X‐ray structure determination of isotactic poly(2‐vinylpyridine)

Abstract

The structure of isotactic poly(2‐vinylpyridine) has been determined from x‐ray fiber data utilizing rigid‐body least‐squares refinement techniques. The polymer exists as a threefold helix with three chains passing through a hexagonal unit cell having the dimensions a = b = 15.49 Å and c = 6.56 Å (fiber axis) and space group P31 or P32. The asymmetric unit consists of three monomeric units (one in each chain), resulting in three crystallographically independent chains in the unit cell. The results show that two of the chains are interlocked through pyridine ring interactions whereas the third chain is less restricted. A statistical structure is proposed in which any two chains in the unit cell can be interlocked, provided they have the same sense. Such a situation permits a completely statistical structure in which half the chains in any crystallite are oriented upward and the other half downward.

Chain Conformation, Crystal Structures, and Structural Disorder in Stereoregular Polymers

“…Two chains experience strong interactions with the neighbors, whereas the third chain interacts weakly with the neighboring chains, giving rise to the frustration. 154 161 Similar frustration has been evidenced for the crystal structure of isotactic poly(2-vinylpyridine) 160,161 (Figure 2.28). Also in this case three independent threefold helices are included in the trigonal unit cell and the frustration is related to a different azimuthal orientation of the chains due to the different interactions between the chains.…”

“…As a consequence, the crystallographic environment of two chains differs significantly from that of the third one. Frustrated polymer structures have been established for various achiral and chiral polymers, 156,157 for instance, the β-form of iPP, 154,158,159 isotactic poly(2-vinylpyridine), 160,161 the α-form of sPS, 150 isotactic poly(t-butylethylene sulfide) 156,162,163 and the β-form of poly(L-lactide), 164 and for biopolymers, for instance, poly(Lhydroxyproline) 165,166 and triethylcellulose. 156,167 Frustrated polymer crystal structures generally display characteristic morphological features and typical diffraction patterns.…”

Polymer Crystallization Processes as Seen from the Growth Front’s Perspective

“…29 The crystal structure of iP2VP is a frustrated one, with three three-fold helices per cell. 30 A characteristic of frustrated structures is that the three helices are not related by any crystallographic element of symmetry: their angular setting in the unit-cell is ''free'' (from a crystallographic point of view). 31 The setting of the helices in iP2VP is such that, even in single crystals, the topography of the growth front is asymmetric: deposition towards the right and deposition towards the left on the growth front is not equivalent.…”

Controlled Handedness of Twisted Lamellae in Banded Spherulites of Isotactic Poly(2‐vinylpyridine) as Induced by Chiral Dopants

“…[10,11] Consistently, the dimensions of a and b wereb othd etermineda s1 5.5 on the basis of the (300) and(030)reflections.For the crystallizationofthe iP2VP complex,i ti si ntuitivet os uggestt hat the introducedc hiral dopants shouldbeexpelled from the crystallineiP2VP owing to the large sizeofthe HMA,sothatthe crystallizationofthe mixtureofiP2VP and HMA shouldadopt an excluded mode. [10,11] Consistently, the dimensions of a and b wereb othd etermineda s1 5.5 on the basis of the (300) and(030)reflections.For the crystallizationofthe iP2VP complex,i ti si ntuitivet os uggestt hat the introducedc hiral dopants shouldbeexpelled from the crystallineiP2VP owing to the large sizeofthe HMA,sothatthe crystallizationofthe mixtureofiP2VP and HMA shouldadopt an excluded mode.…”

“…The diffractions are indexed on the basis of a frustrated trigonal crystal structure with a unit cell with the parameters a = b =15.49 Å and c =6.56 Å 10. 11 Consistently, the dimensions of a and b were both determined as 15.5 Å on the basis of the (300) and (030) reflections. For the crystallization of the iP2VP complex, it is intuitive to suggest that the introduced chiral dopants should be expelled from the crystalline iP2VP owing to the large size of the HMA, so that the crystallization of the mixture of iP2VP and HMA should adopt an excluded mode.…”