Monomers with Triple Bonds

A Iky nes have been polymerized using ionic and radical initiators, but the polymer molecular weights are low. High molecular weights are obtained by using Ziegler-Natta coordination catalysts (Sec. 8-4d-2) [Chien et al., 1980]. The polymers are of considerable interest in terms of their potential as (semi)conducting materials. 

Nitriles have been polymerized by radical and ionic initiators. The polymer structures are often quite complex, although anionic polymerization yields the cleanest reaction [Wohrle, 1972, 1983 Wohrle and Knothe, 1988], 

Polymerization of isocyanides to polyiminomethylenes is best achieved with cationic initiators, although anionic and radical polymerizations also occur [Millich, 1988]. 

Bevington, Chain Polymerization I, in Comprehensive Polymer Science, Vol. 3, G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, eds., Pergamon Press, New York, 1990. 

Brandrup, J. andE. H. Immergut, eds., Polymer Handbook, 3rded., p. II-316, Wiley-Interscience, New York, 1989. 

Burstall, M. L. and F. E. Treloar, Carbonium Ions, Chap. 1 in The Chemistry of Cationic Polymerization, P. H. Plesch, ed., Macmillan, New York, 1963. 

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Reactions (1) and (4) are essentially the same as the addition of reactive species to the monomer, which is the same as the initiation and propagation reactions in the free radical chain growth polymerization. However, the kinetic chain length in vacuum is very short, and in a practical sense these reactions can be considered to be stepwise reactions. Cycle I consists of reactions of reactive species with a single reactive site, and cycle II is based on divalent reactive species. Reaction (3) is a cross-cycle reaction from cycle II to cycle I. The growth via cycle I requires the reactivation of the product species, whereas cycle II can proceed without reactivation as long as divalent reactive species or monomers with double bond or triple bond exist. 

Figure 7.12. The partial pressure of N2 in each experiment is shown as a horizontal line crossing the pressure-decay curve. As can be seen, the system pressure decreases beyond the partial pressure of N2 in a mixture, indicating that N2 is incorporated into the plasma polymer (and thus disappears from the gas phase). Such a copolymerization of an unusual monomer has been observed for N2, CO, and H2O and is particularly efficient with monomers containing triple bond(s), double bond(s), or aromatic structure(s) (type I and type II monomers).

Three events are involved with chain-growth polymerization catalytic initiation, propagation, and termination [3], Monomers with double bonds (—C=C—R1R2—) or sometimes triple bonds, and Rj and R2 additive groups, initiate propagation. The sites can be anionic or cationic active, free-radical. Free-radical catalysts allow the chain to grow when the double (or triple) bonds break. Types of free-radical polymerization are solution free-radical polymerization, emulsion free-radical polymerization, bulk free-radical polymerization, and free-radical copolymerization. Free-radical polymerization consists of initiation, termination, and chain transfer. Polymerization is initiated by the attack of free radicals that are formed by thermal or photochemical decomposition by initiators. When an organic peroxide or azo compound free-radical initiator is used, such as i-butyl peroxide, benzoyl peroxide, azo(bis)isobutylonitrile, or diazo- compounds, the monomer s double bonds break and form reactive free-radical sites with free electrons. Free radicals are also created by UV exposure, irradiation, or redox initiation in aqueous solution, which break the double bonds [3]. 

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. 

Thiazyl halide monomers undergo a variety of reactions that can be classified under the general headings (a) reactions involving the 7i-system of the N = S triple bond, (b) nucleophilic substitution, (c) halide abstraction, and (d) halide addition. The cycloaddition of NSF with hexafluoro-1,3-butadiene provides an example of a type (a) reaction. 

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. 

Wegner G. Topochemical reactions of monomers with conjugated triple bonds. VI. Topochemical polymerization of monomers with conjugated triple bonds. Makromol Chem 1972 154 35-48. 

