The role of copper(I) complexes in the selective formation of oxazoles from unsaturated nitriles and diazoesters

peer reviewedThe 1,3-dipolar addition of ketocarbenes (generated from diazoesters) to nitriles is promoted at room temperature by palladium acetate and even more efficiently by copper trifluoromethanesulphonate. The reduction of copper(II) to copper(I) is a key step in the catalytic process, as shown by kinetic studies, EPR and polarography. © 1975

Anionic polymerization of various methacrylates initiated with LiCl-complexed sBuLi

A simple alkyl lithium initiator (sBuLi) complexed with LiCl (10 molar equiv.) has been used to initiate the anionic polymerization of various methacrylic monomers, i.e. methyl methacrylate (MMA), tert-butyl methacrylate (tBuMA), glycidyl methacrylate (GMA), and dimethyl amino ethyl methacrylate (DMAEMA) in tetrahydrofuran at -78°C. Only the homopolymerization of tBuMA proceeds in a living manner, as evidenced by both the linear plot of experimental molecular weight (Mnexp) vs theoretical ones (Mncal,) (slope % 0.93) and monomer resumption experiments. However, three types of block copolymers, i.e. PtBuMA-b-PMMA, PtBuMA-b-PGMA, PtBuMA-b-PDMAEMA, have been successfully synthesized with a predictable molecular weight, and narrow molecular weight distribution

Radical addition to 2‐isopropenyl‐5‐butoxyoxazole

The preparation and the spectroscopic analysis of a dimeric adduct (V) obtained from 2‐isopropenyl‐5‐butoxyoxazole (III) and α,α‐azobis‐isobutyronitrile (AIBN) (IV) are reported. It is noteworthy that (III) inhibits completely the homopolymerization of styrene. This is in strong opposition to the facile homopolymerization and copolymerization of 2‐isopropenyl‐4,5‐dimethyloxazole with styrene. The smooth formation of (V) is also in sharp contrast to the lack of reactivity of (III) towards cationic initiators. Copyright © 1986 John Wiley & Sons, Inc

Design of polymer blend rheology: 4. Effect of polymethacrylic ionomers on the melt viscosity of polyamide m x D,6

Rheological properties of blends of polyamide m x D,6 (PA) with random copolymers of methyl methacrylate and methacrylic acid (P(MMA-co-MAA)) and the related ionomers (P(MMA-co-metal MA)), respectively, have been investigated at 260°C. Addition of small amounts of suitable ionomers (up to 5 wt%) remarkably increases the melt viscosity of PA. At low shear rates and depending on the metal cation of the ionomer, the rheofluidity of PA is reduced by at least two orders of magnitude. The PA melt viscosity increases with the cation as follows: Ni2+ < Ba2+ < Mg2+ < Li+ < Na+ < K+ < Cs+. The major effect is believed to occur when the polymer compatibility is improved to the point where a finely dispersed two-phase system with a low interfacial tension is reached, as a result of strong ion-dipole interactions. Polyblends show a rheothinning behaviour which agrees with the reversibility of H-bonding and dipolar interactions

Shear thickening of halato-telechelic polymers in apolar solvents

Short-length polymers selectively end-capped with a metal carboxylato group at both ends, i.e, metal carboxylato-telechelic polymers, exhibit an unusual shear-thickening behaviour in apolar solvents, depending on the main experimental parameters that control the ion-pair association, such as metal cation, concentration and temperature. In contrast to the non-ionic precursors, metal carboxylato-telechelics are indeed responsible for a marked increase in the solution viscosity in a range of shear rates between 0.1 and 1000 s(-1). The shear-rate dependence of the solution viscosity has been analysed in a close relationship to metal counterion, polymer concentration, temperature and addition of polar compounds to the apolar solvent. As a rule, the dilatant behaviour depends strongly on the formation of polymer aggregates in relation to the mutual interactions of the ion pairs. A consensus is now emerging on the origin of the shear-thickening effect, which should be found in inter-aggregate associations rather than in a transition from intramolecular to intermolecular associations of the individual chains