Polymers, chain type electron diffraction

Figure 2 is a typical electron diffraction pattern. A distinct smearing of the intensity was observed in the b direction and increased with the % index. A possible origin of this may be due to a small disordering in the packing. The type of disorder can be derived from the Fourier transform as being due to a slip in the c direction between polymer chains. In some diffraction micrographs where little beam destruction occurred, the smeared reflections are seen to really consist of many distinct spots. 

The most direct evidence of the crystallinity in polymers is provided by x-ray diffraction studies. The x-ray patterns of many crystalline polymers show both sharp features associated with regions of three-dimensional order, and more diffuse features characteristic of molecularly disordered substances like liquids. The occurrence of both types of feature is evidence that ordered regions (called crystallites) and disordered regions coexist in most crystalline polymers. X-ray scattering and electron microscopy have shown that the crystallites are made up of lamellae which are built-up of folded polymer chains as explained below. 

In their neutron diffraction studies of p-type doping of PPP, Stamm and Hocker [179] have determined the setting angle (p of the chains in the pristine polymer to be 57° 3°. In this refinement, the authors started from the data by Kovacic et al. [169], but assumed a monoclinic P2i/a structure with /i=I00°. While a number of later studies by others confirm that the value of 4> is around 57°, Stamm et al. [180] find a much lower value of 45° in their electron diffraction work. The neutron study yields lateral coherence lengths L of 60 A for Kovacic PPP and 150 A for Yamamoto PPP. 

Quite early on, structural investigations showed [17] that the mesogens in the main chain and the side chain orient parallel to one another. This was confirmed by electron microscopy [18], X-ray diffraction [6,7,13, 14, 17, 19, 20] and HNMR spectroscopy [21]. Following the general classification of LC side-chain polymers (Figure 2) [22], these polymers should be classified as type III. In these combined LC polymers, the polymer chains and mesogens orient parallel to one another to define the LC director. 

The CK" ion can act either as a monodentate or bidentate ligand. Because of the similarity of electron density at C and N it is not usually possible to decide from X-ray data whether C or N is the donor atom in monodentate complexes, but in those cases where the matter has been established by neutron diffraction C is always found to be the donor atom (as with CO). Very frequently CK acts as a bridging ligand - CN- as in AgCN, and AuCN (both of which are infinite linear chain polymers), and in Prussian-blue type compounds (p. 1094). The same tendency for a coordinated M CN group to form a further donor-aceeptor bond using the lone-pair of electrons on the N atom is illustrated by the mononuclear BF3 complexes... 

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