Cationic cyclopolymerization

Cationic cyclopolymerization of difunctional 1,4-diisopropenylben-zene and other l,4-bis(l-alkylvinyl)benzenes to form polyindanes is also a step polymerization because protonation and deprotonation occur in every step of monomer addition [Eq. (28)] [34]. 

Si NMR has been used in conjunction with C NMR for study of transfer to monomer in the cationic cyclopolymerization of diallylmethylphenylsilane [52]. The process is represented in equation (3.12) but the number-average degree of polymerization (DP ) of the product is low and is remarkably insensitive to the concentration of the monomer in the polymerizing system and to other experimental conditions. It is supposed [53] that transfer to monomer occurs readily according to equation (3.13)... 

Figure 7.13 Proposed mechanism for cationic cyclopolymerization of l,2 5,6-dianhydro-D-mannitol (13).

Kakuchi, T., Satoh, T., Umeda, S. etal. (1995) Regio- and stereoselectivity in cationic cyclopolymerizations of 1,2 5,6-dianhydro-3,4-di-0-methyl-D-mannitol and -L-iditol and the synthesis of Poly[(l —> 6)-2,5-anhydro-3,4-di-0-methyl-D-glucitol]. Macromolecules, 28,5643-5648. 

However, alloocimene has been found to undergo cationic cyclopolymerization (see Scheme 1) when treated with Bp30Et2 in ice-cold ethyl chloride solution (like myrcene, see above). The prepared polyalloocimene was found to be soluble in... 

Al-Phenyl-iV-allylmethacrylamide (23) gives a polymer with a five-membered ring structure with true asymmetric centers in the main chain by free-radical cyclopolymerization [63]. When the polymerization is carried out in the presence of SnCl4/(-)-menthol, the resulting polymer was optically active ([a]] -5.6°). Chiral induction was also observed in the copolymerization of 23 with MMA. Cationic cyclopolymerization of 24 using a ZnClJ 10-camphorsulfonic acid (25) initiator system gives an optically active polymer having a 1,3-dioxane structure in the main chain([a]435-17°)[64]. 

The ionic chain polymerization of unsaturated linkages is considered in this chapter, primarily the polymerization of the carbon-carbon double bond by cationic and anionic initiators (Secs. 5-2 and 5-3). The last part of the chapter considers the polymerization of other unsaturated linkages. Polymerizations initiated by coordination and metal oxide initiators are usually also ionic in nature. These are called coordination polymerizations and are considered separately in Chap. 8. Ionic polymerizations of cyclic monomers is discussed in Chap. 7. The polymerization of conjugated dienes is considered in Chap. 8. Cyclopolymerization of nonconjugated dienes is discussed in Chap. 6. 

All the above discussion has centred on cationic polymerizations. It should be realized that all the other types of homopolymerization mentioned for the monomers can occur in copolymerizations as well [14, 159]. Even cyclopolymerizations [160] and charge transfer reactions [161, 162] are known. But sorting out the exact reactions that are occurring and the efficiency with which they occur has a long way to go. 

Cyclopolymerization of 2-methyl-l,5-hexadiene is catalyzed by a cationic zir-conocene complex [75]. Isolation of methylenecyclopentane derivatives 55-57 from the low molecular weight oligomeric products provides convincing evidence for chain transfer via P-methyl elimination. 

Kakuchi and Yokota have reported the enantioselective cyclopolymerization of divinyl acetal and divinyl catechol using a chiral cationic initiator 31/ZnCl2 (Scheme 15) [104,105]. The resultant polymer contains only cyclic units, however the relative ratio of cis and trans rings is not reported. By comparing the CD spectra of the polymer and a model compound, it was suggested that the trans rings of the polymer were predominantly of one absolute configuration. 

Butler (7), however, has developed one of the most interesting and effective industrial cationic polymers by free radical polymerization of N,N-dimethyldiallylammonium chloride (DMDAC). The polymerization process involves an intra-intermolecular cyclopolymerization which results in a polymer which was originally reported to have a 6-membered piperidinium ring as a repeating unit in the polymer chain (8). 

The principle of cyclopolymerization has been applied to the synthesis of macrocyclic ether-containing polymers which may simulate the properties of crown ethers. l,2-Bis(ethenyloxy)benzene (a 1,7-diene) and l,2-bis(2-ethenyloxyethoxy)benzene (a 1,13-diene) are typical of the monomers synthesized. Homopolymerization of the 1,7-diene via radical and cationic initiation led to cyclopolymers of different ring sizes homopolymerization of the 1,13-diene led to cyclic polymer only via cationic initiation. Both monomer types were copolymerized with maleic anhydride to yield predominantly alternating copolymers having macro-cyclic ether-containing rings in the polymer backbone. 

