DSC analysis of compatibility of poly(phenyl methacrylate) and some poly(xylenyl methacrylates)

Glass transition temperatures of blends of (1) poly-(phenyl methacrylate) and poly(2,3-xylenyl methacrylate), (2) poly-(phenyl methacrylate) and poly(2,6-xylenyl methacrylates and (3) poly-(2,3-xylenyl-) and poly(2,6-xylenyl methacrylate) were measured. The data obtained suggest the existance of compatibility for blends of poly(xylenyl methacrylates) mentioned and incompatibility for both poly(phenyl methacrylate)/poly(xylenyl methacrylate) systems.     

Synthesis, structural investigation and thermal stability of aqua magnesium(II) phthalocyanine bis(diethylamine) solvate

Aqua magnesium phthalocyanine bis(diethylamine) complex was obtained in the crystalline form and its crystal structure was determined by single-crystal X-ray diffraction. The Mg atom is 4 + 1 coordinated by four N isoindole atoms and one O atom. The MgPc moiety is non-planar, the Mg(II) is deviated by 0.492(2) Å from the N₄-isoindole plane towards the oxygen atom of water molecule. The arrangement of MgPc(H₂O) and diethylamine molecules is determined by O–HN hydrogen bonds and π–π interactions. The complex is stable up to 140 °C. At this temperature the complex loses diethylamine molecules and next at 200 °C loses the water molecule and finally converts into β-MgPc.     

Synthesis and properties of hydrophilic segmented poly(urethanes) based on poly(ethylene glycols) and glycerol monostearate

Poly(urethanes) having the structure of comb-shaped copolymers were synthesized from glycerol monostearate, poly(ethylene glycols) with M _n = 300–6000, and 1,6-hexamethylene diisocyanate. Effects of the molecular mass of segments and of the contents of soft segments and side chains on both the glass transition temperature of the soft segment and on the melting point and the enthalpy of melting of crystalline phases involving soft segments and side chains were studied by DSC and IR spectroscopy. The resulting comb-shaped copolymers were shown to exhibit thermoplastic and hydrophilic behavior. It was demonstrated that the ultimate tensile strength, yield stress, and Young’s modulus of copolymer films increase with an increase in the molecular masses of soft and hard segments with their ratio maintained constant.     

DSC Monitoring of the Spin Crossover in Fe(II) Complexes

Heat flow to [Fe(bzimpy)²](ClO₄)₂⋅0.25H₂O complex (bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) (I) was measured between 300 and 460 K by differential scanning calorimetry. This exhibits a well-developed peak characteristic of the first-order phase transitions at temperature 403 K. The enthalpy and entropy of transition from low-spin to high-spin state has been determined to be ΔH=17 kJ mol⁻¹ and ΔS=43.0 Jmol⁻¹ K⁻¹. Heat flow to [Fe(bzimpy_−1H)₂]⋅H₂O complex (bzimpy _−1H=deprotonated bzimpy) (II) was measured between 300 and 580 K. The spin crossover in this system is accompanied with liberation of crystal water on the first heating. To monitor the structural changes during the spin crossover, powder diffraction data have been collected as a function of temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of branching on the thermal properties of novel branched poly(4‐ethyleneoxy benzoate)

Poly(4‐ethyleneoxy benzoate) (PEOB) was synthesized by the self‐condensation of ethyl 4‐(2‐hydroxyethoxy) benzoate (E4HEB) under transesterification conditions. Branched PEOB was prepared by the condensation of E4HEB with an AB₂ monomer, ethyl 3,5‐bis(2‐hydroxyethoxy) benzoate (EBHEB), under similar conditions. Varying amounts of branching (0–50%) were introduced into the linear polymer by changes in the composition of the comonomers in the feed. The solution viscosity of the polymers indicated that they had reasonable molecular weights; the extent of branching in these copolymers was established from their ¹H NMR spectra. Differential scanning calorimetry studies indicated that, as expected, the introduction of branching drastically affected the percent crystallinity of the copolymers (as seen from their ΔH_m, the enthalpy of melting), and when the extent of the incorporation of the AB₂ monomer exceeded 10 mol %, the copolymers were completely amorphous. The melting temperatures of the copolymers decreased with an increase in the branching content, whereas the peak crystallization temperature in quenched (amorphous) samples followed the exactly opposite trend. The glass‐transition temperatures (T_g) of the branched copolymers first decreased at low extents of branching, passed through a minimum, and then increased to attain the T_g of the pure hyperbranched polymer of EBHEB. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 261–268, 2000     

