Shear induced molecular alignments of a side-chain liquid crystalline polyacetylene containing biphenyl mesogens

Mesomorphic properties of a side chain liquid crystalline polyacetylene, poly(11-{[(4'-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PA9EO7), are investigated using polarized optical microscope, X-ray diffraction, and transmission electron microscope. Polymer PA9EO7 forms enantiotropic smectic A and smectic B phases. It also exhibits an additional high order smectic phase, a sandwich structure consisting of different molecular packing of biphenyl mesogenic moieties from that of alkyl spacers and terminals, when it is prepared from its toluene solution. Shearing the polymer film at its smectic A phase generates banded texture with the alignment of the backbones parallel to the direction of shear force. While at its high order smectic phase, the mesogen pendants of the polymer are arranged parallel to the direction of shear. The different mesomorphic behaviors arise from different molecular alignments influenced by the fluidity.

Nanometer scale mechanical study on well defined nanostructured chain aggregation of polyethylene

Two kinds of polyethylene chain aggregation with chain axis perpendicular and parallel to the supported substrate were designed and successfully obtained from melt under an electric field and by melt-drawn method

Multiple melting behavior of isotactic polypropylene and poly(propylene-co-ethylene) after stepwise isothermal crystallization

The multiple melting behavior of several commercial resins of isotactic polypropylene (iPP) and random copolymer, poly(propylene-co-ethylene) (PPE), after stepwise isothermal crystallization (SIC) were studied by differential scanning calorimeter and wide-angle X-ray diffraction (WAXD). For iPP samples, three typical melting endotherms appeared after SIC process when heating rate was lower than 10 degreesC/min. The WAXD experiments proved that only alpha-form crystal was formed during SIC process and no transition from alpha1- to alpha2-form occurred during heating process. Heating rate dependence for each endotherm was discussed and it was concluded that there were only,two major crystals with different thermal stability. For the PPE sample, more melting endotherms appeared after stepwise isothermal crystallization. The introduction of ethylene comonomer in isotactic propylene backbone further decreased the regularity of molecular chain, and the short isotactic propylene sequences could crystallize into gamma-form crystal having a low melting temperature whereas the long sequences crystallized into alpha-form crystal having high melting temperature.

An unusual organic-inorganic chain-like hybrid complex [(CuCl)(2)(o-phen)](infinity) (o-phen=o-phenanthroline)

A novel organic-inorganic hybrid complex [(CuCl)(2) (o-phen)](infinity) 1 (o-phen = o-phenanthroline) has been hydrothermally synthesized and structurally characterized by elemental analyses, XPS spectrum, TG analysis, and single-crystal X-ray diffraction. Compound I crystallizes in the monoclinic system, space group P2(1)/n, a = 3.7285(7) Angstrom, b = 19.603(4) Angstrom, c = 16.757(3) Angstrom, beta = 95.83(3)degrees, V = 1218.4(4) Angstrom(3), Z = 4, lambda(MoKalpha) = 0.71073 Angstrom (R(F) = 0.0643 for 2559 reflections). Data were collected on an R-axis RAPID diffractometer at 293 K in the range of 1.60 < θ < 27.48degrees. The title compound exhibits a one-dimensional chain-like scaffolding constructed by the unusual [Cu3Cl3] hexagon motifs by, sharing opposite edges. Only Cu(1) sites of the [Cu3Cl3] hexagon are coordinated with N donors of o-phen groups. Furthermore, the three-dimensional supermolecular architecture is formed by C-H...Cl hydrogen bonds between o-phen groups and CuCl chains.

Graphical representation and the similarity of DNA primary sequences

In this article, graphical representations of DNA primary sequences were generated. Topological indices and molecular connectivity indices were calculated and used for the comparison of similarities among eight different DNA segments. The satisfactory results were achieved by this analysis.

