Double twist in helical polymer "soft" crystals

In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first time a double-twist molecular orientation in a helical crystal has been observed.

Preparation and luminescence properties of the ternary europium complex incorporated into an inorganic polymer matrix by a sol-gel method

Ternary europium complexes with thenoyltrifluoroacetone (TTA) and phenanthroline (phen) were incorporated into SiO2/polymer matrix by a sol-gel method. The gels exhibit the characteristic emission bands of europium ion. In addition, Eu3+ presents a longer fluorescence lifetime in gel than in the corresponding pure complex powder. Concentration effects on the luminescence intensity were investigated. The reasons that are responsible for above results are also discussed in the context.

Ring-opening polymerization of epsilon-caprolactone by lanthanocene catalysis

Ring-opening polymerization of epsilon-caprolactone (CL) catalyzed by lanthanocenes, O(C2H4C5H3CH3)(2)YCl (Cat-YCl) and Me2Si[(CH3)(3)SiC5R3](2)NdCl (Cat-NdCl) has been carried out for the first time. It has been found that both yttrocene and neodymocene are very efficient to catalyze the polymerization of CL, giving high molecular weight poly(epsilon-caprolactone) (PCL). The effects of [cat]/[epsilon-CL] molar ratio, polymerization temperature and time, as well as solvents were investigated and polymerization temperature is found to be the most important factor affecting the polymerization. The bulk polymerization gives higher molecular weight PCL and higher conversion than that in solution polymerization. NaBPh4 was found to promote the polymerization of epsilon-caprolactone, and thus to increase both the polymerization conversion and MW of poly(epsilon-caprolactone).

Metallocene polyethylenes with broad or bimodal molecular weight distribution

Seven new binuclear titanocenes with different linking bridges, unsubstituted or substituted on the Cp rings, were synthesized and tested for their effect on ethylene polymerization in the presence of MAO. The polyethylenes thus obtained had broad MWD or even bimodal GPC curves, as compared with that from two reference mononuclear titanocenes. This is explained by the difference in degree of steric hindrance around the active center sites imposed by the bulky substituted ligands assuming different configurations in the rotation of the catalyst molecules. Lower polymerization temperatures alleviate the effect of these configuration differences, as reflected in change in MW and (M) over bar(w)/(M) over bar(n). This effect is not caused by decomposition or disproportionation of the binuclear titanocenes as evidenced by the stability of the catalyst.

A novel method of studying polymer biodegradation

A novel combination of laser light scattering (LLS) and the micronization of a water-insoluble polymer into narrowly distributed nanoparticles stable in water has provided not only an accurate, reliable and microscopic method to study polymer biodegradation, but also a novel and fast way to evaluate the biodegradability of a given polymer. Using poly(epsilon-caprolactone) (PCL) as a typical example, we have shown that its biodegradation time can be shortened by a factor of more than 10(3) times in comparison with the time required to biodegrade a thin film (10 x 10 x 0.1 mm(3)). Moreover, the biodegradation kinetics can be in-situ monitored in terms of the decrease of the time-average scattering intensity and the particle number. A comparison of static and dynamic LLS results revealed that the enzyme, Lipase Pseudomonas, ''eats'' the PCL nanoparticles in an one-by-one manner and the enzymatic biodegradation of PCL follows a zero-order kinetics. (C) 1998 Elsevier Science Ltd. All rights reserved.

Effects of La3+ on lipid fluidity land structural transitions in human erythrocyte membranes

The effects of La3+ on the structure and function of human erythrocyte membranes were investigated by fluorescence polarization, spin-labeled electron spin resonance (ESR) and differential scanning calorimetry (DSC). The results showed that increasing concentrations of La3+ inhibited (Na++K+)-ATPase and Mg2+-ATPase activities. La3+ lowered the lipid fluidity of erythrocyte membranes and induced structural transitions in erythrocyte membranes.

Effects of the compatibilizer PP-g-GMA on morphology and mechanical properties of PP/PC blends

Effects of the compatibilizer polypropylene grafted with glycidyl methacrylate(PP-g-GMA) on the morphology, thermal, rheological and mechanical properties of polypropylene and polycarbonate blends (PP/PC) were studied. It was found that the addition of PP-g-GMA significantly changed their morphology. The mean size of domains reduced from 20 mu m to less than 5 mu m. The dispersed domain size is also strongly dependent upon the content of PP-g-GMA. The interfacial tension of PP/PC/PP-g-GMA (50/30/20) is only about one-tenth of PP/PC (70/30). The crystallization temperature of PP in PP/PC/PP-g-GMA is 5-8 degrees C higher than that of PP in PP/PC blends. Characterization studies based on mechanical properties, differential scanning calorimetry, rheology and morphological evidence obtained by using scanning electron microscopy support the hypothesis that an in-situ copolymer PP-g-PC was formed during the blending process. (C) 1997 Elsevier Science Ltd.

