Vinyl-polymerisation mit Cu(I)-tert-Butoxid

Ohne Zusammenfassung     

Coerced photodimerization reaction in the solid state through amine salt formation

Photodimerization of fumaric or several γ-form trans-cinnamic acids proceeded successfully in the solid state through amine salt formation with ammonia or some aromatic heterocyclic amines (especially, imidazole). It appears that this success is due to a small size or a planar structure of the amine. A layered or a channel-type clathrate crystal structure was revealed, respectively.     

Pyrimidine derivatives and related compounds. 38. Synthesis of 1,3-oxazine-2,4-diones and their reaction with nucleophiles. Ring transformation of 1,3-oxazines to pyrimidines

5,6-Unsubstituted 1,3-oxazine-2,4-diones ( 3 ) and 6-unsubstituted 5-methyl-1,3-oxazine-2,4-diones ( 4 ) were prepared by reduction of the corresponding 6-chloro derivatives ( 1 and 2 ). Treatment of 6-chloro-3-methyl-1,3-oxazine-2,4-dione ( 1a ) with sodium azide, sodium cyanide, secondary amines and aniline gave the corresponding 6-substituted compounds ( 7, 9, 10 and 11 ) while the reaction of 1a and 2a,b with primary aliphatic amines such as methylamine and ethylamine caused a ring transformation to pyrimidine ring system giving barbituric acids ( 13a-d ).     

Efficient synthesis of 2,9-disubstituted 8-hydroxyadenine derivatives

An efficient and general method for the synthesis of 2,9-disubstituted 8-hydroxyadenines, which are expected to have various biological activities, was realized. 5-Amino-4-cyano-2-hydroxyimidazoles(1) were prepared from aminomalononitrile and isocyanates as key intermediates. The condensation of 1a with amidines, imidates, guanidine, urea and thioureas afforded 8-hydroxyadenines (2-6) possessing various substituents at the 2-position. Furthermore, selective alkylation of 2-amino- and 2-hydroxyadenines (4 and 6) successively proceeded to give the corresponding 2-alkylamino- and 2-alkoxyadenines (5 and 7), respectively. 2-Alkylthioadenines (15) were prepared by an analogous reaction of 1a with benzoyl isothiocyanate and subsequent S-alkylation. The imidazoles 1 are most useful intermediates for the synthesis of 8-hydroxyadenine derivatives.     

Preparation of poly(N-normalpropyl- acrylamide) gel beads

 The gel beads of N-normal-propylacrylamide are prepared by the radical copolymerization of N-normalpropylacrylamide and N,N′-methylene-bis-acrylamide in water. The optimum reaction conditions to obtain the gel beads are revealed from the phase diagram of the reaction system together with the scanning electron microscopy of the reaction products. The scanning electron microscopy of the reaction products also indicates the formation of the spherical gel beads of sub-micron size ranging from 250 to 500 nm in diameter. The viscosity measurements of the suspension of the gel beads indicate that the concentration dependence of the viscosity of the suspension is well described by Einstein’s theory of the viscosity of colloidal particles. The intrinsic viscosity of the suspension of gel beads is then determined. The density of the gel beads, which was obtained from the intrinsic viscosity of the suspension, indicates that the gel beads are in the swollen state at a temperature of 20 ^°C. Received: 12 September 1997 Accepted: 17 December 1997     

Relation of the chemical structure of polycyanurates to thermal and mechanical properties

Forty polycyanurates were prepared by the interfacial polycondensation of 2-substituted 4,6-dichloro-s-triazines with various aromatic diols. Nitrobenzene was used as a solvent, aqueous sodium hydroxide as an acid acceptor, and a cationic emulsifier as an accelerator. The rate of reaction was largely increased by ultrasonic irradiation. The polymer yield was in the range 57–91%, and the reduced viscosity was 0.41–3.5. The polymers were soluble in chloroform, nitrobenzene, and o-dichlorobenzene but insoluble in common organic solvents such as alcohol, acetone, and hydrocarbons. A clear film was obtained from the chloroform-soluble polymers after evaporation of the solvent. The softening temperature and the thermal stability of each polycyanurate was significantly related to the substituent on the s-triazine nucleus as well as to the diol component in the molecular chain. Polymers of favorable properties were derived from 2-substituted 4,6-dichloro-s-triazines with R = ? C₆H₅, ? N(C₆H₅)₂, ? N(C₆H₁₁)₂, ? N(C₆H₅)(SO₂C₆H₄CH₃), or carbazyl and aromatic diols such as 4,4′-dihydroxybenzophenone, Bisphenol A, or phenolphthalein. These polymers showed tensile strength of 500–670 kg/cm², elongation at break of 2.9–6.0%, and a minor weight loss at 300–350°C.     

