聚对苯二甲酸乙二酯非晶区反式构象结构的探讨

<正> 聚对苯二甲酸乙二酯(PET)的重复单元中有乙撑基。它的碳碳键内旋转产生反式构象(T)和左右式构象(G)。用其不同的构象来表征PET的聚集态结构,对研究结构与性能的关系是十分重要的。许多工作都已指出,乙撑基反式构象的谱带热处理时随结晶度的增加而增加。X-射线衍射的结果证实     

Subglass-transition-temperature annealing of poly(ethylene terephthalate) studied by FTIR

Using FTIR spectroscopy we have examined conformational changes in the quenched and slowly cooled amorphous PET films during physical aging process. It was observed that the amount of trans conformers for quenched sample decreased upon sub-T_g annealing. For the slowly cooled sample that corresponds to a state closer to equilibrium, the amount of trans conformers hardly decreased, but increased gradually during sub-T_g annealing process. The conformational populations of these two samples tend to be identical with annealing time. These results demonstrate that sub-T_g annealing will lead to closer interchain packing and result in the formation of new cohesional entanglements along the chains. In situ FTIR studies on the conformational changes of these samples were also carried out during heating up of the sample through the glass transition region. The results showed that incremental changes of the amount of trans conformers in Samples Q and SC were gradual, while an abrupt change of trans conformers occurred in the sub-T_g annealed samples. These results were in agreement with the formation of the interchain cohesional entanglement due to sub-T_g annealing. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 783–788, 1998     

Unique morphological and thermal behaviors of reorganized poly(ethylene terephthalates)

Bulk poly(ethylene terephthalate) PET has been reorganized both morphologically and conformationally by processing from its inclusion complex (IC) formed with γ‐cyclodextrin (CD). In the narrow channels of its γ‐CD‐IC crystals the included guest PET chains are isolated from neighboring PET chains and the ethylene glycol (EG) units adopt the highly extended g±tg? kink conformations, whose cross‐sectional diameters are ～80% of the diameter of the fully extended, all‐trans crystalline PET conformer, though they are nearly (～95%) as extended. When the highly extended, unentangled guest PET chains are coalesced from their γ‐CD‐IC crystals by exposure to hot water, host γ‐CDs are removed and the PET chains are presumably consolidated into a bulk sample with a morphology and constituent chain conformations not normally found in PET samples solidified from their randomly coiling, possibly entangled, disordered melts and solutions. Observations by polarized light and atomic force microscopies provide visual evidence for widely different semicrystalline morphologies developed in coalesced and as‐received PETs when crystallized from their melts, with possibly chain extended, small crystals and spherulitic, chain‐folded, large crystals, respectively. DSC observations reveal that coalesced PET is rapidly crystallizable from the melt, while as‐received PET is slow to crystallize and is easily quenched into a totally amorphous sample. Analyses of ¹³C‐NMR data strongly indicate that the PET chains in the noncrystalline regions of the coalesced sample remain predominantly in the highly extended kink conformations, with g±tg? EG units, which are required by their inclusion into PET‐γ‐CD‐IC crystals, while the predominantly amorphous PET chains in the as‐received sample have high concentrations of gauche± ? CH₂? CH₂? and trans ? O? CH₂? ,? CH₂? O? EG bond conformations. ¹³C‐NMR T₁(¹³C) and T_1ρ(¹H) relaxation studies show no evidence of a glass transition for coalesced PET, while the as‐received sample shows abrupt changes in both the MHz [T₁(¹³C)] and kHz [T_1ρ(¹H)] motions at T ～ T_g. Preliminary observations of differences in their macroscopic properties are attributed to the very different morphologies and conformations of the constituent chains in these PET samples. Apparently the kink conformers in the noncrystalline regions of coalesced PET are at least partially retained for extended periods even in the melt and are rapidly crystallized upon cooling. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 386–394, 2004     

New directions of matrix ir-spectroscopy

By use of thermal molecular beam IR matrix spectroscopy and IR irradiation in selected frequency ranges the vibrational spectra of conformers of 1,2-difluoroethane and methylvinylether will be discussed. The former molecule affords a case, where by comparison of CO₂ laser and 3000 cm^?1 irradiation the barriers to interconversion gauche?trans may be estimated. Methylvinylether on the other hand is a molecule, whose conformers may be interconverted by a 1-photon process in the 3000 cm^?1 region, but not by photons with frequency lower than 1400 cm^?1.     

