Isoprene value-added

With isoprene in THF the situation is more complicated. While with Li as counterion the system is chemically stable up to 0 °C, with Na" considerable instability arises even at 40 °C. In the former situation reasonable kinetic behaviour is exhibited and u.v. absorption spectra show the presence of three types of anionic centre with absorption maxima at 287, 305, and - 335 nm. The first is assigned to a cis species, the second to the corresponding trans isomer, and the third to some irreversibly isomerized entity whose structure is still by no means certain. At low temperatures — —40 °C) in the absence of common ion salts, as with butadiene polymerizations, fast reactions occur owing to the presence of free anions, predominantly in the trans form, and addition of common ion species depresses the rate to very low values. Above —20 °C under ion pair conditions polymerization via the cis isomer of the active centre appears to be abundant, but, unlike butadiene, there is the added complication in the possibility of 3,4- and 1,2-terminal units arising (20) and (21). In THF the... 

A value of unity (or nearly unity) for the monomer reactivity ratio signifies that the rate of reaction of the growing chain radicals towards each of the monomers is the same, i.e. kn ki2 and 22 — A 2i and the copolymerization is entirely random. In other words, both propagating species and M2 have little or no preference for adding either monomer. The copolymer composition is the same as the comonomer feed with a completely random placement of the two monomers along the copolymer chain. Such behavior is referred to as Bemoullian. Free-radical copolymerization of ethylene and vinyl acetate and that of isoprene and butadiene are examples of such a system, but this is not a common case. Random monomer distributions are obtained more generally in a situation where both types of radicals have exactly the same preference for the same type of monomer as represented by the relationship... 

Durkee and co-workers have prepared polyferrocene block copolymers for use in catalysis.223 The reported polymers were synthesized via sequential anionic polymerization of vinylferrocene and isoprene, followed by oxidation using silver triflate. The fraction of ferrocene converted to ferrocenium was directly proportional to the amount of Ag+ added. These materials were tested for their catalytic activity toward the Michael addition reaction of ethyl-2-oxycyclopentane barboxylate and methylvinylketone. These materials showed k values similar in magnitude to the rates of iron(III) chloride. 

We noticed previously that, when resins are added to the copolymer blend, the plateau modulus decreases (which is what we call a dilution effecf, as opposed to the thermodynamic effecf on the Tg described above). The entanglement network of the isoprene part of the copolymers is swollen and the molecular weight between two entanglement points increases by following the relevant power law [Eq. (19)], where the experimental values of n may range from 2 (theoretical value) to 2.5 for concentrated polymer solutions and melts as well as for the copolymers in the present study [4, 5, 20, 24, 25]. This topological effect is the same as for the isoprene part of diblock and triblock copolymers. 

Rate coefficients for the reactions of OH and O3 with 2- and 3-methyl-3-butene-1,2-diol and l,2-epoxy-3-methyl-3-butene, the latter having been reported very recently as product from isoprene + O3 [11], were determined by use of a relative rate technique. In the O3 experiments sufficient CO was added to scavenge > 90 % of OH radicals eventually being formed. For the O3 reaction of the diols absolute measurements were carried out in addition by monitoring the decay of O3 under pseudo-first order conditions. Absolute and relative rate data were in good agreement. The average values at 295 2 K are ... 

It was anticipated that the copolymerization of substituted 1,1-dipheny-lethylenes with dienes such as butadiene and isoprene would be complicated by the very unfavorable monomer reactivity ratio for the addition of poly(-dienyl)lithium compounds to 1,1-diphenylethylene [133, 134]. Yuki and Oka-moto [133, 134] calculated values of ri=54 and ri=29 in hydrocarbon solutions for the copolymerization of 1,1-diphenylethylene (M2) with butadiene (Mi) and isoprene (Mi), respectively. Although the corresponding values in THE are ri(butadiene)=0.13 and ri(isoprene)=0.12, this would not be an acceptable solution since THE is known to form polymers with high 1,2-microstructures [3]. Anionic copolymerizations of butadiene (Mi) with excess l-(4-dimethyla-mino-phenyl)-l-phenylethylene (M2) were conducted in benzene at room temperature for 24-48 h using scc-butyllithium as initiator [189]. Anisole, triethy-lamine and ferf-butyl methyl ether were added in ratios of [B]/[RLi]=60, 20, 30, respectively, to promote copolymerization and minimize 1,2-enchainment in the polybutadiene units. Narrow molecular weight distribution copolymers with Mn=14xl0 to 32x10 (Mw/Mn=1.02-1.03) and 8, 12, and 30 amine... 

---