Liquid crystalline phases, microtwinning in crystals and helical chirality transformations in a main-chain chiral liquid crystalline polyester

A main-chain nonracemic chiral liquid crystalline polymer was synthesized from (R)-(-)4'-{w-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-decyloxyl-4-biphenylcarboxylic acid. This polymer contained 10 methylene units in each chemical repeating unit and was abbreviated PET(R*-10). On the basis of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy experiments, chiral smectic C (S-C*) and chiral smectic A (S-A*) phases were identified. Both flat-elongated and helical lamellar crystal morphologies were observed in transmission electron microscopy. Of particular interest was the flat-elongated lamellar crystals were constructed via microtwinning of an orthorhombic cell with dimensions of a = 1.42 nm, b = 1.28 nm, and c = 3.04 nm. On the other hand, the helical lamellar crystals were exclusively left-handed, which was opposite to the right-handed helical crystals grown in PET(R*-9) and PET(R*-11) (having 9 and 11 methylene units, respectively). Note that these three polymers had identical right-handed chiral centers (R*-). Therefore, a single methylene unit difference on the polymer backbones on an atomic length scale substantially changed the chirality of the crystals in the micrometer length scale. Furthermore, aggregates of these helical crystals in PET(R*-10) did not generate banded spherulites in polarized light microscopy. Possible reasons for this change and loss of helical senses (handedness) on different length scales in chirality transferring processes were discussed.

Non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene

The non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene were investigated via DSC at cooling rates from 2.5 to 20 degreesC/min, and subsequent heating at rate of 10 degreesC/min. To verify the effect of molecular weight and branching content on crystallization, three group samples were chosen: (1) linear polyethylene with low molecular weight and high molecular weight; (2) low molecular weight polyethylene with low branching content and high branching content; (3) high molecular weight polyethylene with low branching content and high branching content. The results show that crystallization temperature, crystallinity, melting temperature and crystallization rate are highly branching content-dependent. Molecular weight effect is less important, compared to branching content. A dramatic decrease of crystallization temperature, crystallinity, crystallization rate and melting temperature was observed for branched samples. The non-isothermal kinetics was analyzed via the methods, developed by Gupta and Mo Zhi-shen, and good agreement was obtained.

Compatibilization by main-chain thermotropic liquid crystalline ionomer of blends of PBT/PP

The miscibility and mechanical properties of the blends of polybutylene terephthalate (PBT) and polypropylene (PP) with a liquid crystalline ionomer (LCI) containing a sulfonate group on the terminal unit as a compatibilizer were assessed. SEM and optical microscopy (POM) were used to examine the morphology of blends of PBT/PP compatibilized by LCI. DSC and TGA were used to discuss the thermal properties of PBT/PP blends with LCI and without LCI. The experimental results revealed that the LCI component affect, to a great extent, the miscibility and crystallization process and mechanical property of PBT/PP blends, The fact is that increasing LCI did improve miscibility of PBT/PP blends and the addition of 1% LCI to the PBT/PP blends increased the ultimate tensile strength and the ultimate elongation.

Polydispersity of ethylene sequence length in metallocene ethylene/alpha-olefin copolymers. II. Influence on crystallization and melting behavior

In this work, crystallization and melting behavior of metallocene ethylene/alpha-olefin copolymers were investigated by differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The results indicated that the crystallization and melting temperatures for all the samples were directly related to the long ethylene sequences instead of the average sequence length (ASL), whereas the crystallization enthalpy and crystallinity were directly related to ASL, that is, both parameters decreased with a decreasing ASL. Multiple melting peaks were analyzed by thermal analysis. Three phenomena contributed to the multiple melting behaviors after isothermal crystallization, that is, the melting of crystals formed during quenching, the melting-recrystallization process, and the coexistence of different crystal morphologies. Two types of crystal morphologies could coexist in samples having a high comonomer content after isothermal crystallization. They were the chain-folded lamellae formed by long ethylene sequences and the bundlelike crystals formed by short ethylene sequences. The coexistence phenomenon was further proved by the AFM morphological observation.

Compatibilization of side-chain, thermotropic, liquid-crystalline ionomers to blends of polyamide-1010 and polypropylene

A novel side-chain, liquid-crystalline ionomer (SLCI) with a poly(methyl hydrosiloxane) main chain and side chains containing sulfonic acid groups was used in blends of polyamide-1010 (PA1010) and polypropylene (PP) as a compatibilizer. The morphological structure, thermal behavior, and liquid-crystalline properties of the blends were investigated by Fourier transform infrared, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. The morphological structure of the interface of the blends containing SLCI was improved with respect to the blend without SLCI. The compatibilization effect of greater than 8 wt % SLCI for the two phases, PA1010 and PP, was better than the effects of other SLCI contents in the blends.