The cyclopolymerization of the title compound (St-Cj-St), C3 cyclopolymerization, is reviewed. The polymerization has the similar behavior to the fluorescence emission of 1,3-diphenylpropane and its derivatives (n=3 rule or C3 rule). The monomer and its derivatives were prepared by the convenient method from the corresponding a-phenethylalcohol derivatives, using dimethyl sulfoxide-ZnCl2 CCl3COOH system. St-C3 St gave a cyclopolymer only by cationic initiators, and the presence of cyclized units in the main chain was elucidated by several spectroscopic analyses and also by the isolation of cyclocodimers obtained from the reaction of the monomer with styrene in the presence of the catalytic amount of CF3SO3H. 

The intra- and intermolecular interaction between cationic center and tt-electron system have attracted many chemists and much knowledge on the interaction has been accumulated (1). In 1975, we intended to apply such a kind of interaction to cyclopolymerization. Thus, it is expected that the transition state leading to a strained cyclic unit in the polymerization could be stabilized by the intramolecular attractive interaction between cationic growing-end and ir-system There had been few examples of cyclopolymerizations giving strained units. A paracyclophane unit was employed as a strained cyclic unit in the polymer main chain. In Table I are summarized some cyclophanes with their strain energies. 

We found that radical, anionic, and coordination polymerization gave benzene-insoluble polymer or soluble polymer as shown in Table V (26). These polymers, however, did not exhibit the characteristic spectra for [3.3]paracyclophane units above mentioned. Therefore they were concluded not to be cyclopolymer. Only cationic initiators could induce cyclopolymerization of St-Cj-St (27, 28). 

C3 cyclopolymerization has not yet been finished and has still some interesting unsolved problems as mentioned in this paper. A few of initial objects, however, have been accomplished. That is, it gave the new material which has high n-basicity due to cyclophane units. The future progress is hoped to present further more novel materials produced by the principle of C3 cyclopolymerization where the attractive interaction between cationic site and aromatic n-system functions during the polymerization. 

The synthesis and polymerization characteristics of 1,4-dimethylenecyclohexane are described. Cationic polymerization of this monomer yields relatively low molecular weight polymers containing appreciable amounts of endocyclic double bonds. In contrast to our earlier claim, 1,4-dimethylenecyclohexane does not seem to cyclopolymerize to a significant extent. 

Polycarbosilanes with silicon-containing six-membered rings in the backbone can be synthesized by cyclopolymerization of organosihcon monomers bearing two olefinic substituents. Poly(methylene-(l-sila-3,5-cyclohexanylene))s (15) are obtained by cyclopolymerization of dialkyldiallylsilanes. Coordination polymerization by Ziegler-type catalysts (87-89), cationic polymerization by AlBrs (90-92), and radical polymerization induced by AIBN (93) have been reported (eq. 15). 

The first report of a n-self-doped conducting polymer was provided by Wudl et al. in which a chargebalancing cationic site was incorporated into the polymer [46]. This polymer was poly(dipropargylhex-poly(dipropargylhexylamine) and was prepared from cyclopolymerization of A-hexyldipropargylamine, shown in Figure 20.61. The resultant polymer was also found to contain 20% of the species shown in Figure 20.62. 

Anionic polymerization of o-divinylbenzene was examined by Aso et al. [294]. The authors used n-BuLi, phenyllithium, and naphthalene/alkali metal in THF, ether, dioxane, and toluene at temperatures between —78 and 20 °C. Generally, it was found that as with radical and cationic initiators, a competition between cyclopolymerization and conventional 1,2-polymerization occurs, with the tendency for cyclization to be lower than with the other mechanisms. The polymerization initiated with the lithium organic compounds resulted in polymers with up to 92% double bonds per monomer unit (THF, 20 °C). Polymerization with lithium, potassium, and sodium naphthalene also showed a rather weak tendency for cyclization. In THF at 0°C and 20 °C the cyclization tendency increased with decreasing ionic radii of the counter cation, while in dioxane the reverse effect was observed, and in ether still another dependence was found (K > Li > Na). Nitadori and Tsuruta [299] used lithium diisopropyl amide in THF at 20 °C to polymerize m- and p-divinylbenzene. The authors obtained soluble products with molecular weight up to 100 000 g/mol (GPC) and showed the polymers to contain pendant double bonds by IR and NMR spectra. It seemed to be important that a rather large excess of free amine (the initiator was formed by reaction of -BuLi with excess diisopropylamine) was present in the polymerization mixture. In later studies [300,301] a closer view was taken on polymerization kinetics and the steric course of the polymerization reaction. 

Divinyl ether monomers undergo cyclopolymerization under free-radical as well as cationic conditions. If the polymerizations are carried to high conversion (>30 to 35%), gelation occurs. However, the soluble polymers that are produced at high dilution and low conversion often have rather complex backbone structures. For example, the polymerization of divinyl ether proceeds to give a polymer that incorporates tetrahydrofuran, vinyloxy, and dioxabicyclo[3.3.0]octane units [137,138] ... 

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