Determination of thallium in potassium chloride and electrolyte replenishers by electrothermal atomic absorption spectrometry

Thallium in potassium chloride and electrolyte replenishers was determined by electrothermal atomic absorption spectrometry (ETAAS) with direct injection of a resin suspension. Thallium(III) was extracted on fine particles of a cellulose nitrate resin (CNR) from dilute HCl (pH 1.6) in the presence of ammonium pyrrolidine-1-carbodithioate. The CNR particles were collected on a membrane filter by filtration under suction, suspended in 1.0 mL 10mM HNO3, and then delivered directly to ETAAS as the suspension. The effects of chloride ions were thoroughly investigated. The results showed that the addition of 0.5mM NaCl to the suspension (10mM HNO3) was recommended, after CNR and a membrane filter holding the CNR were washed thoroughly with 0.025M HCl, to eliminate interference from chloride ions. No chemical modifier was required. Extraction from the solution containing up to 2M chloride ion was allowable. The proposed method gave a concentration factor of 50 for a 50 mL sample volume. The detection limit (3sigma, n = 5) was 1 ng (20 pg/mL). The relative standard deviation was 4.9% (n = 5) at 30 ng level of thallium. The content of thallium in potassium chloride was 15.7-32.8 ng/g, and in electrolyte replenishers was 0.18-4.16 ng/mL.     

Higher-order susceptibilities of the regular and the random Ising model on the Cayley tree. I

Explicit expressions for the fourth-order susceptibility (⁴), the fourth derivative of thebulk free energy with respect to the external field, are given for the regular and the random-bond Ising model on the Cayley tree in the thermodynamic limit, at zero external field. The fourth-order susceptibility for the regular system diverges at temperature T _c ⁽⁴⁾ = 2k _B ^–1 J/ln{1+2/[(z–1)^3/4–1]}, confirming a result obtained by Müller-Hartmann and Zittartz [Phys. Rev. Lett. 33:893 (1974)]; Herez is the coordination number of the lattice,J is the exchange integral, andk _B is the Boltzmann constant. The temperatures at which ⁽⁴⁾ and the ordinary susceptibility (²) diverge are given also for the random-bond and the random-site Ising model and for diluted Ising models.     

Self-assembly of ionic liquid (BMI-PF6)-stabilized gold nanoparticles on a silicon surface: chemical and structural aspects

Ultrafine monodisperse gold nanoparticles (AuNPs) were synthesized by an elegant sputtering of gold onto 1- n-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF(6)) ionic liquid. It was found that the BMI-PF(6) supramolecular aggregates were loosely coordinated to the gold nanoparticles and were replaceable with thiol molecules. The self-assembly of BMI-PF(6)-stabilized AuNPs onto a (3-mercaptopropyl)trimethoxysilane (MPS)-functionalized silicon surface in 2D arrays, followed by dodecanethiol (DDT) treatment, have been demonstrated using X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and contact angle measurements. DDT treatment of tethered AuNPs revealed two types of interactions between AuNPs and the MPS-functionalized surface: (a) AuNPs anchor through Au-S chemisorption linkage resulting in strong immobilization and (b) some of the AuNPs are supported by physisorption, driven by BMI-PF(6). The attachment of these particles remains unchanged with sonication. The replacement of BMI-PF(6) aggregates from physisorbed AuNPs with DDT molecules advances the dilution of their interaction with the MPS-functionalized surface, and they subsequently detach from the silicon surface. The present finding is promising for the immobilization of ionic liquid-stabilized nanoparticles, which is very desirable for electronic and catalytic device fabrication. Additionally, these environmentally friendly AuNPs are expected to replace conventional citrate-stabilized AuNPs.