Structural and conformational changes during thermally‐induced crystallization of poly(trimethylene terephthalate) by infrared spectroscopy

Conformational changes occurring during thermally‐induced crystallization of poly(trimethylene terephthalate) (PTT) by annealing have been studied using density measurement, differential scanning calorimetry (DSC), and mid‐infrared spectroscopy (MIR). Infrared spectra of amorphous and semicrystalline PTT were obtained, and digital subtraction of the amorphous contribution from the semicrystalline PTT spectra provided characteristic MIR spectra of amorphous and crystalline PTT. The normalized absorbance of 1577, 1173, and 976 cm^?1 were plotted against the crystallinity showing that these bands can be used unambiguously to represent the trans conformation while the band at 1358 cm^?1 can be used to represent gauche conformation of methylene segment. The presence of a weak band at 1358 cm^?1 in the amorphous spectrum suggested that a small amount of gauche conformation is present in the amorphous phase. Infrared spectroscopy has been used for the first time as a means to estimate the trans and gauche conformations of methylene segments in PTT as a function of T_a. The amount of gauche conformation was plotted against the crystalline fraction and the extrapolation of this plot to zero crystalline fraction provided a value of 0.07, suggested that the pure amorphous phase consist of ～ 7% gauche conformation. It was found that the amorphous and crystalline gauche conformation increases at the expense of amorphous trans conformation during thermally induced crystallization of PTT. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1497–1504, 2008     

Gauche- and trans-n-butane and their IR-induced interconversion in solid neon

Both conformers of n-butane are trapped from the gas phase in solid Ne at 4 K. Broad band infrared irradiation (mainly the CH-stretching region) induces interconversions, the quantum yield for the gauche — trans isomerization being approximately eight times higher than that for the reverse process. The energy difference between the conformers was found to be ?3.05 kJ mol^?1. The vibrational spectra of both conformers are given.     

RECOVERY OF AMORPHOUS POLY(ETHYLENE TEREPHTHALATE)FILM UNIAXIALLY DRAWN JUST BELOW THE GLASS TRANSITION TEMPERATURE*

Isothermal recovery in the macroscopic length of homogeneously deformed specimens of amorphous poly(ethyleneterephthalate) (PET) film sample uniaxially drawn at 69℃ to the draw ratios λ_0=1.26～2.20 were studied at temperaturesaround the glass transition temperature (T_g = 73℃). Experimental results indicate that the length recovery took place in twodistinct steps: a fast first step (fast relaxation) followed by a slow second step (slow relaxation). The relaxation processeswere accompanied by the reversion of trans-conformers (1340 cm~(-1)) to gauche, and the dichroic function of the 1340 cm~(-1)band characterizing the segmental orientation along the chain direction decreased to a very low value at the end of the fastrelaxation. This fact led us to assign the fast relaxation as the segmental orientation while the slow relaxation as relaxation ofthe global chain orientation. It was found that the slow relaxation follows a single exponential function, with relaxation timesstrongly dependent on the temperature resembling the glass transition process. The fast relaxation does not follow a singleexponential decay, presumably a distribution of relaxation times is involved.     

Vibrational analysis of tertiary alkyl chlorides

Vibrational spectra were obtained for 2-chloro-2-methylpentane, 3-chloro-3-methylpentane, 2-chloro-2-methylhexane, and 3-chloro-3-methylhexane. All four compounds exist in T_HHH and T_CHH conformations in the neat liquid, and the T_HHH' conformer of the last named compound also seems to be present. Only the T_HHH conformer is present in the crystalline state of the two pentanes, but the hexanes could not be made to crystallize and both conformers were present in the solid. A 44-parameter modified valence force field was used in normal coordinate calculations, with fifteen force constants being adjusted to fit 188 assigned frequencies below 1500 cm^?1 of six molecules (two conformers each of 2-chloro-2-methylbutane, 2-chloro-2-methylpentane, and 3-chloro-3-methylpentane). The resulting force constant values were used in zero-order calculations of the two hexanes as an aid in interpreting vibrational spectra for those compounds.     

