Heat capacities of water swollen hydrophilic polymers above and below 0°C

The heat capacities of water swollen poly[2-(2-hydroxyethoxy)ethyl methacrylate] were determined in a DSC-2 calorimeter within the temperature range 220–350K for concentrations from 0 to 1,2g of water per 1g of the polymer. At temperatures above 0°C the partial specific heat capacity of water in gel is concentration independent and equal to the specific heat capacity of pure liquid water. It seems, therefore, that water does not form stable icelike structures near polymer chains. To analyze phase transformations of water in gel below 0°C, general thermodynamic equations were derived and used as a basis for suggesting criteria which allow to decide whether in a given experiment the phase transformation proceeded in an equilibrium way. In measurements below the melting point of ice the conditions for an equilibrium process consist in the preceding heating of the frozen sample to a temperature close to the melting point, followed by cooling to 220K. The assessed composition dependence of the melting point depression is consistent with the dependence of activity on concentration obtained from measurements of water vapour sorption at 35°C. Analysis of data on the heat capacity below 0°C led to the conclusion that at a water content of 0,4g/g and lower, or at temperatures below 250K the crystallization of water from gel was inhibited by kinetic factors originating probably in the reduced diffusivity of water in gel, due to the reduced mobility of polymer chains. Hence, non-freezing water need not be identical with “strongly bound” water; in the study of water structure in polymers based on heat capacities, preference should be given to data obtained at usual and elevated temperatures.     

NMR observations of drawn polymers VI. Poly (ethylene oxide)

Wide line NMR spectra of cold drawn poly(ethylene oxide) (PEO) were recorded at temperatures between ?196°C. and 66°C. as a function of the alignment angle between the draw direction and the magnetic field. Line width, second moment, and mobile fraction were determined and are discussed in terms of segmental motion. In agreement with other authors two motional processes were found. (1) The β-process, commencing at temperatures around ?45°C., probably occurs in non-crystalline regions and causes the emergence of a narrow NMR line in addition to the broad one. (2) The β-process was observed between 0°C. and the melting point (66°C.) and led to a pronounced decrease of the width of the broad line and of the second moment. This decrease was anisotropic and was greatest at the alignment angle γ = 45°. As a consequence of this the dependence of the line width and of the second moment on γ is changed: whereas both these quantities show at low temperatures (<0°C.) a maximum at γ = 45° and an absolute minimum at γ = 0°, near the melting point, a minimum close to γ = 45° and an absolute maximum at γ = 0° were found. These changes are explained by oscillations of the helical molecules around their axes in crystalline regions.     

Mechanical relaxation in poly(2.6-dimethyl-1.4-phenylene oxide) in the glassy state

Dynamic mechanical properties (sound velocity, v, and damping factor, Q^?1) have been determined in poly(2.6-dimethyl-1.4-phenylene oxide) over a wide range of temperature (from 80 to 500°K) at acoustic frequencies. The examined polymer exhibits two mechanical relaxation effects, one, α, at temperatures above 480°K, characterized by a sudden strong drop of the elastic modulus and by a rapid increase of the damping factor with increasing temperature, and another, β, below the glass transition point, T_g, characterized by a small drop of the elastic modulus, between 290 and 370°K, and by a damping maximum at about 370^K (f_m = frequency corresponding to the maximum ? 7000 Hz). The α relaxation effect has been attributed to the thermal excitation of cooperative motions in the chain, while the secondary β relaxation has been interpreted as due to oscillation of aromatic rings around C? O? C bond. The damping maximum, for the lateer, is shifted toward higher temperatures with increasing frequency, following an ARRHENIUS -type equation with an apparent activation energy of about 20 kcal/mole.     

The influence of temperature on the relations between thermal death,growth and yield in Candida utilis

In the yeast Candida utilis an associative temperature profile was found with respect to thermal death and growth. The cardinal temperatures were the following: optimum temperature for growth, 36°C, minimum temperature of thermal death, 37.9°C; final maximum temperature for growth, 40.1°C; initial maximum temperature for growth, 40.7°C. The growth yield on glucose only decreased near the final maximum temperature for growth.     

Thermal stability and crystallization kinetics of poly(ether ether ketone)

Thermogravimetric analysis (TGA), dynamic rheological analysis and polarized light microscopy were used to assess the thermal stability of poly(ether ether ketone) (PEEK). Samples were exposed to temperatures in the range 385–415°C for times up to 30 min in both air and nitrogen atmosphere. The results indicated that neither TGA nor dynamic rheological analysis detected PEEK degradation at temperatures up to 415°C and heating times up to 30 min in nitrogen. It is suspected that degradation, chain branching, and crosslinking occur in PEEK at high temperatures in the melt. In nitrogen atmosphere, the growth rates of spherulites at 290°C and 300°C leveled off for melting temperatures around 400°C and decreased with increasing melting temperature. This study suggests that when the melt of PEEK has been equilibrated at 400°C for 15 min in nitrogen, the subsequent crystallization behavior (isothermal and nonisothermal) is nearly independent of the prior thermal history. The rates of crystallization of PEEK then were measured in the temperature range of 270–325°C. Kinetic analysis indicated that PEEK exhibits a regime II → III transition at 296°C.     

