Survey of the long spacing of polyamides crystallized from solution

A series of linear, aliphatic polyamides in which the number of carbon atoms in the repeat unit ranged from three to twenty-four was crystallized from solution. All gave lath-shaped crystallization products (usually aggregated in the form of sheaves) that were unmistakable lamellar. Sedimented mats of the crystals were examined by lowangle and wide-angle x-ray diffraction. Each polyamide had a characteristic layer thickness (fold length) which was determined by the length of the repeat unit and the number of hydrogen bonds in the lamella. The thickness was independent of other variables examined including crystallization conditions. The polyamides studied cover a wide range: they border on polypeptides at the one extreme and approach polyethylene at the other. For all these materials there emerged a unifying pattern which relates chemical structure directly to chain folding.     

Polyhalogenated polyamides IV. Synthesis and characterization of polyhalogenated polyamides in a melt–solid process at high temperature and in solution at low temperature

A new series of polyhalogenated, principally polybrominated polyamides have been prepared either by polymerization in a melt-phase process at high temperature or by a low-temperature solution process. The polymers were obtained from perchloroterephthaloyl-, perbromoterephthaloyl-, and 2,5-dibrometerephthaloyl dichlorides and tetrabromophthalic anhydride with aromatic and aliphatic diamines. They were characterized by elemental analysis, infrared spectroscopy, intrinsic viscosities, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and flame-resistance testing.     

Improved in‐solution trypsin digestion method for methanol–chloroform precipitated cellular proteomics sample

Methanol–chloroform based protein precipitation is an essential step in many liquid chromatography–tandem mass spectrometry‐based cellular proteomics applications. However, re‐solubilization of the total protein precipitate is difficult using regular in‐solution digestion protocol. Sodium deoxycholate is reported as an efficient surfactant for re‐solubilization of membrane fractions. In this study, we demonstrated an application combining methanol–chloroform based protein precipitations and deoxycholic acid assisted re‐solubilization of pellets to evaluate the improvement of protein identifications in mass spectrometry‐based bottom‐up proteomics. We evaluated the modified method using an equal amount of Raw 264.7 mouse macrophage cell lysate. Detailed in‐solution trypsin digestion studies were presented on methanol–chloroform precipitated samples with or without deoxycholic acid treatments and compared with popular sample digestion methods. A mass spectrometric analysis confirmed an 82% increase in protein identification in deoxycholic acid‐treated samples compared to other established methods. Furthermore, liquid chromatography–tandem mass spectrometry analysis of an equal amount of proteins from methanol–chloroform precipitated, and methanol–chloroform/deoxycholic acid‐treated macrophage cell lysate showed a 14% increase and 27% unique protein identifications. We believe this improved digestion method could be a complementary or alternative method for mammalian cell sample preparations where sodium dodecyl sulfate based lysis buffer is frequently used.     

Generalized Swain–Schaad relations including tunneling and temperature dependence

The Swain–Schaad relation, which relates the kinetic isotope effects of the three hydrogen isotopes, is extended by including tunneling and temperature dependence. The new version shows that the effect of tunneling on the Swain–Schaad exponent is opposite to that usually assumed and depends on the degree of assistance the tunneling receives from other vibrations.     

Radiation-induced cis–trans isomerization of polyisoprenes and temperature dependence of the equilibria

The cis-trans interconversion of polyisoprenes in solutions induced by γ-radiation in the presence of a sensitizer, which is any one of organic bromides or n-butyl mercaptan, was studied by using hevea and gutta percha as starting substances. The percentage cis remaining or converted after irradiation were determined by the infrared absorption. The equilibrium constants for the interconversion at 22, 60, and 100°C. were found to be 3.00, 5.25, and 7.33, respectively. The first-order rate constants for cis → trans and trans → cis isomerizations at 22°C. were calculated to be 9.05 and 2.91, respectively. The results were interpreted by the mechanism proposed by Golub, according to which the double bonds from π complexes with radiolytic fragments from sensitizers give a radical transition state capable of interconversion. However, our results showing that heating shifts the equilibrium toward trans isomer are not in accord with the mechanisms of the radiation-induced isomerization of polybutadiene of Golub and those for photoisomerization of aromatic azo compounds.     

