Polymers with Triple Bonds

Polymers with triple bonds and heteroatoms in the macromolecule chain were among the first photoconducting polymers [8, 93-96]. The structural formulas for some among nearly seventy polymers investigated may be represented by 

The photoconductivity spectrum after preliminary irradiation of polymer is given by curve 2. The observed redistribution of the peaks is partly reversed on prolonged exposure to air. The bathochromic shift of the shorter wavelength peak depends on the exposure time. Ultraviolet irradiation produces a slight change in the polymer colour. Such irradiation increases, likewise, the photo-electromotive force a 1.5 h irradiation increases it 10 times. The photoconductivity spectrum is situated at longer wavelengths than the photo-electromotive force spectrum. 

The presence of a photoconductivity peak at 610 nm at the threshold of the absorption spectrum (curve 4) is a common phenomenon in inorganic semiconductors and is explained by competition between surface and volume recombination processes of the charge carriers. The optical activation energy determined from the spectral photoconductivity threshold is equal to 1.82 + 0.02 eV. The thresholds of the photoelectromotive force and the absorption spectra are likewise in agreement with this value. It is remarkable that the same value has been found for the activation energy of the dark conductivity in this polymer 

The sign of the dominant charge photocarriers in most of the polymers investigated has been found to be positive. The photosensitivity increase under ultraviolet irradiation might be connected with the photoionization of polymer molecules and the creation of local, positively charged centers acting as photoelectron traps. This mechanism seems to be confirmed by the electron spin resonance method. 

The photosensitivity and its increase after ultraviolet illumination was confirmed by electrophotographic methods for polymers with triple bonds 

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Table 1. Photoconducting polymers with triple bonds [93-96]...

Polymers with triple bonds have been applied in electrophotography [176] and were the first among organic photoconductors with sensitized by dyes photoconductivity [19,20]. 

Spectral research permits us to obtain additional information about the role of the molecular structure in photoelectrical properties. The photosensitivity of the copper acetylenides is higher than in polymers with triple bonds without copper atoms. So the coordinating metal atoms and n-electrons of the acetylenic bonds play an important role in increasing the photosensitivity. 

As already shown, the sensitized spectra follow the dye absorption. Most of the dyes have sufficiently narrow absorption bands. This does not permit us to obtain the panchromatic sensitivity in the sufficiently broad spectral range. It was proposed to use the polymers with conjugated bonds as sensitizers [21]. The broad diffuse absorption spectra are inherent to such compounds. One can expect higher thermal stability from such sensitizers. In addition the application of binder may be omitted from the preparation of the photosensitive layers, for example, in electrophotography. Polymers with triple bonds, polyphenylenes and polyoxiphenylenes were used as sensitizers [10, 14, 278-280]. The typical results are shown in Fig. 47. The main rules for photoconductivity sensitized by polymers were the same as for the dyes. Optimum sensitization was obtained at the concentration of the sensitizer of 10 1-10-2 g/cm3 relative to the polymeric photoconductor weight. 

Kudryavtsev, Yu.P. Oxidative dehydropolycondensation — a new method to synthesize polymers with triple bonds. In Progress of Polymer Chemistry. Nauka, 1969 87-112. 

POLY ACETYLENES AND POLYMERS WITH TRIPLE BONDS IN THE MAIN CHAIN... 

Urethane curing systems have been long used as solid propellants. Recently, a triazole curing system has been introduced into a new binder recipe in which azide groups in the polymer react with triple bonds of a dipolarophile curing agent [101]. 

Mond process The purification of nickel by the formation and decomposition of nickel carbonyl, monomer A small molecule from which a polymer is formed. Examples CH2=CH2 for polyethylene NH2(CH2)6NH2 for nylon, monoprotic acid A Bronsted acid with one acidic hydrogen atom. Example CH COOI I. monosaccharide An individual unit from which carbohydrates are considered to be composed. Example C6H(206, glucose, multiple bond A double or triple bond between two atoms. 

