Raman Structural Study of Copolymers of Propylene with Ethylene and High Olefins

Nascent form of random copolymers of propylene with ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene was studied by Raman spectroscopy. The most significant spectral alterations with a change in propylene content were observed in two lines at 809 and 841 cm⁻¹. The first line corresponds to vibrations of polypropylene helical chains in the crystalline phase, while the second one is associated with vibrations of polypropylene helical chains having isomeric defects. Raman data confirm that conformational composition and phase state of copolymer macromolecules strongly depend on the comonomer content as well as on the size of the comonomer units.     

Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

In this study, memory effect of mesomorphic isotactic polypropylene (iPP) was investigated using polarized optical microscope and small‐angle X‐ray scattering. Differing from classical memory effect, mesomorphic iPP melt had a higher growth rate and a higher memory temperature. The relative growth rate increased with increasing crystallization temperature. Lauritzen–Hoffman plots indicated that the increased growth rate arose from reduced surface nucleation barrier. The highest memory temperature was estimated to be 185 °C, which was close to the equilibrium melting point of iPP crystal. Additionally, Small‐angle X‐ray scattering measurements showed that a liquid crystal layer might exist between lamellar and amorphous layers. Based on above results, a crystallization model was proposed. In the mesomorphic iPP melt, there exist aggregates structurally similar to β phase except α‐phase crystal residuals, which cannot act as nucleation sites or transform to β crystal through surface nucleation. The only way for the aggregate is to transform to α crystal during crystal growth. The aggregate decreases the surface nucleation barrier and promotes the helical growth, leading to higher growth rate. Only when the aggregate relaxes to polymer coils through thickening at a higher temperature, can the memory effect be erased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1573–1580     

Temperature‐dependent polymorphic crystalline structure and melting behavior of poly(butylene adipate) investigated by time‐resolved FTIR spectroscopy

The polymorphic crystalline structure and melting behavior of biodegradable poly(butylene adipate) (PBA) samples melt‐crystallized at different crystallization temperatures were studied by differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) spectroscopy. The crystalline structure and melting behavior of PBA were found to be greatly dependent on the crystallization temperature. By comparison of the FTIR spectra and the corresponding second derivatives between the α‐ and β‐crystal of PBA, the spectral differences were identified for the IR bands appeared at 1485, 1271, 1183, and 930 cm^?1 and the possible reasons were presented. Especially, the 930 cm^?1 band was found to be a characteristic band for the β‐crystal. Combining the DSC data with the analysis of normalized intensity changes of several main IR bands during the melting process, the melting behaviors of the α‐ and β‐crystal were clarified in detail. It is demonstrated by the in situ IR measurement that the β‐crystalline phase would transform into the α‐crystalline phase during the melting process, and the solid–solid phase transition from the β‐ to α‐crystal was well elucidated by comparing the intensity changes of the 1170 and 930 cm^?1 bands. The dependence of the β‐ to α‐crystal phase transition on the heating rate was revealed by monitoring the intensity ratio of the 909 and 930 cm^?1 band. It was suggested that at the heating rate of 0.5 or 1 °C/min, the percent amount of the transformed α‐crystal from the β‐crystal was much higher than that at the higher heating rate. The β‐crystal transforms into the α‐crystal incompletely at the higher heating rate because of the less time available for the phase transition. In addition, the β‐ to α‐crystal phase transition was further confirmed by the IR band shifts during the melting process. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1997–2007, 2009     

Orientation-induced crystallization in isotactic polypropylene melt by shear deformation

