Isobutylene polymerization is initiated by Cp*TiMe2(μ-Me)B(C6F5)3, formed by combining Cp*TiMe3 and B(C6F5)3 in a 1:1 ratio. The polymerization process exhibits the signature of a carbocationic mechanism, as molecular weights generally increase with decreasing temperature, polydispersities are ∼2, and polymers contain vinylidene end groups. Initiation probably occurs via η-coordination of a molecule of monomer to the cationic species [Cp*TiMe2]+, while propagation and chain transfer proceed as with conventional Lewis acid initiators. Although addition of the proton trap 2,6-di-tert-butylpyridine does have an adverse effect on polymerization, this is not because traces of possible protic initiators are being scavenged but rather because the 2,6-di-tert-butylpyridine coordinates to the titanium cation and inhibits activation of monomer. Further evidence that [Cp*TiMe2]+ behaves as a carbocationic initiator is that the system induces dimerization of 1,1-diphenylethylene to 1,3,3-triphenyl-3-methylindan and also the formation of isobutylene−isoprene copolymers (butyl rubber) in which the isoprene is incorporated via trans-1,4-addition, again typical of conventional initiators. This initiator system is the first metallocene-based carbocationic initiator system to be discovered, and it also appears to be one of the more active.

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Chemical and thermal characterization of poly(d,l‐lactide‐co‐glycolide) (PLGA) composites filled with hydroxyapatite (HA) or carbon nanotubes (CNT) were evaluated by infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and dynamic–mechanical–thermal analysis. The morphology and distribution of the nanoparticles were studied by transmission electron microscopy. The composites were prepared by solvent casting using 30% HA or 1, 3, and 5% of pristine and functionalized CNT as nanoparticles and PLGA 75:25 and PLGA 50:50 as copolymer matrix. The Coats–Redfern and E2 function methodologies were used to calculate the reaction order and the activation energy (Ea) of the thermal degradation process. It was found that the addition of nanoparticles increased the glass transition temperature (Tg) of the composites. Also, higher degradation temperatures and Ea values were obtained for PLGA–HA composites and compared with the neat copolymer, and the opposite behavior was exhibited by PLGA–CNT composites. The thermal and mechanical properties were highly dependent on the morphology and dispersion of the filler. The functionalization process of CNT promoted, to some extent, a better distribution and dispersion of CNT into the matrix, and these composites exhibited a slight enhancement on storage modulus. On the other hand, PLGA–HA composites showed a good dispersion but no improvement on the storage modulus below Tg. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

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The desulfurization of fossil fuels by transition‐metal catalysis is a step closer to reality. The example of benzo[b]thiophene, whose reactivity resembles that of the sulfur‐containing components of crude oil, demonstrates the substitution of S by Ru to yield sulfur‐free organometallic compounds such as the trinuclear 50‐electron cluster 1.

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