The outlined polymorph selection of iPB-1 revealing by incorporation of a dentritic polymer

By incorporating a hydrophilic dentritic polyester into polymorphic isotactic polybutene-1 (iPB-1), we successfully decreased its viscosity as designed to trigger the melt crystallisation of form III due to the proposed decrease of the interactions between the iPB-1 chain sequences. In addition to the usual form II formation, the form III formation resulting from cooling the iPB-1 melt at suitable cooling rates has been verified by the DSC, WAXD, and in-situ synchrotron WAXS measurements. It was proposed that the form III melt crystallisation occurs after the 4/1 helix conformation formation in the iPB-1 melt and the following alignment of the resulting 4/1 helices. Once the interactions between the iPB-1 chain sequences are sufficiently strong as in the usual iPB-1 melt, the collapse of the 4/1 into the 11/3 helix conformation would occur and finally trigger the generally observed melt crystallisation of form II. Thus, we first outlined the polymorph selection process of iPB-1 based on the helix conformation formation and the following alignment of the helices which finally result in crystallisation of iPB-1 into corresponding crystal forms. The results are helpful for understanding of both the polymorph selection of polymorphic polymers like iPB-1 and the general polymer crystallisation.     

Thermotropic phase behaviour of sodium oleate as studied by FT-Raman spectroscopy and X-ray diffraction

The thermotropic behaviour of sodium oleate (NaOl) has been studied in the temperature range 10–125°C by using Fourier transform-Raman spectroscopy, X-ray diffraction and differential scanning calorimetry (DSC). The temperature dependence of conformationally sensitive bands in the CH₂ stretching (2800–2900 cm⁻¹), C–C stretching (1050–1150 cm⁻¹) and CH₃ rocking region (830–900 cm⁻¹) has been used to characterize the order/disorder behaviour of alkyl chains. It is found that in phase I, NaOl exhibits the crystalline ordered lamellar structure with a repeat period of 4.51 nm. The first broad peak in the DSC trace is due to superposition of two transitions (phase I to phase II and phase II to phase III), therefore, it is not possible to determine the lamellar structure of phase II. This broad transition from phase I to phase III is associated with the melting of methyl-sided chains and increase in gauche conformers in carboxylate-sided chains. Finally, NaOl undergoes a transition from crystalline to a liquid crystalline phase IV, which is associated with the melting of the carboxylate-sided chain.     

Deformation temperature and lamellar thickness dependency of Form I to Form III phase transition in syndiotactic polypropylene during tensile stretching

Phase transition from form Ⅰ to form Ⅲ in syndiotactic polypropylene crystallized at different conditions during tensile deformation at different temperatures was investigated by using in situ synchrotron wide angle X-ray diffraction technique. In all cases, the occurrence of this phase transition was observed. The onset strain of this transition was found to be crystalline thickness decided by crystallization temperature and drawing temperature dependent. The effect of drawing temperature on this phase transition is understood by the changes in mechanical properties with temperature. Moreover, crystalline thickness dependency of the phase transition reveals that this form Ⅰ to from Ⅲ phase transition occurs first in those lamellae with their normal along the stretching direction which have not experienced stress induced melting and recrystallization.     

Desired form of polymorphism of 6-chloro-2,4-dinitroaniline crystals grown by controlled growth temperature in melt growth

In this paper, the important form of a polymorphism of 6-chloro-2,4-dinitroaniline (CDA) crystals grown by the melt growth technique and its structure, physical, properties were discussed. Single crystals of form II and form III were grown by spontaneous nucleation of CDA melt. Unit cell parameters of these two forms were determined by the single-crystal X-ray diffraction technique. A powder X-ray diffraction pattern obtained from single-crystal data was compared with the experimental pattern. Functional groups presented in the molecules were identified by FTIR spectra, and packing difference between the two forms was realized by splitting of the absorption band and inter- and intramolecular interaction. DSC and TG/DTA analyses confirmed that each form has its own melting peak around 160 (form II) and 162 °C (form III) and there is no phase transition occurring between these forms. Harmonic vibrational frequency (β) of CDA was evaluated theoretically using HF/6-31G level and this value was compared with the experimental Kurtz–Perry technique. The calculated HOMO-LUMO energy shows that charge transfer occurred within the molecules.     

