Butadiene block copolymers, tensile

The same dependence of tensile elongation characteristics on block copolymer structure that was observed in this work has been reported for styrene/butadiene block copolymers. Table 3. The importance of the hard/soft/hard sequence is evident since the hard/ soft (A/B) sequence has very low elongation. This corresponds in this work to incompletely extended polymer. Table 2. 

Tensile modnlns of poly-p-phenylene [83], relaxation modulus in LDPE [84], diglycidyl ether bisphenol A epoxy resins [85], and styrene-butadiene block copolymers with doped polyaniline [86]. 

Currently, more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts. The formed copolymer has better mechanical properties and a narrower molecular weight distribution. A random copolymer with ordered sequence can also be made in solution using butyllithium, provided that the two monomers are charged slowly. Block copolymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts. Butadiene polymerizes first until it is consumed, then styrene starts to polymerize. SBR produced by coordinaton catalysts has better tensile strength than that produced by free radical initiators. 

The resulting TPE can either be used alone or blended with aliphatic oil and polypropylene. In the former case a higher tensile strength and elongation at break are obtained in comparison with the commercially available styrene-hydrogenated butadiene-styrene block copolymers, especially at high temperatures. 

Figure 6. Variations of tensile strength as a function of composition of butadiene (BU) and styrene (ST)polymers and copolymers. Key A, polystyrene homopolymer B, 52/48 BU/ ST block copolymer C, 70/30 BU/ ST block copolymer D, 75/25 BU/ ST block copolymer E, 75/25 BU/ ST random copolymer F, butadiene homopolymer.

Smith, T.L., Dickie, R.A., 1969. Viscoelastic and ultimate tensile properties of styrene-butadiene-styrene block copolymers. J. Polym. Sci. Polym. Symp. 26 (1), 163-187. 

Thermoplastics such as polypropylene, polycarbonate, nylon, and thermo set such as epoxy, as well as thermoplastic elastomers such as butadiene-styrene di block copolymer, have been reinforced with carbon nanofibers for example. Carbon nanofibers with 0.5 wt% loading were dry-mixed with polypropylene powder by mechanical means, and extruded into filaments by using a single screw extruder. Decomposition temperature and tensile modulus and tensile strength have increased because of dispersion of CNF [121] (Fig. 8.19). 

Although an ethylene vinyl acetate copolymer was immiscible in NR blends, addition of a 6 phr ethylene vinyl acetate block copolymer enabled compatibilization of heterogeneous NR/acrylonitrile butadiene rubber blends. These blends increased the tensile strength, the elongation at break and tear strength due to an increase in the interfacial adhesion between the blended components by increasing the rigidity of the matrix in the presence of the ethylene vinyl acetate copolymers. ... 

Understanding of the mechanisms in rubber modified polymers have benefited from methods used by Michler et al. [493-495] for the in situ deformation of rubber modified amorphous polymers and butadiene-styrene block copolymers. The techniques used were microscopic investigations of deformed samples, including in situ deformation of thin sections by TEM and AFM. Deformation tests in the SEM included investigation of the samples using special tensile devices at different temperatures (from -150°C to 200°C) in an SEM or ESEM. Deformation... 

When Szwarc et al. discovered [15,16], or rediscovered [17,18], the anionic living polymerization, a completely different preparation of these elastomers was proposed the study of TPEs passed from infancy to maturity. These authors used sodium metal naphthalene diinitiators to prepare poly (styrene-l>-isoprene-6-styrene), which was probably the first TPE with a perfectly defined structure. However, this copolymer could not be commercialized, as most of the poly-isoprene units were -3,4-, with poor elastomeric properties. It is only when the polymerization was initiated by alkyllithium that poly(styrene-l>-isoprene- -styrene) and poly (styrene-butadiene- -styrene) were obtained with the classical TPE properties very high tensile strength and elongation at break, very rapid elastic recovery, and no chemical crosslinking. Bailey et al [19] announced the existence of these materials in 1966 and Holden et al [20] published the corresponding theory in 1967 and extended it to other block copolymers. 

Figure 21.6 Effect of composition and block size on tensile properties of styrene -butadiene - styrene triblock copolymers (1 kg/cm2 = 0.1 MPa)...

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