Development of orientation-induced precursor structures (nuclei) prior to crystallization in isotactic polypropylene melt under shear flow was studied by in-situ synchrotron small-angle X-ray scattering (SAXS) and rheo-optical techniques. SAXS patterns at 165°C immediately after shear (rate = 60 s⁻¹, t_s = 5 s) showed emergence of equatorial streaks due to oriented structures (microfibrils or shish) parallel to the flow direction and of meridional maxima due to growth of the oriented layer-like structures (kebabs) perpendicular to the flow. SAXS patterns at later times (t = 60 min after shear) indicated that the induced oriented structures were stable above the nominal melting point of iPP. DSC thermograms of sheared iPP samples confirmed the presence of two populations of crystalline fractions; one at 164°C (corresponding to the normal melting point) and the other at 179°C (corresponding to melting of oriented crystalline structures). Time-resolved optical micrography of sheared iPP melt (rate = 10 s⁻¹, t_s = 60 s, T = 148°C) provided further information on orientation-induced morphology at the microscopic scale. The optical micrographs showed growth of highly elongated micron size fibril structures (threads) immediately after shear and additional spherulities nucleated on the fibrils at the later stages. Results from SAXS and rheo-optical studies suggest that a stable scaffold (network) of nuclei, consisting of shear-induced microfibrillar structures along the flow direction superimposed by layered structures perpendicular to the flow direction, form in polymer melt prior to the occurance of primary crystallization. The scaffold dictates the final morphological features in polymer.     

In situ FTIR spectroscopic study of the regularity bands and partial‐order melts of isotactic poly(propylene)

An experimental method to determine the order degree of isotactic poly(propylene) (iPP) via regularity bands was developed using fast heating Fourier transform infrared spectroscopy. The various regularity bands can be rearranged in terms of the order degree from high to low: 940, 1 220, 1 167, 1 303, 1 330, 841, 998, 900, 808, 1 100 and 973 cm^–1. When the crystalline iPP melts, partially ordered melt is formed. With a decreasing degree of order of the partially ordered melt, the crystallization peak shifts to lower temperatures and the exothermal enthalpy becomes larger.     

Thermo-physical characterization of some paraffins used as phase change materials for thermal energy storage

Three phase change paraffinic materials (PCMs) were thermophysically (phase-transition temperatures, latent heat, heat capacity at constant pressure, density, and thermal conductivity) investigated in order to be used as latent heat storage media in a pilot plant developed in Plovdiv Bulgaria. Raman structural investigation probes aliphatic character of the E53 sample, while the E46 and ECP samples contain also unsaturated components due to their Raman features within 1,500–1,700 cm^?1 range. Orthorhombic structure of the three PCMs was evidenced by the Raman modes at the 1,417 cm^?1. The highest latent heat value, ΔH, of phase transitions among the three materials was represented by summation of a solid order–disorder, and melting latent heat was encountered by the E53 paraffin, i.e., 194.32 J g^?1 during a μ-DSC scan of 1 °C min^?1. Conversely, the ECP composite containing ceresin component shows the lowest latent heat value of 143.89 J g^?1 and the highest thermal conductivity of 0.46 W m^?1 K^?1 among the three phase change materials (PCMs). More facile melt-disordered solid transition with the activation energy of 525.45 kJ mol^?1 than the lower temperature transition of disorder–order (E _a of 631.73 kJ mol^?1) during the two-step process of solidification for the E53 melt are discussed in terms of structural and molecular motion changes.     

Regularity modes in Raman spectra of polyolefins: Part I. Propylene/olefin copolymers

Behavior of the regularity modes of isotactic polypropylene is analyzed in Raman spectra of a number of random propylene/olefin copolymers. The regularity modes at 809, 841, 973, 998, and 1220 cm⁻¹ decrease in intensity with growth of the content of the incorporated monomer. For the lines at 809, 973, and 1220 cm⁻¹ the rate of intensity damping varies depending on the structure of the incorporated monomer. The type of the incorporated monomer has inconsiderable effect on the evolution of intensity of the regularity bands at 841 and 998 cm⁻¹. Anomalous behavior of the mode at 1220 cm⁻¹ was observed for the propylene/1-butene copolymers.     

