Cationic polymerization of dimethyl ketene

By ionic polymerization, dimethyl ketene can lead to polyketone, polyester or polyacetal. In the presence of AlBr₃ as Lewis acid initiator, pure polyketone can be obtained in nitrobenzene/carbon tetrachloride (50/50, v/v). With other cationic initiators or solvents, a mixture of polyketone and polyester was characterized. According to experimental conditions, a cyclic trimer was also observed by backbiting reaction, a cyclic dimer by heating to room temperature and a cyclic lactone when acetone was used as solvent. ¹³C n.m.r. is the most effective technique to determine polyketone purity. For example, an important modification of f.t.i.r. spectrum was noticed after melting and crystallization of the polymer with appearance of new bands which could correspond to polyester or polyacetal bands regarding to literature data. In fact, these bands correspond to change in morphology and ¹³C n.m.r. spectrum shows no structure modification. Polyketone degradation occurs at about 340 °C and the polymer is stable for several hours at 205 °C.     

Contribution of two approaches using electrospray ionization with multi‐stage mass spectrometry for the characterization of linseed oil

A detailed characterization of triacylglycerols (TAGs) present in linseed oil samples from a local producer was performed using electrospray ionization and two mass spectrometric approaches; direct infusion multi‐stage mass spectrometry (MSⁿ) experiments and liquid chromatography/tandem mass spectrometry (LC/MS/MS) using non‐aqueous reversed‐phase chromatographic conditions. The combination of both approaches permitted the identification of 26 TAGs. Comparison of the two analytical approaches showed that discrimination of regioisomers was achieved from MS³ data while other isobaric species were separated and identified by LC/MS/MS analysis. The results we obtained were also compared with those previously reported. The TAG composition of the studied linseed oil is qualitatively identical to that of linseed oils from various sources in Europe, Canada, Argentina or India. However, a few differences were observed with regard to the proportions of some TAGs; these can be explained by variations in the culture conditions, climate, and variety of the seeds. Copyright © 2009 John Wiley & Sons, Ltd.     

Ruthenium carbonyl complexes in catalytic epoxidation of olefins co‐catalyzed by isobutyl‐aldehyde

The present work shows the catalytic activity of a series of carbonyl ruthenium complexes in the epoxidation of olefins co‐catalyzed by isobutyl‐aldehyde. The complexes display catalytic activity in the epoxidation of the cyclohexene with high selectivity. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of Polymerization Temperature on Reactivity of 1- and 2.Vinyl Naphthalenes

Reactivity ratios relative to the copolymerizations of 1-vinyl naphthalene and 2-vinyl naphthalene with styrene have been determined at different specific temperatures. In the case of the system 1-vinyl naphthalene-styrene, the Arrhenius plot exhibits a curve when the temperature is above -50°C. This is explained by the depropagation contribution, The value of the enthalpy of polymerization calculated by using the Lowry relation is in satisfactory agreement with that obtained from calorimetric determinations. From activation enthalpies and entropies it appears that the selection of the two monomers by the cation is entropically controlled for 2-vinyl naphthalene and enthalpically controlled for 1-vinyl naphthalene.     

New air-stable catalysts for general and efficient suzuki-miyaura cross-coupling reactions of heteroaryl chlorides

[reaction: see text] New air-stable PdCl(2){P(t)Bu(2)(p-R-Ph)}(2) (R = H, NMe(2), CF(3),) complexes represent simple, general, and efficient catalysts for the Suzuki-Miyaura cross-coupling reactions of aryl halides including five-membered heteroaryl halides and heteroatom-substituted six-membered heteroaryl chlorides with a diverse range of arylboronic acids. High product yields (89-99% isolated yields) and turn-over-numbers (10,000 TON) are observed.     

Influence of temperature and nature of photoinitiator on the formation kinetics of an interpenetrating network photocured from an epoxide/methacrylate system

This paper deals with the synthesis of an interpenetrating network made of dimethacrylate and dicycloepoxide oligomers by photopolymerization. More particularly, the influence of several parameters (among which the photoinitiator nature and the reaction temperature) on the polymerization kinetics of each oligomer was studied. Two complementary analysis techniques were then used : the photocalorimetry and the RTIR spectroscopy. The study proceeded in several steps. Firstly, photopolymerization of each monomer was studied. Then, the same study was carried out on mixture of both monomers under conditions in such way than only one network is formed. It was shown that the second compound played the role of plasticizer on the network formed by the first monomer. Finally, the dimethacrylate/dicycloepoxide mixture was studied in the presence of both radical and cationic photoinitiators to synthesize an interpenetrating network (IPN). At 30 °C, ultimate products show a very incomplete epoxide conversion whereas the yield in methacrylic double bonds reaches 70%. On the other hand, epoxy functions react a little more than methacrylic double bonds at 90 °C. It was also shown that the presence of a radical photoinitiator is not necessary, and even slightly unfavourable, since the cationic photoinitiator is able to initiate both radical and cationic polymerization mechanisms.