Melting and crystallization behavior of aliphatic polyketones

The basic crystallization and melting behavior of three aliphatic polyketones were studied using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and optical microscopy. One resin was a perfectly alternating copolymer of ethylene and carbon monoxide, while the other two resins were terpolymers in which 6 mol % propylene was substituted for ethylene. Small decreases in the melting point and percent crystallinity of these materials were displayed with repeated melting. This behavior was attributed to light crosslinking as a result of condensation reactions occurring at temperatures in the melting range. WAXS showed that, after cooling to room temperature, the crystalline form in the copolymer was the α‐phase, while that in the terpolymers was the β‐phase. Optical microscopy revealed that the materials produce both negative and mixed birefringence spherulites under the conditions studied. SAXS measurements showed that the lamella thickness was largely a function of the temperature of crystallization. Attempts were made to measure the equilibrium melting temperature of these resins using several available techniques. The best value of the equilibrium melting temperature was concluded to be 278 ± 2°C for the copolymer. The results varied over a wide range for the terpolymers, but it is suggested that appropriate values are of order 252°C for the terpolymers. Crystallization kinetics studies, carried out under isothermal conditions using DSC, were evaluated using the Avrami equation. Results showed the Avrami exponent to lie in the range of 2–3. Spherulite growth rates were interpreted in terms of the secondary nucleation theory of Lauritzen and Hoffman. A transition from regime II to regime III was discovered. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2124–2142, 2002     

Polymeric amines by chemical modifications of alternating aliphatic polyketones

Alternating, aliphatic polyketones were chemically modified by using di‐amines to obtain polymeric products having pendant amino groups. The used reaction, Paal‐Knorr, involves the formation of pyrrole rings along the polyketone backbone. The corresponding kinetics and final conversions are clearly dependent, among others, on statistical factors (two adjacent carbonyls must react in order to obtain ring formation) as well as on the steric hindrance (sterically hindered amino groups react very slow). The corresponding reaction products (polymeric amines) display very interesting physical properties in aqueous solution. These have been characterized by using dynamic light scattering, Cryo‐electron microscopy, fluorescence techniques, etc. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dependence of structure of polymer side chain on water structure in hydrogels

To investigate the effects of structure of polymer side chains on structure of water in hydrogels, Raman spectra of polyacrylamide (PAA) and poly-N,N,-dimethylacrylamide (PDMAA) hydrogels were measured. PAA and PDMAA have similar chemical structures, except for the side chain structure. The result shows that the frequency of the O–H stretching mode for the PAA hydrogel decreases as the water content decreases, while that for the PDMAA hydrogel increases. Furthermore, the analysis of the relative intensities of the O–H stretching modes shows that the number density of tetragonal water structures differs between the hydrogels. We conclude that most of the bound water molecules in the PAA hydrogel form four strong hydrogen bonds with the hydrophilic groups in the side chain of PAA, whereas those in the PDMAA hydrogel form weak hydrogen bonds with surrounding water molecules. The water structure is an important factor governing the physical and chemical properties of gel materials.     

The structure of a cyanobiphenyl side chain liquid crystalline poly(silylenemethylene)

The structure of a side chain liquid crystalline poly(silylenemethylene) (-(SiCH₃R-CH₂)-: R=O(CH₂)₁₁O-Ph-Ph-CN, Ph=phenyl) (CN-11) has been studied by X-ray diffraction and differential scanning calorimetry (DSC). The DSC results showed that CN-11 has transitions at ∼92 °C (T₂) and ∼147 °C (T₁) during both cooling and immediate heating. A third transition occurred at ∼50 °C (T₃) during heating after annealing at room temperature. The X-ray fiber pattern of the CN-11 annealed at room temperature showed several wide and small angle reflections which were indexed by a monoclinic unit cell with parameters a=16.8 Å, b=7.42 Å, c=43.6 Å and β=102.1° (b: fiber direction), representing a crystal structure with layer thickness of ∼43 Å. Upon heating at T₃, the crystal structure became less ordered (but somewhat more ordered than smectic A (S_A) and smectic C (S_C)). This was followed by S_A (or S_C) phase at T₂, and ultimately an isotropic state (I) at T₁. The observed layer thickness (∼43 Å) is about ∼1.5 times the most extended side chain length, indicating a double-layer structure with tilted or interdigitated side chains. The X-ray fiber pattern had a four-point pattern at d=4.52 Å, suggesting that the side chains in the crystal are likely to be tilted by 56° from the polymer fiber axis.     

