Polybutadiene chains

Thermoplastic Elastomers. These represent a whole class of synthetic elastomers, developed siace the 1960s, that ate permanently and reversibly thermoplastic, but behave as cross-linked networks at ambient temperature. One of the first was the triblock copolymer of the polystyrene—polybutadiene—polystyrene type (SheU s Kraton) prepared by anionic polymerization with organoHthium initiator. The stmcture and morphology is shown schematically in Figure 3. The incompatibiHty of the polystyrene and polybutadiene blocks leads to a dispersion of the spherical polystyrene domains (ca 20—30 nm) in the mbbery matrix of polybutadiene. Since each polybutadiene chain is anchored at both ends to a polystyrene domain, a network results. However, at elevated temperatures where the polystyrene softens, the elastomer can be molded like any thermoplastic, yet behaves much like a vulcanized mbber on cooling (see Elastomers, synthetic-thermoplastic elastomers). 

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 effect is found to be more pronounced with polybutadienes, i.e., natural and synthetic rubbers. In the polybutadiene chain, the hydrogen atom of theCH2 group is more liable due to the neighbouring double... 

Figure 15 Sketch of the local environment along a polybutadiene chain of cis-and trans-conformers. For sp3-hybridized carbon atoms (indicated by the gray spheres), the chemical shift is different when they belong to a cis-monomer than when they belong to a trans-monomer. For sp2-hybridized carbon atoms (shown by black spheres) in a cis-monomer, NMR shows a different chemical shift whether they have another cis-monomer as a neighbor or a trans-monomer as a neighbor, and it is similar for the sp2-hybridized carbon atoms in the trans monomer.

The second technique makes extensive use of multifunctional diphenylethy-lene compounds to produce e.g. A2B2 star copolymers with A and B polystyrene and polybutadiene chains, respectively [66],... 

Compared to the NMR spectrum,of the polybutadiene (80% 1,2) initiator, new bands appear on the spectra of block polymers for each fraction (Figure 9). These bands correspond to the acrolein blocks attached to the polybutadiene chains. In particular we can observe the presence of ... 

Figure 6.6 Processive enzyme mimic in which host Mnll slides over a polybutadiene chain and at the same time oxidizes its double bonds.

When /i-BuLi adds to 1,3-butadiene, lithium-terminated polybutadiene chain ends result. In hydrocarbon media, 1,4-addition is favored. 

Members of a Japanese group (101, 102), using polybutadiene as their base polymer, were able to metalate the allylic position of the polybutadiene chain. The allylic anion was then allowed to react with additional monomer to produce a grafted polybutadiene copolymer, Eqs. (33) and (34). 

More precisely, the magnetic relaxation depends on the variable of gelation, i.e., the density of crosslinks, and is closely related to the modulus of elasticity, E, on the one hand and to the swelling ratio, Qm, on the other hand. Long polybutadiene chains are currently randomly crosslinked, using sulfur they can serve to illustrate the NMR approach to the characterisation of vulcanised polymers. It has been shown that the... 

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. ... 

Fisher124,125 has studied the stress-strain and optical properties of three SBS block copolymers containing, respectively, 31,40 and 49% polystyrene as a function of temperature. He has shown that these materials are two phase systems in which the polybutadiene chains form an elastomeric phase and the polystyrene chains a glassy phase acting as physical crosslinks. Fisher126 has also obtained electron micro-... 

The Thermoelastic 125 (30% by weight of polystyrene) has been studied by Canter132 as a function of temperature using a specimen moulded at 150 °C. Differential scanning calorimetry has revealed the presence of two transitions. The lower transition temperature corresponds to Tg of polybutadiene chains and the upper transition temperature corresponds to Tg of styrene chains. The upper transition has also been studied by temperature dependence of the torsional modulus. 

In previous publications (7,14, 17) it was presumed that the microstructure of the ultimate unit of the polybutadiene chain arose from the mode of its attachment to the central atom in the 7r-allylic complex, so that the syn (or anti) isomer yielded trans- (or cis)-1,4-enchainment. 

The property of homogeneity of the coq/Ti functions is well illustrated from polybutadiene chains, observing of nuclei [14], Polybutadiene is a flexible polymer whose viscoelastic properties have been extensively studied over a very broad temperature-frequency range [11]. The first criterion of application of this analysis is the observation of a nearly... 

This equation applies to any chain microstructure provided the Ti reference temperature is defined with respect to the glass transition temperature Tg, corresponding to the observed polybutadiene chain [11]. 

Figure 5. Spin-lattice relaxation rates of protons, attached to polybutadiene chains, as a function of the variable coq a( T-Tj) to= 32 ( ), 60 (O) and 100 (A) MHz.

We recently performed FAD experiments on polybutadiene chains labelled with anthracene in the middle of the chain (Fig. 7), embedded in a matrix of homopolymers unlabelled chains. The concentration of labelled chains was about 1 %. 

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