A study of phase separation of crystalline and miscible polymer blends. Poly(ε-caprolactone)/poly(styrene-co-acrylonitrile)

The phase separation of a crystalline and miscible polymer blend, poly(ε-caprolactone) /poly(styrene-co-acrylonitrile) (PCL/SAN), has been studied by differential scanning calorimetry (DSC), using a SAN containing 28.3% of acrylonitrile units. Several phenomena can be associated with the occurrence of phase separation depending upon the composition of the mixture. Following annealing at high temperatures, below and above the phase separation temperature T_c, three cases can be distinguished. In Case I, there is no sign of crystallization during quenching and DSC scanning, but a melting peak is observed at T_c, and above. In Case II, there is no crystallization on quenching but it does occur during the DSC run; the shift of the crystallization peak can then be related to T_c. In Case III, there is crystallization on quenching, and additional crystallization during the DSC run; the change of area of the crystallization peak is indicative of T_c. From these observations, the phase diagram of the system was determined. © 1993 John Wiley & Sons, Inc.     

Crystallization and melting behaviour of poly(m-xylene adipamide)

The melting and crystallisation behaviour of poly(m-xylene adipamide) (MXD6) are investigated by using the conventional DSC, X-ray diffraction and polarised light microscopy. Triple, double or single melting endotherms are obtained in subsequent heating scan for the samples after isothermal crystallisation from the melt state at different temperatures. The lowest melting peak can be ascribed to the melting of secondary crystals. The melting of primary crystals causes the medium melting peak and the highest melting peak is attributed to the melting of recrystallised species formed during heating. Following the Hoffman–Weeks theory, the equilibrium melting temperature is equal to 250°C and the equilibrium melting enthalpy ΔH _m ⁰ to 175 J g^–1. Then, using the Lauritzen–Hoffmann theory of secondary crystallisation, the analyse of the spherulitic growth shows that the temperature of transition between the growing regimes II and III is equal to 176°C. Finally the Gibbs-Thomson relationship allows the determination of the distribution function of crystalline lamellae.     

Thermal, phase transition, and thermal kinetics studies of carbamazepine

The thermal, phase transition of carbamazepine dihydrate and the solid-state transformation of carbamazepine from form III to form I were performed by Differential scanning calorimetry (DSC), Thermo gravimetry (TG–DTA), and X-ray powder diffraction.The non-thermal kinetic analysis of carbamazepine dihydrate and form III was carried out by DSC at different heating rates in dynamic nitrogen atmosphere. The model-free model, the Kissinger method, was used to give the Arrhenius parameters. Arrhenius plots from the kinetic model yielded activation energies corresponding to dehydration of dihydrate and melting of anhydrate CBZ form I were 95.28, 966.06 kJ mol^?1, the pre-exponential factors were 8.34E+11 and 1.41E+149, respectively. For the transformation of carbamazepine from form III to form I, activation energies corresponding to the melting of CBZ form III, recrystallization of form I, and melting of form I were 1160.81, 710.89, 1265.89 kJ mol^?1, the pre-exponential factors were 2.29E+144, 4.43E+91, and 1.61E+151, respectively. As a comparison, Ozawa method was used to verify the activation energy values obtained by Kissinger method. The result shows a close activation energy values between two methods.     