Structure and molecular conformation of tussah silk fibroin films: Effect of methanol

Structural changes of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20°C were studied as a function of methanol concentration and immersion time. X-ray diffraction measurements showed that the α-helix structure, typical of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallization to β-sheet structure was observed following immersion of tussah films for 30 min in methanol solutions ranging from 20 to 60% (v/v). IR spectra of tussah films untreated and methanol treated for 2 min exhibited strong absorption bands at 1265, 892, and 622 cm^?1, typical of the α-helix conformation. The intensity of the bands assigned to the β-sheet conformation (1245, 965, and 698 cm^?1) increased for the sample treated with 40% methanol for 30 min. Raman spectra of tussah films with α-helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm^?1. Following α → β conformational transition, amide I and III bands shifted to 1668, and to 1241, 1230 cm^?1, respectively. The band at 1106 cm^?1 disappeared and new bands appeared at 1095 and 1073 cm^?1, whereas the intensity of the bands at 530 and 376 cm^?1 decreased significantly. ©1995 John Wiley & Sons, Inc.     

Oxygen‐barrier properties of cold‐crystallized and melt‐crystallized poly(ethylene terephthalate‐co‐4,4′‐bibenzoate)

This study examined the oxygen‐transport properties of poly(ethylene terephthalate‐co‐bibenzoate) (PETBB55) crystallized from the melt (melt crystallization) or quenched to glass and subsequently isothermally crystallized by heating above the glass‐transition temperature (cold crystallization). The gauche–trans conformation of the glycol linkage was determined by infrared analysis, and the crystalline morphology was examined by atomic force microscopy. Oxygen solubility decreased linearly with volume fraction crystallinity. For melt‐crystallized PETBB55, extrapolation to zero solubility corresponded to an impermeable crystal with 100% trans glycol conformations, a density of 1.396 g cm^?3, and a heat of melting of 83 J g^?1. From the melt, PETBB55 crystallized as space‐filling spherulites with loosely organized lamellae and pronounced secondary crystallization. The morphological observations provided a structural model for permeability consisting of impermeable platelets randomly dispersed in a permeable matrix. In contrast, cold‐crystallized PETBB55 retained the granular texture of the quenched polymer despite the high level of crystallinity, as measured by the density and heat of melting. Oxygen solubility decreased linearly with volume fraction crystallinity, but zero solubility corresponded to an impermeable defective crystal with a trans fraction of 0.83 and a density of 1.381 g cm^?3. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2489–2503, 2002     

Anionic polymerization of 2,7‐di‐t‐butyldibenzofulvene: Synthesis,structure, and photophysical properties of the oligomers with a π‐stacked conformation

2,7‐Di‐t‐butyldibenzofulvene (tBu₂DBF), a bulky dibenzofulvene derivative, was polymerized using n‐butyllithium as initiator in tetrahydrofuran at ?78 °C and in toluene at 0 °C. tBu₂DBF afforded mainly oligomers up to trimer even at [monomer]₀/[initiator]₀ = 20 ([monomer]₀ = 0.2 M) at ?78 °C and 0 °C, indicating that this monomer is much less reactive than dibenzofulvene (DBF), its parent compound. The reaction at the same [monomer]₀/[initiator]₀ ratio at an elevated [monomer]₀ gave a small amount of insoluble polymer. The oligomers indicated a hypochromic effect in the absorption spectra and only monomer emission in the fluorescent spectra. The conformation of the trimer and the dimer was examined by means of NOESY NMR spectra and semiempirical calculations. In the trimer conformation, the fluorene moieties of the central and the initiation‐side monomeric units were found to be closely stacked on top of each other, while the termination‐side monomeric unit appeared to be in a faster conformational dynamics compared with the other monomeric units. Although the dimer seemed to have a relatively flexible conformation, a π‐stacked structure appeared to be involved in the conformational dynamics to show hypochromicity. The results of this study suggest that the reported intramolecular excited dimer (excimer) formation of the poly‐ and oligo(DBF)s [J Am Chem Soc 2003, 125, 15474] is based on a slight, local conformational change upon photo absorption, leading to a closer π‐stacked alignment of two neighboring fluorene units than that in the ground state. Such a local conformational transition may be difficult for the tBu₂DBF trimer because of steric repulsion of the t‐butyl groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 561–572, 2006     

