Polymers alkyl-substituted

In contrast to the alkyl substituted polymers, the P-phenyl compounds, [Ph(Me)PN]n and [Ph(Et)PN]n are brittle, brown colored materials which are quite soluble in THF and are readily plasticized by trace amounts of solvent. Determination of molecular weight... 

Examination of the absorption spectra of the new polysilane materials reveals a number of interesting features (14). As shown in Table III, simple alkyl substituted polymers show absorption maxima around 300-310 nm. Aryl substitution directly on the silicon backbone, however, results in a strong bathochromic shift to 335-345 nm. It is noteworthy that 4, which has a pendant aromatic side group that is buffered from the backbone by a saturated spacer atom, absorbs in the same region as the peralkyl derivatives. This red shift for the silane polymers with aromatic substituents directly bonded to the backbone is reminiscent of a similar observation for phenyl substituted and terminate silicon catenates relative to the corresponding permethyl derivatives... 

For most of the unbranched alkyl substituted polymers, in solvents of high refractive index, the smooth transition described by the above model changes to an abrupt, first order like transition (8). This has been described in terms of electronic-conformational coupling ( n ). The thermochromism for the n-propyl methyl polymer is summarized in Figure for two solvents. 

A significant difference between poly(RCOT)s and unsubstituted polyacetylene is that the former bear substituents which may perturb their electronic properties. The optical absorbances (Table 10-3) probe this to some extent, but electrochemical data are more sensitive. For example, whereas polyCs ec-butylCOT) and poly(Me3SiCOT) have similar absorption spectra, both the formal reduction and oxidation potentials of the silyl-substituted polymer are shifted positive of the alkyl-substituted polymer (Fig. 10-27). This is expected, based on the more electropositive nature of the silyl substituent [139]. Also, while the effects are not large, the substitution of either an electron-donating (para-methoxyphenyl) or an electron-withdrawing (para-trifluoromethylphenyl) substituent do perturb the polymer s electronic properties, with the latter material being harder to oxidize and easier to reduce than the former. 

Ribbon 58 was obtained as an insoluble powder, whereas cyclodehydrogenation of the alkyl-substituted polymers 62 and 63 resulted in ribbons 59 and 60, respectively, as waxy materials with excellent solubilities. This allowed for detailed structural characteri2ations to be conducted in conventional organic solvents. 

Grafting of flexible hydrocarbon chains on the conjugated polythiophene backbone greatly improves polymer solubility and flexibility and, for this technological reason, alkyl-substituted polymers have been the object of much research work. 

---