Crystallization kinetics of narrow molecular weight distribution metallocene short-chain-branched polyethylene

Isothermal and non-isothermal crystallization kinetics of three metallocene-catalysed short-chain-branched polyethylene (SCBPE) fractions with different degree of branching were investigated by using differential scanning calorimetry (DSC). Narrow molecular weight fractions (M-w = 20,000 and M-w/M-n < 1.15) are used and the degree of branching (CH3 per 1000C) are 1.6, 10.4, 40 respectively. The regime I - II transition temperature are 119.8C, 115.9 degreesC, 113.3 degreesC with the decreasing of degree of branching. Increasing the branch content decreases the rate of secondary nucleation, i,relative to the rate of surface spreading and so increases the range of supercooling over which regime I exists. The rate of bulk crystallization for both isothermal and non-isothermal crystallization decreases with the increasing of degree of branching. Both Ozawa Equation and Kissinger Equation are invalid for non-isothermal crystallization kinetics of SCBPE fractions,that means the effects of the branched chain on crystallization process are more complex than expected.

Investigating mechanical response of single chain polystyrene particles by scanning probe techniques

Single chain polystyrene particles were obtained by dilute solution casting method. The sample with both single chain polystyrene particles and multi-chain (more than 1000 molecular chains) polystyrene particles was obtained by a little more concentrate solution. Force modulation technique showed that single chain polystyrene particles were softer than multichain polystyrene particles. On the other hand, nanoindentation experiments on multi-chain particles and bulk polystyrene manifested that the elastic modulus of multi-chain polystyrene particles was very close to that of bulk polystyrene. Therefore, it was concluded that single chain polystyrene particles were softer than bulk polystyrene,which indicated that the density of intrachain entanglement points in the single chain polystyrene particles was not as large as that of the interchain entanglement points in the bulk state.

Aromatic poly(ester imide)s and poly(amide imide)s having 1,1 '-binaphthyl-2,2 '-diyls in the main chain

Full Paper: Two new 1,1'-binaphthyl-2,2'-diyl-based dianhydrides, i.e., 2,2'-bis(3,4-dicarboxybenzamido)-1,1'-binaphthyl dianhydride (BNDADA) and 2,2'-bis(3,4-dicarboxybenzoyloxy)-1,1'-binaphthyl dianhydride (BNDEDA), were synthesized and polymerized with various aromatic diamines to afford polyimides through the traditional two-step method. The polyimides with inherent viscosities ranging from 0.27 to 0.70 dl . g(-1) showed excellent solubilities in polar solvents such as DMAc, DMSO and NMP etc., except of the poly(ester imide) prepared from BNDEDA and benzidine. Poly(ester imide)s based on BNDEDA can also be readily dissolved in weakly polar solvents such as THF, CH2Cl2 and CHCl3. The glass transition temperatures of these polyimides are in the range of 210-310 degrees C; the 5% weight loss temperatures are in the range of 390-465 degrees C in nitrogen and 384-447 degrees c in air. These polymers from light yellow, tough films that were transparent above 365 nm. The effects of different flexible units attached in the 2- and 2'-positions, i.e., amide, ester and ether, on the properties of the polyimides obtained are discussed.

Lateral habits of single crystals of metallocene-catalyzed low molecular weight short chain branched polyethylene from the melt

The lateral habits of low molecular weight short chain branched polyethylene single crystals from the melt were studied. Three crystallization temperatures (102, 104 and 106 degrees C) were selected for single crystal growth. It was found that the lateral habits of single crystals were asymmetric at all the crystallization temperatures selected. The electron diffraction patterns and tilting series experiments evidenced that there existed chain tilting in all the lamellae. It was the chain tilting that lead to the asymmetry of the growth rate and of lateral habits of the single crystals about the b-axis. The lateral habits substantially changed from the growth at 102 degrees C where the truncated lozenge single crystals formed with straight (110) faces to the growth at 104 degrees C where the lenticular single crystals appeared. This change occurred at 20 degrees C lower than that in a low molecular weight linear polyethylene with the same molecular weight. Furthermore, kinetics theory analysis evidenced that the change of lateral habits from truncated lozenge to lenticular shape resulted from the transition of growth regime. The results were the same as that of high molecular weight linear polyethylene but different to that of low molecular weight linear polyethylene. It may be attributed by the existence of short branched chains. (C) 2000 Elsevier Science Ltd. All rights reserved.