Raman spectrum and secondary structure of the phage λ operator site OL1: evidence for multiple nucleoside conformations in an aqueous B-form DNA

The laser Raman spectrum of O_L1 has been obtained in the region 600–850 cm⁻¹ and the data have been interpreted in terms of different nucleoside conformations within the 17 base pair operator site. The O_L1 sequence, which is one of the tightest binding sites for the cI and Cro repressors of bacteriophage λ, displays several Raman conformation markers indicative of more than one backbone geometry for the same double-stranded DNA helix. Specific assignments for the Raman conformation markers are suggested by analogy with spectra of DNA single crystals and DNA fibers of known structure. Two Raman bands diagnostic of B-DNA backbone geometry are observed at 825 ± 3 and 838 ± 3 cm⁻¹, and may be due, respectively, to inequivalent conformations of GC and AT pairs. In addition, a weak band at 706 cm⁻¹ and a shoulder near 807 cm⁻¹ are consistent with a minor contribution from residues which assume the A-DNA backbone geometry or a structurally related configuration. The complex bandshape in the 650–700 cm⁻¹ interval, which is resolved into four peaks by Fourier deconvolution, is also consistent with the presence of multiple nucleoside conformers in O_L1 in physiological conditions.     

Ionic conductivity probed in main chain liquid crystalline azobenzene polyesters

Three main chain thermotropic liquid crystalline (LC) azobenzene polymers were synthesized using the azobenzene twin molecule (P4P) having the structure Phenylazobenzene‐tetraethyleneglycol‐Phenylazobenzene as the AA monomer and diols like diethylene glycol, tetraethylene glycol (TEG), and hexaethylene glycol as the BB comonomer. Terminal ? C(O)OMe units on P4P facilitated transesterification with diols to form polyesters. All polymers exhibited stable smectic mesophases. One of the polymers, Poly(P4PTEG) was chosen to prepare composite polymer electrolytes with LiCF₃SO₃ and ionic conductivity was measured by ac impedance spectroscopy. The polymer/0.3 Li salt complex exhibited a maximum ionic conductivity in the range of 10^?5 S cm^?1 at room temperature (25 °C), which increased to 10^?4 S cm^?1 above 65 °C. The temperature dependence of ionic conductivity was compared with the phase transitions occurring in the sample and it was observed that the glass transition had a higher influence on the ionic conductivity compared to the ordered LC phase. Reversible ionic conductivity switching was observed upon irradiation of the polymer/0.3 Li salt complex with alternate UV and visible irradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 629–641     

Thermal decomposition of liebigite

Summary A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of liebigite. Water is lost in two steps at 44 and 302°C. Two mass loss steps are observed for carbon dioxide evolution at 456 and 686°C. The product of the thermal decomposition was found to be a mixture of CaUO₄ and Ca₃UO₆. The thermal decomposition of liebigite was followed by hot-stage Raman spectroscopy. Two Raman bands are observed in the 50°C spectrum at 3504 and 3318 cm^-1 and shift to higher wavenumbers upon thermal treatment; no intensity remains in the bands above 300°C. Three bands assigned to the υ₁ symmetric stretching modes of the (CO₃)^2- units are observed at 1094, 1087 and 1075 cm^-1 in agreement with three structurally distinct (CO₃)^2- units. At 100°C, two bands are found at 1089 and 1078 cm^-1. Thermogravimetric analysis is undertaken as dynamic experiment with a constant heating rate whereas the hot-stage Raman spectroscopic experiment occurs as a staged experiment. Hot stage Raman spectroscopy supports the changes in molecular structure of liebigite during the proposed stages of thermal decomposition as observed in the TG-MS experiment.     

