Nuclear spin relaxation in poly(diethylsiloxane)

Earlier work showed that heating causes poly(diethylsiloxane) to undergo a first-order transition from a semicrystalline solid to a more mobile viscous—crystalline material. The latter is composed of two phases and analogies between polymer and liquid crystal morphology and behavior have been made. The viscous—crystalline phase in PDES appears to be unique since the literature is devoid of other documented examples. In this study, spin—lattice and spin—spin relaxation times were measured over a wide temperature range. They show a glass transition at 138°K, a crystal—crystal transition at 206°K, and a transition around 250°K which results from translational motion of the polymer chains with respect to each other. This motion is observed in the amorphous phase at a lower temperature than in the crystalline phase. Translational motion in the crystalline phase is observed on melting of the crystallites. The spin—spin data permitted monitoring of the molecular motions in each phase and the data suggest that these phases exert some influence on the molecular motions of each other. The viscous—crystalline phase in PDES may represent a unique model for studying and understanding “precrystalline” behavior and structure in amorphous solids.     

Characterization of crystalline and amorphous content in pharmaceutical solids by dielectric thermal analysis

Morphological and thermodynamic transitions in drugs as well as their amorphous and crystalline content in the solid state have been distinguished by thermal analytical techniques, which include dielectric analysis (DEA), differential scanning calorimetry (DSC), and macro-photomicrography. These techniques were used successfully to establish a structure versus property relationship with the United States Pharmacopeia standard set of active pharmaceutical ingredient (API) drugs. A distinguishing method is the DSC determination of the amorphous and crystalline content which is based on the fusion properties of the specific drug and its recrystallization. The DSC technique to determine the crystalline and amorphous content is based on a series of heat and cool cycles to evaluate the drugs ability to recrystallize. To enhance the amorphous portion, the API is heated above its melting temperature and cooled with liquid nitrogen to ?120 °C (153 K). Alternatively a sample is program heated and cooled by DSC at a rate of 10 °C min^?1. DEA measures the crystalline solid and amorphous liquid API electrical ionic conductivity. The DEA ionic conductivity is repeatable and differentiates the solid crystalline drug with a low conductivity level (10^?2 pS cm^?1) and a high conductivity level associated with the amorphous liquid (10⁶ pS cm^?1). The DSC sets the analytical transition temperature range from melting to recrystallization. However, analysis of the DEA ionic conductivity cycle establishes the quantitative amorphous and crystalline content in the solid state at frequencies of 0.10–1.00 Hz and to greater than 30 °C below the melting transition as the peak melting temperature. This describes the “activation energy method.” An Arrhenius plot, log ionic conductivity versus reciprocal temperature (K^?1), of the pre-melt DEA transition yields frequency dependent activation energy (E _a, J mol^?1) for the complex charging in the solid state. The amorphous content is inversely proportional to the E _a where the E _a for the crystalline form is higher and lower for the amorphous form with a standard deviation of ±2%. There was a good agreement between the DSC crystalline melting, recrystallization, and the solid state DEA conductivity method with relevant microscopic evaluation. An alternate technique to determine amorphous and crystalline content has been established for the drugs of interest based on an obvious amorphous and crystalline state identified by macro-photomicrography and compared to the conductivity variations. This second “empirical method” correlates well with the “activation energy” method.     

Molecular-topological structure of γ-irradiated polytetrafluoroethylene

The molecular-topological structure of polytetrafluoroethylene (PTFE) has been studied in the range of ?100 to +450°C by thermomechanical spectrometry. Revealed in this temperature range is a fourblock topological structure composed of one amorphous (T _g = 16°C) and three crystalline (low-melting (T _m = 315°C), intermediate (T _m ¹ = 355°C), and high-melting (T _m ² = 388°C)) polymorphs. At a dose of 1 kGy, the long-range orientation of chains in the intermediate and high-melting crystalline blocks of PTFE is replaced by short-range orientation of the cluster association structure. At doses of 100?C500 kGy, the latter structure transitions to the amorphous state and the irradiated samples acquire a semicrystalline structure of the two-block type. The molecular-mass distribution function of interjunction chains of the pseudo-network of the amorphous block is bimodal in character and its maxima are noticeable shifted toward lower masses with an increase in the radiation dose. As the dose increases, the crystallinity decreases and the molecular mobility of amorphized chains is enhanced. As a result, both the glass transition and the molecular flow onset temperatures of the polymer are reduced.     

