1.3-Butadiene oligomers

Synonyms Atactic butadiene polymer BR Buta-1,3-diene Butadiene homopoiymer 1,3-Butadiene, homopolymer Butadiene oligomer Butadiene poiymer 1,3-Butadiene, poiymers Butadiene resin Butadiene rubber Poiy-1,3-butadiene cis-Poiybutadiene Polybutadiene latex Polybutadiene resin Polybutadiene rubber ClassiTication Polymer elastomer latex Empirical (C4H6) ... 

Butadiene monomer. See 1,3-Butadiene Butadiene oligomer Butadiene polymer. See Polybutadiene... 

Polypentadiene Isoprene oligomers Butadiene, isoprene and chloro-prene polymers... 

Brominated C rbon te Oligomers. There are two commercial brominated carbonate oligomer (BrCO) products. Both are prepared from tetrabromobisphenol A and phosgene. One has phenoxy end caps [28906-13-0] and the other trihromophenoxy [71342-77-3] end caps. These are used primarily in PBT and polycarbonate/acrylonittile—butadiene—styrene (PC/ABS) blends. 

Other high molecular weight hydrocarbon polymers are not biodegradable, but oligomers of <7j -l,4-isoprene (83), butadiene (84), and styrene (85), are degradable. And there has been further confirmation of biodegradation of oligomeric ethylene (86). 

The checkers obtained erratic results in this step, possibly because of surface effects or trace impurities in the pressure vessel. In two other runs, only 16.8-18.8 g of crude product were obtained. In one case, high boiling oligomers were formed, but none of the desired product was produced. Impurities in the diene or dienophile did not appear to be the problem since runs which employed recrystallized 3-acetyl-2(3H)-oxazolone and redistilled 2,3-dimethyl butadiene also gave variable results. 

This strategy is used for the synthesis of three different exact-mass telechelic oligomers. GPC, NMR, and GC/MS evidence indicates that clean depolymerization chemistry occurs for all three samples. Poly( 1,4-butadiene) (38) is broken down into oligomeric units with two, three, and four repeat units using catalyst 23. Catalyst 14 is more efficient and produces even lower molecular weight oligomers, primarily one and two repeat units. When allylchlorodimethylsilane is used instead of ethylene with 14, telechelic dimers are the only product. 

Butadiene and isoprene give rise to mixtures of what are usually called telom-ers, namely 1 1 telomers between the amine and the 1,3-diene (trae hydroamination products), 1 2 telomers and even higher homologs together with oligomers of the diene as exemplified in Eq. (4.41). 

A wide variety of new approaches to the problem of product separation in homogeneous catalysis has been discussed in the preceding chapters. Few of the new approaches has so far been commercialised, with the exceptions of a the use of aqueous biphasic systems for propene hydroformylation (Chapter 5) and the use of a phosphonium based ionic liquid for the Lewis acid catalysed isomerisation of butadiene monoxide to dihydrofuran (see Equation 9.1). This process has been operated by Eastman for the last 8 years without any loss or replenishment of ionic liquid [1], It has the advantage that the product is sufficiently volatile to be distilled from the reactor at the reaction temperature so the process can be run continuously with built in product catalyst separation. Production of lower volatility products by such a process would be more problematic. A side reaction leads to the conversion of butadiene oxide to high molecular weight oligomers. The ionic liquid has been designed to facilitate their separation from the catalyst (see Section 9.7)... 

Scheme 1. Catalytic cycle of the [Ni°L]-catalyzed cyclo-oligomerization of 1,3-butadiene affording Cg-cyclo-oligomer products (according to Wilke et al.) 14...

The enantioface and also the configuration (s-trans, s-cis) of the prochiral butadienes involved in the several elementary steps are of crucial importance for the stereocontrol of the cyclo-oligomer formation. Oxidative coupling, for example, can occur between two cA-butadienes, two /rum-butadienes or between cis- and /nmv-butadiene with either the same or the opposite enantioface of the two butadienes involved. The several stereoisomers are exemplified for the [Ni°(butadiene)2L] active catalysts for cyclodimer formation, that are schematically depicted in Fig. 1, together with the related stereoisomers of the ry ri fC1) and bis(r 3) octadienediyl-Ni11 species 2a and 4a, respectively. For each of the individual elementary steps there are several stereochemical pathways, which are exemplified in Fig. 1 for the... 

The c,c,t-CDT and c,t,t-CDT production paths are shown to be not assisted by incoming butadiene, while the square-planar transition state involved along the all-t-CDT path is significantly stabilized by an axial coordination of butadiene. Hence, the all-t-CDT route becomes the most facile of the three CDT production paths with a free-energy barrier for reductive elimination of 23 kcal mol-1, that perfectly corresponds with experimental estimates.44 Accordingly, the production of C12-cyclo-oligomers requires moderate reaction conditions,9 although 7b represents a thermodynamic sink within the catalytic cycle. 

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