Copolymerization butadiene-pentadiene

A study on the homo- and copolymerization of a variety of dienes such as 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, E-l,3-pentadiene, E-l,3-hexadiene, E-l,3-heptadiene, E-l,3-octadiene, E,E-2,4-hexadiene, E-2-methyl-l,3-pentadiene, 1,3-cyclohexadiene mainly focused on mechanistic aspects [139]. It was shown that 1,4-disubstituted butadienes yield frans-1,4-polymers, whereas 2,3-disubstituted butadienes mainly resulted in cis- 1,4-polymers. Polymers obtained by the polymerization of 1,3-disubstituted butadienes showed a mixed trans-1,4/cis-1,4 structure (60/40). The microstructures of the investigated polymers are summarized in Table 26. 

This section summarizes the copolymerization of conjugated dienes with other monomers catalyzed by transition metal complexes. Some of the reactions here were also mentioned in the previous section. The catalyst CpTiCl3/MAO is active not only for the polymerization of 1,3-butadiene, isoprene, 1,3-pentadiene, and styrene but also for the copolymerization of these individual monomers [82]. 

The investigation carried out on homopolymerization and copolymerization of diene monomers included in PHTP allowed us to make evident that the same stereochemical control exists for the two processes (], 24). In both cases 1,4-trans units only are produced, thus permitting a straightforward sequential analysis. The only difference concerns regioselectivity, which is somewhat lower in copolyraerization. For instance, poly(butadiene-co-pentadiene) contains 1 - 3% of head-to-head pentadiene-pentadiene dyads with adjacent tertiary carbons. 

Most unsaturated substances such as alkenes, alkynes, aldehydes, acrylonitrile, epoxides, isocyanates, etc., can be converted into polymeric materials of some sort—either very high polymers, or low-molecular-weight polymers, or oligomers such as linear or cyclic dimers, trimers, etc. In addition, copolymerization of several components, e.g., styrene-butadiene-dicyclo-pentadiene, is very important in the synthesis of rubbers. Not all such polymerizations, of course, require transition-metal catalysts and we consider here only a few examples that do. The most important is Ziegler-Natta polymerization of ethylene and propene. 

An important extension of Ziegler-Natta polymerization is the copolymerization of styrene, butadiene and a third component such as dicyclo-pentadiene or 1,4-hexadiene (see below) to give synthetic rubbers. Vanadyl halides rather than titanium halides are then used as the metal catalyst. 

By using rare earth metals or radicals it is possible to copolymerize 1,3-butadiene and other dienes with cis-, A linkage [3,498]. Polymers of 1,3-butadiene and isoprene at any ratio can be obtained. Copolymes of 1,3-butadiene and 1,3-pentadiene can be produced with catalysts on the basis of vanadium chelates. 1,3-Butadiene is almost completely converted to trans-, A units, whereas 1,3-pentadiene yields 50 to 60% 1,4-addition and 40 to 50% 1,2-addition products. At a 1,3-pentadiene content of 26 to 45wt%, the copolymers are amorphous, featuring high rigidity [499-501]. Diethylaluminum chloride, nickel naphthenate, and water catalyze the copolymerization of 1,3-butadiene and acetylene. The low-molecular-weight copolymers contain mostly cis-Q-Q double bonds [502]. 

Chloro-1,3-butadiene can be polymerized with styrene [528]. The anionic block copolymerization of 1- or 2-phenyl-1,3-butadiene with styrene leads to block polymers of low molecular weight [529]. Similar copolymers are described of 1,3-pentadiene with styrene. With alkyllithium there is no reaction of 1,4-diphenyl-1,3-butadiene with styrene [530]. 

Diolefins, such as butadiene, isoprene, substituted butadienes, 2,4-hexadiene, 1,3-pentadiene, and 1,4-pentadiene, are all known to undergo free-radical-initiated copolymerization with MA. In the absence of initiators, the well-known diene-dienophile reaction can occur to give Diels-Alder products (see Chapter 4). It has also been claimed that it is possible to prepare butadiene-MA copolymers with Ziegler-type catalysts (see Chapter... 

A comparison of the copolymerization properties of butadiene, isoprene, 2,3-dimethylbutadiene, 2,4-hexadiene, 1,3-pentadiene, and 1-methoxybuta-diene with MA is found in Table 10.7. Films obtained by drying solutions of the copolymers were generally tough and flexible. The copolymers contained >75% cw-1,4 unsaturation. 

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