Amorphous polyacrylonitrile: Synthesis and characterization

Amorphous polyacrylonitrile was successfully synthesized with bis(pentamethyleneimino)magnesium in heptane at 70°C. The amorphousness of the polymer increased with rising polymerization temperature and was favored by the nonpolar solvent. The polymer showed regular head-to-tail sequences which were confirmed by converting the polymer into polyacrylic acid and polymethylacrylate. The amorphous PAN produced a broad x-ray diagram with a maximum at 2θ = 16.1° and a less intense halo at 2θ = 27.5°. This pattern did not change after heat treatment. The synthesis of amorphous PAN strongly supports Imai's hypothesis that polyacrylonitrile consists of paracrystalline and amorphous phases. The amorphous PAN also tends to support Minami's assignment of the two absorptions in the temperature dependence of the dynamic loss tangent; the absorption at the lower temperature (110°C) is due to molecular motions in the paracrystalline phase and the absorption at the higher temperature (160°C) is attributed to the molecular motions in the amorphous region.     

A new mesogenic fluorene derivative: 2,7-bis(4-pentylphenyl)-9,9-diethyl-9H-fluorene

The title compound, 2,7-bis(4-pentylphenyl)-9,9-diethyl-9H-fluorene, is a new mesogenic compound containing the fluorene moiety. It exhibits a monotropic nematic liquid crystalline behaviour, with isotropisation temperature of 53°C. The compound is also polymorphic in the solid state, with one crystal phase melting at 103°C and another one melting at 71°C. The crystal and molecular structure of the high melting solid phase have been determined from single crystal X-ray diffraction analysis. Crystals are monoclinic, with cell dimensions a = 16.649(6) Å, b = 8.305(3) Å, c = 24.598(7) Å, β = 111.60(2)?, space group P2₁/c and four molecules in the unit cell. Refinement leads to R = 0.0558. The two terminal alkyl chains and one phenyl ring are disordered over two split positions. The imbricated molecular packing observed in the solid state seems to resemble that of the nematic phase that is formed upon cooling the melt.     

Thermoresponsive ketoprofen-imprinted monolith prepared in ionic liquid

A thermoresponsive imprinted monolith with the ability of molecular recognition for ketoprofen was prepared for the first time. The smart monolith was synthesized in a stainless steel column using acrylamide (AAm) and 2-acrylamide-2-methyl propanesulfonic acid (AMPS) as functional monomers, which can form interpolymer complexation to restrict access of the analyte to the imprinted networks at low temperatures. To avoid a high back pressure of the column derived from neat dimethyl sulfoxide (DMSO) as a porogenic solvent that is needed to solve polar AMPS, an ionic liquid, [BMIM]BF₄, was introduced into the pre-polymerization mixture. The molecular recognition ability towards ketoprofen of the resulting thermoresponsive molecularly imprinted polymer (MIP) monolith displayed significant dependence on temperature compared with a non-imprinted column (NIP), and the greatest imprinting factor was achieved at the transition temperature of 35 °C (above 10). Furthermore, the number of binding sites of the smart MIP monolith at 35 °C was about 76 times as large as that at 25 °C. In addition, Freundlich analyses indicated that the thermoresponsive MIP monolith had homogeneous affinity sites at both 25 and 35 °C with heterogeneity index 0.9251 and 0.9851, respectively.     

Degradation of nitric acid-trbeated bulk polyethylene

LDPE samples with differing branching content were treated with fuming nitric acid for times up to 180 h at 60°C. The samples were examined by differential scanning calorimetry and small angle X-ray diffraction. While the crystal thickness derived from the X-ray long period remains practically constant throughout treatment timet, a conspicuous sharpening and shifting of the melting curves to higher temperatures witht is observed. It is suggested that the shift in melting peak is caused by the contribution of the dicarboxylic groups attached to the crystal surface after treatment. It is further shown that the shift depends inversely on the crystal thickness. The comparison of melting points for long time nitric acid treated PE samples with data from dicarboxylic acids has permitted the derivation of an expression for the melting temperature of longer molecular diacids.     