Hydrodynamically induced crystallization of polymers from solution

Summary This paper primarily describes an investigation into the origin of persistent lamellar overgrowth of fibrillar crystals with a Shish-kebab morphology. Fibers grown from stirred p-xylene solutions of high molecular weight polyethylene at 108 °C exhibited an average spacing of 1 x 10³ Å between the lamellae when cooled down to room temperature in a normal way. Fibers quenched in liquid nitrogen displaved smaller lamellae with a periodicity of 0.4 x 10³ Å.It was found that the lamellae could be dissolved at 108 °C and recrystallized isothermally on the backbones at temperatures up to 94.6 °C. The spacing between the lamellae increased strongly with temperature in the range between 90.0 °C and 94.6 °C.The temperature dependence of this periodicity could be accounted for by the theory of secondary nucleation in polymer crystallization. The Poisson distribution of the numbers of lamellae along the backbones also suggests that lamellar growth is essentially controlled by the crystallization kinetics.The fibrillar polyethylene crystals grown at elevated temperatures from flowing solutions may be visualized as backbones constituted by partially crystallized polymer molecules and dangling ends extending from the backbones into the surrounding solution resembling centipedes.

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Zusammenfassung Dieser Bericht befaßt sich mit einer Untersuchung des Ursprungs von persistenter lamellarer Überwachsung von Faser-Kristallen mit Schaschlik-Morphologie.Faser-Kristalle, gewachsen aus geruhrten Xylol-Lösungen von hochmolekularem Polyäthylen bei 108 °C, zeigen ein mittleres Intervall zwischen den Lamellen von 1 x 10³ Å, wenn auf normae Weise abgekühlt zur Zimmertemperatur. Fasern, abgeschreckt im flüssigen Stickstoff, zeigen kleinere Lamellen mit einem Zwischenraum von etwa 0.4 x 10³ Å. Es wurde festgestellt, daß die Lamellen bei 108 °C gelöst werden können und von neuem auf den Faserkernen bis zu 94.7 °C kristallisieren. Die Temperaturabhangigkeit dieser Periodizität kann erklärt werden auf Grund der Theorie der sekundären Keimbildung bei polymerer Kristallisation. Wie sich zeigt, gruppiert sich die lamellare Überwachsung um den Kern entsprechend einer Poisson-Verteilung, was darauf hinweist, daß die lamellare Überwachsung wesentlich durch die Kristallisationskinetik bedingt wird.Die faserigen Polyathylenkristalle, bei erhöhter Temperatur hergestellt aus gerührten Lösungen, kann man sich als teilweise kristallisierte Moleküle, im Faserkerne aufgenommen, vorstellen mit langen Kettenenden im umgebenden Lösungsmittel, so ziemlich als einen Tausendfüßler.

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With 12 figures     

The kinetics of flow-induced crystallization from solution

In situ birefringence measurements of the seeded growth in a tubular flow geometry of 0.01 wt% solution of a polyethylene fraction in xylene have been used to determine the flowinduced crystallization kinetics as a function of temperature and flow rate. In contrast to earlier reports on higher molecular weight polyethylene and polypropylene systems, orientational properties of the crystallized fibers do not show a clear correlation with growth conditions (i.e., temperature and flow rate). The combined kinetic data from these experiments and our earlier studies of higher molecular weight polyethylene—xylene and polypropylene—tetralin systems are analyzed in terms of a modified from of the Avrami equation which provides a basis for separately correlating temperature and flow rate effects. The observed temperature dependency of the crystallization process can be interpreted in terms of nucleation and growth models while the flow rate dependency can be interpreted on the basis of entanglement formation arguments. Results showing liquid phase precursor formation in an atactic polystyrene system are also presented to further document the liquidphase separation which can be induced in polymers under flow.     

