Elementary reaction and anionic polymerization of isopropenly t-butyl ketone

Isopropenyl t-butyl ketone (IPTBK) does not undergo radical homopolymerization and its anionic polymerization is a slow equilibrium process with a low ceiling temperature, which is due to its limited conjugation imposed by steric hindrance. Equimolar reactions of IPTBK with several anionic initiators were carried out, products isolated and identified by ¹H-and ¹³C-NMR, and product distributions determined by GC. While n-butyllithium and phenyllithium preferentially produce allyl alcohols, Grignard reagents predominantly undergo β-addition to produce mono-adducts, and a significant amount of dimers. t-Butyllithium and t-butylmagnesium chloride provide the cleanest β-addition with minimal dimer formation and no carbonyl addition. However, Grignard reagent do not yield a polymer. The 1:1 reaction mixture of IPTBK with t-butyllithium is very stable at 0°C, providing a methyl-terminated mono-adduct quantitatively when quenched with methyl iodide after 29 h. Addition of a second IPTBK to the mono-adduct anion appears to be affected by the low ceiling temperature. Although t-butyllithium can efficiently reduce as well as add to di-t-butyl ketone, such reactions are minor in the presence of IPTBK. Anionic polymerization of IPTBK with t-butyllithium was carried out under several conditions. The 1:1 model reactions and the lack of acidic hydrogens in its structure suggest that anionic polymerization of IPTBK with t-butyllithium may be “living.” The molecular weight distribution of the polymers ranged from 1.1 to 1.6 with the number-average molecular weight varying from 2,800 to 233,500. Group transfer polymerization of IPTBK produced only a six-membered lactone.     

A theoretical approach to the kinetics of polymer degradation in solution

After main-chain scission in a polymer, the frequency of encounter between segments in the different fragments is related to the separating process between the fragments. The relationship obtained shows that the separating time is proportional to M ^½, where M is the molecular weight, when the excluded volume disappears. When good solvent is used, the half-time for the separation is obtained as τ_½ = const. M ^0.16–0.22, which is approximated to the experimental data obtained previously (τ_½ = const. M ^0.34 and τ_½ = const. M ^0.22) for the degradations of polyisobutene and poly(phenyl vinyl ketone), respectively. The increase of the half-time with increasing coil density can be explained by the excluded volume. The inverse proportionality of the diffusion of segments to solvent viscosity explains the proportionality of the half-time to microviscosity. The above separating process reverses the reaction between polymer radicals. From their dependence on the chain length, τ_½/k_D = const. M ^½ (where k_D is the specific rate for the reaction), is estimated. Such an approximation holds, regardless of the type of solvent.     

Retardation of radical polymerization rate by phenoxy radical produced from T-butylperoxy phenylcarbonate

T-butylperoxy phenylcarbonate (BPPC) was prepared. Its decomposition rate constant in cumene is given by k_d = 2.39 × 10¹⁵ exp(?17,300/T), where T is the absolute temperature. When BPPC decomposes to polymerize styrene at 100°C, it produces 12% phenoxy radical to total primary radicals. The phenoxy radical hardly adds to styrene and reacts the other primary radicals and polymer radical. Thus it retards the rate of polymerization.     

Termination rate constant in radical polymerization

On the basis of the assumption that the primary radical immerses into a polymeric radical, the rate constant of primary radical termination was derived. By applying and developing further the same treatment, the rate constant of chain termination was derived. This rate constant was experimentally confirmed. It was found that the rate constant of chain termination for the polymerization of some methacrylates depends on the distance of translation of radical chain end per collision, solvent viscosity, and the Taft polar constant for ester group.     

Separation of N2@C60 and N@C60

We describe the HPLC separation and identification of N@C60 and N2@C60. These species were observed after eleven sequential HPLC separations. Their retention times are in the same range as those of the other noninteractive endohedral species of C60, such as noble gas endohedral C60. The separation factors of these endohedrals were evaluated by using a mixture of hexane/toluene as eluent. We note that this is the first evidence for the N2@C60 molecule existing in the form of endohedral C60 complex.     

Catalyzed intramolecular olefin insertion into a carbon-carbon single bond

Intramolecular insertion of a C-C double bond into a C-C single bond was achieved by treatment of cyclobutanone bearing an o-styryl group at the 3-position with a catalytic amount of a cationic rhodium(I)-dppp complex. Initially, rhodium is inserted between the carbonyl carbon and the alpha-carbon of the cyclobutanone. Intramolecular coordination of the vinyl group results in its migratory insertion into the C-Rh linkage. Reductive elimination affords benzobicyclo[3.2.1]octan-3-one. Notably, a ring-opened alpha,beta-unsaturated ketone was obtained when dppe was used instead of dppp. In this reaction, rhodium cleaved the bond between the alpha sp3 carbon and the beta sp3 carbon of the cyclobutanone. The coordinating vinyl group directs this new regioselectivity of cleavage observed with the dppe ligand.     

