Mechanical relaxation mechanism of epoxide resins cured with aliphatic diamines

The mechanism of low-temperature relaxations in bisphenol-A-type epoxide resins cured with aliphatic diamines, with aliphatic diamines in the presence of salicylic acid as an accelerator, and with tertiary amines was investigated to compare the dynamic mechanical properties and the chemical structure of these networks. Mechanical relaxations are observed at about ?140 and ?60°C. The former relaxation is denoted the γ relaxation and the latter the β relaxation. The β relaxation of the cured epoxide resins containing hydroxyether groups is a sum of contributions from the relaxation of these groups and of other parts of the network structure. A new relaxation due only to the motion of the hydroxyether group can be estimated from the difference of tanδ curves between the aminecrosslinked and ether-crosslinked systems. The γ relaxation is attributed to the motion of a polymethylene sequence consisting of at least four carbon atoms.     

Photodegradable polyamides

Unique photodegradable polyamides have been prepared by solution polymerization of diphenyl α-truxillate or δ-truxinate with hexamethylene or nonamethylenediamine, followed by melt polymerization. Photochemical properties of resulted polyamides were studied spectroscopically and are discussed in terms of photoreversibility and monomeric derivatives for comparison. Solution viscosity of the polymer was decreased by irradiation with a high-pressure mercury lamp. The polymers from α-truxillic acid depolymerize by the action of monochromatic light of 224 mμ to give rise to cinnamyl groups faster than those from δ-truxinic acid. On the photodegradation of polyalkylene-δ-truxinamide, two types of scission of cyclobutane were found: symmetrical scission, giving rise to two cinnamyl groups, and a symmetrical scission, giving rise to one trans-stilbene and one fumaramide linkage. The intense absorption peak due to cinnamyl groups at 272 mμ of partially photodepolymerized films diminished by the action of 304 mμ light; this can be accounted for by the recombination of cinnamyl groups into cyclobutane ring and some unidentified crosslinking reactions. The photochemical behavior of cyclobutane in the polyamides studied proved to be consistent with that of monomeric derivatives reported previously. The study on thermal properties of the polymers by DTA and TGA revealed that this type of polyamide is quite stable as high as 350°C unless significant steric effects are involved.     

Ni(0)/ZnCl(2)-promoted coupling of enones and enynes. Domino process via formation of three C-C bonds and cleavage of one C-C bond

Domino coupling of enones and enynes, which proceeds via the formation of three carbon-carbon bonds and the cleavage of one carbon-carbon bond, was developed using a Ni(0) and ZnCl2 system.     

A Mn12 single-molecule magnet [Mn12O12(OAc)12(dpp)4] (dppH = diphenyl phosphate) with no coordinating water molecules

The preparation and physical characterization are reported for a novel single-molecule magnet [Mn(12)O(12)(OAc)(12)(dpp)(4)] (dppH = diphenyl phosphate) with no coordinating water molecules. The crystal structure analysis reveals that there are four five-coordinate Mn(III) ions with Mn.H approaches. Addition of water in CD(2)Cl(2) solution was monitored by (1)H NMR, which showed that H(2)O could coordinate to a vacant site of a five-coordinate Mn(III) ion in solution. The measurements and analyses of magnetization hysteresis and ac magnetic susceptibility indicate that the title complex is a single-molecule magnet with a quantum tunneling behavior, whose ground state was tentatively assigned to S = 10 with g = 1.78 and D = -0.60 K.     

Relativistic theory of a hydrogen atom in a superstrong magnetic field

The Dirac equation for a hydrogen atom in a static, uniform magnetic field is transformed by a modified FWT transformation into a mixed form; relativistic for perpendicular motion and semi-relativistic for parallel motion. In this way the adiabatic approximation can easily be obtained.     

Four-center type photopolymerization in the crystalline state. V. X-ray crystallographic study of the polymerization of 2,5-distyrylpyrazine

Changes in crystal structure during polymerization and oligomerization of 2,5-distyrylpyrazine have been investigated by x-ray crystallography. The polymer and the oligomer as obtained are three-dimensionally oriented, and the directions of the three axes of the resultant crystals coincide with those of the original crystal. The space group of the products also agrees with that of the monomer. It is concluded that the polymer and the oligomer crystals approximately duplicate the molecular arrangement in the monomer crystal. The polymerization mechanism is discussed on the basis of the crystal structures.