Hydrodynamically induced crystallization of polymers from solution

Summary This paper primarily describes the large diversity in morphology of fibrillar polyethylene crystals precipitated from stirred solutions at elevated temperatures. Shish-kebabs crystallized at 112°C from stirred xylene solutions of linear polyethylene exhibit lamellar overgrowths having thicknesses of the order of 150 Å from which it was concluded i. a. that at crystallization temperatures above 100°C only backbones are formed and that the surrounding polymer molecules deposit epitaxially on the substrate at lower temperatures. The variation in the appearance of the overgrowth and the inhomogeneity of the samples can be traced back to irregular stacking and to differences in washability of the fibrillar crystals, these differences being largely due to the non-uniform flow pattern along the various stirrer parts. Unusual lamellar shapes, interconnections, sheets between lamellae, the veil on the Shish-kebab noted byKeller andMachin, may well be explained byKeith, Padden andVadimskys mechanism of crystallization-induced orientation of macromolecules between the lamellae and the consequent formation of extendedchain crystals. The lamellar overgrowth appears to be arranged along the backbone according to a logarithmic normal distribution, and the average diameter of the lamellar crystals increases with the average spacing, both being approximately equal in size. The fibrillar crystals end in smooth tapered tails having lengths varying between 5 and 8 .These observed fibre ends agree best with the unroll model proposed for fibrillar crystal growth in flow fields if on the average each molecule introduces one chain fold and the chain ends are randomly assimilated by the crystal lattice. Linear polyethylene below molecular weight of 50×10³ and low density polyethylene did not crystallize in fibrillar habit. whereas copolymers of ethylene and slight amounts of propylene and butylene proved capable of forming fibrillar crystals and isotactic polypropylene yielded smooth and overgrown fibres.

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Zusammenfassung Der Bericht befaßt sich zuerst mit der großen morphologischen Mannigfaltigkeit faseriger, bei erhöhter Temperatur aus gerührten Lösungen gefällter Polyäthylenkristalle. Bei 112°C aus gerührten Xylollösungen von linearem Polyäthylen herauskristallisierte Schaschlik-Strukturen zeigen eine lamellare Überwachsung mit einer Dicke von etwa 150 Å, woraus u. a. geschlossen wird, daß sich bei Kristallisations-temperaturen über 100°C nur Faserkerne bilden und daß die umringenden polymeren Moleküle sich bei niedrigeren Temperaturen epitaxial auf dem Substrat ablagern. Die Verschiedenheit in der Form der Überwachsung und die Inhomogenität der Proben lassen sich erklären durch eine unregelmäßige Ablagerung auf dem Rührer und durch Unterschiede in der Auswaschbarkeit der faserigen Kristalle, welche Unterschiede weitgehend auf das nicht einheitliche Strömungsbild längs der verschiedenen Rührerteile zurückzuführen sind. Ungewöhnliche lamellenartige Formen, interlamellare Verbindungen, Häutchen zwischen den Lamellen und die vonKeller undMachin festgestellte Verschleierung der Schaschlikgebilde lassen sich sehr gut durch denKeith-, Padden- undVadimsky-Mechanismus einer durch die Kristallisation verursachten Orientierung von Makromolekülen zwischen den Lamellen und durch die anschließende Bildung von extended-chain Kristallen erklären. Wie sich zeigt, gruppiert sich die lamellare Überwachsung um den Kern entsprechend einer logarithmischen Normalverteilung; der mittlere Durchmesser der lamellaren Kristalle nimmt zu mit der mittleren Größe der Zwischenabstände, wobei beide ungefähr gleich groß sind. Die faserigen Kristalle enden in allmählich spitz auslaufenden Gebilden mit Längen von etwa 5 bis 8 . Diese Faserenden stimmen gut überein mit dem für das Wachsen faseriger Kristalle in Strömungsgebieten vorgeschlagenen unroll-Modell, falls im Durchschnitt jedes Molekül eine Kettenfaltung einleitet und die Kettenenden willkürlich in das Kristallgitter aufgenommen werden. Lineares Polyäthylen mit einem Molekulargewicht unter 50×10³ und Hochdruckpolyäthylen kristallisieren nicht in der faserigen Form, während —wie sich zeigt—Copolymere von Äthylen und geringen Propylen- und Butylenmengen in der Lage sind, faserige Kristalle zu bilden und isotaktisches Propylen schöne und überwachsene Fibrillen ergibt.