Development of high‐strength fibers from aliphatic polyketones by melt spinning and drawing

We have investigated the formation of high‐strength, high‐modulus fibers from four aliphatic polyketone resins. One resin was a perfectly alternating copolymer of ethylene and carbon monoxide, while the other three were terpolymers containing up to 6 mol % propylene. The mechanical properties were measured as a function of processing conditions, and the structures of the filaments were characterized using birefringence, WAXS, SAXS, SEM, and thermal analysis. Fibers formed from all resins develop very high molecular orientations and a microfibrillar structure. Fibers having room temperature tenacities as high as 10 gpd (～1.1 GPa) were obtained. Tensile moduli reached values as high as 120 gpd (～13 GPa). The melting point of the fibers was primarily dependent on the composition of the resin, while the maximum strength and modulus were largely determined by the maximum draw ratio achieved. The maximum draw ratio achieved in the present experiments was greater for the terpolymers than for the copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1794–1815, 2001     

On the nature of the active state of silver during catalytic oxidation of methanol

Under the applied high reaction temperatures (900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (O) apart from O atoms dissolved in the bulk (O). Methanol oxidation to formaldehyde proceeds through this O species as demonstrated by application of a variety of spectroscopic techniques.     

Effect of phenol substitution on the network structure and properties of linear aliphatic diamine-based benzoxazines

A series of aliphatic diamine-based benzoxazines with different phenolic substitutions have been synthesized and characterized. Molecular structure of the monomers is verified by ¹H and ¹³C NMR, FTIR, and elemental analysis. The site of polymerization is regiospecified and the type of linkage in the network structure is manipulated by selectively blocking the ortho, para, and meta positions in the aromatic rings of the monomer. The controlled network structures and their properties are compared to those formed by the polymerization of aliphatic diamine-based benzoxazines prepared from unsubstituted phenol in order to provide insight into their structures. Investigation on the melting point, polymerization kinetics, gelation, and T_g and sub-T_g thermal transition is all reported on these systematically controlled structure polybenzoxazines.     

Main‐chain liquid‐crystalline polymers containing azobenzene mesogen having long lateral aliphatic side chain: effect of copolymerization on thermal and phase behaviors

Homo‐ and copolyesters of derivatives of hydroxyazobenzenecarboxylic acid with various percentage compositions of m‐hydroxy benzoic acid (m‐HBA)/p‐hydroxy benzoic acid (p‐HBA) were synthesized and characterized. The properties of the copolyesters were compared with their corresponding homopolyesters. The solubility of the copolyesters with m‐HBA increased because of the decrease in the rigidity of the polymer chain attributed to the introduction of nonlinear molecules, whereas the solubilities of the copolyesters with p‐HBA changed only slightly compared to their corresponding homopolyesters. Thermal and phase behaviors of the polymers were characterized by TGA, DSC, and polarizing light microscopy (PLM) methods. Above 30% composition of m‐HBA, the thermal stability of the copolyesters with m‐HBA decreased compared to that of the homopolyester P1, whereas the copolyesters of p‐HBA possessed greater thermal stability than that of their homopolyesters at all compositions. The introduction of the long, flexible alkyl side chain laterally to the backbone of the azobenzene moiety drastically reduced the transition temperature of the homopolyester, but without destroying the mesophase. The effect of copolymerization on liquid‐crystalline behavior and transition temperature of the copolymers was discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1976‐1982, 2004     

聚硅氧烷侧链液晶的研究进展

综述了近年来国内外聚硅氧烷侧链液晶的研究进展，着重介绍了几种主要类型的聚硅氧烷侧链液晶，即近晶型、向列型、胆甾型、偶氦苯型、鱼骨形、光学非线性聚硅氧烷侧链液晶的制备、性能和发展动态，并对其应用前景进行了展望。     

Quantitative evaluation of sp/sp hybridization ratio in cluster-assembled carbon films by in situ near edge X-ray absorption fine structure spectroscopy

We present a near edge X-ray absorption fine structure spectroscopy characterization of nanostructured carbon films containing carbynoid species. By a careful data analysis and normalization of the spectra at the carbon K-edge we have quantitatively evaluated the extent of valence sp hybridization of the films. A sp/sp² ratio between 10% and 25% has been obtained. This result allowed the evaluation of the ratio between the sp and sp² Raman cross section at different excitation laser wavelengths.     