Effects of ethanol on the temperature profile of Saccharomyces cerevisiae

Ethanol at concentrations above 3% (w/v) decreased the maximum temperature for growth of Saccharomyces cerevisiae in batch culture. At 9% (w/v), the highest concentration tested, the maximum temperature suffered a decrease of about 10 degrees centigrade. At effective concentrations ethanol shifted the ARRHENIUS plots of growth and death in the superoptimal temperature range to lower temperatures while an associative temperature profile was maintained. Thus at a concentration of 6% (w/v), ethanol depressed the optimum temperature for growth from 37 °C to 25 °C, the final maximum temperature for growth from 40 °C to 33 °C and the initial maximum temperature for growth from 44 °C to 36 °C. The results indicate that during alcoholic batch fermentation these three cardinal temperatures are variables, the values of which decrease with increasing ethanol concentration. When the ethanol concentration becomes high enough to depress them successively below the process temperature, the yeast population becomes increasingly subject to ethanol-enhanced thermal death. Implications of the findings for the production of fermentation ethanol in batch and continuous processes are discussed.     

Thermostability analysis of major histocompatibility complex class I molecules by temperature gradient gel electrophoresis

Empty major histocompatibility complex (MHC) class I molecules present on the surface of RMA-S (26°C) cells were loaded with the iodinated peptides APGNYPAL, FAPGNYPAL (SEV-9) and RGYVYQGL (VSV-8), respectively. The thermostability of these peptide-loaded MHC class I molecules was assessed using temperature gradient native polyacrylamide gel electrophoresis. A linear temperature gradient perpendicular to the direction of electrophoresis yielded a graphical representation of the melting of MHC class I molecules. The class I signal disappeared when the peptide melted out of the groove, and gave rise to a second signal due to released peptide. APGNYPAL-loaded class I molecules melted at 11°C with considerable release even at 0°C. VSV-8-loaded class I molecules melted first at 36°C, whereas SEV-9-loaded molecules melted at about 22°C. A discrimination between the binding of SEV-9 to K^b and D^b molecules was seen in the melting patterns. Results are discussed in correlation with known crystallographic structures of class I molecules containing peptides in the binding groove.     

Hydrogen bonding in monodisperse and polydisperse oligo(ethylene glycol)s

Infrared spectra of monodisperse (DP ≤ 35) and polydisperse (average DP ≤ 45) oligo(ethylene glycol)s are recorded for melts and for solids over a temperature range (+70°C to -80°C). Spectra in the hydroxyl stretching region show that the solid monodisperse oligomers with DP ≤ 25 at temperatures well below the melting point have highly ordered lamella end surfaces with hydroxyl groups from adjacent lamellae hydrogen bonded in long chains, whereas the solid polydisperse oligomers of comparable chain length have disordered lamella end surfaces with hydroxyl-ether as well as hydroxyl-hydroxyl hydrogen bonding.     

The structures of poly(vinyl fluoride) at elevated temperatures and after heavy rolling

The structures of poly(vinyl fluoride), (P(VF)), were investigated at elevated temperatures and after heavy rolling at various temperatures. In the former case the marked increases in both crystallite size and the unit cell a-dimension above 140°C were accompanied by a reduction in crystallinity, indicating a melting and recrystallization process. When compared to the polyethylenes, thermal behavioural differences may be attributed to the polarity of the P(VF) molecules. Notable changes in deformation structure were obtained upon varying the rolling temperature. Above 60°C heavy rolling produced a hexagonal {101 0} 〈0001〉 texture, the paracrystallites having a clearly oriented lamellar structure. At 60°C and below more complex textures were produced, the microparacrystallites of the predominant component having a platy morphology. At ?80°C, the deformation structure also showed extensive voiding.     

The temperature profiles of growth,thermal death and ethanol tolerance of the cellobiose-fermenting yeast Candida wickerhamii

The temperature profiles of growth and thermal death of the cellobiose-fermenting yeast Candida wickerhamii was associative with the initial maximum, final maximum, optimum and minimum temperatures for growth around 38°C, 31°C, 31°C and 3°C, respectively. Ethanol enhanced thermal death by increasing the entropy of activation (entropy coefficient 7.2 entropy units mol^?1 l^?1), shifted the supraoptimal part of the profile to lower temperatures without disrupting it and increased the minimum temperature for growth. The temperature profile of ethanol tolerance with respect to growth displayed a narrow temperature plateau (18–22°C) of maximum tolerance (limit 7.4%, v/v, ethanol) while the toxic effects of ethanol increased steeply on either side of the plateau.     

