 | 0.0082 | 0.5127 | ||
H25 | 0.3491 | 0.2280 | 0.0489 | ||
H26 | 0.1382 | 0.1821 | 0.0386 | ||
H27 | 0.2822 | 0.1844 | −0.0263 | ||
H28 | 0.6356 | 0.0939 | 0.0456 | ||
H29 | 0.5678 | 0.0507 | −0.0297 | ||
H30 | 0.6004 | −0.0342 | 0.0332 | ||
H31 | −0.0726 | −0.0905 | 0.1892 | ||
H32 | 0.1255 | −0.1458 | 0.1685 | ||
H33 | 0.0002 | −0.0863 | 0.1097 | ||
H34 | −0.1056 | 0.1216 | 0.1894 | ||
H35 | −0.0326 | 0.1253 | 0.1099 | ||
H36 | 0.0724 | 0.1965 | 0.1688 | ||
H37 | 0.6643 | −0.0270 | 0.3029 | ||
H38 | 0.5695 | 0.0912 | 0.2930 | ||
H39 | 0.5900 | 0.0105 | 0.2273 | ||
H40 | 0.4556 | −0.2022 | 0.2951 | ||
H41 | 0.3819 | −0.1642 | 0.2194 | ||
H42 | 0.2328 | −0.1914 | 0.2803 | ||
H43 | 0.0538 | 0.1821 | 0.4364 | ||
H44 | −0.0159 | 0.0628 | 0.4129 | ||
H45 | 0.0810 | 0.1430 | 0.3569 | ||
H46 | 0.4144 | 0.2247 | 0.4444 | ||
H47 | 0.4406 | 0.1854 | 0.3649 | ||
H48 | 0.5660 | 0.1314 | 0.4258 |
Experimental details
Crystal data | |
Chemical formula | ? |
Mr | ? |
Crystal system, space group | ?, &unitsp; |
Temperature (K) | ? |
a, b, c (Å) | 6.880, 11.910, 18.600 |
α, β, γ (°) | 90, 90, 90 |
V (Å3) | ? |
Z | ? |
Radiation type | ?, λ = ? Å |
µ (mm−1) | ? |
Crystal size (mm) | × × |
Data collection | |
Diffractometer | ? |
Absorption correction | ? |
No. of measured, independent and observed (?) reflections | ?, ?, ? |
Rint | ? |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | ?, ?, ? |
No. of reflections | ? |
No. of parameters | ? |
No. of restraints | ? |
Δρmax, Δρmin (e Å−3) | ?, ? |