Multiple melting behaviour of poly(3-hydroxybutyrate-co-hydroxyvalerate) using step-scan DSC

Melting behaviour and crystal morphology of poly(3-hydroxybutyrate) (PHB) and its copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with various hydroxyvalerate (HV) contents [5 wt.% (PHB5V), 8 wt.% (PHB8V) and 12 wt.% (PHB12V)] have been investigated by conventional DSC, step-scan differential scanning calorimetry (SDSC), wide angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy (HSPOM). Crystallisation behaviour of PHB and its copolymers were investigated by isothermal crystallisation kinetics. Thermal properties were investigated after isothermal crystallisation treatment. Multiple melting peak behaviour was observed for all polymers. SDSC data revealed that PHB and its copolymers undergo melting-recrystallisation-remelting during heating, as evidenced by exothermic peaks in the IsoK baseline (C_p,IsoK, non-reversing signal). An increase in degree of crystallinity due to significant melt-recrystallisation was observed for isothermally crystallised polymers. SDSC proved a convenient and precise method for measurement of the apparent thermodynamic specific heat (C_p,ATD, reversing signal). PHB and PHBV showed different crystal morphologies for similar crystallisation condition. HSPOM results showed that the crystallisation rates reduced and sizes of spherulites were significantly increased as HV content increased.     

Isothermal crystallisation kinetics of poly(3-hydroxybutyrate) using step-scan DSC

The crystallisation kinetics, melting behaviour and morphology, of bacterial poly(3-hydoxybutyrate) (PHB) have been investigated by using differential scanning calorimetry (DSC), step-scan DSC (SDSC), wide angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy (HSPOM). DSC imparted isothermal crystallisation thermal history. The subsequent melting behaviour revealed that all PHB materials experienced secondary crystallisation during heating and the extent of secondary crystallisation varied depending on the crystallisation temperature. PHB samples were found to exhibit double melting behaviour due to melting of SDSC scan-induced secondary crystals, while considerable secondary crystallisation or annealing took place under the modulated heating conditions. The overall melting behaviour was rationalised in terms of recrystallisation and/or annealing of crystals. Interestingly, the PHB materials analysed by SDSC showed a broad exotherm before the melting peak in the non-reversing curve and a multiple melting peak reversing curve, verifying that the melting-recrystallisation and remelting process was operative. HSOM studies supported the conclusions from DSC that the radial growth rate of the PHB spherulites was significantly varied upon the crystallisation conditions. One form of crystals was shown by WAXRD from isothermally crystallised PHB.     

The thermal transition behavior of poly(bis(p-flourophenoxy)phosphazene)

The thermal transition behavior of poly(bis(p-fluorophenoxy)phosphazene) was studied as a representative aryloxy-substituted poly(organophosphazene) using X-ray diffraction, differential thermal analysis and density measurements. The crystal structure of-form contained in as-cast film had marked paracrystalline disorder. The crystal phase transformed into the mesophase atT(1) (110 140 °C). The structure of the-form observed in the mesophase was a representative hexagonal-packing of macromolecular chains which rotate around the chain axes. When the mesophase was cooled to room temperature, a more ordered crystal phase of the-form could appear. The most ordered crystal structure of the-form has a monoclinic unit cell with the following lattice parameters: a=18.9, b=13.2, c=4.90 Å, and=77°. The chain conformation is nearly planar cis-trans, which has been observed commonly in poly(organophosphazenes). The macroscopic deformation of the film sample was also examined, taking into account the microscopic deformation of the lamellar crystal due to the crystal-mesophase transition.     