Über wasserstofffbrücken in polyamiden

The temperature dependence of the IR-spectra of various polyamides in the range of the NH-stretching vibrations was investigated between 25 and 250°C. In agreement with other authors it was found that in partially crystalline polyamides the relative amount of non hydrogen bonded NH-groups was very low below their melting points (below 1%). Near the melting points the amount of free amide groups, however, rises suddenly. In two amorphous polyamides from terephthalic acid and branched diamines we found at room temperature an essentially higher amount of free NH-groups (several percents) than in the partially crystalline aliphatic polyamides. In the two amorphous polyamides the relative amount of free NH-groups changes approximately linear with temperature. The increase above the glass transition temperatures is stronger than beyond the glass transition temperatures. At higher temperatures (230°C) the amount of free NH-groups for all investigated polyamides is estimated to 10–20%.     

Effect of temperature on alanine uptake by membrane vesicles isolated from a psychrophilic marine bacterium

The effect of temperature on the membranes of Ant-300, a psychrophilic marine bacterium, was studied by measuring alanine uptake by isolated membrane vesicles. Uptake was observed from 0 to 35 °C. The maximum initial rate of uptake occurred at 25 °C although more alanine was ultimately taken up at temperatures from 10 to 20 °C. An ARRHENIUS plot of these data shows a single infection point at 7.8 °C. Within 10 min, over 50% of the α-aminoisobutyric acid taken up by whole cells at 5 °C was lost after a temperature shift to 25 °C. Vesicles preloaded with alanine at 5 °C did not become leaky when shifted to 25 °C. In addition, exposure of the vesicles to 25 °C for 30 min did not affect subsequent alanine uptake at 5 °C. The data obtained suggest that the loss of the uptake and permeability control functions of membranes from psychrophilic bacteria at elevated temperatures is not due to degeneration of the membrane itself, but rather to a control or regulatory mechanism associated with whole cells.     

Wet heat-treatment and melting point of nylon 6

The equilibrium melting point of nylon 6 was studied by the differential scanning calorimeter method. The samples were all heat-treated in water in order to diminish the effects of the excess free energies of crystals as possible. The equilibriam melting point was estimated as 250 ± 2°C, though it has some uncertainties. This temperature is much higher compared with 225°C which has been taken as the equilibrium melting point of this material. It was found that the crystal transition from α to γ phase by iodine-treatment is due to the disorder of the lattice and not to the inherent nature of the crystal with the ideal structure. Further, a remarkable bi-axial orientation of crystals was observed in the drawn and heat treated samples. The double orientation takes place when the films are drawn at lower temperatures than the glass transition temperature.     

Crystallization/Melting Kinetics and Morphological Analysis of Polyphenylene Sulfide

Crystallization and melting kinetics of polyphenylene sulfide (PPS) are determined using fast scanning calorimetry. The temperature dependence of half‐time crystallization of isothermally melt‐crystallized PPS shows a downward convex curve with a minimum at 160 °C. The minimum crystallization half‐time is about 3 s. The analysis of heating rate dependence of the melting temperature reveals a zero‐entropy‐production melting temperature of the sample. The microstructure of the sample, which is prepared by fast scanning calorimetry, is investigated by small‐angle X‐ray scattering and polarizing optical microscopy. The crystallinity and lamellar thickness of the sample annealed for 400 s decrease with decreasing crystallization temperature. The size of spherulites becomes small as the isothermal temperature is decreased. Transcrystalline morphology is observed near the surface between the sample and nitrogen gas at a crystallization temperature of 120 °C. The thickness of the transcrystalline layer disappears as the isothermal temperature is increased.     

Dynamic mechanical behaviour of chlorinated polyethylene

Dynamic mechanical measurements of chlorinated polyethylenes with chlorine contents ranging from 5,4 to 31 wt.-% were carried out using a dynamic viscoelastometer. The complex modulus and loss factor were determined at four frequencies in the temperature range from ?150°C to 100°C. Two relaxation processes (α and γ) were observed. The first one occurs at temperatures ranging from 21°C to 40°C, depending on the chlorine content; there is a minimum in the temperature of the α process at about 20 wt.-% of chlorine. The activation energies for this α process are higher than 100 kcal/mol, and therefore this α relaxation is considered to be different from the α relaxation in linear polyethylene. On the other hand, the α relaxation of chlorinated polyethylenes is similar to that of the parent polyethylene, taking place at temperatures ranging from ?137°C to ?116°C (at 3,5 Hz). The activation energies for this α process range from 14 to 26 kcal/mol (1 kcal = 4,184 kJ).     

