Acetylene-based polymers

Increasing interest has been focused on the acetylene-based polymer chemistry relevant to cyclic polyynes — the topic of this chapter [1]. Cyclic polyynes are unique members in the family of sp-carbon allotropes. Like linear polyynes, they are composed of unsaturated carbon atoms covalently... 

II. CATALYTIC SYNTHESIS OF ACETYLENE-BASED POLYMERS A. Homogeneous Systems... 

Thanks to the tremendous progress in the transition metal-catalyzed polymerization of substituted acetylenes as described in the previous sections, it is now possible to access various acetylene-based polymers having desired flrst-order structures. This, in combination with highly advanced organic synthetic technology, provides novel fimctional materials based on polyacetylenes, and the following surveys examples of the design and synthesis of functional substituted polyacetylenes. 

Vinyl acetate (ethenyl acetate) is produced in the vapor-phase reaction at 180—200°C of acetylene and acetic acid over a cadmium, 2inc, or mercury acetate catalyst. However, the palladium-cataly2ed reaction of ethylene and acetic acid has displaced most of the commercial acetylene-based units (see Acetylene-DERIVED chemicals Vinyl polymers). Current production is dependent on the use of low cost by-product acetylene from ethylene plants or from low cost hydrocarbon feeds. 

Originally, vinyl chloride polymers were based on acetylene. The switch to ethylene,chemistry came after the development of the oxychlorination process for vinyl chloride described in Chapter 9. Today very little acetylene-, based vinyl chloride monomer (VCM) processing remains. 

Ziegler-Natta catalysts are not active at all in polymerization of disubstituted acetylenes.415 Mo- and W-based systems (for alkynes with small substituents) and Nb- and Ta-based catalysts (for alkynes with bulky groups), in turn, are very effective catalysts used to convert disubstituted acetylenes into polymers with very high molecular weight.414 415 A polymerization mechanism similar to that of metathesis polymerization of cycloalkenes are supported by most experimental observations.414 423 424... 

Catalytic mercury compounds polyurethane/other polymer production, acetylene-based production of vinyl chloride monomer, vinyl acetate, and acetaldehyde... 

Among carbon fillers, carbon black is most commonly used due to good conduction performance, and metallic oxides are often used to make fiber white. Du Pont produced a composite nylon fiber made up of nylon sheath and conductive polymer core formed by dispersing about 30% carbon Hack in LDPE matrix. When the conductive core content was ca. 4%, the was around 10 cm[96,97]. Toray[98] developed a composite nylon fiber made up of nylon-6 sheath and conductive polymer core formed by dispersing about 30% carbon black in nylon-6 matrix. When the conductive core content was ca. 5%, the was 10 to 10 cm. Other conductive nylon fiber was reported by Unitika[99,100], in which 25% acetylene black was dispersed in nylon-6, which was combined with the same nylon 6 base polymer at a ratio of20/80. The conductive polymer was exposed onto the fiber surface to increase efficiency. A white-colored conductive nylon fiber was also obtained by using titanium dioxide particles with diameters of 2 pm or less coated with tin oxide. A heat resistant conductive nylon fiber was obtained by dispersing carbon black in an aromatic polyamide[101]. 

The catalytic applications of the metal-containing X-Si02-based aerogels has been demonstrated in an important case by Ji [8], who showed that the aerogel in the Pd-form can be reduced and used to catalyze the selective hydrogenation of acetylene in the presence of ethylene about as well as - and perhaps superior to - the known commercial catalysts. Since the methods for the production of ethylene-based polymers employ catalysts that can be poisoned by acetylene, this is a key reaction. Moreover, its selectivity is essential, so that the ethylene itself is not hydrogenated. 