The effect of zirconia substitution on the high-temperature transformation of the monoclinic-prime phase in yttrium tantalate

Amorphous yttrium tantalate, as well as solid solutions containing zirconia, transform on heating to a monoclinic-prime phase and then, with further heating, to a crystalline tetragonal (T) solid solution phase at ～1450?°C. On subsequent cooling the tetragonal phase converts by a second-order displacive transformation to a different monoclinic phase not to the monoclinic-prime phase. On subsequent reheating and cooling, the phase transformation occurs between the monoclinic (M) and tetragonal phases, and the monoclinic-prime phase cannot be recovered. The limit of zirconia solubility in both the monoclinic-prime and monoclinic phases lies between 25 and 28?m/o ZrO₂, consistent with previous first-principles calculations. The monoclinic-prime phase is stable up to at least 1400?°C for 100?h for zirconia concentrations from 0 to ～60?m/o ZrO₂. This temperature exceeds the temperature of the equilibrium M-T phase transformation suggesting that the monoclinic-prime phase transforms directly to the tetragonal phase by a reconstructive transformation and is unaffected by the zirconia in solid solution.     

Isomorphic crystallization of aliphatic copolyesters derived from 1,6-hexanediol: Effect of the chemical structure of comonomer units on the extent of cocrystallization

The crystallization behavior has been investigated for poly(hexamethylene sebacate-co-hexamethylene suberate)s [P(HSe-co-HSu)] and poly(hexamethylene suberate-co-hexamethylene adipate)s [P(HSu-co-HA)] copolyesters by differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectrometer. Cocrystallization of comonomer units was found in the crystalline phase of both P(HSe-co-HSu) and P(HSu-co-HA) copolymers. Moreover, both P(HSe-co-HSu) and P(HSu-co-HA) copolymers exhibit isodimorphism. The PHSe and the PHSu type crystals were respectively developed in P(HSe-co-HSu)s, while the PHSu and the PHA type crystals were developed in P(HSu-co-HA)s respectively. The inclusion of the comonomer units in the PHSu type crystalline lattice is more favored than that in the PHSe type crystal of the P(HSe-co-HSu)s. Meanwhile, it is easier for the comonomer units to be incorporated into the PHA type crystalline lattice than into the PHSu type crystal of P(HSu-co-HA)s. Moreover, comparison between the isomorphic crystallization of P(HSe-co-HSu), P(HSe-co-HA) and P(HSu-co-HA) series copolyesters indicates that minimization of the difference in chemical structure helps in increasing the extent of cocrystallization of comonomer units.     

Europium‐containing cholesteric liquid crystalline polymers in the side chain

Europium‐containing cholesteric liquid crystalline polymers were graft copolymerized using poly(methylhydrogeno)siloxane, cholesteryl 4‐(allyloxy)benzoate (M₁), cholesteryl acrylate (M₂), and a europium complexes monomer (M₃). The chemical structures of the monomers were characterized by Fourier transform infrared and ¹H‐nuclear magnetic resonance. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermo gravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. With an increase of europium complexes units in the polymers, the glass transition temperature (T_g) did not change significantly; the isotropic temperature (T_i) and mesophase temperature range (ΔT) decreased. All polymers showed typical cholesteric Grandjean textures, which was confirmed by X‐ray diffraction. The temperatures at which 5% weight loss occurred (T_d) were greater than 300°C for the polymers. The introduction of europium complexes units did not change the liquid crystalline state of polymer systems; on the contrary, the polymers were enabled with the significant luminescent properties. With Eu³⁺ ion contents ranging between 0 and 1.5 mol %, luminescent intensity of polymers gradually increased and luminescent lifetimes were longer than 0.45 ms for the polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40866.     

Infrared-spectroscopic investigations of molecular order in liquid crystalline side chain polymers

Summary Infrared dichroism was used to determine the order parameters of liquid crystalline side chain polymers. By this the order parameters of the main chain, of the spacer and of the mesogenic group can be obtained separately. Therefore spectra of two liquid crystalline polyacrylates were recorded with polarized light at different temperatures. In a poly(acrylate) with 6 CH₂ groups in the spacer a high order parameter was found not only for the mesogenic group, but also for the spacer and the main chain. The orientation of the poly(acrylate) with a spacer of only 2 CH₂ groups is lower due to the stronger interaction of main chain and mesogenic group.     

