Polysilanes cooperativity

On the other hand, noticeable cooperative preferential screw sense induction was reported in rodlike polysilane copolymers bearing (.S )-2-mcthylbutyl and 2-methylpropyl groups (10) and (R)-2-melhylbutyl and 2-methylpropyl groups (11) in isooctane (Chart 4.3). Since the UV-CD spectral features of the polysilane copolymers are almost identical with those of 4-6 and the Xmax varies sensitively with changes in the molar fraction of chiral substituents and temperature,28 the copolymer systems are suitable for testing the sergeants-and-soldiers phenomenon by their CD-UV spectra. 

The acid and base sensitivity of condensation polymers whether or not under stress, e.g. polycarbonate, polyesters, polyamides and polysilanes under influence of acid or base the condensation bonds are hydrolysed under the cooperative action of mechanical stresses and the environment. A striking example is shown in Fig. 26.11, where the strength retention of PpPTA fibres is plotted versus pH after an exposure of 3 months at room temperature (Van den Heuvel and Klop). The hydrolysis of the polyamide is acid or alkali catalysed, in particular below pH = 3 and above pH = 9. 

The intramolecular cooperative C-F-H interaction was found to affect the rigidity of polysilanes." While 221b showed only negligible, weak Cotton effect, 221a exhibited CD spectra characteristic of a stable helical chain with single-handed screw sense. This effect is attributed to the chain stiffness of 221b induced by the intramolecular weak interaction between the pendent fluorine atoms and the Si backbone. 

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