Employing a molar excess of the alkyne over the active hydrogen of only 12 percent the selectivity (determined by proton NMR after work-up) may be expressed as the ratio of Si-C=CH- to Si-CH2-CH2-CO-, which is about 100 1 [16]. The same reaction, carried out with silicone polymers with 10 or more pendant silicon-bonded hydrogen atoms, proceeds similarly cleanly without noticeable crosslinking by acrylic hydrosilylation. A slight excess of triple bond over Si-H groups is mandatory to suppress this side reaction as well as hydrosilylation of the olefinic group of the 2-silylalkene isomer product (see Table 2.). 

PHAs containing carbon-carbon triple bonds synthesized by P. oleovorans and P. putida grown with 10-undecynoic acid (10-UND=) have been reported [64]. The amount of carbon-carbon triple bond could be controlled between 0% and 100%, but the yield of the PHA containing 100% carbon-carbon triple bond was very low. The repeating units formed from 10-UND= were 3-hydroxy-8-nonynoate (3HN=) and 3-hydroxy-6-heptynoate (3HHp=) units in the amounts of 26 mol% and 74 mol%, respectively. The glass transition temperatures of PHAs synthesized from mixtures of NA and UND= increased from -30°C to -20°C as the content of carbon-carbon triple bond increased from 0% to 100%. These polymers were crosslinked when cations such as Co2+ and Pt2+ were added. 

Fig. 6 Polydiacetylene with alternating double, single, and triple bonds along the polymer backbone...

The most reliable information on the structure of the polymer has been derived from X-ray diffraction and Raman-spectroscopic studies. In a few cases it has been possible to determine in detail the structures of both the monomer and the corresponding polymer. From such measurements and other optical studies the process is considered to be 132 — 133 for a symmetric diacetylene. In polymerizable structures the diacetylene rods are inclined at about 45° to the translation (stack) axis, with the ends of each diacetylene moiety approaching the adjacent triple-bond systems to a distance of s4 A. The polymer is a planar system in extended conformation and having alternate R groups trans to one another. 

While the catalytic reduction of PPEs is powerful, it is necessary to work at high temperatures and with a stainless-steel autoclave, which may not always be practical. Weder et al. reported an alternative way to reduce dialkoxy-sub-stituted PPEs [81]. Treating the PPEs with a mixture of tosylhydrazide and tripropylamine at elevated temperatures gave the reduced species in high yield and excellent purity (Scheme 14). The purported intermediate is diimine, formed by elimination of Ar-S02-H from the hydrazide. Diimine reduces the triple bonds to give the fully reduced polymer. Attempts to utilize the diimine method to reduce dialkyl PPEs, however, failed perhaps due to the more massive steric shielding by the alkyl groups in these polymers. 

Hydroxy-terminated polyester (HTPS) is made from diethylene glycol and adipic acid, and hydroxy-terminated polyether (HTPE) is made from propylene glycol. Hydroxy-terminated polyacetylene (HTPA) is synthesized from butynediol and paraformaldehyde and is characterized by acetylenic triple bonds. The terminal OH groups of these polymers are cured with isophorone diisocyanate. Table 4.3 shows the chemical properties of typical polymers and prepolymers used in composite propellants and explosives.E4 All of these polymers are inert, but, with the exception of HTPB, contain relatively high oxygen contents in their molecular structures. 

D. Where there is no conflict with other guidelines, triple bonds are senior to double bonds, which in turn are senior to single bonds multiple bonds should be assigned the lowest possible locants. Thus, the polymer from 1,3-butanediene polymerized in the 1,4- mode is usually indicated as-(—C—C=C—C — )-but is named as though it were-( - C=C - C - C - )-and named poly(l-butene-1,4-diyl) with the appropriate cis- or tra i-designation. Polyisoprene, typically drawn as-(—CH2 —C(CH3)=CH—CH2 —) —is frequently named poly(2-methyl-1,3-butadiene) but is named as though its structure were-(C(CH3)=CH—CH2—CH2 — ) —with the namepoly(l-methyl-1 -butene-1,4-diyl). 

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