1,4 Polybutadiene microstructure

Polymer Characterization. The copolymer composition and polybutadiene microstructure were obtained from infrared analysis and checked for certain copolymers using 13C NMR. 

Figure 4. Polybutadiene microstructure versus the mole ratio of Ba t-butoxide-hydroxide to n-BuLi. Conditions solvent, toluene 30°C.

Microstructure of Polybutadienes. Microstructure strongly influences the viscosity of the CTPB prepolymer. The viscosity of CTPB increases with increased vinyl content, but for CTPB prepolymers of the required molecular weight, an upper limit of 35% vinyl groups is satisfactory from the standpoint of propellant processing characteristics. It has also been found that the microstructure changes markedly with the synthesis process. Lithium-initiated polymerization yields prepolymers with slightly higher vinyl content than those produced by free radical initiation. 

The polybutadiene microstructure was examined by NMR spectroscopy (27). It was estimated that the polybutadiene segment contained about 7% 1,2-addition and 93% 1,4-addition. The relative amounts of cis and trans structures in the 1,4-adduct could not be resolved by this method. 

Fig. 9. Effect of polybutadiene microstructure on Rafting efficiency ([EtjAlCI] =...

Four chapters in this volume are addressed to the uses of chelated alkali metal complexes in various polymerizations, telomerizations, and polymer grafting applications. They fully cover all of the published work in these areas. There are, however, several general features based on our unpublished results which warrant a general discussion. These include the effect of catalyst ion pair structure on polymerization activity and polybutadiene microstructure, the effect of steric hindrance on catalyst activity, and the mechanisms for chain transfer. 

According to reaction schemes la, lb, and lc, crosslinking is influenced by the type and number of double bonds or allylic hydrogen atoms in the rubber. Polybutadiene microstructure can be controlled easily by suitable anionic polymerization conditions in which parameters like double bond num-... 

Table III illustrates the effect of certain variables on the microstructure of alkali metal-catalyzed butadiene polymers. The percentage of cis-1,4 decreases and the percentage of trans-1,4 increases as the styrene content is increased in lithium-catalyzed butadiene-styrene copolymers. The change of polybutadiene microstructure with styrene content is small and is almost identical to that observed in the free radical-catalyzed butadiene-styrene copolymer system (S).

In general, random SBR with a low amount of block styrene and low amounts of 1,2-butadiene enchainment (<20%) can be prepared in the presence of small amounts of added potassium or sodium metal alkoxides [214, 215]. For example, at 50 °C in the presence of as little as 0.067 equivalents of potassium f-butoxide in cyclohexane, the amount of bound styrene was relatively independent of conversion, in contrast to the heterogeneity observed in the absence of randomizer, that is, tapered block copolymer formation [214]. The polybutadiene microstructure obtained under these conditions corresponds to about 15%... 

Table 9.12 shows how polybutadiene microstructure and macrostructure (i.e., molecular weight, Mw, Mn, polydispersity, and branching) can affect the processability of a polymer (Kumar et al 1996). A study with both cobalt- and neodenium-catalyzed polybutadiene showed the relationship between polydispersity or molecular weight distribution and increases in stress relaxation. Increases in stress relaxation, as measured by the Mooney viscometer, will infer greater difficulty in compound processing, gauge control, nerve, and extrudate or calendered sheet shrinkage (Waddell et al 2004). 

The polybutadiene microstructures of a number of copolymers of butadiene and acrylonitrile were studied by quantitative Raman spectroscopy and a comparison was made with IR studies of these copolymers. The intensities of the v(C C) and the v(CN) bands were also used to determine the amount of each monomer in the copolymer. 24 refs. 

Table 4.2 Typical values of polybutadiene microstructure [5] (in absence of a modifier).

Table 7. Effects of Polar Solvents on Polybutadiene Microstructure ...

Polybutadiene Microstructure. Butadiene polymerizes by addition. Having two double bonds, it forms a variety of polymer structures. One of these, known as the vinyl or 1,2-type, results from addition across just one of the double bonds (eq. 3). 

The chemistries utilized in gas-phase technologies employ the same Ziegler-Natta (314,315) and single-site (metallocene) catalysts (313) described in the processes included below. In gas-phase systems, however, the catalysts are generally solid-supported, but produce the same range of polybutadiene microstructures inherent to the nonsupported catalyst. Several patents also include anionic polymerization systems as useful in gas-phase processes (378). Kinetic modeling work has also been done to better predict the gas-phase polymerization behavior of 1,3-butadiene (379). 

MICROSTRUCTURE VARIATION IN POLYBUTADIENE MICROSTRUCTURE (VINYL. CIS AND TRANS)... 

Beckman AccuLab 3 spectrometer was used for IR analysis of polybutadiene microstructure. The absorption coefficients reported by Morero, et al. were used for the calculation of the microstructure. Varian EM 360 spectrometer was used for the proton NMR composition analysis. 

A base polymer particularly interesting for studying the effect of the aforementioned mechanisms on rubber failure is polybutadiene. In fact, polybutadiene microstructure can be changed in an extremely wide range, by making use of the host of catalyst systems. developed by the ingenuity of chemists, just starting with the same monomer. 

Microstructure variation in polybutadiene microstructure (vinyl, cis and tram). 

The dependence of polybutadiene microstructure on Ba /Mg mole ratio is shown in Fig. 9, at a fixed Mg/Al ratio of 6/1 and for polymerizations in cyclohexane at 50°C. Tran -content is seen to... 

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