Splitting of DTA-peaks in polyethylene and its relation to the crystalline texture

Linear polyethylene crystallized from the melt or heat-treated at temperature above 110°C. shows in the DTA thermogram an additional endothermal maximum T_m¹ at a temperature lower by 10 to 20°C. compared with the normal maximum T_m⁰. The appearanee of T_m¹ depends on the crystallization temperature, time, and temperature of heat-treatment. For a constant crystallization time, the difference between T_m⁰ and T_m¹ decreases with increasing of the crystallization temperature; at a constant crystallization temperature it increases with the crystallization time. By treating those specimen with two endothermal maxima at a temperature near that of T_m¹, T_m¹ splits into two peaks. This effect is interpreted by the assumption, that those crystalline regions which first correspond to the T_m¹ maximum, partly form more stable crystals of greater thickness and higher melting point, and partly melt with subsequent formation of little crystallites of lower melting point during cooling. Under suitable conditions, the three endothermic peaks also can be observed with branched polyethylene.     

Temperature‐Induced Polymorphic Crystals of Poly(butylene adipate)

The melting behavior, crystal structure, and spherulitic morphology of melt‐crystallized poly(butylene adipate) (PBA) at a temperature range from 25 to 35 °C have been investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and optical microscopy. Two distinct melting behaviors with double peaks have been observed after melt‐crystallizing at different temperatures. X‐ray analysis proves that these two behaviors arise from two forms of PBA crystal structures. The β‐form crystals are formed at temperatures below 31 °C, while the α‐form crystals are formed above 29 °C. When the crystallization temperature is 30 ± 1 °C, a mixture of α‐form and β‐form crystals has been formed. The influences of annealing treatment and sample preparation method on the two forms of PBA crystal structures have been discussed. The results indicate that the low temperature‐formed β‐form crystals are very sensitive to the preparation conditions.

The melting curves at different heating rates for poly(butylene adipate) after melt‐crystallized at 25 °C and 33 °C, respectively.     

Study of conformational transitions of graft copolymers by UV spectrophotometry

UV absorption spectra of solutions of vinyl acetate polymers grafted on ethylene oxidepropylene oxide blockcopolymers in (90:10, v/v) ethanol/water mixture are investigated. The spectra of graft copolymers are clearly different from those of blends of the same composition. Conformational transitions of these copolymers occur in dilute solution at 35 and 60°C; the transitions are evidenced by UV differential spectra either compensated with solvent at the same temperature or with solution at 20°C. The absorbance measured at fixed wavelength as a function of temperature shows a change of slope at the transition points. However, the difference between the energies of solution and solvent as measured from differential spectra does not vary monotonously with temperature. It exhibits two minima corresponding to the transition temperatures. The plot of either this energy difference or the ratio of solvent maximum absorbance over solution maximum absorbance (from differential spectra) versus concentration allows to establish a critical concentration. Below this concentration a solution of grafted copolymers may be looked upon as dilute.     

Influence des conditions de fusion et de cristallisation sur la morphologie superstructurale du polypropylène isotactique cristallisé au dessus de 130°C

The morphology of polypropylene samples cooled from the melt and then isothermally crystallized above 130°C, was studied by optical polarization microscopy. If the temperature of the melt is raised above 175°C, the spherulitic superstructure is fully destroyed. Isothermal crystallization involves negative or positive birefringence which mainly depends on the temperature of crystallization (above or below 130°C). If the temperature of the melt is raised to 172°C, that is to say at a temperature at which no birefringence is detectable, isothermal crystallization leads to negative spherulites above 155°C and to positive ones below 155°C. If the melt is heated between 172°C and 175°C, crystalline lamellae are partially destroyed and they further lead to crystallization of small positive spherulites, which are located inside the initial spherulitic superstructure. These observations are explained in terms of a quadritic arrangement of the lamellae of crystallized polypropylene. Moreover, the crystallization temperature of 155°C appears as a true transition temperature beyond which tangential lamellae cannot exist; this always implies negative birefringence of the spherulites, whatever the melting conditions are.     

Thin film melt polymerized single crystals of poly(p-oxybenzoate)

The morphology of poly(p-oxybenzoate) polymerized from p-acetoxybenzoic acid (pABA) in constrained thin films at temperatures between 130°C and 315°C for various times is described. Polymerization below the melting point of the monomer, 196°C, occurs by a sublimationrecrystallization-melting process, with polymerization occuring in the melt. Lamellar crystals, often bilayered, are found that are ca. 100 Å thick as well as single disclination domains. Electron diffraction patterns indicate the presence of either phase I or II in a given crystal, with the unit cell for phase II being proposed; the molecular axes are normal to the lamellae. Polymerization above 200°C results in holes in the lamellae; it is suggested that polymerization also is in the form of lamellae followed by the hole formation as further reaction occurs in the crystalline state, initial “crystal” growth at all temperatures is in the liquid crystalline state.