Poly phenylacetylenes

Poly(phenylacetylene) and poly(diphenylacetylene) consist of polyaromatic conjugated fragments side by side with polyene chains. The photosensitivity strongly depends from acceptor concentration, supermolecular structure, the synthesis procedure [177], The acceptor molecules inclusion increased the photosensitivity, the optimum of which was obtained for heterogeneous phases with a large interface area. The transition of the amorphous structure into the crystal one promoted the photosensitivity increase. The maximum quantum yield of 10 3 was at the energy 3 eV, mobilities were varied from 10-9 to 10-6 m2 V-1 s-1. 

For poly(phenylacetylene) doped with acceptor iodine molecules the long wavelength bands at 940 nm were ascribed to CT complexes [178, 179]. The band model with trap controlled conductivity was used to the photoconductive 

The investigation of the quantum yield of the poly(diphenylacetylene) and its complex with TNF show that maximum photosensitivity was at 25% of the acceptor content [184]. This relates to the case when all the conjugated blocks form complexes with TNF. The strong dependence of the quantum yield on the electric field strength permitted the explanation of the photosensitivity in the framework of Onsager s theory with a thermalization distance of 2 nm. 

5 Poly(phenylene), Poly (thiophene), Poly(phenylenesulfide) 

Polythiophene is a highly crystalline polymer with the chain analog to cis-polyacetylene. The sulfur atoms stabilize the structure and interacts poorly with 

The ethynyl groups of ethynylbenzenes undergo polymerization by the action of Group 6, 7, and 9 transition metal catalysts, often used for olefin metathesis, to give the corresponding polyenes which are frequently called poly(phenylacetylene)s (43) [15, 47]. 

A pair of Ullman s nitronyl nitroxide radicals bearing m- and p-ethynylphenyl groups at position 2 of the imidazoline ring (7 and 8) undergo polymerization in the presence of 

With the idea of avoiding the potential bimolecular coupling reaction of the radical centers in the solution-phase chemical oxidation reactions, a photochemical approach was adopted. Diazo compounds 10 and 12 were treated with the Rh catalyst under basic conditions to give the poly(acetylene)s 43 [R and m- /7-(/i-C,9H39)C6H4]C(N2)] of 200000 [8]. While photolysis of the diazo groups proceeded smoothly on neat films at 2 K and broad EPR si- 

11 Building Blocks for High-Spin Molecules and Molecular Assemblies 

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Fig. 2. A poly(phenylacetylene) dendrimer with an energy gradient across the conjugation length of the acetylene units from the periphery to the focal point...

A few synthetic helical polymers are known to act as chiral selectors.7a,918d l8k i9d i9h ancj are widely used as chiral stationary phases (CSP) in gas or liquid chromatography.73,53 Recently, it has been reported that the preference of one helical sense in isotropic solution can be induced by some interaction between optically inactive polymers and chiral solvents/additives. Examples of this include poly(n-hexyl isocyanate)18d l8k and poly(phenylacetylene)s bearing functional group.19d 19h The polysilane derivatives also show chiral recognition ability in solution at room temperature. Poly(methyl-ft-pinanylsilane) includes two chiral centers per bulky hydrophobic pinanyl side group28 and... 

Over the past decade, literally dozens of new AB2-type monomers have been reported leading to an enormously diverse array of hyperbranched structures. Some general types include poly(phenylenes) obtained by Suzuki-coupling [54, 55], poly(phenylacetylenes prepared by Heck-reaction [58], polycarbosilanes, polycarbosiloxanes [59], and polysiloxysilanes by hydrosilylation [60], poly(ether ketones) by nucleophilic aromatic substitution [61] and polyesters [62] or polyethers by polycondensations [63] or by ring opening [64]. 

Some conducting polymers with a conjugated polyvinyl structure, such as polyacetylene and poly(phenylacetylene), seem likely to be energetic enough, and reactive enough, to give trouble undoped, if they actually have the supposed structure [7],... 

Tang BZ, Xu HY (1999). Preparation, alignment, and optical properties of soluble poly(phenylacetylene)-wrapped carbon nanotubes. Macromolecules 32 2569-2576. 

Yashima et al. showed an example where the polymer helicity was controlled by enzymatic enantioselective acylation of the monomers [109]. Optically active phenylacetylenes containing hydroxyl or ester groups were obtained by the kinetic resolution of the corresponding racemic hydroxy-functional phenylacetylene (see Scheme 16). Polymerization of the phenylacetylenes afforded an optically active poly(phenylacetylene) with a high molecular weight (Mn = 89kDa PDI = 2.0) and... 

Scheme 16 Synthesis of optically active poly(phenylacetylene) from optically active phenylacetylenes [109]...

