Syntheses and radical ring-opening polymerization behavior of vinylcyclopropanone cyclic acetals having exomethylene and phenyl groups

Syntheses and radical ring-opening polymerizations of vinylcyclopropanone derivertives having cyclic six-membered acetal, exomethylene, and phenyl groups; 1-vinyl-6-methylene-4,8-dioxaspiro[2.5&]octane ( 2b ), 1-vinyl-5,7-dimethyl-6-methylene-4,8-dioxaspiro[2.5]octane ( 2c ), 1-vinyl-5-phenyl-4,8-dioxaspiro[2.5]octane ( 2d ), and 1-vinyl-5,7-diphenyl-4,8-dioxaspiro[2.5]octane ( 2e ), were carried out. The monomers were prepared by reactions of 1,1-dichloro-2-vinylcyclopropane and the corresponding diols in DMF in the presence of sodium hydride. Radical polymerizations of 2b – 2e were carried out at 60, 80, and 120°C in the presence of an appropriate initiator (3 mol % vs. monomer) in degassed sealed ampoules for 20 h. Although colorless transparent polymers (M̄_n 2300–13,500) were isolated by preparative HPLC for the most monomers, a crosslinked polymer was obtained in the case of 2b . The structures of the polymers were determined to consist of single and double ring-opening units. The content of the double ring-opened unit was 25–75% by comparison of IR spectra to a model compound. It is suggested that the double ring-opened propagating chain end is stabilized by the substituents on the cyclic acetal rings. The two-center energies of the cyclopropane ring and activation energy of ring-opening calculated by molecular orbital methods may explain the selectivity in the cleavage of the cyclopropane ring, and the degree of double ring-opening. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2501–2512, 1997     

Cationic equilibrium ring-opening polymerization of bicyclic monomers and its application to chemical recycling

Spiro orthoesters give poly(cyclic orthoester)s by single ring-opening polymerization in the presence of acid catalysts, and this process undergoes the equilibrium polymerization. We have applied the function of equilibrium polymerization to chemical recycling of polymeric materials. Crosslinked poly(cyclic orthoester)s, prepared by radical additions of poly(cyclic orthoester)s possessing exomethylene groups and dithiols, efficiently decrosslinked to bifunctional spiro orthoesters in the presence of CF₃CO₂H in CH₂Cl₂. The dithiol-linked bifunctional spiro orthoester monomers, prepared by the radical additions of spiro orthoester possessing exomethylene group and dithiols, afforded the corresponding crosslinked polymers in the presence of CF₃CO₂H as a catalyst in bulk. The decrosslinking of the obtained crosslinked polymer proceeded quantitatively to obtain the corresponding bifunctional monomer at room temperature in CH₂Cl₂. Further, an acid-catalyzed reversible crosslinking-decrosslinking of a polymer having a spiro orthoester group in the side chain was carried out. The copolymer obtained by the radical copolymerization of 2-methylene-1,4,6-trioxaspiro[4.6]undecane with acrylonitrile was treated with CF₃CO₂H at −10 °C in CH₂Cl₂ to afford the crosslinked polymer quantitatively. The crosslinked polymer was then treated with CF₃CO₂H at room temperature at a low concentration in CH₂Cl₂ to recover the original polymer.     

Design of latent catalysts and their application to polymer synthesis

Design of latent catalysts such as benzyl sulfonium, benzyl ammonium, benzyl pyridinium, benzyl phosphonium, and hydrazinium salts, and their application to polymer synthesis have been described. They have been demonstrated as excellent thermal or photolatent catalysts for polymerizations of cyclic monomers such as epoxides, bicyclo orthoesters, spiro orthocarbonates, and vinyl monomers such as styrene and vinyl ethers.     

The molecular basis of myeloid malignancies

Myeloid malignancies consist of acute myeloid leukemia (AML), myelodysplastic syndromes (MDS) and myeloproliferative neoplasm (MPN). The latter two diseases have preleukemic features and frequently evolve to AML. As with solid tumors, multiple mutations are required for leukemogenesis. A decade ago, these gene alterations were subdivided into two categories: class I mutations stimulating cell growth or inhibiting apoptosis; and class II mutations that hamper differentiation of hematopoietic cells. In mouse models, class I mutations such as the Bcr-Abl fusion kinase induce MPN by themselves and some class II mutations such as Runx1 mutations induce MDS. Combinations of class I and class II mutations induce AML in a variety of mouse models. Thus, it was postulated that hematopoietic cells whose differentiation is blocked by class II mutations would autonomously proliferate with class I mutations leading to the development of leukemia. Recent progress in high-speed sequencing has enabled efficient identification of novel mutations in a variety of molecules including epigenetic factors, splicing factors, signaling molecules and proteins in the cohesin complex; most of these are not categorized as either class I or class II mutations. The functional consequences of these mutations are now being extensively investigated. In this article, we will review the molecular basis of hematological malignancies, focusing on mouse models and the interfaces between these models and clinical findings, and revisit the classical class I/II hypothesis.     

Fluorescence and amplified emission properties of single-crystal 2,5-bis(4-biphenylyl)thiophene

Ligth amplification properties are investigated for single crystals of commercially available 2,5-bis(4-biphenylyl)thiophene. Depending on growth methods, three kinds of crystals are obtained having different fluorescence spectra in blue-green color. Under optical pumping, their amplified spontaneous emission (ASE) bands appear at different wavelengths. The solution-grown crystal shows ASE bands at λ = 464 and 494 nm which are assigned to the 0–1 and 0–2 transitions, respectively. By contrast, the vapor- and slide-boat-grown crystals show a red-shifted 0–1 band at λ = 496 and a 0–2 band at 520 nm, respectively.     

149Sm and 57Fe nuclear resonant inelastic scattering of filled skutterudites SmFe4X12 (X: pnictogen)

¹⁴⁹Sm and ⁵⁷Fe nuclear resonant inelastic scattering (NRIS) measurements were carried out on SmFe₄P₁₂, SmFe₄As₁₂ and SmFe₄Sb₁₂. A clear dip structure of the ⁵⁷Fe NRIS spectrum was found in SmFe₄P₁₂, which was not clearly observed for SmFe₄As₁₂ and SmFe₄Sb₁₂. On the other hand, the line width of the phonon excitation in the ¹⁴⁹Sm NRIS spectrum increases with increasing the ionic radius of the pnictogen. These findings imply that the hybridization between the Sm and Fe phonon modes is correlated to changes in the ionic radius of the pnictogen.