Polystyrene-polyacetylene

Several attempts have been made with the couples polystyrene-polyacetylene (PS-PA) or polyisoprene-polyacetylene (PI-PA) (20,21,22). The choice of the PA as the companion polymer is quite understandable. PA has been the most studied and is the simplest polymer providing a high conductivity while it is doped. A huge amount of work has been devoted to PA films, but PA films are inhomogeneous, insoluble, and poorly characterized. 

In addition to the above-mentioned polymers, other addition polymers such as polyolefin, polystyrene, polyvinylethers, polychloral, polyisocyanides, polyacetylene, and polyethers were synthesized and evaluated as the precursors for the preparation of CSPs. Some of them were coated or chemically bonded to silica gel and tested for the chiral resolution of different racemic compounds. 

I proceed by first describing in Sec. II the construction of a molecular-orbital model suitable for interpreting molecular FES and UVA spectra. Then, this model is extended to encompass intramolecular (Sec. Ill) and intermolecular (Sec. IV) relaxation. The paper concludes with an indication of the applications of the model to interpret FES and UVA from polyacetylene (11) and from two pendant-group polymers, polystyrene and poly(2-vinyl pyridine) (9, 10). 

In the examples of our work on organic molecular and polymeric solids that follow, first some contributions to the UPS line widths in condensed molecular solids are discussed for two prototype systems, anthracene and isopropyl benzene then the UPS of two.aromatic pendant group polymers, polystyrene and poly(2-vinyl pyridine), are discussed and compared with some spectra concerning the simplest linear conjugated polymer, polyacetylene. 

FIGURE 1.2. Molecular structure of widely used it-conjugated and other polymers (a) poly(para-phenylene vinylene) (PPV) (b) a (solid line along backbone) and it ( clouds above and below the a line) electron probability densities in PPV (c) poly(2-methoxy-5-(2 -ethyl)-hexoxy-l,4-phenylene vinylene) (MEH-PPV) (d) polyaniline (PANI) (d.l) leucoemeraldine base (LEB), (d.2) emeraldine base (EB), (d.3) pernigraniline base (PNB) (e) poly(3,4-ethylene dioxy-2,4-thiophene)-polystyrene sulfonate (PEDOT-PSS) (f) poly(IV-vinyl carbazole) (PVK) (g) poly(methyl methacrylate) (PMMA) (h) methyl-bridged ladder-type poly(jf-phenylene) (m-LPPP) (i) poly(3-alkyl thiophenes) (P3ATs) (j) polyfluorenes (PFOs) (k) diphenyl-substituted frares -polyacetylenes (f-(CH)x) or poly (diphenyl acetylene) (PDPA). 

Recent evidence indicates that the influence of molecular structure on gas permeation through polymers is complex. For example, reports investigating series of structurally varied polyimides (5-7), polyacetylenes (2), polystyrenes (2) and silicone polymers (12) show that gas transport rates within a particular polymer class can vary dramatically depending upon the structure of the monomer present. These observations on materials where the monomer changes while the functional "link" remains constant suggest that structural factors other than the polymer class are significant in determing gas transport properties. 

Figure 5.12. UV/vis spectra of polyacetylene/polystyrene block co-polymers, The ratio of acetylene to graft sites was increased from A to D. (Reprinted with permission from ref. 51)...

Most polymers (typified by polystyrene and polyethylene) are electrically insulating and have conductivities doped with iodine to become electrically conducting (values have now been reported up to olO Scm ) represented a pivotal discovery in polymer science that ultimately resulted in the award of the Nobel Prize for Chemistry in 2000 [4]. The study of electrically conducting polymers is now well advanced and two extremes in the continuum of transport mechanisms exist. If the charge carriers are present in delocalized orbitals that form a band structure along the polymer backbone, they conduct by a delocalization mechanism. In contrast, isolated groups in a polymer can function as acceptors or donors of electrons and can permit... 

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