New solutions to the problems of chain orientation and chain continuity in structure analysis of fibrous polymers. A reconsideration of the structure of polyisobutene

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.

Computing details

Figures

(yill)

Crystal data

?	β = 90°
Mr = ?	γ = 90°
?, &unitsp;	V = ? Å^3
a = 6.880 Å	Z = ?
b = 11.910 Å	? radiation, λ = ? Å
c = 18.600 Å	× × mm
α = 90°

Data collection

h = ?→?	l = ?→?
k = ?→?

Refinement

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	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