Multiple Melting Endotherms of Syndiotactic Polystyrene in β Crystalline Form

Multiple melting behaviors have been studied extensively. Syndiotactic polyStyrene(SPS), in 6 crystalline form exhibited such phenomena. It was suggested that arecrystallization process occurred since it has been clarified that no other modificationswere observed during the DSC heating scanl. In this study, a series of SPS samples in 0form were prepared by cooling from the melt at various cooling ratesl and the factors thatinfluence the multiple melting behavior of SPS in 0 form were exam…     

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene γ Form

The crystallization behavior of syndiotactic polystyrene(s PS) γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl's crystallization theory. On the basis of the differential scanning calorimetric results, it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness, which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization. Further temperature dependent small-angle X-ray scattering(SAXS) measurement revealed the evolution of the γ form lamellae upon heating until phase transition, involving three different regimes: lamellae stable region(25-90 °C), melt-recrystallization region(90-185 °C) and pre-phase transition region(185-195 °C). As a result, recrystallization line, equilibrium recrystallization line and melting line were developed for the s PS γ form crystallization process. Since the melt of γ form involved a γ-to-α/β form phase transition, the melting line was also denoted as the phase transition line in this special case. Therefore, the equilibrium crystallization temperature and melting(phase transition) temperatures were determined at around 390 and 220 °C on the basis of the thermodynamic phase diagram of the s PS γ form.     

Oriented Nanoporous Host δ Phases of Syndiotactic Polystyrene as a Tool for Spectroscopic Investigation of Guest Molecules

An efficient method to align low-molecular-mass molecules by enclosing them as isolated guests of the nanoporous host δ phase of syndiotactic polystyrene oriented films, is presented. This new method is compared with the classic method consisting in the absorption of low- molecular-mass molecules as a solute of amorphous phases of highly oriented semicrystalline polymeric films. It is shown that this new molecular alignment method provides a powerful tool to study in detail several features (spectroscopic properties, molecular motions) of relevant molecules, by separating with unprecedented selectivity their anisotropic spectral responses. The reported results refer to infrared and solid-state-²H-NMR spectra.     

Deformation Temperature and Lamellar Thickness Dependency of FormⅠto Form Ⅲ Phase Transition in Syndiotactic Polypropylene during Tensile Stretching

Phase transition from form Ⅰto form Ⅲ in syndiotactic polypropylene crystallized at different conditions during tensile deformation at different temperatures was investigated by using in situ synchrotron wide angle X-ray diffraction technique. In all cases, the occurrence of this phase transition was observed. The onset strain of this transition was found to be crystalline thickness decided by crystallization temperature and drawing temperature dependent. The effect of drawing temperature on this phase transition is understood by the changes in mechanical properties with temperature. Moreover, crystalline thickness dependency of the phase transition reveals that this form I to from III phase transition occurs first in those lamellae with their normal along the stretching direction which have not experienced stress induced melting and recrystallization.     

Studies on the Effect of Glass Transition on the Crystalline Transition in Syndiotactic Polystyrene – Solvent Complexes

Summary: Amorphous syndiotactic polystyrene (sPS) was crystallized at room temperature in Norbornadiene (bicyclo[2,2,1]-hepta-2,5-diene), Mesitylene (1,3,5- Trimethylbenzene), 3-Carene (3,7,7-trimethyl bicyclo[4,1,0]hept-3-ene) and DMN (1,4-Dimethylnaphthalene) to form the sPS-solvent complex (δ form) with respective solvent molecules. In situ HTFTIR studies showed that the δ form to γ form transformation temperature occurs well below the glass transition temperature of sPS, which is depressed due to the presence of solvent in the amorphous phase; higher the solvent content in the complex, lower the transition temperature. Glass transition temperatures determined by Modulated differential scanning calorimetry (MDSC) coincide with the transition temperatures, indicating that the δ form transforms into γ form at the glass transition temperature for these complexes. Such a behavior is very different from the behaviour of the sPS- solvent complexes formed by dichloromethane, chloroform, toluene, o-dichlorobenzene, decalin (cis-trans) etc. and for these complexes the transition occur well above the T_g. 1     

Synthesis of Syndiotactic Polystyrene with Novel Titanocene Catalysts Activated by Modified Methylaluminoxane

Thesynthesisofsyndiotacticpolystyrene(sPS)hasattractedmuchinterestforitspropertiesandapplications.Half-sandwichtitanoceneandmethylaluminoxane(MAO)catalystshavebeenfoundtobethefavourprecursorstocatalyzesyndiospecificpolymerizationofstyrene'-,'.MAOascocatalystsalwayscontainssomeamountoffreetrimethylaluminum(TMA)bothinaformcoordinatedtoMAOandasfreeTMA".However,therolesoftheTMAcoexistinginMAOarestillnuclear.Inthispaper,severalmodifiedmethylaluminoxanes(m-MAO)whichcontaineddifferentpercen…     

Critical Exponents of Thermal Phase Transitions ofκ-Carrageenan in Various Salt Solutions

Summary: The steady state fluorescence (SSF) technique was employed to study the phase transitions of κ-carrageenan in NaCl and KCl solutions. Pyranine was used as a fluorescence probe for monitoring these transitions. Scattered light, I_sc, and fluorescence intensity, I, was monitored against temperature to determine transition temperatures and exponents. It was observed that transition temperatures are strongly correlated with the NaCl and KCl contents. The weight-average degree of polymerization, DP_w and gel fraction G, exponents (γ and β) were measured and found to be in accord with the classical Flory-Stockmayer model.     