Synthesis of a New Liquid Crystalline Polymer as a Highly Active β-Nucleator and Its Effect on Melting and Crystallization Behaviors of Isotactic Polypropylene

A new nematic liquid crystalline polymer as a highly active β-nucleator (LCP-N) of isotactic polypropylene (iPP) was synthesized and characterized. The effect of LCP-N on thermal behavior of the iPP was investigated with differential scanning calorimetry. LCP-N showed a melting transition at 85.0°C and a nematic to isotropic phase transition at 278.0°C. The incorporation of LCP-N could lead to substantial changes in the thermal behavior of the iPP. The nucleating activity of LCP-N mainly depended on its content, mesogenic molecular structure, and thermal history of processing. A high content of β-form could be obtained by the combined effect of the optimum LCP-N concentration and crystallization temperature and time. The Φ_β reached 77% when the LCP-N content, crystallization temperature, and crystallization time were 0.4 wt.%, 125°C, and 1 h, respectively.     

Crystal structure of poly(octamethylene terephthalate) determined by X‐ray fiber diffraction and molecular modeling

Poly(octamethylene terephthalate) (POT), a semicrystalline aromatic polyester, is synthesized by melt‐condensation reaction, and its thermal property and crystal structure are investigated by using differential scanning calorimetry, X‐ray diffraction, and molecular modeling methods, respectively. It is revealed that the synthesized POT sample has comparably low melting temperature of 131 °C and forms one crystalline phase. Based on two‐dimensional X‐ray fiber diagram and molecular modeling analyses, the crystal structure of POT is identified to be triclinic with dimensions of a = 4.560 Å, b = 5.597 Å, c = 18.703 Å, α = 104.87°, β = 119.45°, and γ = 100.32°, in which one chemical repeating unit of POT with all‐trans conformation of octamethylene group is packed according to the space group of . © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 276–283, 2009     

Structure of maltodextrin gels — a small angle X-ray scattering study

The structure of maltodextrin gels was investigated by small angle X-ray scattering. The inhomogeneities in the maltodextrin gels are molecular aggregates with maximum dimensions of almost 300 nm. Their shape can be approximated by oblate ellipsoids of revolution with an axial ratio of 0.1. The radius of gyration of the aggregates amounts to about 90 nm. For this reason in the nomenclature of Papkov the gels are polymer gels of the 2^nd type. The melting of these aggregates is measured by SAXS with a position sensitive detector in the range near 56 °C.     

Effect of the Linking Structure of Nonlinear Optical Side Groups on the Phase Behavior of an Aromatic Polyester Backbone

Summary: The phase behavior of poly(p‐phenylene terephthalate)s (PPT) with pendant side groups, N‐(4‐nitrophenyl)ethylaminoethanol (NPE) and N‐(4‐nitrophenyl)‐L ‐prolinol (NPP) has been studied by using differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXS), and second harmonic generation (SHG). PPT‐NPE showed a layered liquid crystalline morphology while PPT‐NPP showed a completely amorphous structure. Compressive or shear stress applied on the polymer melt surface at 210 °C induced a more prominent layered structure of PPT‐NPE whereas the amorphous structure of PPT‐NPP remained unchanged under the stress. In order to understand this phase difference in terms of the repeat structure, we attempted theoretical ab initio Hartree‐Fock, and DFT calculations for the monomers and molecular dynamics for the bulk state. The results indicated that molecular configurations are a good way of microscopically understanding the phases of rigid backbone polymers with functional side groups: The NPT (constant particle number, pressure, and temperature) simulation data at 210 °C agree qualitatively with the experimental data and the difference between PPT‐NPE and PPT‐NPP could be understood using rotational energy barrier, steric hindrance and inter‐chain interactions. X‐ray diffractometer (XRD) simulation patterns for the oligomers are also in qualitative agreement with the experimental WAXS data and the structural parameters of stacks of PPT‐NPE chains are estimated to be layer distance (4.6 Å), backbone distance (21.5 Å), and side distance (12 Å).

     

Effect of synthesis time on physical properties and catalytic activities of synthesized HZSM-5 on the fast pyrolysis of Jatropha waste