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With 25 figures in 28 details     

A study of the crystallization of the n-alkane C246H494 from solution: Further manifestations of the inversion of crystallization rates with temperature

The newly available, strictly uniform n-alkane, C₂₄₆H₄₉₄, has been crystallized from dilute solution. The rates of crystallization were followed by differential scanning calorimetry (DSC) as a function of temperature. Two pronounced rate inversions were registered. The dissolution temperatures of the crystals formed show a sharp discontinuity at the temperature of the rate minimum. From this it is inferred (reinforced by the precedent of previous work on C₁₉₈H₃₉₈) that a transition from extended to once folded crystallization is taking place at the temperature of the minimum. The methods by which the rate curves were constructed are laid out in step by step detail, leaving no possible doubt about the reality of the rate inversion. The rate inversion is attributed to “self-poisoning,” and this concept is extended to embrace the wider issue of mutually interacting competition of possible phase variants (“polymorphs”) of which the extended and folded chain crystals represent one special example. In addition, some further effects are noted and discussed regarding solubility behavior. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1775–1791, 1997     

Some considerations concerning the temperature dependence of the bulk crystallization rate constants of polymeric materials

The experimentally estimated ‘normalized’ rate constants of the bulk crystallization of poly(L-lactic acid) and natural rubber at different temperatures have been used in order to test different equations describing the temperature dependence of the normalized crystallization rate constants. Ten of these expressions are variants of the well-known Turnbull-Fisher relationship k = k₀ exp[-U*/R(T - T_∞)] exp[K_g/T(ΔT)f] which differ essentially by the assumed number of fixed parameters [one or two Williams, Landel, and Ferry (WLF) constants i.e., U* = C₁ and/or C₂]. Two additionally used equations are expressions derived on the basis of the above mentioned general relation, which introduce T_g instead of T_∞ = T_g - C₂ as the low temperature limit of crystallization and two energies of activation, for nucleation and crystal growth, respectively. It is shown that the temperature dependence of the normalized bulk crystallization rate constants is more accurately described if three parameters (beside k₀, U*, and K_g or the respective activation energies) are assumed to be adjustable and when instead of the widely accepted expression for the low temperature limit, T_∞ = T_g - C₂(K) with C₂ = 51.6 or 30°C, respectively, T_g (i.e., C₂ = 0°C) is considered. A qualitative explanation for this finding is suggested in terms of the increasing mobility of the crystallizing segments at temperatures above T_g, taking into account that generally the glass transition is considered to be a ‘freezing in’ process. © 1997 John Wiley & Sons, Inc.     

On the temperature dependence of the rate in barrierless reactions in solution

We present a theoretical study of the temperature dependence of the relaxation rate in barrierless reactions. It is shown that a small change in the relative positions of the ground and excited potential surfaces can lead to a significant change in the relaxation rate. We suggest that a small shift of the potential surfaces, during the isoviscous temperature variation, may be responsible for the solvent-induced crossover from an apparent negative activation energy to a large positive activation energy observed in recent experiments.     

The temperature dependence of the micellisation of chlorpromazine hydrochloride in aqueous solution

The association characteristics of the weakly associating drug chlorpromazine hydrochloride have been examined over the temperature range 10–35 °C by means of conductimetric measurements. Critical micelle concentrations (cmc) have been determined by the application of a recently developed numerical method [Pérez-Rodríguez et al. (1998) Langmuir 14:4422] especially designed for the analysis of the association pattern in highly polydisperse systems of low aggregation number. The cmcs determined in this manner are used in combination with the mass-action model to obtain the thermodynamic parameters of the micellisation process, in particular the surface and hydrophobic contributions to the free energy. The use of exact forms of equations for the thermodynamics of micellisation applicable to systems of low aggregation number leads to values of the enthalpy of micellisation in reasonable agreement with experimentally determined values. Received: 6 January 2000/Accepted: 9 February 2000     