Crystal structures and chemistry of double perovskites Ba2M(II)M′(VI)O6 (M=Ca, Sr, M′=Te, W, U)

Structures of the double perovskites Ba₂M(II)M ′(VI)O₆ (M=Ca, Sr, M′=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2/m (M′ =W) and (M′=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P2₁/n (M′=U) or cubic (M′=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba₂SrTeO₆ and Ba₂CaUO₆, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba₂SrWO₆ and Ba₂CaWO₆ in the temperature range between 80 and 723 K. It was found that the rhombohedral structure exists in Ba₂SrWO₆ above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba₂CaWO₆ undergoes a structural phase transition at low temperature to the tetragonal I4/m structure.     

The application of simultaneous chemiluminescence and thermal analysis for studying the glass transition and oxidative stability of poly(N-vinyl-2-pyrrolidone)

A computer-controlled chemiluminescence (CL) instrument incorporating a differential scanning calorimeter was used to simultaneously acquire photochemical and enthalpic data for poly(N-vinyl-2-pyrrolidone) (PVP). Samples were subjected to a linear temperature ramp under nitrogen and their luminescence response recorded. The resultant dynamic CL peak is attributable to the decomposition of hydroperoxide groups and the subsequent mutual termination of secondary polymer peroxyl radicals. It is shown that dynamic CL can be used to characterize the level of oxidation in PVP, which in commercial samples, may be partly related to the level of residual polymerization inititor and to the drying process. The temperature at which maximum CL emission occurs correlates with the glass transition temperature (T_g) of the polymer and increases with increasing molecular weight. A marked increase in the T_g of PVP occurs after it is aged in air for 24 h at 120°C. This is due to the loss of adsorbed moisture from the polymer which was confirmed by thermogravimetric analysis. Oxidation profiles of PVP were obtained by plotting the integrated CL peak area as a function of aging time. The profiles are compared with data obtained from isothermal CL and viscosity measurements. Gas perturbation experiments suggest that when drying PVP under nitrogen at elevated temperatures significant populations of longlived macroalkyl radicals are formed which can peroxidize the polymer on exposure to air. © 1993 John Wiley & Sons, Inc.     

Preparation and thermal properties of asymmetrically substituted poly(silylenemethylene)s

Poly(silylenemethylene)s of the types [SiMeRCH₂]_n and [SiHRCH₂]_n were prepared by the ring-opening polymerization (ROP) of 1,3-disilacyclobutanes (DSCBs) containing n-alkyl substituents, such as C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, and n-C₆H₁₃, or a phenyl group on the Si. These new polymers include a monosilicon analog of poly(styrene), [SiHPhCH₂]_n. Improved synthesis routes to the DSCB monomers were developed which proceed through Grignard ring closure reactions on alkoxy-substituted chlorocarbosilanes. All of these asymmetrically substituted polymers were obtained in high molecular weight form, except for [SiHPhCH₂]_n. The configurations of all of the polymers were found to be atactic. The aryl-substituted polymers have higher glass transition temperatures (T_gs) and thermal stability than those of the alkyl-substituted poly(silylenemethylene)s. Unlike the polyolefins of the type [C(H)(R)CH₂]_n, where T_g drops continuously from R = Me to n-Hex, the T_gs of the n-C_nH_2n+1 (n = 2–6)-substituted [SiMeRCH₂]_n PSM's appear to reach a maximum (at −61°C) for the R = n-Pr-substituted polymer. Moreover, where it was possible to make direct comparisons among similarly substituted atactic polymers, all of the poly(silylenemethylene)s were found to have lower T_gs than their all-carbon analogs. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3193–3205, 1997     

Structures and crystal chemistry of the double perovskites Ba2LnB′O6 (Ln=lanthanide B′=Nb and Ta): Part I. Investigation of Ba2LnTaO6 using synchrotron X-ray and neutron powder diffraction