Vibrational Spectra, Assignment, Conformational Stability and Ab Initio/DFT Calculations for 1-Nitropropane

The infrared spectra (4000–400 cm^{– 1}) of solid and the Raman spectra (3500–30 cm^{– 1}) of liquid and solid 1-nitropropane, CH₃CH₂CH₂NO₂, have been registered. Both the trans and gauche conformers have been identified in the fluid phase, while the trans form remains in the stable solid. Temperature dependence (190–230K) of the liquid 1-nitropropane Raman spectra has been carried out. From these data, the enthalpy difference was determined to be 870 ± 105 J-mol^–1, with the gauche conformer being the more stable rotamer. Ab initio and DFT calculations at different levels of approximation (HF, MP2, B3LYP, B3PW91) gave optimized geometries, harmonic force fields, and vibrational frequencies for the trans and gauche conformers. All the calculations (except the B3PW91/6-31G* level) predicted gauche as the low-energy conformer. Theoretical force constants are analyzed for formulating constraints in the molecular force field model of 1-nitropropane.     

用傅里叶变换红外光谱法研究聚对苯二甲酸乙二酯的结构

用傅里叶变换红外光谱法,将一系列不同温度下退火的PET光谱与熔融淬火的PET光谱进行数字吸光度相减,得到不同结晶状态的“反式构象光谱”。进一步将不同温度退火的“反式构象光谱”(240℃和120℃)彼此相减,可得到“纯晶区的光谱”和“非晶区的反式构象光谱”。通过差示光谱的比较,发现一些新的谱带和谱带的变化。可用PET 的晶区和非晶区中其分子链的内旋转构象的变化解释。     

Low-resolution microwave,infrared and Raman spectra,ab initio calculations and conformational analysis of 1-bromo-2-methoxyethane

The microwave spectrum of gaseous 1-bromo-2-methoxyethane, BrCH₂CH₂OCH₃, has been recorded from 18.0 to 27.0 GHz at low resolution. The Raman spectra of the gas, liquid, and solid along with the infrared spectra of the gas and solid have been recorded from 3500 to 50 cm^–1. A comparison of the vibrational spectra obtained for the fluid phases with those obtained for the annealed solid indicates the presence of more than one conformer in the fluid phases. The presence of two asymmetric rotors allows for five possible conformations, a majority of which are present in the gaseous phase. It is concluded that the conformation present in the solid phase is that of the gauche/trans (GT) form, where the first term refers to the carbon-bromine bond and the second term to the carbon-oxygen bond (methoxy group). In the gas phase the major absorption in the microwave spectrum is a result of the trans/trans (TT) form although it is certain that other conformations are also present. From a variable temperature study of the Raman spectrum of the liquid, the enthalpy difference between the conformers of the—OCH₃ group was found to be 850 ±115 cm^–1 (2.43±0.33 kcal/mol) whereas the difference between the conformers of the—CH₂Br group as found to be 510±24cm^–1 (1.46±0.07 kcal/mol). The conformational energy differences, vibrational frequencies, and structural parameters have been obtained from ab initio calculations with the STO-3G^* basis set, and these theoretical values are compared to the experimental values. All of these results are compared to similar data for some corresponding molecules.Taken in part from the thesis of R. A. Larsen which was submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

Spectra and structure of small ring compounds. LIX

The Raman (3200 to 10 cm^–1) and far infrared (380 to 60 cm^–1) spectra of gaseous fluorocyclobutane,c-C₄H₇F, have been recorded. A series of Q-branches observed in both of these spectra beginning at 166 cm^–1 with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fit to an asymmetric potential function of the form:V (cm^–1)=(1.76±0.05)10³X+(4.88±0.28)10⁴X²+(2.12 ±0.16)10³ exp(–5.66±0.41)10X² with a reduced mass function ofg ₄₄= 0.00386–0.00295X+0.03485X²+0.1228X³ +0.3459X⁴, whereX is the ring puckering coordinate. Utilizing this potential, the difference between the puckering angles for the two conformers was calculated to be 4° with the equatorial conformer having the larger value of 28°. This potential function is consistent with an energy difference between the equatorial and axial forms of 447 cm^–1 (1.28 kcal/mol) and a barrier to ring inversion from the equatorial to the axial conformation of 713 cm^–1 (2.04 kcal/mol). Experimental values for the enthalpy difference between the two conformers have been determined for both the liquid (400±30 c^–1) and gas (413±43 cm^–1) from investigations of the Raman spectra at variable temperatures. The conformational stability, enthalpy difference, structural parameters, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G, 6-31 G^*, and 6-31 G^** basis sets.For part LVIII, seeStruct. Chem. 1991,2, 195.Taken in part from the thesis of M. J. Lee, which has been submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree, May 1991.     