Characterization,crystallization kinetics,and melting behavior of poly(ethylene succinate) copolyester containing 10 mol % butylene succinate

Copolyester was synthesized and characterized as having 89.9 mol % ethylene succinate units and 10.1 mol % butylene succinate units in a random sequence, as revealed by NMR. Isothermal crystallization kinetics was studied in the temperature range (T_c) from 30 to 73 °C using differential scanning calorimetry (DSC). The melting behavior after isothermal crystallization was investigated using DSC by varying the T_c, the heating rate and the crystallization time. DSC curves showed triple melting peaks. The melting behavior indicates that the upper melting peaks are associated primarily with the melting of lamellar crystals with various stabilities. As the T_c increases, the contribution of recrystallization slowly decreases and finally disappears. A Hoffman‐Weeks linear plot gives an equilibrium melting temperature of 107.0 °C. The spherulite growth of this copolyester from 80 to 20 °C at a cooling rate of 2 or 4 °C/min was monitored and recorded using an optical microscope equipped with a CCD camera. Continuous growth rates between melting and glass transition temperatures can be obtained after curve‐fitting procedures. These data fit well with those data points measured in the isothermal experiments. These data were analyzed with the Hoffman and Lauritzen theory. A regime II → III transition was detected at around 52 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2431–2442, 2008     

Crystal modifications and multiple melting behavior of poly(L‐lactic acid‐co‐D‐lactic acid)

The crystal modifications and multiple melting behavior of poly(L ‐lactic acid‐co‐D ‐lactic acid) (98/2) as a function of crystallization temperature were studied by wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). It was found that the disorder (α′) and order (α) phases of poly(L ‐lactic acid) (PLLA) were formed in cold‐crystallized poly(L ‐lactic acid‐co‐D ‐lactic acid) samples at low (<110 °C) and high (≥110 °C) temperatures, respectively. A disorder‐to‐order (α′‐to‐α) phase transition occurred during the annealing process of the α′‐crystal at elevated temperatures, which proceeded quite slowly even at the peak temperature of the exotherm P_exo but much more rapidly at higher temperature close to the melting region. The presence or absence of an additional endothermic peak before the exotherm in the DSC thermograph of the α′‐crystal was strongly dependent on the heating rate, indicating that a melting process involved during the α′‐to‐α phase transition. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Poly(L‐lactide) crystallization induced by multiwall carbon nanotubes at very low loading

Poly(L ‐lactide) (PLLA)/multiwall carbon nanotube (MWNT) composites were prepared by the solvent‐ultrasonic‐casting method. Only very low concentrations of MWNTs (<0.08 wt %) were added in the composites. Isothermal and nonisothermal crystalline measurements were carried out on PLLA/MWNT composites to investigate the effect of MWNTs on PLLA crystalline behavior. DSC results showed that the incorporation of MWNTs significantly shortened the crystalline induction time and increased the final crystallinity of the composite, which indicated MWNTs have a strong nucleation effect on PLLA even at very low concentrations. The nonisothermal crystallization measurements showed that the MWNTs greatly speed up crystallization during cooling. From isothermal crystallization results, both PLLA and PLLA/MWNT composites samples closely followed a relationship based on Lauritzen‐Hoffman theory, with the regime II to III transition shifting to lower temperature with increasing MWNT concentration. A double melting peak appeared in both nonisothermal and isothermal measurements. The conditions under which it appeared were found to closely depend on the regime II‐III transition temperature obtained from Lauritzen‐Hoffman theory. From the magnitude and position of melting peaks, it is proposed that the double melting peak is caused by a disorder‐order crystal phase transition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2341–2352, 2009     

Thermotropic phase behavior of long-chain alkylammonium-alkylcarbamates

A series of alkylammonium-alkylcarbamates with different chain length including transdermal permeation enhancer Transkarbam 12 have been prepared and characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), temperature-dependent Fourier transform infrared spectroscopy (FTIR) and temperature-dependent X-ray powder diffraction. Four transitions have been observed including solid-solid transition (I), melting (II), decomposition of the carbamate salt (III) and boiling of the released amine (IV). The first transition was connected with rearrangement of the hydrocarbon chain packing and unusual shift of symmetric CH₂ stretching vibration in the IR spectra to lower wavenumbers indicated increase of conformational order. The second transition represented melting of the molecule and the third one was attributed to the decomposition of the carbamate salt into two amine molecules and carbon dioxide as evidenced by combination of DSC and TGA curves.     