Thermal decomposition of the hydrotalcite

Summary A combination of thermogravimetry and hot stage Raman spectroscopy has been used to study the thermal decomposition of the synthesised zinc substituted takovite Zn₆Al₂CO₃(OH)₁₆·4H₂O. Thermogravimetry reveals seven mass loss steps at 52, 135, 174, 237, 265, 590 and ~780°C. MS shows that the first two mass loss steps are due to dehydration, the next two to dehydroxylation and the mass loss step at 265°C to combined dehydroxylation and decarbonation. The two higher mass loss steps are attributed to decarbonation. Raman spectra of the hydroxyl stretching region over the 25 to 200°C temperature range, enable identification of bands attributed to water stretching vibrations, MOH stretching modes and strongly hydrogen bonded CO₃^2--water bands. CO₃^2- symmetric stretching modes are observed at 1077 and 1060 cm^-1. One possible model is that the band at 1077 cm^-1is ascribed to the CO₃^2- units bonded to one OH unit and the band at 1092 cm^-1is due to the CO₃^2- units bonded to two OH units from the Zn-takovite surface. Thermogravimetric analysis when combined with hot stage Raman spectroscopy forms a very powerful technique for the study of the thermal decomposition of minerals such as hydrotalcites.</o:p>     

Azine bridge formation during the electrografting of acrylonitrile

We report the electrografting of polyacrylonitrile (PAN) films onto evaporated gold, silver, and copper substrates, and onto platinum foil. The FTIR spectra of the films are virtually identical to library spectra of PAN and show no evidence of the cyclization observed by some authors. Raman spectra of the same films, however, display a broad absorption band centered at ～1520 cm^?1 and a second band at 1096 cm^?1, which are neither present in spin‐coated films of commercially obtained PAN nor are they present in the FTIR spectra. These previously unreported Raman bands are dependent on a number of factors in the electrografting process; the working electrode metal, the monomer concentration, the solvent used, and the electrochemical protocol used for cleaning the working electrode. The relative intensity of the bands was found to be strongest in films grown on platinum and weakest in those grown on gold, and stronger in thin films (<50 nm) than in thick films (>100 nm). We suggest that these new spectral features are associated with azine‐linked polymer chains in a ladder‐like structure close to the electrode surface as a result of the predominantly isotactic brush‐like conformation of the polymer during the early stages of electrografting. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1685–1695, 2009     

Temperature dependence of molecular conformation in uniaxially deformed isotactic polypropylene investigated by combination of polarized FTIR spectroscopy and 2D correlation analysis

Evolution of molecular conformation in uniaxially deformed isotactic polypropylene (iPP) as a function of temperature is investigated by time‐resolved polarized Fourier‐transform infrared spectroscopy. It is observed that oriented crystals (microfibrils) induced by deformation possess better thermal stability compared with isotropic spherulites. 2D correlation analysis reveals that the relaxation process of ordered helices in deformed iPP could be divided into two regions referring to the melting of different crystalline structures. No obvious sequential change of ordering conformations observed in low temperature region is attributed to melting of defective or destructed crystals. However, notable sequential changes of helices occur in the high temperature region; interestingly, long helices are more thermally stable than short helices. The central region of microfibrils is suggested to consist of a large amount of long helical bundles, and the short ordering segments are primarily located in the outer lateral surfaces. A physical picture of the conformational distribution in deformation‐induced microfibrils is thus gained. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 673–684     

Bis(bis(triphenylphosphin)iminium)-μ-nitrido-bis(azidophthalocyaninato(2–)ferrat(IV))-Triiodid Diethylether-Disolvat: Synthese,Eigenschaften und Kristallstruktur