High Temperature Phase Transitions in Na_xCoO_2 Materials

1 INTRODUCTION In recent years, much attention has been focused on the NaxCoO2 system due to its notable properties and potential technologic applications as a cathode material in high-energy density, reversible solid state battery systems[1, 2]. Recently, large thermoelectric power[3～6] in NaxCoO2 and superconductivity (～4 K) in hydrated NaxCoO2yH2O (x = 0.35, y = 1.33) ma- terial have been observed[7]. This hydrated layered phase is the first 3d-transition metal oxide with superco…     

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene <Emphasis Type="Italic">γ</Emphasis> Form

The crystallization behavior of syndiotactic polystyrene (sPS) γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl's crystallization theory.On the basis of the differential scanning calorimetric results,it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness,which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization.Further temperature dependent small-angle X-ray scattering (SAXS) measurement revealed the evolution of the γ form lamellae upon heating until phase transition,involving three different regimes:lamellae stable region (25-90 ℃),melt-recrystallization region (90-185 ℃) and pre-phase transition region (185-195 ℃).As a result,recrystallization line,equilibrium recrystallization line and melting line were developed for the sPS γform crystallization process.Since the melt of γform involved a γto-α/β form phase transition,the melting line was also denoted as the phase transition line in this special case.Therefore,the equilibrium crystallization temperature and melting (phase transition)temperatures were determined at around 390 and 220 ℃ on the basis of the thermodynamic phase diagram of the sPS γform.     

Phase relations in the vicinity of the compound YBa2Cu3O7 − δ at constant oxygen pressure

The phase relations in part of the BaOY₂O₃CuO system were investigated by differential thermal analysis coupled with thermographimetric measurements, X-ray and microprobe analysis, microstructural examinations in a light microscope and in a scanning electron microscope and inductive measurements of the superconducting transition temperatures. The superconducting compound YBa₂Cu₃O_{7 − δ} shows no homogeneity range with respect to the metallic constituents. Solidus temperature for the pseudobinary BaCuO₂CuO and formation temperatures for the compounds in the copper-rich part of the phase diagram are given.     

Thermal Behavior of Syndiotactic Polystyrene/1,2‐Dichloroethane Gels and Stoichiometry of Polymer‐Solvent Compounds

Abstract

The phase behavior of syndiotactic polystyrene (sPS)/1,2‐dichloroethane (DCE) gels has been investigated by differential scanning calorimetry (DSC) and wide angle x‐ray diffraction (WAXD) for different gel formation conditions. DSC data show that the gel melting temperatures are independent of the cooling conditions leading to gel formation, whereas the melting enthalpies of the gels depend on the cooling history. WAXD measurements show that for low concentration gels the sPS/DCE clathrate structure is obtained, whereas for high concentration gels both the clathrate structure and the solvent‐free β phase can be obtained. Furthermore, the onset of formation of the β phase is dependent on the cooling rate. In light of combined DSC and WAXD data, the reliability of the DSC in evaluating the absolute stoichiometry of polymer‐solvent compounds formed in sPS/DCE gels is discussed.     

Transitions of Chain＇s Conformation in the Lytropic Condensation of Macromolecules

详细讨论了稀溶液、亚浓溶液、浓溶液和极浓溶液中分子链构象的演变,考察了在溶致凝聚过程中分子链的链间相互作用、关联作用和分子链尺寸的变化规律,给出了排除体积的严格定义,引入热关联效应、长程关联效应和全高斯链浓度等概念。指出在不同浓度溶液中,分子链在不同尺度上构象状态不同;在从孤立单链态（良溶液中）向多链聚集态的溶致凝聚过程中,单链的尺寸一直在收缩,由Flory尺寸RF缩小至无扰尺寸Ro。这是大分子凝聚过程的一个特点。     

Diethyl Tartrate on Polystyrene Bead as Chiral Stationary Phase in Liquid Chromatography

ＤｉｅｔｈｙｌＴａｒｔｒａｔｅｏｎＰｏｌｙｓｔｙｒｅｎｅＢｅａｄａｓＣｈｉｒａｌＳｔａｔｉｏｎａｒｙＰｈａｓｅｉｎＬｉｑｕｉｄＣｈｒｏｍａｔｏｇｒａｐｈｙＱｉｎｇＹａｎＬＩＵ；ＸｉａｏＪｕｎＷＵ；ＪｉＧａｎＨＥ；ＧｕｏＱｕａｎＬＩＵ（Ｉｎｓｔｉｔｕｔ...     

