Sheet-like polymer

The spacer-bridged ditin compound MeCl2Sn(CH2)3SnCl2Me239 was reported to contain, in the solid state, hexacoordinated tin atoms as a result of strongly unsymmetrical intermolecular Sn—Cl—Sn bridges with Sn—Cl distances in the range of 2.381(1)—3.484(1) A, giving rise to the formation of a sheet-like polymer. 

Blumstein used montmorillonite clays as layered templates in which monomers could be adsorbed to form monolayers between the lamellar layers subsequently, different monomers were tested for the preparation of sheet-like polymers... 

The ribbon polymer is related to the less-flexible ladder and sheet polymers discussed before. One might expect very much different viscous behavior of such molecules in the melt. The interpenetrating networks [8] can have interesting elastic properties since each network may respond differently and interact with the other. The two-dimensional flexible polymers have recently been explored. They also belong to the sheet-like polymers. 

From studies in solution and in the sohd state, a number of structures both sheet-like [14] and helical [19, 21, 24—36] have been proposed over the years for these polymers. Poly(/9-alanine) 3 for example crystallizes as extended chains [14]... 

Fibrillation can be achieved mechanically by drawing and pulling thin sheets of polymer. This is compounded if twisting is also involved. A rough idea of this process can be demonstrated by cutting several ribbons of film from a trash bag. Take one and pull. It will elongate and eventually form a somewhat thick filament-like material. Do the same to another strip but also twist it. 

The biological properties of HA in aqueous solution is controlled by reversible tertiary structures, as defined by NMR spectroscopy. Evidence suggests a ft-pleated sheet-like array stabilized by H- and hydrophobic bonds. Easy transitions between secondary and tertiary structures occur that are convenient mechanisms for switching between functions. The 20 kDa or 50-disaccharide unit is around the size at which such stable tertiary structures are expected to form.199,200 Polymers greater than 20 kDa provide the preferred substrate for Hyal-2. The enzyme cleaves at a much slower rate once the HA substrate loses tertiary structure. The hyaladherins may also provide additional substrate specificity.201 The array of hyaladherins that bind to tertiary HA structures may differ from those that bind to HA chains with exclusively secondary structure. The substrate specificity of Hyal-2 may depend on a combination of differences in bound hyaladherins and on secondary versus tertiary structure. 

Crystalline silicon is the most widely used semiconductor material today, with a maiket share of above 90%. Because of its indirect electronic band structure, however, the material is not able to emit light effectively and therefore carmot be used for key applications like light-emitting diodes or lasers. Selected one- or two-dimensional silicon compounds like linear or branched polysilylenes [1] or layered structures like siloxene [2], however, possess a direct band gap and therefore exhibit intense visible photoluminescence. Siloxene, a solid-state polymer with a sheet-like layered structure and an empirical formula Si H (OH) , in particular, is considered as an alternative material for Si-based liuninescent devices. Detailed studies of stmctural and photophysical properties of the material, however, are strraigly impeded by its insolubility in organic solvents. 

The more complex adsorption kinetics for PPPS in Fig. 2 suggests that it cannot be described by a simple diffusion model. The sigmoidal shape also indicates that cooperative processes have to be taken into account, and these may be rate-limiting. In the case of a rigid polymer like PPPS one may assume a nematic ordering of the rod-like polymers in two-dimensional sheets and the pressure change - may reflect the amount U (t) of polymers in... 

Interesting arrangements of the side-chains in peptide-based poly(isocya-nide)s have been reported. The polymers obtained from 50a and 50e exhibit /1-helix structures, in which the Ala-Ala as well as Ala-Ala-Ala side-chains are organized in a /1-sheet-like fashion (Scheme 40) [68, 69]. In this /1-helix-... 

---