Impact behavior of phenolphthalein poly(ether sulfone) ultrahigh molecular weight polyethylene blends

This work presents the structure and impact properties of phenolphthalein poly(ether sulfone) blended with ultrahigh molecular weight polyethylene (PES-C/UHMWPE) at different compositions. The addition of UHMWPE can considerably improve the Charpy and Izod impact strength of the blends. The fracture surface is examined to demonstrate the toughening mechanics related to the modified PES-C resin. (C) 1998 John Wiley & Sons, Inc.

Electrochemical investigation of DNA adsorbed on conducting polymer modified electrode

Detection of DNA is a very important task for molecular biology and biomedical field. We have investigated electrochemical behavior of double-stranded DNA and single-stranded DNA adsorbed on conducting polymer modified electrode in presence of cobalt complex. The possibility of using such electrode as gene detector is discussed.

Physical diffusion and electron-transfer dynamics of electroactive solutes in polymer electrolytes .3. Effect of the polymer solvents

The diffusion coefficients(D-app) and the heterogeneous electron transfer rate constants(k(s)) for ferrocene in several polymer solvents were determined by using steady-state voltammetry. The temperature dependence of the two parameters indicates Arrhenius behavior, The polymer solvent effects on diffusion and electron transfer dynamics of ferrocene were discussed.

Physical diffusion and electron-transfer dynamics of electroactive solutes in polymer electrolytes .1. Effect of the nature of electroactive solutes

The diffusion coefficients(D-app) and the heterogeneous electron-transfer rate constants(k(s)) for ferrocene and its seven derivatives in MPEG/LiClO4 electrolyte were determined by using steady-state voltammetry. The two parameters increase with increasing temperature, indicating Arrhenius behavior. The effects of the nature of electroactive solute molecules on D-app, k(s), and the half-wave potentials(E-1/2) are discussed.

Synthesis and miscibility studies of rodlike flexible polyimide molecular composites via para-para linked aromatic poly(amic ester) precursors

Para-para linked aromatic poly(amic ester) precursors of rodlike polyimide (PI) BPDA-PDA and polyetherimide (PEI) HQDPA-ODA were synthesized. The para-para linked poly(amic ester)s were employed in this work to obtain, in theory, full-imidized polyimides. The two precursors were mixed by dissolving them in N, N'-dimethyl acetamide and subsequently coagulating in methanol. After thermal imidization, the miscibility behaviour of the resulting composites has been studied by means of dynamic mechanical analysis (d.m.a.) and differential scanning calorimetry (d.s.c.). The composites show a single glass transition temperature (T-g) at both d.m.a. and d.s.c. in which the T-g increases with increasing PI content. These Tg values are reproducible in repeated heating cycles, suggesting the true miscibility of the blends. (C) 1997 Elsevier Science Ltd.

Heterogeneous nucleation effects of neodymium oxide on polyamide-1010

In this paper microcrystalline structures of polyamide-1010 (PA1010) mixed with neodymium oxide (Nd2O3) were studied by Wide Angle X-ray Diffraction (WAXD) and Small Angle X-ray Scattering (SAXS). Crystallization behavior was investigated by DSC. The transition and relaxation of macromolecules in the crystalline phase were explored by Differential Scanning Calorimetry (DSC). It was revealed that neodymium oxide plays an important role in PA1010 crystallization as a heterogeneous nucleating agent. It can improve the crystallization rate, reduce crystallite size and introduce crystal imperfections. The microcrystalline structure was imposed by the addition of Nd2O3 However, the heterogeneous nucleation effect obviously does not exert its influence on the transition and relaxation of macromolecules in the crystalline phase.

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.

Laser light scattering of the molecular weight distribution of unfractionated phenolphthalein poly(aryl ether sulfone)

Two unfractionated samples of phenolphthalein poly( aryl ether sulfone) (PES-C) were characterized in CHCl3 at 25 degrees C by applying a recently developed laser light-scattering (LLS) procedure. The Laplace inversion of precisely measured intensity-intensity time correlation function lead us first to an estimate of the characteristic line-width distribution G(Gamma) and then to the translational diffusion coefficient distribution G(D). A combination of static and dynamic LLS results enabled us to determine D = (2.69 x 10(-4))M(-0.553), which agrees with the calibration of D = (2.45 x 10(-4))M(-0.55) previously established by a set of narrowly distributed PES-C samples. Using this newly obtained scaling between D and M, we were able to convert G(D) into a differential weight distribution f(w)(M) for the two PES-C samples. The weight-average molecular weights calculated from f(w)(M) are comparable to that obtained directly from static LLS. Our results showed that using two broadly distributed samples instead of a set of narrowly distributed samples have provided not only similar final results, but also a more practical method for the PES-C characterization. (C) 1997 John Wiley & Sons, Inc.