The catalytic fast pyrolysis of Jatropha waste using synthesized HZSM-5 zeolites was investigated using an analytical pyrolysis-GC/MS (Py-GC/MS) technique. HZSM-5 zeolite was successfully synthesized by hydrothermal method at 160 °C with various synthesis times of 0, 24, and 72 h. From the XRD results, the as-synthesized powder before crystallization (HZSM5-0 h) showed the amorphous phase, while samples with synthesis times of 24 and 72 h (HZSM5-24 h and HZSM5-72 h) showed the high crystalline phase of HZSM-5 with the main peaks at the 2θ of 7.9°, 8.8°, 23.1°, 23.7°, and 23.9°. The particle of HZSM5-72 h appeared in cubic-shaped crystal compared to the HZSM5-24 h. HZSM5-72 h had a higher surface area of 625 m²/g with an average larger pore diameter of 27.97 Å and pore volume of 0.28 cm³/g. The effect of biomass to catalyst ratios of 1:1, 1:5, and 1:10 was investigated at 500 °C. It was found that the aromatic and aliphatic selectivity depended on the synthesis time of HZSM-5 reflected in their surface areas, pore sizes, and catalyst content. The highest aromatic and aliphatic hydrocarbon of almost 95 % was obtained when a large amount of HZSM-5 (synthesized for 72 h) was used which could lead to the high heating values of bio-oils. The HZSM5-72 h also contributed to eliminate the undesirable oxygenated compounds such as acids, aldehydes, and ketones. Nevertheless, there are still a few percentages of N-containing components that may require further denitrogenation prior to utilization of the obtained liquid fuel.     

Phase Transitions in UHMWPE Fiber Compacts Studied by in situ Synchrotron Microbeam WAXS

Summary: The temperature dependence of the structure of either cross‐linked or non‐cross‐linked ultra‐high‐molecular‐weight polyethylene (UHMWPE) fiber compacts was studied by synchrotron microbeam wide‐angle X‐ray scattering (WAXS), focusing on the fiber‐fiber interface. The phase transition sequence is: melting of the monoclinic phase in the fiber skin, which was completed by 135 °C; melting of the unconstrained orthorhombic phase, by 152 °C; melting of the constrained orthorhombic phase and a orthorhombic‐hexagonal phase transition until 157 °C; and gradual melting of the hexagonal phase, up to 165 °C. Cross‐linking provides additional thermal stabilization.

Histograms of the azimuthally averaged X‐ray intensity as a function of temperature for cross‐linked ultra‐high‐molecular‐weight polyethylene fiber compacts molded at 145 °C.     

Thermal properties and the structure of amorphous Sb2Se3 thin film

The amorphous Sb₂Se₃ film with a thickness ~0.9 µm was prepared by thermal evaporation and its composition was confirmed using an energy-dispersive X-ray analysis. The amorphous state was checked by an X-ray diffraction analysis. The optical gap E _g ^opt was determined to be 1.32 eV. The glass transition temperature could not be found by either a differential scanning calorimetry or a thermomechanical analysis. The film was crystallized and characterized using the quasi-isothermal method. The temperature dependence of the isobaric heat capacity was raised monotonously and no drop over the course of the crystallization was observed. The temperature-modulated thermomechanical analysis determined a temperature T = 133 °C which can be assumed to be the temperature of the structural reorganization beginning. Raman spectra of amorphous Sb₂Se₃ revealed that the vibrations of both the amorphous and crystalline phase are close to one other. Raman scattering revealed that both the short and the medium-range order of amorphous and crystalline phases are similar.     

Thermal behaviour of the anticancer drug carboxyethylgermanium sesquioxide

The thermal behaviour of carboxylethylgermanium sesquioxide (Ge-132) was studied by using DSC, TG and FTIR. A crystalline-amorphous transition peak and a decomposition peak were observed below 320 °C. The conclusion drawn by Minoru Tsutsai that Ge-132 gave no indication of the decomposition or the melting below 320 °C has been proved not to be consistent with reality.     

Pressure‐induced amorphization and disordering on cooling in semi‐crystalline polymers: calorimetric evidence for inverse melting in one component system

We report some unusual phase behaviour, of general implication for condensed matter, on the polymer poly‐4‐methyl pentene‐1 (P4MP1) induced by changes in pressure (P) and temperature (T), as observed by in‐situ X‐ray diffraction and high pressure DSC. Upon increasing pressure beyond a threshold value, the polymer, crystalline at ambient conditions, looses its crystalline order isothermally. The process is reversible. This behaviour is observed in two widely separated temperature regions, one below the glass transition temperature (< 50°C) and one close to the melting temperature (250°C), thus showing solid state amorphization and inversion in the melting temperature with increasing pressure. This further suggests inverse melting, i.e. re‐entrant of the two widely separated liquid and amorphous phases along the T‐axis at fixed P. This is confirmed experimentally as disordering in the crystalline structure on cooling. The inverse melting in P4MP1 raises the possibility of exothermic melting and endothermic crystallization as anticipated by Tammann (1903), see reference 1. The anticipated exothermic melting and endothermic crystallization is confirmed experimentally in the one component system P4MP1. We are observing similar features in a range of polymers.     

