Butadiene polymerization scheme

Diene Polymers Polymerization of a 1,3-diene yields a polymer having true asymmetric centers in the main chain and ozonolysis of the polymer gives a chiral diacid compound (12) whose analysis of optical purity discloses the extent of chiral induction in the polymerization (Scheme 11.2) [12,35-39], The polymerization of methyl and butyl sorbates methyl and butyl styrylacrylates and methyl, ethyl, butyl, and /-butyl 1,3-butadiene-1-carboxylates using (+)-2-methylbutyllithium, butyllithium/(-)-menthyl ethyl ether, butyllithium/menthoxy-Na, butyllithium/bomeoxy-Na, butyllithium/Ti((-)-menthoxy)4, and butyllithium/bomyl ethyl ether initiators [35-37] and that of 1,3-pentadiene in the presence of... 

Scheme 51 Stereospecific butadiene polymerization based on a MMAO-activated neodymium methyl complex supported by a dianionic modification of neutral 2,6-diimino-pyridine [190]...

Scheme 55 Proposed activation and butadiene polymerization for MAO-activated Nd(z 3-C3H5)3 dioxane and Nd(/]3-C3H5)X2 THF catalysts (adopted from [152,153]). R-C4H6 = polybutadienyl residue (growing polymer chain). R = abstracted allyl or halide X...

To explain these changes in selectivity, a reaction scheme for allyllithium-catalyzed butadiene polymerization is formulated (Scheme 4), which is derived tentatively on the basis of experimental and theoretical investigations of the structure and reactivity of the allyllithium compounds. 

Aqueous dispersions of poly(vinyl acetate) and vinyl acetate-ethylene copolymers, homo- and copolymers of acrylic monomers, and styrene-butadiene copolymers are the most important types of polymer latexes today. Applications include paints, coatings, adhesives, paper manufacturing, leather manufacturing, textiles and other industries. In addition to emulsion polymerization, other aqueous free-radical polymerizations are applied on a large scale. In suspension polymerization a water-irnrniscible olefinic monomer is also polymerized. However, by contrast to emulsion polymerization a monomer-soluble initiator is employed, and usually no surfactant is added. Polymerization occurs in the monomer droplets, with kinetics similar to bulk polymerization. The particles obtained are much larger (>15 pm) than in emulsion polymerization, and they do not form stable latexes but precipitate during polymerization (Scheme 7.2). 

The catalytic capabilities of the Tp ML complexes for this transformation have also been applied to the functionalization of macromolecules such as polyolefins. Thus polybutadienes (Scheme 6a) or styrene-butadiene rubbers (Scheme 6b) have been modified upon addition of carbene units from EDA that were incorporated into the unsaturated C=C bonds of the polymeric chain, providing interesting features to the isolated materials the incorporation of polar groups provided distinct properties regarding their potential use as adhesives, but maintaining the structure of the parent polymer. 

Polymerization schemes free of termination had been considered in earlier days. For example, the kinetic scheme of non-terminated polymerization was developed by Dostal and Mark20) in 1935. Similarly, non-terminated, sodium-initiated polymerization of butadiene was visualized by Ziegler, and in fact the need of a termination step was not appreciated at that time. Later, several examples of non-terminated polymerization were considered by Flory21), who also discussed some ramifications of such schemes. 

There are many possible schemes for addition reactions of diene monomers from electronical and steric viewpoints. Because the monomer molecules arrange along the direction of the channels, a,co-addition may selectively take place in one-dimensional inclusion polymerization. Therefore, conjugated polyenes, such as dienes and trienes, may selectively polymerize by 1,4- and 1,6-addi-tion, respectively. 1,3-Butadiene polymerized via 1,4-addition exclusively in the chaimels of urea and perhydrotriphenylene. while the same monomer polymerized via both 1,2- and 1,4-additions in the channels of deoxycholic acid and apocholic acid. Moreover, we have to evaluate head-to-tail or head-to-head (tail-to-tail) additions in the case of dissymmetric conjugated diene monomers such as isoprene and 1.3-pentadiene. 

