RAMAN-SPECTROSCOPIC STUDY OF CRYSTAL PHASE-TRANSITION IN BIS(N-UNDECYLAMMONIUM) TETRACHLOROZINCATE

The solid-solid phase transition of [n-C11H23NH3]2ZnCl4 Complex have been studied by Raman spectroscopy. The results show that the occurence of the structural phase transitions mainly related to the change of packing structure and molecular conformation o

GLASS-TRANSITION AND CRYSTALLIZATION OF POLY(VINYL ALCOHOL)-G-POLY(METHYL METHACRYLATE) GRAFT-COPOLYMERS

The glass transition behaviour, microphase separation morphology and crystallization of poly(vinyl alcohol)-g-poly(methyl methacrylate) graft copolymers (PVA-g-PMMA) were studied. A lamellar microphase separation morphology was formed, even for a copolyme

SYNTHESIS AND PROPELLER-PROPELLER TRANSITION OF OPTICALLY-ACTIVE POLY(DIPHENYL-O-TOLYLMETHYL METHACRYLATE)

Diphenyl-o-tolylmethyl methacrylate (DPTMA) was synthesized and polymerized using initiators of organolithium complexes with (+) - (2S,3S) -dimethoxy-1,4-bis(dimethylamino) butane (DDB) and (-) -sparteine (Sp) as the chiral ligands. DDB was suitable for its complex effective to prepare optically active poly(diphenyl-o-tolylmethyl methacrylate) (PDPTMA) with one-handed helical conformation, whereas only low-molecular weight polymer was formed when Sp was used as ligand due to the repulsive hindrance between the triarylmethyl group and the ligand. A new mutarotation, propeller-propeller transition, was observed for PDPTMA from the optical rotation curves and CD spectra in THF solution. The equivalent period of PDPTMA was estimated to be 14 angstrom based on the x-ray diffraction. (C) 1993 John Wiley & Sons, Inc.

SYNTHESIS AND PROPELLER PROPELLER TRANSITION OF OPTICALLY-ACTIVE POLY(DIPHENYL-O-METHOXYPHENYLMETHYL METHACRYLATE)

Diphenyl-o-methoxyphenylmethyl methacrylate was polymerized with several organolithium complexes of chiral ligand such as (-)-sparteine (Sp) and (S,S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane (DDB). (+)-DDB was effective in preparing a polymer of high optical rotation, whereas (-)-Sp only gave oligomers with low optical rotation for the repulsive hindrance between the bulky ester group and the rigid ligand. The optical rotation of the polymer decreased rapidly to a constant value due to the propeller-propeller transition, which has been demonstrated by H-1 n.m.r. and circular dichroic spectra.

STUDIES ON THE REACTIONS OF TRANSITION-METAL HYDRIDES WITH HETEROCUMULENES .6. REACTION OF CP2ZR(H)CL WITH RNCS (R=C6H5, 2-C10H7, C-C6H11 AND N-C4H9)

The novel NS-containing zirconacycle complexes Cp2ZrCl[SC(H)NR] (1a, R = C6H5; 1b, R = 2-C10H7; 1c, R= C-C6H11; 1d; R = n-C4H9) were obtained by insertion reactions of Cp2Zr(H)Cl with RNCS. 1(a-d) could react further with Cp2Zr(H)Cl to yield a sulphur-bridging compleX (Cp2ZrCl)2S (2) and a Schiff base RN=CH2. The crystal structure of la has been determined by X-ray analysis.

STUDIES ON OLEFIN-COORDINATING TRANSITION-METAL CARBENE COMPLEXES .20. SYNTHESIS OF 1,3-CYCLOHEXADIENE(DICARBONYL) [ETHOXY(ARYL)-CARBENE]IRON COMPLEXES AND THEIR PHOSPHINE ADDUCTS - CRYSTAL-STRUCTURE OF C6H8(CO)2FEC(OC2H5)C6H4CH3-O

Reaction of 1,3-cyclohexadiene(tricarbonyl)iron (1) with ortho-substituted aryllithium reagents ArLi (Ar=o-CH3C6H4, o-CH3OC6H4, o-CF3C6H4) in ether at low temperature, and subsequent alkylation of the acylmetalates formed with Et3OBF4 in aqueous solution at 0-degrees-C or in CH2Cl2 at -60-degrees-C gave the 1,3-cyclohexadiene(dicarbonyl)[ethoxy(aryl)carbene]iron complexes (eta4-C6H8)(CO)2FeC(OC2H5)Ar (3, Ar = o-CH3C6H4; 4, Ar = o-CH3OC6H4), and the isomerized product (eta3-C6H8)(CO)2FeC(OC2H5)C6H4CF3-o (5), respectively, among which the structure of 3 has been established by an X-ray diffraction study. Complex 3 is monoclinic, space group P2(1) with a = 8.118(4), b = 7.367(4), c = 14.002(6) angstrom, beta = 104.09(3)-degrees, V = 812.2(6) angstrom3, Z = 2, D(c) = 1.39 g cm-3, R = 0.056, and R(w) = 0.062 for 976 observed reflections. Complexes 3 and 5 were converted into the chelated allyliron phosphine adducts(eta3-C6H8)(CO)2(PR31)FeC(OC2H5)Ar (6, Ar = o-CH3C6H4, R1 = Ph; 7, Ar = o-CH3C6H4, R1 = OPh; 9, Ar = o-CF3C6H4, R1 = Ph), by reaction with phosphines in petroleum ether at low temperatures.