The structure of 14 compounds in the series Ba₂LnTaO₆ have been examined using synchrotron X-ray diffraction and found to undergo a sequence of phase transitions from I2/m monoclinic to I4/m tetragonal to cubic symmetry with decreasing ionic radii of the lanthanides. Ba₂LaTaO₆ is an exception to this with variable temperature neutron diffraction being used to establish that the full series of phases adopted over the range of 15-500 K is P2₁/n monoclinic to I2/m monoclinic to rhombohedral. The chemical environments of these compounds have also been investigated and the overbonding to the lanthanide cations is due to the unusually large size for the B-site in these perovskites.     

Mechanical and thermal properties of rigid polyurethane foams derived from sodium lignosulfonate mixed with diethylene-, triethylene- and polyethylene glycols

Sodium salt of lignosulfonic acid (LS), which was obtained as by-product of cooking process in sulfite pulping, was solved in diethylene, triethylene or polyethylene glycol. Three series of polyurethane foams (LSPU) were synthesized by varying the LS content from 0 to 33 wt%. Apparent density (ρ) of LSPU foams ranged from 0.08 to 0.18 g cm⁻³ and was affected by both LS content and oxyethylene chain length. Glass transition temperatures increased with increasing amount of LS and with decreasing oxyethylene chain length. Thermal gravimetry analysis indicated that the LS component decomposes first and that the thermal stability increases with decreasing oxyethylene chain length. Compression strength and compression modulus increased linearly with increasing apparent density. It is concluded that LS is successfully utilized as a hard segment of rigid PU foams, whose thermal and mechanical properties can be tuned by changing the amount of LS and the length of soft oxyethylene chains.     

Structures and crystal chemistry of the double perovskites Ba2LnB′O6 (Ln=lanthanide and B′=Nb, Ta):: Part II—Temperature dependence of the structures of Ba2LnB′O6

The structures of eight members of the series of double perovskites of the type Ba₂LnB′O₆ (Ln=La³⁺-Sm³⁺ and Y³⁺ and B′=Nb⁵⁺ and Ta⁵⁺) were examined both above and below room temperature using synchrotron X-ray powder diffraction. The La³⁺ and Pr³⁺ containing compounds had an intermediate rhombohedral phase whereas the other tantalates and niobates studied have a tetragonal intermediate. This difference in symmetry appears to be a consequence of the larger size of the La³⁺ and Pr³⁺ cations compared to the other lanthanides. The temperature range over which the intermediate symmetry is stable is reduced in those compounds near the point where the preferred intermediate symmetry changes from tetragonal to rhombohedral. In such compounds the transition to the cubic phase involves higher order terms in the Landau expression. This suggests that in this region the stability of the two intermediate phases is similar.     

Quantitative Determination of Crystallinity of α-Lactose Monohydrate by DSC

In pharmaceutical practice it is important and useful to know the crystallinity of materials and to monitor it during formulation development, production processes and storage. The purpose of this study was to assess the quantitative capability of DSC for determining crystallinity in crystalline/amorphous powder mixtures and to compare the accuracy of the DSC method with that of conventional powder X-ray diffraction. Alpha-lactose monohydrate was chosen as the model material. On the basis of this study it can be concluded, that DSC method can be applied safely for semiquantitative evaluation of the crystallinity of lactose samples consisting of an amorphous content higher than 20%. This revised version was published online in August 2006 with corrections to the Cover Date.     