The electronic structure effect in heterogeneous catalysis

Using a combination of density functional theory calculations and X-ray emission and absorption spectroscopy for nitrogen on Cu and Ni surfaces, a detailed picture is given of the chemisorption bond. It is suggested that the adsorption bond strength and hence the activity of transition metal surfaces as catalysts for chemical reactions can be related to certain characteristics of the surface electronic structure.     

Study of the distribution of the molecular orientation in thick polyethylene samples by X-ray diffraction, infra-red dichroism and Raman spectroscopy

The molecular orientation in thick polyethylene samples has been studied by wide-angle X-ray diffraction, i.r. dichroism and Raman spectroscopy. The original specimens, with dimensions of the order of a centimetre, were cut to obtain 1 mm thick platelets on which the measurements were made. The mean coefficient of the second-order Legendre polynomial, P₂, was calculated from X-ray diffraction and from the 1894 cm⁻¹ i.r. band for the crystalline phase, from the 909 cm⁻¹ i.r. band for the vinyl end groups and from the 1130 and 1060 cm⁻¹ Raman bands for the all-trans C-C conformers. The fourth-order coefficient, P₄, was also determined from X-ray diffraction and Raman spectroscopy for a series of cylindrical rods of draw ratios (λ) ranging from 6 to 20. An excellent correlation is observed between the P₂ coefficients measured from different X-ray reflections and from the 1894 cm⁻¹ i.r. band. The Raman spectroscopy results show that the all-trans bonds located in the amorphous phase are aligned perpendicular to the extrusion direction for the λ = 6 rod, and gradually reorient towards the fibre axis for λ values up to 20, while the P₂ and P₄ coefficients calculated for the crystalline phase remain constant at λ ≥ 12. The variation of the orientation through the thickness of the samples was investigated for the cylindrical rods and for an H-shaped moulding produced by extrusion and rolling. Minor differences in the degree of molecular orientation were detected between the centre and the surface of the rods, whereas important variations were measured for the H-shaped sample.     

Polymers with iodonium salt structure in the side chain

Summary We investigated the synthesis of polymer-bound iodonium salts with chloride as anion by polymer analogous reaction. The structure of polymers was determined with NMR-spectroscopy, MS-analysis as well as by model substances. The polymers give transparent films on glass, they decomposed during irradiation and eliminated HCl. The HCl-elimination in the films can be detected with indicators and also with potentiometric titration with AgNO₃.     

The influence of starting materials on the structure of ultrafine carbon powders

The primary ultrafine carbon powders were prepared by sol–gel supercritical fluid drying method using different starting materials. After heat-treatment at 1100 and 2600°C, respectively, the ultrafine carbon powders were obtained. The properties of primary ultrafine carbon powders and their annealed products were characterized by TEM, XRD, Raman spectra and nitrogen adsorption. The results reveal that starting materials have influence on the structure of ultrafine carbon powders.     

Residual stresses and crystalline quality of heavily boron-doped diamond films analysed by micro-Raman spectroscopy and X-ray diffraction

X-ray diffraction analysis and micro-Raman spectroscopy measurements have been used for stress studies on HFCVD diamond films with different levels of boron doping. The boron incorporation in the film varied in the range 10¹⁸-10²¹ boron/cm³. The grain size, obtained from SEM images, showed grains with 2-4-μm average size, which decreases when the doping level increases. The thickness of the films obtained by SEM cross-section view decreased from 8 to 5 μm as the doping level increased from 0 (undoped film) to 10²¹ boron/cm³. The total residual stress was determined by measuring, for each sample, the (331) diamond Bragg diffraction peak for Ψ-values ranging from −60° to +60°, and applying the sin² ψ method. For the micro-Raman spectroscopy the spectral analysis performed on each sample allowed the determination of the residual stress, from the diamond Raman peak shifts, and also the diamond purity, which decreases from 99 to 75% as the doping level increases. The type and magnitude of the residual stress obtained from X-ray and micro-Raman measurements agreed well only for undoped film, disagreeing when the doping level increased. We attributed this discrepancy to the domain size characteristic of each technique.