Facile method for the preparation of lyso-GM1 and lyso-GM2

This paper reports a facile method for the preparation of lyso-GM1 [Gal beta1-->3GalNAc beta1--> 4(Neu5Ac alpha2-->3)Galbeta1-->4Glc beta1-->1'-sphingosine] and lyso-GM2 [GalNAc beta1-->4(Neu5Ac alpha2-->3)Gal beta1-->4Glc beta1-->sphingosine], respectively, from GM1 [Galbeta1-->3GalNAc beta1-->4(Neu5Ac alpha2-->3)Galbeta1-->4Glc beta1-->1'-Cer] and GM2[GalNAc beta1-->4(Neu5Ac alpha2-->3)Galbeta1-->4Glc beta1-->1'-Cer], using sphingolipid ceramide deacylase and high performance anion-exchange chromatography (HPAEC). The enzymatically released lyso-GM1 and/or lyso-GM2 was effectively separated from its parent ganglioside by HPAEC using a Mono Q HR 5/5 column with an Amersham Biosciences fast protein liquid chromatography system. The yield was almost quantitative and the separation completed in approximately 3 h. This method is more convenient and effective than the conventional method using alkaline hydrolysis and silicic acid chromatography to generate and purify lyso-gangliosides.     

Recent results in muonium solution kinetics

Using Muonium Spin Rotation (MSR) techniques the aqueous solution kinetics of several muonium addition reactions and spin conversion interactions have been studied. The addition reactions show both diffusion and activation-controlled reaction rates with isotope effects between 1 and 3 for diffusion-control and between 7 and 31 for activation-control reactions. Barrier energies are typically 15 kJ/mole and 30 kJ/mole, respectively, for these processes in water. Spin-conversion interactions involving Ni_(aq ⁺² and Ni(cyclam)⁺² complexes showed that spin-conversion of triplet Mu by a paramagnetic solute occurs at or near the diffusion-controlled limit while the chemical reaction with the diamagnetic configuration of Ni(cyclam)⁺² occured some 100 times slower at k_M 5×10⁸M^–1s^–1.     

Gelation of colloidal crystals without degradation in their transmission quality and chemical tuning

A single-domain colloidal crystal with high transmission quality, prepared by a shear-induced process, was fixed as a hydrogel film by photopolymerization. Upon gelation, the original optical quality was almost perfectly preserved. By replacing the solvent, the gelled crystal could be converted to smaller lattice constant crystals without significant degradation in its transmission characteristics. The conversion results in a stop-band wavelength coverage across the entire visible light range.     

Study on broad line magnetic resonance absorption of drawn poly(ethylene terephthalate)

Summary The structural changes of drawn poly(ethylene terephthalate) are observed as a function of the temperature of heat-treatment and the angle between the fiber axis and the magnetic field, using with NMR. The results of this experiment show that the low stretched sample C-2 is structureless, but that samples C-3 and C-4 stretched higher than sample C-2 are the doublet structure, and that the more highly stretched sample C-5 is structureless again.The calculated line shapes are compared with the observed line shapes, and they are found in satisfactory agreement with the observed ones. From the results, it becomes clear that the condition of the occurrence of the doublet structure depends on the orientation of the benzene ring proton pair.

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Zusammenfassung Die Strukturänderung von gestrecktem Polyäthylenterephthalat wurde mittels der NMR als Funktion der Wärmebehandlungstemperatur und des Winkels zwischen der Faserachse und dem magnetischen Feld beobachtet. Die Ergebnisse dieser Untersuchungen zeigen, daß die schwach gestreckte Probe C-2 strukturlos ist, während die stärker gestreckten Proben C-3 und C-4 eine Dublettstruktur haben.Eine noch stärker gestreckte Probe C-5 ist wiederum strukturlos. Die gerechneten Linienformen der NMR wurden mit den beobachteten Linienformen verglichen, und es wurde gefunden, daß die vorigen mit den letzteren genügend gut übereinstimmen. Es ist offenbar, daß es von der Orientierung des Protonenpaares des Benzolrings abhängig ist, ob die Dublettstruktur beobachtet wird.