Crystallization,morphology, and thermal behavior of poly(p‐phenylene sulfide)

This article deals with the structure, crystallization, morphology, and thermal behavior of poly(p‐phenylene sulfide) (PPS) with low‐molecular mass, probed by DSC, optical, and electron microscopy. The growth rates of spherulites were measured over the temperature range 235–275°C. A regime II–III transition was found at T = 250°C. The regime transition was accompanied by a morphological change from sheaflike structure to classical spherulites. The Avrami equation poorly described the isothermal crystallization of PPS, for the occurrence of mixed growth mechanisms and secondary crystallization, in agreement with the morphology and the thermal behavior. Two melting peaks were detected on DSC curves and attributed to the melting of crystals formed isothermally at T_c by primary and secondary crystallization. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 415–424, 2001     

Multiple melting behavior in isothermally crystallized poly(trimethylene terephthalate)

Melting behavior of poly(trimethylene terephthalate) (PTT) after isothermal crystallization from the melt state was studied using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques. The subsequent melting thermograms for PTT isothermally crystallized within the temperature range of 182-215 °C exhibited triple (for crystallization temperatures lower than ≈192 °C), double (for crystallization temperatures greater than ≈192 °C but lower than ≈210 °C), or single (for crystallization temperatures greater than ≈210 °C) endothermic melting phenomenon. These peaks were denoted peaks I, II, and III for low-, middle-, and high-temperature melting endotherms, respectively. For the triple melting phenomenon, it was postulated that the occurrence of peak I was a result of the melting of the primary crystallites, peak II was a result of the melting of recrystallized crystallites, and peak III was a result of the melting of the recrystallized crystallites of different stabilities. In addition, determination of the equilibrium melting temperature T_m⁰ for this PTT resin according to the linear and non-linear Hoffmann-Weeks extrapolation provided values of 243.6 and 277.6 °C, respectively.     

A new approach for the estimation of the melting enthalpy of metastable crystalline compounds using differential scanning calorimetry

This article focuses on the development of an innovative method, based on thermodynamic considerations and with the use of Differential Scanning Calorimetry (DSC), for the estimation of the melting enthalpy of crystalline compounds which are metastable near their melting temperature. The curves obtained, at various heating rates, are analysed in two steps. In the first step, the area of a zone generated by the melting endothermic peak is calculated following a specific method. In the second step, the melting enthalpy is extracted from this area through an enthalpy balance. This method is applied to both identified crystallographic forms, named form I and form II, respectively, of Etiracetam (UCB Pharma). The results show that the melting enthalpy of the stable form II compare well with the ones obtained using conventional methods. The curves of the metastable form I present thermal instabilities (partial solid–solid polymorphic transition and beta-recrystallization) near the form I melting peak leading to difficulties for a direct determination of the melting enthalpy by conventional methods. The proposed method is therefore very useful for the estimation of the form I melting enthalpy.     

The use of high-speed differential scanning calorimetry (Hyper-DSC™) to study the thermal properties of carbamazepine polymorphs

The thermal properties of two polymorphs of the drug carbamazepine, Forms I and III, were studied using high-speed differential scanning calorimetry (DSC). Previously, accurate determination of the heat enthalpy of fusion of Form III has not been possible using DSC at typical heating rates, due to concurrent exothermic recrystallisation to the higher-melting Form I. Here, it is demonstrated that heating rates of 250° C/min altered the kinetics of the melting transition of Form III such that this concurrent exothermic recrystallisation was inhibited. This allowed direct measurement of the enthalpy of the melting endotherm for Form III from a single transition. The enthalpy of this transition was found to be 109.5 J/g. Further investigations were then performed to test the utility of this technique in quantifying relative amounts of Forms I and III in mixtures of the two polymorphs. It was demonstrated that a limit of detection of 1% (w/w) was possible in this system. However, accurate quantification was not possible due to seeding effects initiating recrystallisation to Form I in these mixtures, even at these elevated heating rates. The utility of this novel technique as a fast analytical tool for studying the polymorphic behaviour of metastable polymorphs has been successfully demonstrated.     