Post-irradiation free-radical reactions in poly(ethylene terephthalate)

Exposure of poly(ethylene terephthalate) to γ-rays results in the formation of radical I, radical II (tentatively), and to an unassigned radical (III) which is responsible for a central peak in the ESR spectrum. It is believed that completely amorphous samples of polymer contain radicals II and III. On heating, the radicals decay, and the relative proportion of radical III increases. The kinetics of the overall decay process were followed by measuring the decrease in peak height with time. After an initially rapid reaction the decay of the radical population conformed to second order kinetics. An Arrhenius plot of the logarithm of specific rate versus 1/T indicated two lines which intersected at 72°C, which is close to the glass transition temperature. The activation energies were 112 kcal/mole above 72° and roughly 25 kcal/mole below 72°C. Reference to reports in the literature suggests that this decay can be explained by long-range movement of the polymer molecules, even in the glassy solid. The decay of radical I in the crystalline regions of an oriented sample was shown to follow first-order kinetics. As the decay occurs at temperatures as low as 100°C (the melting point is about 260°C), it seems that decay by normal physical movement is unlikely. The results might be explained by invoking the hypothesis of chemical migration of free radical sites by hydrogen atom hopping.     

Crystallization and thermal properties of PLLA comb polymer

Poly(L ‐lactide) (PLLA) on poly(2‐hydroxyethyl methacrylate) (PHEMA) backbone was prepared by a combination of atom transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP). The structure of the comb polymer was analyzed by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering (SAXS), and differential scanning calorimetry (DSC). WAXD result indicates that the comb polymer has α crystalline modification with a 10₃ helical conformation. Lamellar parameters of the crystalline structure were obtained by one‐dimension correlation function (1DCF) calculated from SAXS results. The calculations show that the thickness of crystalline layer is controlled by annealing temperature and comb structure. DSC was applied to study kinetics of the crystallization and melting behavior. Two melting peaks on melting curves of the comb polymer at different crystallization temperature were detected, and the peak at higher temperature is attributed to the melt‐recrystallization. The equilibrium melting temperature is found to be influenced by the comb structure. In this article the effects of the comb structure on Avrami exponent, equilibrium melting point and melting peak of the comb polymer were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 589–598, 2008     

Controlling the properties of HDPE in the presence of low-molecular-mass additives of various types

To develop materials with new mechanical and improved rheological properties on the basis of common polyolefins, ultrahigh-molecular-weight PE and HDPE of medium molecular masses, the polymers have been modified with low-molecular-mass additives: crystalline organic disulfides (dithiaalkanes), liquid oligomer phenylmethylsiloxane, and oligooxypropylene glycol. It has been shown that the studied disulfide additives at low concentrations (up to 10% of the mass of PE) have no significant effect on the content and quality of the crystalline phase of HDPE. (The degree of crystallinity, enthalpy, and melting temperature change weakly.) In this case the plasticity of the modified PE improves: the tensile modulus and dynamic modulus decrease, whereas the elongation at break increases. In the presence of organic disulfides, the effective viscosity of the PE melt decreases. Unlike oligomeric phenylmethylsiloxane and oligooxypropylene glycol, dithiaalkanes are inert to the components of metallocomplex catalysts. Thus, the modification of PE with the aforementioned additives may be performed via their addition to the final polymer or in the course of the synthesis of the polymer.     

Structure of bis-(1,1,1-trifluoro-2-(methylimino)pentanoato-4)copper(II). Thermal properties of N-methylsubstituted copper(II) β-iminoketonates

The single crystal X-ray diffraction (XRD) method was used to determine the structure of the [Cu(mi-tfac)₂] (mi-tfac = MeC(O)CHC(NMe)CF₃) complex at the temperature of 150 K. The crystallographic data are as follows: space group Pnna, a = 11.8798(16) Å, b = 12.0315(16) Å, c = 10.6259(14) Å, V = 1518.8(4) ų, Z = 4, R = 0.0288. The structure is molecular, the coordination environment of copper in the molecule adopts a distorted tetrahedral geometry. The Cu–O and Cu–N distances are 1.9182(13) Å and 1.9610(16) Å respectively, the OCuN chelate angle is 94.18(5)°. The thermal properties of the compounds [Cu(mi-tfac)₂] and [Cu(RC(O)CHC(NMe)R)₂] (R = Me, ^t Bu) in the condensed phase have been studied by the methods of thermogravimetry and differential scanning calorimetry. The thermodynamic characteristics of the melting processes have been determined.