On the temperature dependence of amide I frequencies of peptides in solution

The temperature dependence of the amide I vibrational frequencies of peptides in solution was investigated. In D2O, the amide I' bands of both an alpha-helical oligopeptide, the random-coil poly(L-lysine), and the simplest amide, N-methyl acetamide (NMA), exhibit linear frequency shifts of approximately 0.07 cm(-1)/degrees C with increasing temperature. Similar amide I frequency shifts are also observed for NMA in both polar (acetonitrile and DMSO) and nonpolar (1,4-dioxane) organic solvents, thus ruling out hydrogen-bonding strength as the cause of these effects. The experimental NMA amide I frequencies in the organic solvents can be accurately described by a simple theory based on the Onsager reaction field with temperature-dependent solvent dielectric properties and a solute molecular cavity. DFT-level calculations (BPW91/cc-pVDZ) for NMA with an Onsager reaction field confirm the significant contribution of the molecular cavity to the predicted amide I frequencies. Comparison of the computations to experimental data shows that the frequency-dependent response of the reaction field, taken into account by the index of refraction, is crucial for describing the amide I frequencies in polar solvents. The poor predictions of the model for the NMA amide I band in D2O might be due, in part, to the unknown temperature dependence of the refractive index of D2O in the mid-IR range, which was approximated by the available values in the visible region.     

Thermal lens investigation of the temperature dependence of the refractive index of organo–aqueous solutions

The thermal lens technique has been used to experimentally determine the temperature of maximum refractive index (TMRi) of low molarity aqueous methanol solutions. The well-known decrease in the measured TMRi is observed with increasing concentration of methanol. At the TMRi, the temperature dependence of refractive index (dn/dT) is zero, resulting in the absence of a thermal lens signal. In this work, the observed changes in the TMRi are related to the changes in the expansion coefficient of the water and to a lesser extent, to changes in the polarisability coefficient of the water. It is also seen that the enhancement in the thermal lens parameter upon the addition of methanol to water is related primarily to the change in expansion coefficient of the aqueous solution.     

The temperature dependence of vibration–vibration energy exchange between CO and COS

The present study reports the measurement of the V–V energy transfer rates for the CO*? COS system in the temperature range of 195 to 370°K. The measured rates exhibit a slight inverse temperature dependence. The experimental results are compared to prediction based on a model of long-range dipole–dipole interactions between colliding molecules. The effect of single quantum rotational transitions is compared to that of multiquantum rotational transitions.     

Thermal properties of polyamides containing 1,3–cyclohexane rings

The effect of the 1,3–cyclohexane rings in the chain backbone on thermal properties of polyamides, especially the glass-transition temperature, has been studied using polyamides based on 1,3–cyclohexanebis(methylamine). The increase in glass-transition temperature was far greater than that obtained with the analogous polymers containing m–benzene rings. However, the effects of 1,4–cyclohexane and p-benzene rings are nearly equal. Several possible causes for this difference are examined. It is concluded that restricted chain mobility due to steric hindrance of the cis-1,3–cyclohexane ring, the predominant isomer, is the most likely cause of the difference.     

Synthesis of polyamides and polyureas containing leucine–tyrosine linkages

Monomers with leucine–tyrosine linkages were synthesized using diphenyl phosphoryl azide as a coupling reagent. Leucyltyrosylpoly(propylene glycol) bis(2-aminopropyl ether) tyrosylleucine (monomer 1 ) has a longer spacer: poly(propylene glycol) bis(2-aminopropyl ether) (Jeffamine® D-400), and leucyltyrosyliminohexamethyleneiminotyrosylleucine (monomer 2 ) has a shorter spacer: hexamethylenediamine. Polyureas from monomers 1 and 2 with hexamethylene diisocyanate and methylenedi-p-phenyl diisocyanate were synthesized. Polyamide, polyesteramide from monomer 2 were synthesized. The characterization of these polymers using ¹H-NMR, ¹³C-NMR, solid-state ¹³C-NMR, IR, GPC, and also thermal analysis are presented. © 1997 John Wiley & Sons, Inc.     

Density of silanol groups on the surface of silica precipitated from a hydrothermal solution

The physicochemical properties of amorphous silica precipitated from a hydrothermal solution were studied. Low-temperature nitrogen adsorption in conjunction with the BET method was used to determine the specific surface area of this silica. Based on thermogravimetry data, the total content of water was estimated. A comparison of the thermogravimetry data with the Zhuravlev physicochemical constants made it possible to determine the temperature dependences of the concentration of surface and internal silanols over a temperature range of from 200 to 1200°C. A new type of amorphous silica with enhanced internal water content was revealed. The distinctions between the mechanisms of the removal of surface and internal water were established.