Microstructur diene rubbers

The simplest diene rubber for hydrogenation is BR. The structure of the hydrogenated BR (HBR) depends on the different microstructures present in BR. Hydrogenation of BR with high 1,4 structure converts this elastomeric polymer into a tough semicrystalline... 

Kinetics in Non-Polar Media. Polymerization of vinyl monomers in non-polar solvents, i.e., hydrocarbon media, has been almost entirely restricted to the organolithium systems (7), since the latter yield homogeneous solutions. In addition, there has been a particularly strong interest in the polymerization of the 1,3-dienes, e.g., isoprene and butadiene, because these systems lead to high 1,4 chain structures, which yield rubbery polymers. In the case of isoprene, especially, it is possible to actually obtain a polymer with more than 90% of the eis-1,4 chain structure (7, 8, 9), closely resembling the microstructure of the natural rubber molecule. 

Hydrocarbon Solvents One of the most important synthetic and commercial aspects of anionic polymerization is the ability to prepare polydienes [poly(l,3-dienes)] with high 1,4-microstructure using lithium as the counterion in hydrocarbon solutions [3, 156]. The key discovery was reported in 1956 by scientists at the Firestone Tire and Rubber Company that polyisoprene produced by lithium metal-initiated anionic polymerization had a high (>90%) cm-1,4-microstructure similar to natural rubber [47], In general, conjugated 1,3-dienes [CH2=C(R)-CH=CH2] can polymerize to form four constimtional isomeric microstructures as shown below. The stereochemistry of the anionic polymerization of isoprene and... 

The distinctive feature of lanthanide and in particular Ziegler-Natta catalysts is that they allow one to synthesise polydienes with a high content of c/s-1,4-units. In most cases, lanthanides are used in the form of blends and concentrates. About 50% of lanthanides consumed worldwide are used for the production of catalysts for various chemical processes. Using lanthanide catalysts in the manufacture of synthetic rubbers can increase the number of these processes. A large number of studies have been devoted to polymerisation of dienes with lanthanide catalytic systems. Many of these studies are concerned with the problems related to the mechanism that controls the microstructure of polydienes. Although not all aspects of stereoregulation have been clarified, many problems have been solved and possible explanations offered for some of the others [1-4]. 

Gomaa, E., Microstructure and miscibility of acrylonilrile-butadiene rubber/ethylene-propylene-diene monomer blends studied by positron annihilation spectroscopy, J. Appl. Polym. ScL, 105, 2564-2570 (2007). 

Much less recognized is the possible influence of tacticity on copolymer properties when a-olefin monomer units are a minor component, and crystallinity is not based on a tactic a-olefin sequence but on a different comonomer such as ethylene. In this chapter, this tacticity effect is shown for ethylene-rich ethylene/propylene (EP) copolymers, where the crystallizable sequences are based on ethylene, that is, a comonomer that does not have tacticity requirements. In particular, this chapter describes in detail the microstructure of EP copolymers having industrially relevant compositions (ethylene content 80-55 mol%), with particular focus on the placement of propylene units along the ethylene-based macromolecular chains and their influence on copolymer properties. This subject is, of course, related to the industrial relevance of EP copolymers and ethylene/propylene/diene monomer terpolymers (EPDMs) (collectively referred to as EP(D)Ms), which presently represent the most widely produced saturated rubbers. ... 

It is explained that most rubber products due to the development of cracks, as a result of being subjected to environmental factors. This paper reviews in depth the underlying failure mechanisms, and discusses ways and means of minimising them. It presents the effects of polymer molecular weight, the styrene content of SBR, and the diene microstructure on fracture and fatigue life of the vulcanisates. It also discusses the role played by carbon black and vulcanising systems on fracture and fatigue. 56 refs. 

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