Thermally stimulated current (TSC) study of the Tg and Tll transitions in anionic polystyrenes

The thermally stimulated current (TSC) technique has been used to investigate three anionic polystyrenes of M?_n 17,000, 71,700, and 1.55 × 10⁶, i.e., M < M_c, M > M_c, and M ? M_c, where M_c is the entanglement molecular weight. A current maximum near T_g designated T_Mg, has relaxation times which follow an Arrhenius equation. A second current maximum at T > T_g appears to be the T_ll process and is designated T_Mll. Relaxation times for it follow a Vogel equation. T_Mg and T_Mll vary with molecular weight, increasing below M_c and leveling off above M_c at a temperature of about 170°C. Values of T_Mg and T_Mll are compared with values of T_g and T_ll obtained from torsional braid analysis, which involves melt flow; and with differential-scanning-calorimetric values on fused films, where there is no transport of polymer. It is concluded from such cross-comparisons that TSC, at least for polystyrene, is a quasistatic test which may involve microscopic viscosity. Macroscopic viscosity does not play a role. The ratio T_Mll/T_Mg is in the range 1.10–1.16, similar to T_ll/T_g values by other methods. A few comments about T_ll in atactic poly(methyl methacrylate) by the TSC method are given.     

Tuneable pseudorotaxane formation between a biotin-avidin bioconjugate and CBPQT4+

A biotinylated 1,5-dialkoxynaphthalene derivative has been shown to have the ability to bind strongly to avidin and thus act as an artificial binding site for cyclobis(paraquat-p-phenylene) thereby facilitating the formation of a tuneable pseudorotaxane-based bioconjugate.     

Synthesis of P,N-heterocycles from omega-amino-H-phosphinates: conformationally restricted alpha-amino acid analogs

P,N-heterocycles (3-hydroxy-1,3-azaphospholane and 3-hydroxy-1,3-azaphosphorinane-3-oxide) are synthesized in moderate yield from readily available omega-amino-H-phosphinates and aldehydes or ketones via an intramolecular Kabachnik-Fields reaction. The products are conformationally restricted phosphinic analogs of alpha-amino acids. The multigram-scale syntheses of the H2N(CH2)(n)PO2H2 phosphinic precursors (n = 1, 2, 3) and some derivatives are also described.     

Synthese et reactivite d''organometalliques perfluores. VII [1] reactivite comparee de derives perfluoroalkyles satures et insatures de l''etain et du mercure vis-a-vis d''electrophiles.

The reactivity of some derivatives of perfluorooctenyl-tin, perfluorooctenyl-mercury and perfluorooctyl-mercury towards protic acids, especially hydrogen chloride, is studied.

The easy cleavage of the tin - sp² carbon bond is painted out, and used to study possibilities of transferring the perfluorooctenyl radical on mercury, upon reaction with mercuric salts.

The mercury-perfluoroalkyl radical bond is shown to be, on the contrary, very resistant to an electrophilic attack.

These results are compared to those concerning the hydrocarbon analogs, and an interpretation, relied to the electronic density on the carbon atom bound to the metallic atom, is given.     

Les melanges polyester/poly(bromure de vinyle)

DSC measurements indicate that poly(vinyl bromide) (PVB) is miscible with several polyesters [poly(caprolactone), poly(valerolactone), poly(butylene adipate) and poly(hexamethylene sebacate)] but immiscible with others [poly(α-methyl-α-n-propyl-β-propiolactone), poly(α-methyl-α-ethyl-β-propiolactone) and poly(ethylene adipate (PEA)]. However, it is known that poly(vinylchloride) (PVC) is miscible with all these polyesters but PEA. The more limited degree of miscibility of PVB with polyesters, as compared with the case of PVC, is surprising in view of the similar properties of the bromine and chlorine atoms.     

Proprietes des α-phenylselenoaldehydes reactions de wittig conduisant a des α-hydroxyesters et cetones β,γ-ethyleniques et a des aldehydes α,β-ethyleniques

Wittig and Wittig-Horner reactions with α-phenylselenoaldehydes lead to allylic selenides. The corresponding selenoxides undergo 2,3-sigmatropic rearrangement providing a route to α-hydroxy β,γ-ethylenic esters and ketones in good yields. In a same way, we prepare, also enals with an additionnal carbon.     

Synthesis and reactivity of sulfur and silyl substituted α-alkylidene-β-lactams

Synthetically valuable α-alkylidene-β-lactams are produced from the addition of chlorosulfonyl isocyanate to allenyl sulfides.     

One more simple proof of the Craig–Sakamoto theorem

We give one more elementary proof of the Craig-Sakamoto’s theorem: given such that ; then AB=0.