Polyoxymethylene single crystals

It is known that polyoxymethylene in the crystalline phase takes the all gauche conformation with a 9/5 helix [21]. However, the amorphous phase has a distribution of gauche and frans-conformations. Figures 7.10 and 7.11 show the CPMAS NMR spectra and powder pattern spectra of polyoxymethylene, respectively [22]. Sample A is a polyoxymethylene single crystal. To produce Sample B, Sample A is heated to 200°C and then quenched in ice water. Sample C is a melt-quenched sample of bulk polyoxymethylene and sample D is a bulk polyoxymethylene heated and cooled at a rate of... 

Figure 5.1 (a) The solution-grown polyoxymethylene single crystal, (b) spherulites of melt-cooled polyethylene sample and the hierarchical structure, (c) extended-chain crystals of polyoxymethylene (whisker), and (d) the shish-kebab structure. (See color insert.)... 

Kobayashi, M., Matsumoto, Y, Ishida, A., Ute, K. and Hatada, K. (1994). Polymorphic structures and molecular vibrations of linear oligomers of polyoxymethylene studied by polarized infrared and Raman spectra measured on single crystals. Spectrochim. Acta A, 50, 1605-17. [128]... 

In the literature not much attention has been paid to the initial part of the isotherm. Due to analytical limitations, the trends in this region often are rather uncertain. With human plasma albumin (HPA) adsorbing on either polystyrene latex (10) or single crystals of polyoxymethylene (11) it has been observed that the slope of the initial part of the isotherm becomes less steep with increasing pH. Anticipating the discussion in the following section. 

Single crystals of organic polymers were observed as early as 1927 by Staudinger. It became the subject of intensive investigations after an observation that linear polyethylene can crystallize into single crystals. The observations made on polyethylene were followed by observations that it is possible to grow single crystals of other polymers. Some of them are polyoxymethylene, polyamides, polypropylene, polyoxyethylene, cellulose, and others. 

Figure 1.10. Surface replica of molded polyoxymethylene fractured at liquid nitrogen temperatures. While the lamellae to the lower left are oriented at an angle to the fracture surface, the lamellae elsewhere are nearly parallel to the fracture surface. The important point is that lamellae (resembling those in single crystals) are stacked up like cards or dishes in the bulk state. (Geil, 1963.)...

Iguchi et al. have also studied the kinetics of polyoxymethylene crystallization in the presence of added needle-like single crystals. They observed spheruHtes and cylindrites developing from the needles, composed of folded chain lamellae. From the overall temperature-dependence of growth rates, they observed a change in mechanism and lower surface free energy terms than non-epitaxial crystallization. 

Fig. 16-3. Logarithmic plots of storage and loss shear moduli against frequency in Hz reduced to 70 C for single crystal blocks of polyoxymethylene, from measurements at different temperatures from 23 to 1 i 5 C. (Miki. ) Reproduced, by permission, from Polymer Journal.

Morphologies As shown in Rgure 5.1a, the crystallization of polyoxymethylene (POM) from a dilute solution produces a single crystal when we main-... 

Figure 8.12 Polymer decoration epitaxial crystallization on the fold surface. Polyethylene vapors were deposited on the surface of single crystals of polyoxymethylene (POM) at room temperature. The resulting PE decoration is made of edge-on lamellae oriented normal to the POM growth faces, with the deposited PE chains parallel to the growth front. The distance between POM fold planes (0.386 nm) imposes the monoclinic (010) PE contact plane, in which chains are separated by =0.4 nm [68].

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