Infrared and Raman Spectra,Conformational Stability,Ab Initio Calculations,and Vibrational Assignments for Cyclopropyldifluorosilane

The infrared (3200–30 cm^–1) spectra of gaseous and solid Cyclopropyldifluorosilane, c-C₃H₅SiF₂H, and the Raman spectra (3200–20 cm^–1) of the liquid with quantitative depolarization values and the solid have been recorded. Both the syn (cis) and skew (gauche) conformers have been identified in the fluid phases, but only the syn conformer remains in the solid. Variable temperature (–55 to –100°C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. From these data, the enthalpy difference has been determined to be 73 ± 10 cm^–1 (209 ± 29 cal mol^–1), with the syn conformer being the more stable rotamer, which is at variance with the predictions from ab initio calculations. A complete vibrational assignment is proposed for both conformers based on infared band contours, relative intensities, depolarization values, and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G* calculations. Utilizing the frequencies of the silicon–hydrogen sketch, the rm Si—H bond distances of 1.474 and 1.472 Å have been obtained for the syn and skew conformers, respectively. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G* and 6-311 +G** basis sets at levels of restricted Hartree-Fock (RHF) and/or Moller–Plesset (MP) to second order. The potential energy terms for the conformer interconversion have been obtained from the MP2/6-31G* calculation. The results are discussed and compared to those obtained for some similar molecules.     

Spectra and structure of silicon containing compounds

The Raman (50 to 3200 cm^–1) and infrared (50 to 3500 cm^–1) spectra of chlorodimethylmethoxysilane, Cl(CH₃)₂SiOCH₃, in the vapor and solid phases have been recorded. Raman spectra of the liquid including depolarization ratios have also been recorded. Optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing the RHF/3–21G* and RHF/6–31G* basis sets. The calculations from both of these basis sets indicated the gauche conformer to be significantly more stable than the trans conformer. Since the gauche has twice the multiplicity of the trans form it is unlikely that the trans conformer will be detected in the fluid phases at room temperature. This is supported by the fact that no infrared or Raman bands were found to vanish in the spectra of the crystalline solid. The vibrational frequencies have been calculated using appropriate scaling factors, and the vibrational spectra are interpreted in detail. The results have been compared with those obtained for some related molecules.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthdayFor part XX, see J Raman Spectrosc 26:in press (1995)Analytical R/D Department, Organic Products Division, Miles Inc., Bushy Park Plant. Charleston, SC 9411, USAChemistry Department, Mu'tah University, P.O.Box 7, Mu'tah-Karak, JordanDepartment of Chemistry, Moscow State University, Moscow, B-234, RussiaDepartment of Ceramic Engineering, Inha University, Nam-Ku, Incheon 160, KoreaDepartment of Chemistry, University of Oslo, P.O.Box 1033, 0315 Oslo, Norway     

Infrared absorption and magnetic circular dichroism of Cs2ZrCl6:Ir4+

The E″_g(²T_2g) å U′_g(²T_2g) transition of Ir⁴⁺ in Cs₂ZrCl₆ is observed in the infrared energy range 5000–6000 cm^?1 by absorption and magnetic circular dichroism spectroscopy. The resolved vibrational structure provides detailed information about the change in vibrational frequencies on excitation and the transition intensity mechanism. The energy of the transition requires the Ir⁴⁺ spin-orbit coupling parameter ζ to be ≈ 2800 cm^?1.     

