Polybutadiene chain structure

Although the exact nature of the active center in polymerizations of butadiene with these Ba-Mg-Al catalysts is not known, we believe that the preference for trans-1,4 addition is a direct consequence of two aspects of this polymerization system, namely (1) the formation of a specific organobarium structure in a highly complexed state with Mg and A1 species, and (2) the association of the polybutadiene chain end with a dipositive barium counterion which is highly electropositive. 

The concept of using block copolymers for preparation of nanoscopically structured material and surfaces was advanced further by introducing a third block in the chain structure [29]. One of the consequences of the multiphilicity and versatility of the ABC triblock copolymers is their tremendous richness and diversity in morphology. One of the most peculiar structures is shown in Fig. 28 where the helices of a polybutadiene microphase are wound around columns of polystyrene which are embedded in a matrix of polymethylmethacrylate. Complementary to the TEM studies of the bulk morphology (Fig. 28a,b), SFM has been used to image the surface structure of the triblock copolymer films. Figure 28c shows the wrapped PS cylinders oriented parallel to the surface, where one... 

The comparison of copolymers SB, BMS and BVN with the same compositions and molecular weight and exhibiting all a lamellar structure has shown that the extension of the macromolecular chains depends upon the nature of the nonpolybutadiene blocks. The extension of the chains increases in the order styrene, a-methylstyrene, vinylnaphtalene and the extension of the polybutadiene chain is caused by that of the adjoined chain85. ... 

Most of the data referred to above were obtained in earlier work, and were based on infrared spectroscopy. In recent years, more reliable data were obtained by means of NMR spectroscopy, using both and resonances (9-14). Some of these investigations suggested that, aside from the dramatic effects of polar solvents on the chain structure in organolithium systems, there were some subtle effects even in non-polar media, e.g., caused by initiator concentration and type of non-polar solvent. Sinn and coworkers ( ), for example, used infrared spectroscopy to show an effect of butyl lithium concentration on the chain structure of polyisoprene and polybutadiene. Hence an extensive study was carried out recently (, M) on the influence of reaction parameters on the chain structure of polybutadiene and polyisoprene prepared in non-polar media. 

Effect of Initiator Concentration and Solvents on Chain Structure of Lithium Polybutadiene... 

Table I also shows that the initiator and monomer concentration can also markedly affect the chain structure in nonpolar media (these factors apparently have no effect in the presence of polar solvents). Thus, the highest cis-1,4 content in the case of both polybutadiene and polyisoprene is obtained in the absence of any solvents and at very low initiator levels.

TABLE VIII Chain Structure of Emulsion Polybutadiene and SBR°... 

The control of chain structure and molecular weight afforded by the organolithium polymerization of dienes, has, of course, been of great technological interest [161,162,209]. Such product developments have been mainly in the form of (1) polybutadiene elastomers of various chain structures [162, 198,209] and functional end groups [210], (2) liquid polybutadienes [211], (3) butadiene-styrene copolymers (solution SBR) [69, 161, 162, 209], and (4) styrene-diene triblock copolymers (thermoplastic elastomers) [212]. 

The range of structures for which local conformational dynamics have been simulated is rather limited at this point. A number of workers have simulated polyethylene-like chains [27, 32, 35, 39, 42, 59, 60, 79]. For this structure, the effect of various torsion potentials have been explored [27,39], Recent work has added side-groups to this model [59]. Qualitatively, higher barriers and the addition of side-groups slow dynamics, as would be expected. Simplified versions of polyisoprene [24] and polybutadiene [61] (structures as shown in Fig. Ic) have so been studied. In this section we compare these simulations with each other and with experiments. 

Complications in Propagation When there is more than one unsaturated bond in the monomers, propagation can occur in a different mechanism, thereby affecting the chain structure. For example, in the synthesis of polybutadiene, polymerization can lead to three different products ... 

Having two conjugated double bonds, butadiene can result in various isomeric structures in the polybutadiene chain, as shown in Fig. 1. When both double bonds participate in 1,4-addition, the remaining double bond in the polymer backbone can exist as two geometric... 

Hydrogenation of polybutadiene converts both cis and trans isomers to the same linear structure and vinyl groups to ethyl branches. A polybutadiene sample of molecular weight 168,000 was found by infrared spectroscopy to contain double bonds consisting of 47.2% cis, 44.9% trans, and 7.9% vinyl. After hydrogenation, what is the average number of backbone carbon atoms between ethyl side chains ... 

Whilst c /5-1,4-polybutadiene is a rubber, 1,2-polybutadiene is thermoplastic. Such a material is very similar in structure to polybut-l-ene except that the hydrocarbon side chain is unsaturated ... 

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