Bis(bis(triphenylphosphine)iminium) μ-Nitrido-bis(azidophthalocyaninato(2–)ferrate(IV)) Triiodide Diethylether Di-Solvate: Synthesis, Properties, and Crystal Structure Bis(bis(triphenylphosphine)iminium) μ-nitrido-bis(azidophthalocyaninato(2–)ferrate(IV)) triiodide is prepared as a diethylether di-solvate by substitution of μ-nitrido-bis(pyridinephthalocyaninato(2–)iron(IV)) pentaiodide with bis(triphenylphosphine)iminium azide in acetone and precipitation by slow diffusion of diethylether. The doublesalt crystallizes monoclinically in the space group C12/c1 with cell parameters: a = 34.567(9) Å, b = 20.237(9) Å, c = 21.251(5) Å, β = 119.79(2)°; Z = 4. The Fe atoms are located almost in the centre (Ct) of the (N_iso)₄ planes (d(Fe–Ct) = 0.080(1) Å; N_iso: isoindoline N atom). The average Fe–N_iso distance is 1.947(5) Å, the Fe-(μ-N) distance 1.650(1) Å. The Fe-(μ-N)–Fe skeleton is linear (177.4(4)°). Both waving pc^2– ligands are in a staggered conformation (skew angle φ = 38.5(5)°). Fe coordinates linear azide (d(Fe–N_azide) = 2.152(7) Å) with an angle of 121.2(6)°. The isolated triiodide ion is almost linear (d(I–I) = 2.936(2) Å). The PNP cation obtains an hybrid conformation (∠(P–N–P) = 157.4(2)°). The asymmetrical Fe-(μ-N)–Fe stretching vibration is observed in the IR spectrum at 997 cm^–1, the symmetrical one is selectively enhanced in the resonance Raman (RR) spectrum at 478 cm^–1. The corresponding I–I stretching vibrations of the triiodide ion are present in the actual spectra at 134 (IR) and 115 cm^–1 (RR). An IR band at 334 cm^–1 is attributed to the asymmetrical Fe–N_azide stretching vibration.     

On the nature of the active centres in the initial stages of methacrylonitrile anionic polymerization—I: Spectral studies

The active centres in the initial stage of methacrylonitrile anionic polymerization have been studied by means of electronic and i.r.-spectra as well as by use of model compounds. The attachment of the first monomer unit to the initiator causes formation of the carbanion

, characterized by an absorption band at 2020–2055 cm^?1. Addition of more monomer units leads to the appearance of a new band at 2100 cm^?1, due to the group

. The appearance of a new band at 2260 cm^?1 and the shift of the band at 2020–2055 cm^?1 towards higher frequencies, as the number of adjacent monomer units is increased, is explained by interaction of the active centres with the nitrile groups of the polymer chain.     

DFT study on Raman frequencies of molten lead (II) chloride

The study concerns ab inito calculations of the essential Raman frequencies of molten lead (II) chloride near the melting point. Modelling of topologically disordered lead (II) chloride was carried out within the framework of the density functional theory using the Perdew–Burke-Ernzerhof (PBE) functional and optimised basis sets. Calculations were performed for a cluster containing 24 formula units. The optimum geometry of the cluster was determined and the local structure parameters were found. Nano-size effect leads to the picture of damped oscillations on radial atomic density distributions typical of molten salts. Distorted octahedra of PbCl₆ were detected inside the cluster. Ab initio calculation of the Raman spectrum of the octahedral complexes inside the cluster structure was implemented. It was shown that the spectrum has a peak at 192 cm^?1, which agrees well with the experimental Raman spectra of lead (II) chloride melt near the melting point.     

Effect of temperature on frying oils: infrared spectroscopic studies

Frying oils were studied by Fourier-transform infrared (FT-IR) spectroscopy, in the range 4,000–200 cm^?1, at different temperatures, in the liquid and solid states. The infrared spectrum at 15 °C was similar to that at 200 °C. The band at 730 cm^?1 which was assigned to the rocking mode of (–CH₂) disappeared at higher temperature because of the rotational isomerism which occurred in the oil structure. The activation energy (E _a) of the disappearing (–CH₂) band, calculated by use of the chemical dynamic method using the Arrhenius equation, is 8.45 kJ mol^?1. The enthalpy difference (ΔH) between the two rotational isomer bands of the conformational structures of the oil at 730 and 1,790 cm^?1, at different high temperatures, was also calculated, by use of the Van’t Hoff equation; the value obtained was ?10.85 kJ mol^?1.