If one considers a monomer of slightly more complexity, the permutations of possible structures are even larger. Consider for example, the monomer chloroprene (2-chloro-1,3-butadiene, 3, Scheme 16.2). Chloroprene is polymerized by free radical emulsion polymerization to form polychloro-prene, or neoprene rubber. Neoprene is one of the oldest synthetic rubbers, and is used when higher performance is needed than can be provided by the lower cost styrene butadiene rubber (SBR). Being a butadiene derivative, chloroprene contains two conjugated double bonds. Polymerization takes place by the opening of one double bond the second is less reactive. Polymerization results in one of four possible structures. The trans-1,4 (4, Schane 16.2) structure accounts for approximately 87% of the polymer imits at dO C [2],... 

The mechanism of B polymerization is summarized in Scheme 4,9. 1,2-, and cis- and trews-1,4-butadiene units may be discriminated by IR, Raman, or H or nC MMR speclroseopy.1 92 94 PB comprises predominantly 1,4-rra//.v-units. A typical composition formed by radical polymerization is 57.3 23.7 19.0 for trans-1,4- c7a -1,4- 1,2-. While the ratio of 1,2- to 1,4-units shows only a small temperature dependence, the effect on the cis-trans ratio appears substantial. Sato et al9J have determined dyad sequences by solution, 3C NMR and found that the distribution of isomeric structures and tacticity is adequately described by Bernoullian statistics. Kawahara et al.94 determined the microslructure (ratio // measurements directly on PB latexes and obtained similar data to that obtained by solution I3C NMR. They94 also characterized crosslinked PB. 

Polymer synthesis is carried out according to the scheme shown in Figure 9. A major distinction between the Ba-Mg-Al and Ba-Li catalysts is that no polymerization of butadiene or copolymerization of butadiene with styrene occurs when only one of the three catalyst components of Ba-Mg-Al is used alone at 50°C in nonpolar solvents. This behavior contrasts with the potential ability of n-BuLi alone to form polymer in the Ba-Li catalyst system. 

The 7r-back donation stabilizes the alkene-metal 7c-bonding and therefore this is the reason why alkene complexes of the low-valent early transition metals so far isolated did not catalyze any polymerization. Some of them catalyze the oligomerization of olefins via metallocyclic mechanism [25,30,37-39]. For example, a zirconium-alkyl complex, CpZrn(CH2CH3)(7/4-butadiene)(dmpe) (dmpe = l,2-bis(dimethylphosphino)ethane) (24), catalyzed the selective dimerization of ethylene to 1-butene (Scheme I) [37, 38]. 

Scheme 24 Organolanthanide-initiated polymerization of butadiene derivatives...

Diene polymers refer to polymers synthesized from monomers that contain two carbon-carbon double bonds (i.e., diene monomers). Butadiene and isoprene are typical diene monomers (see Scheme 19.1). Butadiene monomers can link to each other in three ways to produce ds-1,4-polybutadiene, trans-l,4-polybutadi-ene and 1,2-polybutadiene, while isoprene monomers can link to each other in four ways. These dienes are the fundamental monomers which are used to synthesize most synthetic rubbers. Typical diene polymers include polyisoprene, polybutadiene and polychloroprene. Diene-based polymers usually refer to diene polymers as well as to those copolymers of which at least one monomer is a diene. They include various copolymers of diene monomers with other monomers, such as poly(butadiene-styrene) and nitrile butadiene rubbers. Except for natural polyisoprene, which is derived from the sap of the rubber tree, Hevea brasiliensis, all other diene-based polymers are prepared synthetically by polymerization methods. 

The synthesis and characterization of a series of dendrigraft polymers based on polybutadiene segments was reported by Hempenius et al. [15], The synthesis begins with a linear-poly(butadiene) (PB) core obtained by the sec-butyllithium-initiated anionic polymerization of 1,3-butadiene in n-hexane, to give a microstructure containing approximately 6% 1,2-units (Scheme 3). The pendant vinyl moities are converted into electrophilic grafting sites by hydrosilylation with... 

Transient tetrasilyldigermene 8557 was clearly obtained by photolysis of 50 and trapped by butadiene (Scheme 14). By contrast, thermolysis of 50 at 60°C, even in the presence of trapping reagents, affords only oligomers, probably because the digermene 85 polymerizes at this temperature before it can be trapped.57... 

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