AN INFRARED SPECTROSCOPIC STUDY OF THE STRUCTURAL PHASE-TRANSITION IN THE PEROVSKITE-TYPE LAYER COMPOUND [N-C16H33NH3]2COCL4

The solid-solid phase transitions in the perovskite-type layer compound [n- C16H33NH3]2CoCl4 have been studied by infrared spectroscopy. A new phase transition at 340 K was found by comparison with differential scanning calorimetry results. A temperature dependence study of the infrared spectra provides evidence of the occurrence of structural phase transitions related to the dynamics of the alkylammonium ions and hydrogen bonds. The main transition at 374 K corresponds to the conformational order-disorder change in the chain, which probably couples with reorientational motions of the NH3 polar heads. GTG or GTG' defects appear in the high temperature disordered phase.

MOSSBAUER-EFFECT STUDIES OF THE PHASE-TRANSITION PROCESS IN EUROPIUM PENTAPHOSPHATE

Mossbauer spectra of europium pentaphosphate are measured at various temperatures (126 to 200-degrees-C). Some Mossbauer parameters, such as isomer shift, electric quadrupole splitting, and asymmetry parameter of the EFG at Eu-151 nuclei are derived from the experimental spectra. The lattice parameters of the crystal are determined at several temperatures. The experimental results indicate that the crystal structure of europium pentaphosphate changes from monoclinic to orthorhombic. All of the temperature dependences of the Mossbauer parameters provide evidence of a phase transition of the crystal. The phase transition temperature can be determined from the curve of the asymmetry parameter of EFG versus temperature to 165-degrees-C.

SEARCH FOR THE BASIC REGULARITIES OF THE TRANSITION EMISSION OF EUROPIUM(II) ION IN COMPLEX FLUORIDES USING PATTERN-RECOGNITION

The relationship between structures of complex fluorides and spectral structure of Eu(II) ion in complex fluorides (AB(m)F(n)) is investigated by means of pattern recognition methods, such as KNN, ALKNN, BAYES, LLM, SIMCA and PCA. A learning set consisting of 32 f-f transition emission host compounds and 31 d-f transition emission host compounds and a test set consisting of 27 host compounds were characterized by 12 crystal structural parameters. These parameters, i.e. features, were reduced from 12 to 6 by multiple criteria for the classification of these host compounds as f-f transition emission or d-f transition emission. A recognition rate from 79.4 to 96.8% and prediction capabilities from 85.2 to 92.6% were obtained. According to the above results, the spectral structures of Eu(II) ion in seven unknown host lattices were predicted.

ANODIC-OXIDATION OF HYDRAZINE ON GLASSY-CARBON MODIFIED BY MACROCYCLIC TRANSITION-METAL COMPLEXES .1. COBALT PROTOPORPHYRIN DIMETHYL ESTER MODIFIED ELECTRODE

The electrocatalytic oxidation of hydrazine (N2H4) on a glassy carbon electrode (GC) modified by monolayer and polymer films of cobalt protoporphyrin dimethyl ester (CoPP) has been studied. Both the monolayer and polymer films of CoPP are very active to the anodic oxidation of N2H4. The activity of CoPP for the anodic oxidation of N2H4 is dependent on the pH of the solution, and the thickness of polymerized CoPP film. The oxidation kinetics were examined by methods of cyclic voltammetry, rotating disc electrodes and steady-state polarization measurement.

MOLECULAR-WEIGHT DEPENDENCE OF THE GLASS-TRANSITION OF CYCLIC POLYSTYRENE

The glass transition temperature (T(g)) of cyclic polystyrene was measured by differential scanning calorimetry. There was a marked difference in the glass transition behaviour between cyclic and linear polystyrene. In the low molecular weight region (M(n) < 5 x 10(3)), the T(g) of the cyclic polystyrene increased with decreasing M(n), contrary to that of linear polystyrene. With M(n) higher than 5 x 10(3), the T(g) of cyclic polystyrene increased with increasing M(n). The T(g) of cyclic and linear polystyrene approached the same constant value when the M(n) was high enough (M(n) > 10(5)). Combining the results of specific volume, it is believed that the variation of T(g) with molecular weight does not depend only on free volume effects but that configurational entropy is also an important factor.

GLASS-TRANSITION TEMPERATURE AND MOLECULAR-PARAMETERS OF POLYMER

A new relationship, which correlates the glass transition temperature (T(g)) with other molecular parameters, is developed by using Flory's lattice statistics of polymer chain and taking the dynamic segment as the basic statistical unit. The dependences of T(g) on the chain stiffness factor (sigma-2), dynamic stiffness factor (beta = -d ln-sigma-2/dT) and molecular weight of polymer are discussed in detail based on the theory. The theory is compared with experimental data for many linear polymers and good agreement is obtained. It is shown that T(g) is essentially governed by the chain stiffness factor at T(g). Moreover, a simple correlation between the parameter K(g) of the Fox-Flory equation (T(g) = T(g)infinity - K(g)/M(n)) and other molecular parameters is deduced. The agreement between theoretical predictions and experimental measurements of K(g) has been found to be satisfactory for many polymers.