Asymmetric polymerization of the mixture of TrMA and MMA initiated by chiral complexes

A mixture of triphenylmethyl methacrylate (TrMA) and methyl methacrylate (MMA) was polymerized with chiral anionic initiator, such as fluorenyl lithium-(-)-sparteine [FlLi-(-)-Sp] and fluorenyl lithium-(+)-2S,3S-dimethoxy-1,4-bis(dimethylamino) butane [FlLi-(+)-DDB] in toluene at -78 degrees C. The results show that after the stable helix formed, when FlLi-(+)-DDB was used as the initiator, TrMA and MMA could be copolymerized, whereas when FlLi-(-)-Sp was used, the two monomers tended to be selectively polymerized into two polymers. This phenomenon has been explained by the existence of helix-selective polymerization. (C) 1997 John Wiley & Sons, Inc.

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.

Thiophene-NPN Ligand Supported Rare-Earth Metal Bis(alkyl) Complexes. Synthesis and Catalysis toward Highly trans-1,4 Selective Polymerization of Butadiene

A series of new rare-earth metal bis(alkyl) complexes [L(1-3)Ln(CH2SiMe3)(2)(THF)(n)] (L-1 = MeC4H2SCH2NC6H4(Ph)(2)P=NC6H2Me3-2,4,6: Ln = Sc, n = 1 (1a); Ln = Lu, n = 1 (1b); L-2 = MeC4H2SCH2NC6H4(Ph)(2)P=NC6H3Et2-2,6: Ln = Sc, n = 1 (2a); Ln = Lu, n = 1 (2b); Ln = Y, n = 1 (2c); L-3 = MeC4H2SCH2NC6H4(Ph)(2)P=(NC6H3Pr2)-Pr-i-2,6: Ln = Sc, n = 0 (3a)) and (LSc)-Sc-4(CH2SiMe3)(2()THF) (4a) (L-4 = C6H5CH2NC6H4(Ph)(2)P=NC6H3Et2-2,6) have been prepared by reaction of rare-earth metal tris(alkyl)s with the corresponding HL1-4 ligands via alkane elimination.

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) approximate to Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) call be easily achieved by varying of the metal center.

Two new coordination polymers of Co(II) with 1,1 '-(1,4-butanediyl)bis(benzimidazole)

Two new compounds, [CoL2(H2O)(2)](NO3)(2). 8H(2)O (1) and [CoL(H2O)(2)(CH3CO2)(2)]. H2O (2), were obtained from self-assembly of the corresponding metal salts with 1,1'-(1,4-butanediyl)bis(benzimidazole) (L). In 1, each cobalt ion is coordinated to four nitrogen atoms from four molecules of L, and to two water molecules. Metal ions are bridged by L ligands to form infinite (4, 4) networks that contain 44-membered rings. The (4, 4) networks of 1 stack in a parallel fashion, resulting in the formation of large channels in the material. In 2, each cobalt ion is coordinated to two N atoms from two L molecules, two water molecules and two carboxylate O atoms from two acetate anions. Each L molecule is coordinated to two cobalt ions, acting as a bridging ligand as in 1. The bridged cobalt ions form an infinite zigzag chain structure.

Networks with hexagonal circuits in co-ordination polymers of metal ions (Zn-II, Cd-II) with 1,1 '-(1,4-butanediyl)bis(imidazole)

Three new compounds, [ZnL1.5(H2O)(SO4)]. 6H(2)O 1, [ZnL1.5(H2O)(2)][NO3](2). 2H(2)O 2 and [CdL1.5(H2O)(2)(SO4)]. 4H(2)O 3 were obtained from self-assembly of the corresponding metal salts with 1,1'-(1,4-butanediyl)bis(imidazole) (L). In both 1 and 2 zinc ion is five-co-ordinated, showing a less-common trigonal bipyramidal co-ordination polyhedron, while cadmium ion of 3 is six-co-ordinated with a common octahedral arrangement. The sulfate ions of 1 and 3 are co-ordinated, however the nitrate ions of 2 are not. Each of the three compounds is composed of a (6, 3) network with the hexagonal smallest circuit containing six metal ions and six L; each L is co-ordinated to two metal ions, acting as a bridging ligand. In 1 the 2-D sheet of (6, 3) networks is interpenetrated in an inclined mode by symmetry related, identical sheets to give an interlocked 3-D structure, while the (6, 3) networks of both 2 and 3 stack in a parallel fashion to construct frameworks having channels.

Phase transition and transition kinetics of a thermotropic poly(amide-imide) derived from 70% pyromellitic dianhydride, 30% terephthaloyl chloride, and 1,3-bis[4-(4 '-aminophenoxy)cumyl]benzene

The phase transition and transition kinetics of a liquid crystalline copoly(amide-imide) (PAI37), which was synthesized from 70 mol% pyromellitic dianhydride, 30 mol% terephthaloyl chloride, and 1,3-bis[4-(4'-aminophenoxy)cumyl]benzene, was characterized by differential scanning calorimetry, polarized light microscopy, X-ray diffraction, and rheology. PAI37 exhibits a glass transition temperature at 182 degreesC followed by multiple phase transitions. The crystalline phase starts to melt at similar to 220 degreesC and forms smectic C (S-C) phase. The Sc phase transforms into smectic A (S-A) phase when the temperature is above 237 degreesC. The S-C to S-A transition spans a broad temperature range in which the S-A phase vanishes and forms isotropic melt. The WARD fiber pattern of PAI37 pulled from the anisotropic melt revealed an anomalous chain orientation, which was characterized by its layer normal perpendicular to the fiber direction. The transition kinetics for the mesophase and crystalline phase formation was also studied.