Study of the thermal behavior of the transition phase of Co(II)–diclofenac compound by non-isothermal method

The Co(II)–diclofenac complex was evaluated by simultaneous thermogravimetry-differential thermal analysis (TG-DTA) and differential scanning calorimetry (DSC). The DTA curve profile shows one exothermic peak because of the transition phase of the compound between 170 and 180 °C, which was confirmed by X-ray powder diffractometry. The transition phase behavior was studied by DSC curves at several heating rates of a sample mass between 1 and 10 mg in nitrogen atmosphere and in a crucible with and without a lid. Thus, the kinetic parameters were evaluated using an isoconversional non-linear fitting proposed by Capela and Ribeiro. The results show that the activation energy and pre-exponential factor for the transition phase is dependant on the different experimental conditions. Nevertheless, these results indicate that the kinetic compensation effect shows a relationship between them.     

Influence of sorbed carbon dioxide on transition temperatures of poly(p-phenylene sulphide)

Static pressure usually increases the transition temperatures of polymers by decreasing their free volume. If the pressurizing medium is soluble in the polymer matrix, the opposing effect of increasing the free volume is possible. Those shifts of transition temperatures were monitored with a medium-pressure Differential Scanning Calorimetry (DSC) device. The influences of sorbed and surrounding gas molecules are demonstrated by changes occurring in the transition temperature regions. The results show the severe plasticizing effect of CO₂ on poly(p-phenylene sulphide) (PPS). The glass transition temperature T_G and the temperature of crystallization T_C are influenced by sorbed gas molecules. They decrease due to sorbed CO₂ molecules. Glass transition is lowered, but is difficult to interpret, as relaxation phenomena which diminish with increasing pressure occur during DSC runs. In crystallites no gas solution is usually possible, so that the melting point of PPS is mainly affected by influences other than plasticization.     

Preparation and physical characterization of forms II and III of paracetamol

The polymorphic forms II and III of paracetamol were obtained by melting the marketed form I. Under the melting and cooling conditions used, it was possible to obtain forms I, II and III. The recrystallization conditions and the physical properties of forms II and III were investigated by means of various techniques: thermomicroscopy, DSC analysis, infrared microspectrometry and X-ray powder diffraction at room temperature and as a function of temperature. Form III was found to be very unstable. However, its formation seems to be an important intermediate step in the preparation of form II.     

Phase transitions and pseudo-spin description in the perovskite CH3NH3PbCl3

The differential scaning calorimetry study of the compound of formula CH₃NH₃PbCl₃ in the temperature range 168 K–181 K shows two phase transitions according to the phase sequence: phase III (P222₁) ← (172K) → phase II (P4/mmm) ← (179K) → phase I (Pm3m) These transitions were characterized by X-ray diffraction, DSC and Raman scattering. The III transition involves mainly the rotational and orientational motions of the organic cation, whereas the antiferroelectric transition at 172K is connected with a complex mechanism involving the freezing of the cation motions coupled with the distorsion of the PbCl₆ octahedra This sequence has been also analysed in terms of pseudo-spin theory.     

Effect of Solvent Annealing Temperature on Crystal Modifications and Phase Transition Behavior of Regioregular Poly（3-octylthiophene）

In present study, the effect of the solvent annealing temperature on the crystal modifications and the phase transition behavior of the subsequently dried poly（3-octylthiophene） （P3OT） film has been investigated by the combination of DSC, WAXD and FTIR techniques. When chloroform is employed as the solvent, it is unexpectedly found that form I and form II crystal modifications of P3OT could be respectively obtained by room temperature and low temperature annealing. Comparing to the mostly used solvent reported for preparing form II, i.e. carbon disulfide （CS2） which is toxic and corrosive, chloroform is less toxic and corrosive and more suitable for solution processing of P3OT. Therefore, this finding provides an alternative way to obtain form II. By temperature dependent IR spectroscopy, the structural evolution of P3OT during the form II to form I phase transition process has also been studied in detail.