Improvement of the thermal stability of cluster‐crosslinked polystyrene and poly(methyl methacrylate) by optimization of the polymerization conditions

The polymerization conditions for polystyrene and poly(methyl methacrylate) crosslinked by 0.5 mol % of the cluster Zr₆O₄(OH)₄(methacrylate)₁₂ were optimized by applying a step polymerization procedure. The onset of thermal decomposition was thus increased up to about 50° for polystyrene and about 110° for poly(methyl methacrylate). The increase in thermal stability correlated with a higher char yield. The glass transition temperatures were also increased by about 15°. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6586–6591, 2005     

DSC study of the miscibility of poly(methyl acrylate)-polystyrene sequential interpenetrating polymer networks

The phenomenon of forced compatibilization has been studied in poly(methyl acrylate)-polystyrene PMA-i-PS sequential interpenetrating polymer networks, IPNs, using differential scanning calorimetry. Both networks in the IPN were prepared using the same amount of ethylene glycol dimethacrylate, EGDMA, as crosslinking agent. The samples were subjected to thermal treatments which included annealing at different ageing temperatures T _a, for 300 min. From the DSC curves, recorded on heating the enthalpy loss during the isothermal annealing, Δh _a was calculated. The dependence of Dh _a with the annealing temperature was used to define the temperature interval in which the conformational mobility is significant. The comparison of the Δh _a(T _a) curves obtained in an IPN and the results obtained with the pure component homo-networks with the same crosslinking density reveal some details of the miscibility of the IPN. In the case of the IPN crosslinked with 10% EGDMA, two peaks are apparent in the Δh _a(T _a) curve, but the high-temperature peak is shifted towards lower temperatures compared to that of the polystyrene network while the low-temperature one is nearly at the same temperature than the one of the poly(methyl acrylate) homonetwork. This means that compatibilization is not complete and phase separation still exists even at this high crosslinking density. The different behaviour of the high and low temperature transitions can be explained by the dynamic heterogeneity of the sample, i.e. by the different length of cooperativity of the conformational rearrangements of PMA and PS domains at any temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calcium‐containing poly(urethane‐urea)s: Synthesis,spectral, and thermal studies

A calcium salt of mono(hydroxypentyl)phthalate [Ca(HPP)₂] was synthesized by the reaction of 1,5‐pentanediol, phthalic anhydride, and calcium acetate. Four different bisureas such as hexamethylene bis(ω,N‐hydroxyethylurea), tolylene 2,4‐bis(ω,N‐hydroxyethylurea), hexamethylene bis(ω,N‐hydroxypropylurea), and tolylene 2,4‐bis(ω,N‐hydroxypropylurea) were prepared by reacting ethanolamine or propanolamine with hexamethylene diisocyanate (HMDI) or tolylene 2,4‐diisocyanate (TDI). Calcium‐containing poly(urethane‐urea)s (PUUs) were synthesized by reacting HMDI or TDI with 1:1 mixtures of Ca(HPP)₂ and each of the bisureas with di‐n‐butyltin dilaurate as a catalyst. The PUUs were well characterized by Fourier transform infrared spectroscopy, ¹H and ¹³C NMR, solid‐state ¹³C–cross‐polarization/magic‐angle spinning NMR, viscosity, solubility, elemental analysis, and X‐ray diffraction studies. Thermal properties of the polymers were also examined with thermogravimetric analyses and differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1809–1819, 2004     

Study of temperature transitions in solid poly(oxymethylene) by thermal analysis methods

Poly(oxymethylene)s with different molecular mass and chemical structure were studied using DSC, dynamic mechanical relaxation, thermomechanical analysis, and thermogravimetry.Molecular mobilities of two types were found in the amorphous phase of poly(oxymethylene). Unconstrained chains of poly(oxymethylene) soften at –70°C and then amorphous chains with different restraints from the crystalline phase are successively activated in a wide temperature interval.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThis work has been supported by DuPont Company     

Synthesis,characterization, and properties of novel poly(ether urethanes)

Novel poly(ether urethanes) were synthesized by homo- and random copolymerization of the m- and p-hydroxyethoxy benzoyl azides. Polymerization proceeded by decomposition and rearrangement of the acid azide group to the isocyanate group, which immediately reacted intermolecularly with the hydroxyl group to produce polyurethanes. These polymers were characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), x-ray diffraction, scanning electron microscopy (SEM), viscosity, and solubility. The thermal stability of these polymers was also studied by TG and DTG (derivative TG).