Unlike W and Mo catalysts, Rh catalysts are not suited to oriho-swhstxtutcd phenylacetylenes because Rh catalysts are rather sensitive to the steric effect. Instead, Rh catalysts are suitable to various phenylacetylenes having polar groups (e.g., ether, ester, amine, carbazole, imine, nitrile, azobenzene, nitro groups) at ra-position, resulting in the formation of high MW poly(phenylacetylenes). Many such examples are found in Table 3. 

WOCI4 is combined with Ph Sn (ratio WOCI4 Plx Sn = 1 2) in 1,4-dioxane/benzene to afford poly(phenylacetylene) efficiently, whose reaches 1.1 x 10 ([77] 1.23 dL g ) and whose m-content is 7i% High polymer yields can be achieved even in the case of a high monomer/catalyst ratio, 1260. The viscosity index, a, of poly(phenylacetylene) formed by this catalyst was determined to be 0.61, indicating a sufficiently flexible chain. 

Among group 8 transition metal catalysts, iron-based Ziegler-type catalysts such as Fe(acac)3-Et3Al(l 3) (acac = acetylacetonate) have been well known from the early stage of the catalyst investigation, which are readily prepared in situ to polymerize sterically unhindered terminal acetylenes such as -alkyl-, r f-alkyl-, and phenylacetylenes. The formed poly(phenylacetylene) has red color and r-cisoidal structure, and is insoluble and crystalline. 

Fig. 15. Electrophotographic spectra for polymers 1 - polydiphenylbuta-diyne, 2 - polyvinylcarbazole, 3 - poly-phenylacetylene, 4 - polyethylene, 5 -polyacrylonitrile, 6 - polyvinylchloride, 7 - polystyrene [13]...

Well-controlled polymerization of substituted acetylenes was also reported. A tetracoordinate organorhodium complex induces the stereospecific living polymerization of phenylacetylene.600 The polymerization proceeds via a 2-1 -insertion mechanism to provide stereoregular poly(phenylacetylene) with m-transoidal backbone structure. Rh complexes were also used in the same process in supercritical C02601 and in the polymerization of terminal alkyl- and arylacetylenes.602 Single-component transition-metal catalysts based on Ni acetylides603 and Pd acet-ylides604 were used in the polymerization of p-diethynylbenzene. 

As discussed earlier, substitution onto the polyacetylene chain invariably has a deleterious effect on dopability and conduction properties. At the same time the stability tends to improve. Masuda et al.583) studied a large range of substituted polyacetylenes and found that stability increased with the number and bulkiness of the substituents, so that the polymers of aromatic disubstituted acetylenes were very stable, showing no reaction with air after 20 h at 160 °C. Unfortunately, none of these polymers is conducting. Deitz et al.584) studied copolymers of acetylene and phenylacetylene they found that poly(phenylacetylene) degrades even more rapidly than does polyacetylene and that the behaviour of copolymers is intermediate. Encapsulation of the iodine-doped polymers had little effect on the degradation, which is presumably at least in part due to iodination of the chain. 

Exclusive polymerization of phenylacetylene takes place, unexpectedly, under hydrosilylation conditions in the presence of a zwitterionic Rh(I) complex, [Rh(COD)]+BPh4, and HSiEt3 to give all-ds-poly(phenylacetylene)285. 

A growing number of reports are appearxng concerning %<3) of materials as determined by THG experiments. Among organics a variety of poly(diacetylenes), e. g., 4-BCMU (4-butoxycarbonylmethylurethane polydiacetylene) (15,109) have been studied as pure materials and as LB films, 110) Crystalline films of poly(4-BCMU) in the red form, were found to have higher %<3) than amorphous films, attributed to the orientational effect of crystallization.(109) The blue form also has been studied. 111) Maximum values of %<3) reported to date are 1 x 10 10 esu at 1.3 l. Poly (phenylacetylene) THG at 1.06 lhas recently been measured. 111) The 2- and 3-photon resonance enhanced value of %<3) determined is 7 x 10 12 esu. 

The results illustrated above show that the CFT method is suitable for making chemical-sensor measurements using both bulk polymers and, in particular, thin film materials that are intrinsically weak conductors. Therefore, the CFT looks premising for such materials as poly(phenylacetylene) derivatives 24., for which carefully shielded electrometer measurements have been required in the past because of current levels at the threshold of detectability. Furthermore, the fact that the CFT always makes AC measurements reduces the problem of DC polarization of electrodes. In addition, the CFT approach should be suitable for other "chemiresistor" applications, such as the metal-substituted phthalocyanines proposed by Jarvis et. al. 2 and for Langmuir—Blodgett films 26. which, because they are so thin, may prove impossible to use in parallel-plate form, but which can be routinely used with the high-sensitivity interdigi-tated-electrode approach provided by the CFT. 

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