Phase equilibria in the aluminium-rich side of the Al–Zr system

The Al-rich phase equilibria in the Al–Zr binary system were investigated experimentally. The phase diagram for compositions up to 40 at.% Zr was determined experimentally by differential thermal analysis and metallography. Three stable intermetallic compounds exist in this region of the diagram: Al₃Zr₂, Al₂Zr, and Al₃Zr. The peritectic melting of Al₃Zr₂ and the congruent melting of Al₂Zr were confirmed. Al₃Zr, the most Al-rich intermetallic compound, melts peritectically, which contradicts information available in the literature. In addition, the reaction between Al₃Zr and the (Al) solid solution seems to be of eutectic nature, in contradiction with previous results found in the literature. Based on these new experimental evidence, a revised phase diagram is drawn.     

Synthesis of α-Aminoarylacetic Acids in the Presence of Phase Transfer Catalysts

Inearlierpublications""aone-stepphasetransfercatalyzedreactionforpreparingaaminoarylaceticacidsfromarylaldehydesandchloroform,usingquaternarysaltsorf3CDasphasetransfercatalyst,wasdescribed;Itwasalsoreportedthatsomereactionsundersonicationconditionoftenoccurmorerapidlyandeasily'.Wenowfindthatthisreactioncanbeadvantageouslyrealizedbyphasetransfercatalysisundersonication.Optimumreactionconditionsweredeterminedwithbenzaldehyde.Inthepresenceoflithiumchloride,theyieldnoticeablydecreases(seeTablel)…     

Stability of Mefenamic Acid in the Inclusion Complex with β-Cyclodextrin in the Solid Phase

The inclusion complex of mefenamic acid with -cyclodextrin was obtained by the method of coprecipitation from diethyl ether. The product was identified by the thermogravimetric and X-ray methods. The complex stability constants were determined by the potentiometric method. The effect of -CD on the solubility and stability of mefenamic acid was analysed.     

Characters of the Plateau of Methanol Increment in Frontal Analysis in Reversed Phase Liquid Chromatography

With insulin methanol-water,and the ion-pairing agent,hydrochloric acid and trifluroacetic acid(TEA),the character of the first plateau(FP)on the elution curve of frontal analysis in reversed phase liquid chromatography(RPLC)was investigated by on-line UV-spectrometry and identified with nuclear magnetic resonance(NMR) spectrometry and mass spectrometry.The profile of the FP is the same as that of a usual elution curve of methanol in frontal analysis(FA).When the insulin concentration was limited to a certain range,the height of the FP was found to be proportional to the insulin concentration in mobile phase and its length companying to shorten,The FP profile on the intersection of two tangents reflects the components of the microstructure in the depth direction of the bonded stationary phase layer and the desorption dynamics of the displaced components.The displaced methanol was quantitatively determined by NMR and on-line UV spectrometries.TFA with high UV absorbance can not be used as an ionpairing agent for the investigation of the FP in RPLC,but if can be used as a good marker to investigate the complicated transfer process of components in the stationary phase in RPLC.A stoichiometric displacement process between solute and solvent was proved to be valid in both usual and FA in RPLC.From the point of view of dynamics of mass transfer, the solutes can only contact to the surface of stationary phase in usual RPLC,while solute can penetrate into it in FA of RPLC.The solvation of insulin in methanol and water solution as an example indicating the usage of the FP in the FA was also investigated in this paper.     

Thermodynamic Analysis of Phase Equilibria in the System Cyclohexane—Methanol

The phase diagram of cyclohexane-methanol was thermodynamically modeledin the range of 150 T/K 360 and at a pressure of 1 bar on the basis ofavailable experimental data. The Gibbs energy functions of four pure solid andtwo mixture phases were taken into consideration. The liquid phase was describedby a model based on mole fraction statistics and the simplified assumption ofmethanol tetramers mixed with cyclohexane monomers. The gas phase was treatedas a nonideal mixture with a Gibbs energy modeled on the basis of the virialcoefficient formalism considering only monomers. The Gibbs energies of the twosolid modifications of pure methanol, as well as pure cyclohexane, were fixedusing literature data. The pressure dependence of the Gibbs energies of the liquidand solid phases were neglected. The complete T-x phase diagram includinggas/liquid equilibria as well as p-x phase diagrams in the range of 20 and 55°C werecalculated. Experimental and calculated data were found to agree reasonably well.     

Confirmation of Disorder α Form of Poly(L-lactic acid) by the X-ray Fiber Pattern and Polarized IR/Raman Spectra Measured for Uniaxially-Oriented Samples

In the present research, we report for the first time the X-ray fiber pattern and polarized IR/Raman spectra taken for the uniaxially oriented disorder α form of PLLA, which can confirm the existence of the disorder PLLA α form (α′-form) and provide some new insight on the structural difference between the order and disorder α forms.     

Magnetic Phase Transitions in a Ni4O4-Cubane-Based Metal–Organic Framework

An unprecedented spin cluster-based network architecture {[Ni^II₂(pdaa)(OH)₂(H₂O)]_n (H₂pdaa=1,4-phenylene diacetic acid)}, comprising 1D linear chains of Ni^II ions crosslinked via Ni₄O₄ cubanes, forms under hydrothermal conditions; this 3D coordination network exhibits magnetic ordering at 23.9 K as well as a second magnetic ordering process at 2.8 K likely associated with a structural phase transition.