The crystal structure and drawing-induced polymorphism in poly(aryl ether ketone)s .1. Poly(oxybiphenyl-4-4'-diyloxy-1,4-phenylenecarbonyl-1,3-phenylenecarbonyl-1,4-phenylene)

Crystal structure and polymorphism induced by uniaxial drawing of a poly(aryl ether ketone) [PEDEKmK] prepared from 1,3-bis(4-fluorobenzoyl)benzene and biphenyl-4,4'-diol have been investigated by means of transmission electron microscopy (TEM), electron diffraction (ED), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) techniques. The melting and recrystallization process in the temperature range of 250-260 degrees C, far below the next melting temperature (306 degrees C), was identified and found to be responsible for the remarkable changes in lamellar morphology. Based on WAXD and ED patterns, it was found that crystal structure of isotropic-crystalline PEDEKmK obtained under different crystallization conditions (melt-crystallization, cold-crystallization, solvent-induced crystallization, melting-recrystallization, and crystallization from solution) keeps the same mode of packing, i.e., a two-chain orthorhombic unit cell with the dimensions a = 0.784 nm, b = 0.600 nm, and c = 4.745 nm (form I). A second crystal modification (form II) can be induced by uniaxial drawing above the glass transition temperature, and always coexists with form I. This form also possesses an orthorhombic unit cell but with different dimensions, i.e., a = 0.470 nm, b = 1.054 nm, c = 5.064 nm. The 0.32 nm longer c-axis of form II as compared with form I is attributed to an overextended chain conformation due to the expansion of ether and ketone bridge bond angles during uniaxial drawing. The temperature dependence of WAXD patterns for the drawn PEDEKmK suggests that form II can be transformed into the more stable form I by relaxation of overextended chains and relief of internal stress at elevated temperature in absence of external tension.

精确测量1／4波片相位延迟量的新方法

提出了一种精确测量1／4波片相位延迟量的新方法。测量光路由激光器、起偏器、被测1／4波片、光弹调制器、检偏器和光电探测器构成。起偏器和检偏器的透光轴相互垂直。被测1／4波片的快轴与光弹调制器的振动轴平行，且与起偏器和检偏器的透光轴分别成±45°夹角。准直激光束依次经过起偏器、被测1／4波片、光弹调制器和检偏器的探测光强由光电探测器接收。利用探测信号的直流分量与二次谐波分量精确计算出被测1／4波片的相位延迟量。实验验证了这种测量方法的有效性，改变初始光强过程中相位延迟量测量结果的复现性为0．012°，检偏器

基于基频分量消光的1/4波片快轴标定方法

提出了一种基于基频分量消光的波片快轴标定方法,并利用琼斯矩阵对其标定原理进行了分析。激光器、起偏器、相位调制器、待标定1/4波片、检偏器和光电探测器构成标定光路,起偏器、检偏器的透光轴与相位调制器的振动轴分别成+45°和0°夹角。准直激光束依次经过起偏器、相位调制器、待标定1/4波片和检偏器,由光电探测器接收。理论分析表明该标定方法标定精度主要取决于检偏器的定位误差。实验验证了该标定方法的有效性,1/4波片快轴标定结果的最大偏差为0.043°,标准差为0.012°,标定精度为0.05°。

基于同步移相技术的1/4波片快轴方位角的实时测量

提出了一种基于同步移相技术的1/4波片快轴方位角的实时测量方法。由正交光栅、光阑、检偏器组和四象限探测器实现同步移相功能。检偏器组由4个不同方位角的检偏器组成。通过检偏器组的四束光束的光强由四象限探测器同时测量。1/4波片的快轴方位角由这四光束的光强得到。由于该方法不需旋转偏振器件，从而实现的1/4波片的快轴方位角的实时测量。

基于同步移相技术的1/4波片相位延迟量的快速测量

提出了一种基于同步移相技术的1/4波片相位延迟量的快速测量方法。由正交光栅、光阑、检偏器组和四象限探测器实现同步移相功能。检偏器组由4个不同方位角的检偏器组成。通过检偏器组的四束光束的光强由四象限探测器同时测量。1/4波片的相位延迟量由这四光束的光强得到。该方法中波片的快轴不需被事先确定。另外光源光强的波动对测量结果没有影响。通过实验验证了该方法的有效性。

Laser-diode-pumped Cr4+,Nd3+: YAG with self-Q-switched laser output of 1.4 W

By use of a laser diode as a pump source, a self-Q-switched laser from a Cr,Nd:YAG crystal is demonstrated. The output Q-switched traces are very stable, the threshold pump power is 3.5 W, the pulse duration is 50 ns, and the slope efficiency is as high as 20%. In addition, the pulse width remains constant while the pulse repetition rate Varies with pump power. (C) 2000 Optical Society of America OCIS codes: 140.0140, 140.2020, 140.3380, 140.3480, 140.3540, 140.3580.