A template mechanism was also proposed for spontaneous polymerization of propargyl chloride in the presence of poly(4-vinylpyridine). The reaction consists of partial (6-8%) alkylation of P4VPy by propargyl chloride which leads to stable complex P4VPy with monomer and then to polymerization. The product obtained contains a conjugated bond system formed by opening triple bonds in the monomer according to reaction ... 

Mo catalysts are uniquely effective in the polymerization of S-containing disubstituted acetylenes. Though there is a possibility that S and O in the monomer deactivate group 5 and 6 transition metal catalysts, the basicity of S is weakened by the conjugation with the triple bond, resulting in the lower coordinating ability to the propagating... 

Experimental observations with the Ti(0- -Bu)4 + Et3Al catalyst support the insertion mechanism versus metathesis polymerization.412 Propagation occurs via the cis opening of the triple bond of the coordinated monomer, leading to addition to the Ti—C bond between the growing polymer chain and the catalyst center ... 

The preparation of polymers from heterocyclic monomers that contain polymerizable functional groups undoubtedly constitutes the most common method of incorporating heterocycles into polymeric materials. Polymer-forming reactions are of two possible types addition reactions and condensation reactions. Addition monomers in general contain a site of unsaturation, i.e. a double or triple bond, through which polymerization occurs by successive single bond formation from one monomer to the next. With condensation monomers a bond is formed between two monomers with concomitant elimination of a... 

Since [4+2] cycloaddition is not very susceptible to steric hindrance, this synthetic concept has meanwhile been increasingly used for the assembly of hyperbranched compounds [41]. A diene combining two dienophile functions in one molecule was used as AB2 monomer for polymerisation (Fig. 4.23). The diene function can then react with a triple bond of a second AB2 monomer to form pentaphenylbenzene units [30]. 

It is worth realising in this connection that the chain carrying the carbene can also be formed by a direct reaction of the monomer with the metal carbyne complex, in spite of the fact that complete scission of the triple bond in this complex does not take place [96] ... 

The mechanism of polymerisation of alkynes with metathesis catalysts requires that the original triple bond of the acetylenic monomer becomes a single bond in the polymer [scheme (5) of Chapter 2], in contrast to the insertion mechanism of acetylene polymerisation with Ziegler-Natta catalysts, where the triple bond becomes a double bond [scheme (1)]. Ideas about the mechanism of metathesis polymerisation of cycloolefins suggested that isolable metal carbenes might promote the polymerisation of cycloolefins suggested that isolable metal carbenes might promote the polymerisation of alkynes, as indeed turned out to be true, as several metal carbenes were found [22-24] to cause alkyne polymerisation. 

A unique odd-even effect of the monomers in the diyne polycyclotrimer-ization was observed. In the aliphatic diynes with an odd number of methylene spacers, their triple bonds locate in the same side, which facilitates the back-biting reaction (Scheme 21). In contrast, in the diynes with an even number of methylene units, their triple bonds locate in the opposite sides these unfavorable positions frustrate the back-biting reaction. Consequently, hb-P32(4) possessed triple bond residues in its final structure, whereas its... 

The Beckmann rearrangement of cyclic oximes results in lactams. This is exemplified in Figure 11.38 with the generation of e-caprolactam, the monomer of nylon-6. The nitrilium ion intermediate cannot adopt the preferred linear structure because it is embedded in a seven-membered ring. Therefore, in this case the intermediate might better be described as the resonance hybride of the resonance forms A (C=N+ triple bond) and B (C+=N double bond). The C,N multiple bond in this intermediate resembles the bond between the two C atoms in benzyne that do not carry H atoms. 

Almost all compounds polymerizing by the radical mechanism belong to the classical monomers with a double or triple bond. Radicals of relatively low reactivity formed from the initiators do not usually attack the bonds of electron-rich atoms (with an excess of electrons). They react readily with electron-deficient atoms. Thus the anionically polymerizing monomers usually also polymerize by a radical mechanism. Typical cationic monomers do not undergo radical polymerization. The quite neutral ethylene forms a transition between the two groups. It polymerizes reluctantly by the radical and ionic mechanisms cationically it only yields oligomers. 

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