Aromatic side groups

The UV-visible absorption and emission spectra and excited state lifetimes of polymers are sensitive to chemical structure, polymer conformation and molecular environment and thus information concerning these properties is accessible by electronic spectroscopy measurements (4-6). One example of the application of such measurements is given in Figure 3 which illustrates the possible energy dissipation pathways which can occur in a polymer containing aromatic side groups following absorption of radiation. 

Figure 3. Energy relaxation pathways in a polymer containing aromatic side groups following absorption of light. (Reproduced with permission from Ref. 21. Copyright 1987 Chemistry in Australia.)...

The polymer resist exhibiting the lowest PE rate or highest etch resistance versus PMMA or oxide is poly(styrene) (see Table IV). This system, like the others of Table IV, is representative of a vinyl pol3mier with general structural formula of -(CH2-CXY)-. Poly(chlorostyrene), a chlorinated derivative of the aromatic poly(styrene), exhibits equal resistance towards all three dry etch processes. Here halogenatlon has not enhanced the etch rate or reduced the resistance as seen before for PTECM, PTFEM, and PMCA nonaromatic systems. Therefore, the aromatic side group must... 

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... 

Also of interest is the use of aromatic side groups different from the phenyl groups present in the commercially important poly(methylphenylsiloxane) or the highly intractible poly(diphenylsiloxane).112-119 Homopolymers and copolymers having p-tolylsiloxane groups have been of particular interest with regard to their formation of liquid-crystalline phases.120121... 

PL of polysilanes with aromatic side groups has been found to be strongly quenched by doping with fullerene (C6o), whereas quenching does not occur in polysilanes with alkyl side chains.85 Poly(methylpropylsilane)... 

Normally polymer structures containing aliphatic backbones are low in smokegenerating character and are generally not self-extinguishing. Additives to such systems to achieve flame-retardancy often enhances smoke generation Polymers with aromatic side groups such as polystyrene have a considerable tendency to generate smoke. 

Abkowitz and Stolka (1990, 1991) compared hole mobilities of poly-silylanes and polygermylenes containing aliphatic pendants with compounds that contain only aromatic side groups. While transport occurred via states associated with the backbone chain in both compounds, the nature of the side groups was shown to influence the temperature dependence of the mobility. The results were described by a small-polaron argument, based on the assumption that the polarizability increases when an aromatic pendant group was substituted... 

V. Sasisekharan, P. K. Ponnuswamy. Studies on the conformation of amino acids. X. Conformations of norvalyl, leucyl, aromatic side groups in a dipeptide unit. Biopolymers. 1971, 10, 583-592. 

Although the bulky aromatic side group generally hinders free segmental motion, henc increasing the Tg of the polymer, the effect of chain separation seems to be dominant in case of OPh, SPh, and the lower hydrogen bond density probably accounting for the decrease in Tg. These polyamides with lower... 

The different thermal behavior of PPBA samples with different tacticities is intriguing and perhaps associated with small differences in the mode of packing of aromatic side groups within the layers, not observable by x-ray diffraction. 

This enhancement of the photoconductivity caused by Ceo doping may be ascribed the photoinduced electron transfer. We have reported that while the photoinduced electron transfer from polysilanes with alkyl substituents to C6o does not occur, the electron transfer from polysilanes with aromatic side groups (e.g. PMPS) to Ceo is effective [13]. Yoshino et al. have also reported that the photoconduction of poly(3-alkylthiophene) is remarkably enhanced upon doping [14]. Sariciftci et al. reported the similar photoinduced electron transfer in oligothiophene/C6o composite films [15]. Therefore, we believe that the photoinduced electron transfer occurs between ji-orbitals of the thienylene rings and those of C6o-... 

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