Rigid rod-like structure

The technique of atomic force microscopy (AFM) has permitted the direct observation of single polysilane molecules. Poly[//-decyl-(high molecular weight (4/w = 5,330,000 and Mn = 4,110,000), PSS, helicity, and rigid rod-like structure due to the aliphatic chiral side chains, was deposited from a very dilute (10-10 Si-unit) dm-3] toluene solution onto a (hydrophobic) atomically flat (atomic layer steps only present) sapphire (1012) surface. After drying the surface for a few minutes in a vacuum, AFM images were taken at room temperature in air in the non-contact mode.204,253 An example is shown in Figure 22, in which the polymer chain is evident as a yellow trace. 

X-ray crystallographic studies during the course of the reaction have demonstrated that the reaction is a typical topochemical process involving a direct rearrangement of the monomer crystal to the polymer crystal having an extended rigid rod-like structure. By x-ray analysis and DSC on the thermal depolymerization of the polymer crystal, a reversible topochemical process has been demonstrated for monomer and polymer crystals. 

Fig. 18. Relation between thermal behavior and molecular weight of cydobutane polymers with rigid rod-like structure, (source Ref. 72)...

Luminescent gold(I) acetylides (74-76) with a rigid rod-like structure have been synthesized. Their photochemical and photophysical properties have been studied in some detail155. The emission properties of the gold acetylides 77 have been studied. This... 

Structural dependence on temperature is now best illustrated by example. Optically inactive poly(hexyl-2-methylpropylsilane) has an a parameter of 1.29 in THF indicating a rigid rod-like structure. Furthermore, in isooctane solution at ambient temperature the peaks of the UV absorption and fluorescence spectra are narrow, they mirror each other, and the Stokes shift is only 3 nm. These are indicative of an almost homogeneous photoexcited energy state with minimal structural variation in the main chain. Notwithstanding this conclusion, when the solution is cooled to -80 °C, the absorptivity increases, the peaks narrow, and the Stokes shift drops to 2.2 nm. It is thus assumed that the polymer attains a perfectly extended rod shape at this temperature. ... 

Although polysilane main chain conformations can range from shrink coiled through to rigid rod-like structures, it is now generally accepted that most of... 

Polymers or associated molecules that form rigid-rod like structures... 

Figure 16 The photo-triggered isomerization of azobenzene at the molecular level (a) and within a liquid crystalline array (b). The trans-form is a rigid rod-like structure (left), whereas the cis conformation (right) is bent. (Adapted with permission from Ref. 44. Royal Society of Chemistry, 2007 and Ref. 45. American Physical Society, 2002.)...

PHBA exhibits a melting point of 600°C. This material was not easy to melt process and probably did not form a liquid crystalline melt. However, modifications of the rigid, rod-like structure can decrease the melting temperature to below 400 C, and render... 

Poly(phenylene vinylene) (PPV) exhibits linear rigid-rod-like structure, with a good tendency to form crystalline morphology. Fig. 15 [84—88]. However, due to lack of functional groups to enhance solubility, this system is intractable and not... 

A liquid crystalline polymer contains rigid rod like structure as discussed earlier which forms the hquid crystal phases. This rod like molecular conformations and chain stiffness give LCPs their most important self-reinforcing properties that are close to that of glass fiber reinforced composites. 

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