Ab initio studies of molecular structures,conformers and vibrational spectra of heterocyclic organics: I. Nicotinamide and its N-oxide

FTIR spectra of nicotinamide and its N-oxide have been recorded and analyzed in the range 400–4000 cm^?1. The stabilities, optimized molecular geometries, APT charges and vibrational characteristics for the two possible conformers of nicotinamide and its N-oxide have been studied theoretically using restricted Hartree–Fock (RHF) and density functional theory (DFT) methods. The E (trans) conformers of nicotinamide and its N-oxide are found to be more stable and less polar than their respective Z (cis) conformers. Due to addition of an O atom at the N₁ site in the NA molecule the magnitudes of atomic charges on all the H atomic sites are found to increase. For all the studied molecules, magnitude of the wagging mode of the NH₂ group is found to be higher than its torsion mode, which is in the reverse order as compared to that for the aniline molecule. Most of the vibrational frequencies have nearly the same magnitude for the two conformers of nicotinamide and its N-oxide, however, significant changes are noticed in their IR intensities, Raman activities and depolarization ratios of the Raman bands. The frequency of the ring breathing mode for the NA molecule is found to decrease by 100 cm^?1 in going to the NANO molecule for both the conformers. The IR intensity for the scissoring mode of the CON(H₂) group is found to decrease significantly for the NA-II conformer as compared to that for the NA-I conformer.     

Intrakonfigurations‐, Trip‐Multiplett‐ sowie anomal polarisierte A1gund A2g‐Übergänge in elektronischen und vibratorischen Resonanz‐Raman‐Spektren von (spinentarteten) trans‐Di(cyano)phthalocyaninatorhenaten

Intraconfigurational, Trip‐Multiplet, and Anomalously Polarised A_1g and A_2g Transitions in Electronic and Vibrational Resonance Raman Spectra of (Spin‐Degenerate) trans ‐Di(cyano)phthalocyaninatorhenates Brown bis(tetra(n‐butyl)ammonium) trans‐di(cyano)phthalocyaninato(2‐)rhenate(II) ( 1 ) is prepared by melting bis(phthalocyaninato(2‐)rhenium(II)) with tetra(n‐butyl)ammonium cyanide. According to electrochemical data, 1 is oxidised by iodine to yield blue tetra(n‐butyl)ammonium trans‐di(cyano)phthalocyaninato(2‐)rhenate(III) ( 2 ), whose cation exchange in the presence of bis(triphenylphosphine)iminium salts has been confirmed by x‐ray structure determination. 1 and 2 dissolve without dissociation of the cyano ligands in conc. sulfuric acid. Dilution with cold water precipitates blue trans‐di(cyano)phthalocyaninato(2‐)rhenium(III) acid. 1 and 2 are oxidised by bromine yielding violet trans‐di(cyano)phthalocyaninato(1‐)rhenium(III). Oxidation of 2 with dibenzoylperoxide and N‐chlorsuccinimide is described. 1 and 2 are characterised by polarised resonance Raman(RR) spectra, FIR/MIR spectra, and UV‐Vis‐NIR spectra. Due to a Kramers degenerate ground electronic state of low‐spin Re^II, a polarisation anomaly of the totally symmetric vibrations a_1g at 598 and 672 cm^–1 with depolarisation ratios ρ_l > 3 is observed in the RR spectra of 1 . Weak bands in the unusual UV‐Vis‐NIR spectrum of 1 , starting at 10200 cm^–1, are attributed to trip‐multiplet (TM) transitions. An electronic RR effect is detected for 2 . The selectively enhanced anomalously polarised line at 1009 cm^–1 with ρ_l ≈ 15 and the (de)polarised lines between 1688 and 2229 cm^–1 are attributed to intraconfigurational transitions A_1g → A_2g > A_1g, B_1g, B_2g, E_g arising from the ³T_1g ground electronic state of low‐spin Re^III split by spin‐orbit coupling and low symmetry (D ). Some of their vibronic bands are detected in the IR spectrum between 1900 and 4000 cm^–1. B and Q transitions of 2 at 16700 and 31900 cm^–1, respectively, as well as eight weak TM transitions are observed between 5050 and 26100 cm^–1.     

