Cyclopolymerization of conjugated dienes

Conjugated dienes like isoprene, butadiene, and chloroprene cyclopolymerize with catalysts consisting of aluminum alkyls, like ethylaluminum dichloride, and titanium tetrachloride [141]. The ladder polymers that form contain fused cyclic structures. The products prepared in hexane are generally insoluble powders, while those prepared in aromatic solvents are soluble even when the 

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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. 

To explain the formation of non-crosslinked polymers from the diallyl quaternary ammonium system, Butler and Angelo proposed a chain growth mechanism which involved a series of intra- and inter-molecular propagation steps (15). This type of polymerization was subsequently shown to occur in a wide variety of symmetrical diene systems which cyclize to form five or six-membered ring structures. This mode of propagation of a non-conjugated diene with subsequent ring formation was later called cyclopolymerization. 

Recently, a metallocene/MAO system has been used for the polymerization of non-conjugated dienes [204, 205]. The cyclopolymerization of 1,5-hexadiene has been catalyzed by Zieger-Natta catalyst systems, but with low activity and incomplete cyclization in the formation 5-membered rings [206]. The cyclopolymerization of 1,5-hexadiene in the presence of ZrMe2Cp2/MAO afforded a polymer (Mw = 2.7 x 107, Mw/Mn = 2.2) whose NMR indicated that almost complete cyclization had taken place. One of the olefin units of 1,5-hexadiene is initially inserted into an M-C bond and then cyclization proceeds by further... 

Cyclopolymerizations are a type of reverse ROP. Non-cyclic monomers, mostly conjugated or non-conjugated dienes, yield rings composing the resulting macromolecule. For example... 

There are a few examples of monocyclopentadienyl compounds that catalyze non-conjugated dienes. The cationic titanium compound [Cp TiMe2] [172] and mono(pentamethylcyclopentadienyl)yttrium alkoxides [53] catalyzed cyclopolymerization of 1,5-hexadiene, whereas neither of them gave highly stere-oregulated polymers. 

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