The first example of chiral polymer from a disubstituted acetylene is a polyd-trimethylsilyl-l-propyne)-based polymer, poly(46), which was synthesized in moderate yields using TaCls-PhaBi (112). Poly(46) displays small optical rotations, and its molar ellipticities of the Cotton effects are up to a few hundreds. The main chain of poly(46) is, therefore, not a well-ordered helix. This is probably because of the less controlled geometrical structure (cis and trans) of the polymer backbone. However, the free-standing film of this polymer achieves an enantioselective permeation of various racemates including alcohols and amino acids. For example, the concentration-driven permeation of an aqueous solution of tryptophan by poly(46) gives 81% enantiomeric excess (ee) of the permeate at the initial stage. A characteristic of the membrane of poly(46) is its ability to enantioselectively recognize 2-butanol and 1,3-butanediol, because the direct resolution of these racemates by hplc is impossible. 

Polybutylene terephthalate (PBT) is a semi-crystalline saturated polyester, which has been produced since 1942. PBT is made by the polycondensation of terephthalic acid or dimethyl terephthalate with 1,4-butanediol in the presence of a catalyst. Terephthalic acid, dimethyl terephthalate and 1,4-butanediol are derived from petrochemicals such as xylene and acetylene. The polymer is noted for high stiffness and strength, high resistance to heat, low water absorption and high dimensional stability. It has moderate chemical resistance and low resistance to strong acids and bases. 

Silylacetylenes are intermediates in the preparation of PhCHOHC CH from benzaldehyde, and a mixture of allene-acetylene isomers results from Me3SiC= CCHjOPh using Bu Li-Base-Bu sB. MegNH adds to the double bond of trimethylsilyl vinylacetylenes, and the conductivity assessed for the (phthalo-cyaninato)silane-acetylene linear polymer. ... 

Liquid- and vapor-phase processes have been described the latter appear to be advantageous. Supported cadmium, zinc, or mercury salts are used as catalysts. In 1963 it was estimated that 85% of U.S. vinyl acetate capacity was based on acetylene, but it has been completely replaced since about 1982 by newer technology using oxidative addition of acetic acid to ethylene (2) (see Vinyl polymers). In western Europe production of vinyl acetate from acetylene stiU remains a significant commercial route. 

The principal chemical markets for acetylene at present are its uses in the preparation of vinyl chloride, vinyl acetate, and 1,4-butanediol. Polymers from these monomers reach the consumer in the form of surface coatings (paints, films, sheets, or textiles), containers, pipe, electrical wire insulation, adhesives, and many other products which total biUions of kg. The acetylene routes to these monomers were once dominant but have been largely displaced by newer processes based on olefinic starting materials. 

Acetylene is condensed with carbonyl compounds to give a wide variety of products, some of which are the substrates for the preparation of families of derivatives. The most commercially significant reaction is the condensation of acetylene with formaldehyde. The reaction does not proceed well with base catalysis which works well with other carbonyl compounds and it was discovered by Reppe (33) that acetylene under pressure (304 kPa (3 atm), or above) reacts smoothly with formaldehyde at 100°C in the presence of a copper acetyUde complex catalyst. The reaction can be controlled to give either propargyl alcohol or butynediol (see Acetylene-DERIVED chemicals). 2-Butyne-l,4-diol, its hydroxyethyl ethers, and propargyl alcohol are used as corrosion inhibitors. 2,3-Dibromo-2-butene-l,4-diol is used as a flame retardant in polyurethane and other polymer systems (see Bromine compounds Elame retardants). 

Common conductive polymers are poly acetylene, polyphenylene, poly-(phenylene sulfide), polypyrrole, and polyvinylcarba2ole (123) (see Electrically conductive polymers). A static-dissipative polymer based on a polyether copolymer has been aimounced (124). In general, electroconductive polymers have proven to be expensive and difficult to process. In most cases they are blended with another polymer to improve the processibiUty. Conductive polymers have met with limited commercial success. 

The commercial process for the production of vinyl acetate monomer (VAM) has evolved over the years. In the 1930s, Wacker developed a process based upon the gas-phase conversion of acetylene and acetic acid over a zinc acetate carbon-supported catalyst. This chemistry and process eventually gave way in the late 1960s to a more economically favorable gas-phase conversion of ethylene and acetic acid over a palladium-based silica-supported catalyst. Today, most of the world s vinyl acetate is derived from the ethylene-based process. The end uses of vinyl acetate are diverse and range from die protective laminate film used in automotive safety glass to polymer-based paints and adhesives. 

---