Conformational stability,barriers to internal rotation,structural parameters,ab initio calculations,and vibrational assignment of cyclopropanecarboxaldehyde

The asymmetric torsional potential function, conformational energy difference, vibrational frequencies, and structural parameters of Cyclopropane-carboxaldehyde have been obtained from ab initio calculations at the 3–21G and/or 6-31G^* baiss set levels. These results have allowed for a reinterpretation or clarification of some of the corresponding results obtained from experiment. The conformations that have the oxygen atom oriented cis and trans to the three-membered ring are observed and calculated to be the most stable and high energy forms in the gaseous phase, respectively. From the ab initio calculations using the 6–31 G^* basis set, the energy difference between the two conformers is 114 cm^–1. For the liquid, the trans conformer is more stable and is the only rotamer present in the annealed solid. Based on a combination of results obtained from ab initio calculations, microwave spectroscopy, and the electron diffraction technique,r _o structural parameters have been obtained for both conformations.     

Chromium(III) complexes ofd(−)tartaric andl(−) mandelic acids

The binary complexes of anhydrous chromium(III) chloride withd(−) tartaric acidl(−) mandelic acids have been characterized by elemental analyses, magnetic susceptibility, vibrational, electronic and circular dichroism spectra. The magnetic susceptibility data are close to the spin only value for a d³ chromium(III) ion. Three (Cr−Cl) vibrational modes in the region 420–290 cm⁻¹ are observed for the formed complexes indicatingC ₂ local symmetry of ligand atoms around the chromium(III) rather thanC ₃, which would allow two modes. In the visible spectra, two peaks in the 21052–22222 and 15384–16129 cm⁻¹ range are observed and are assigned to the⁴ A _2g → ⁴ T _1g (F) and⁴ A _2g → ⁴ T _2g transitions. The parameters (Dq, B,β ₃₅) place the ligands in the higher end of the spectrochemical series and provide reassurance that the hydroxy acid oxygen complexes to chromium(III) ion. The Cotton effects observed in the spin-forbidden band are assigned to the² E(² E _g ),² A ₂(² T _1g ) and² E(² T _1g ), while that in the spin-allowed band are a results of the splitting of the⁴ A _2g (⁴ T _2g ) to⁴ A ₁(⁴ T _2g) and⁴ E(⁴ T _2g ) transitions. The tartaric acid chelates are likely to befac in terms of ligand carboxylate and/or hydroxy groups since stronger and better defined Cotton effects are observed while mandelic acid chelates are weak suggesting formation of themer structure. TMC 2633     

Succinic or glutaric anhydride modified linear unsaturated (epoxy) polyesters

A series of N-alkyl-N-alkyl′-pyrrolidinium-bis(trifluoromethanesulfonyl) imide (TFSI⁻) room temperature ionic liquids (RTILs) has been investigated by means of thermogravimetric analysis (TG), differential scanning calorimetry, FT-IR spectroscopy, and X-ray diffraction analysis. These compounds exhibit a thermal stability up to 548–573 K. The mass loss starting temperature, T _ml, falls in a narrow range of temperatures: 578–594 K. FT-IR spectra, performed before and after 24 h isothermal experiments at 553 and 573 K, have confirmed their great thermal stability. Below the ambient temperature, these compounds exhibit a complex behavior. N-methyl-N-propyl-pyrrolidinium-TFSI is the sole liquid which crystallizes without forming any amorphous phase even after quenching in liquid nitrogen. Its crystalline phase has a melting point, T _m, of 283 ± 1 K. When the amorphous solid is heated, the N-butyl-N-ethyl-pyrrolidinium-TFSI presents a glass transition temperature, T _g, at 186 K followed by a cold crystallization, T _cc, at 225 K, and a final T _m at 262 K. The N-butyl-N-methyl-pyrrolidinium-TFSI exhibits a T _g between 186 and 181 K, its cold crystallization leading to two different solid phases. Solid phase I has a melting point T _I,m = 252 K and phase II, T _II,m = 262 K. When the amorphous phase is obtained at a cooling rate of 10 K/min, its T _cc is 204 K, and a metastable solid phase (III) is obtained which transforms into the phase II at 226 K. However, when the sample is quenched, the amorphous phase transforms into phase II at T _cc = 217 K and phase I at 239 K. P₁₅-TFSI exhibits the most complicated pattern as, on cooling, it leads to both a crystallized phase at 237 K and an amorphous phase at 191 K. On heating, after a T _g at 186 K and a T _cc at 217 K, two solid–solid phase transitions are observed at 239 K and 270 K, the final T _m being 279 K.