Comonomer Composition Research Articles

Effect of the hard‐segment structure on the dielectric relaxation of crosslinked polyurethanes

AbstractTwo series of crosslinked polyurethanes based on poly(tetramethylene ether) glycol soft segments and hexamethylene diisocyanate/1,4‐butane diol and glycerin or castor oil as a hard segments were synthesized, and their dielectric properties were examined. We examined the influence of the structural heterogeneity of the copolymers (as a function of the quantity and structure of the hard segments and crosslinking density, as measured by comonomer composition), frequency, and temperature as experimental variables by observing changes in the dielectric behavior. Two relaxation peaks were observed in the temperature range of −30 to 40°C for polyurethanes with various hard‐segment contents. The dangling chains of the castor oil presented a plasticizing effect that was exerted during the relaxation processes, an effect that was studied. It was found that both the amount and the structure of the hard segment strongly affected the dielectric behavior. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Online monitoring of the copolymerization of 2-(dimethylamino)ethyl acrylate with styrene by RAFT. Deviations from reaction control

Kinetics of copolymerization reactions of 2-(dimethylamino)ethyl acrylate (DMAEA) and styrene by reversible addition fragmentation transfer (RAFT) in N,N-dimethylformamide (DMF) are reported. Novel approaches in the online monitoring of the synthesis of the amphiphilic copolymers by Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) are presented. Automatic withdrawal of separate reactor streams and their subsequent dilution throughout the reaction with organic and aqueous solvents, respectively, allowed different features to be captured. Thus, light scattering data combined with spectroscopic and viscometric measurements in DMF, together with conductivity measurements in aqueous medium provided in real time comonomer conversion, copolymer mass, reduced viscosity, and composition. Continuous data gathered allowed observing and quantifying the DMAEA-linked macroRAFT control agent decomposition, with significant effects on the reaction kinetics. Deviations from controlled behavior were investigated during (co)polymerization reactions under different conditions.Multi-detector Size Exclusion Chromatography (SEC) and NMR were used to bring additional information on the system investigated.

Glass Transition Temperatures of Styrene/4-BrStyrene Copolymers with Variable Co-Monomer Compositions and Sequence Distributions

Glass Transition Temperatures of Styrene/4-BrStyrene Copolymers with Variable Co-Monomer Compositions and Sequence Distributions

Synthesis and characterization of epoxy functionalized cooligomers based on chlorotrifluoroethylene and allyl glycidyl ether

The synthesis of functionalized fluorocooligomers based on chlorotrifluoroethylene (CTFE) and allyl glycidyl ether (AGE) under radical copolymerization is presented. The compositions of comonomers in the cooligomers were determined by three different analyses viz: from 1H and 19F NMR spectroscopy by using 1,3-bis(trifluoromethyl) benzene as the external standard, epoxy equivalent weight value, and elemental analyses. The compositions determined by three methods were matching reasonably well and showed that the resulting poly(CTFE-co-AGE) cooligomers exhibit a tendency for alternation. The distribution of the monomers in the cooligomers was proposed based on the assessment of the reactivity ratios, ri, of both comonomers. These values were determined from the kinetics of radical copolymerization of CTFE with AGE from Fineman-Ross, Kelen-Tudos, and extended Kelen-Tudos methods which led to the assessment of the average reactivity ratios as: rCTFE = 0.20 ± 0.03 and rAGE = 0.15 ± 0.08 at 74 °C. The lower Mn values substantiated the formation of cooligomers rather than copolymers. The formation of cooligomers was attributed to the chain transfer to AGE (by hydrogen abstraction from AGE) from the allylic transfer. The poly(CTFE-co-AGE) cooligomers were soluble in most of the common organic polar solvents. An optimization of cooligomer yields was investigated by using ethyl vinyl ether as a third comonomer and from different initiators. The thermal stabilities of the cooligomers, obtained by thermal gravimetric analysis, showed a 5% weight loss at temperatures over 225 °C under air. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3587–3595, 2010

Polyaromatic-Anion Behavior of Different Polyelectrolytes Containing Benzenecarboxylate Units

The polyaromatic-ion behavior of poly(sodium N-maleoyl-2-aminobenzoate-co-sodium acrylate) in a comonomer composition 1:2, poly(sodium N-maleoyl-4-aminobenzoate-co-sodium acrylate) in a comonomer composition 1:2, and poly(sodium N-maleoyl-4-aminobenzoate-co-N,N-dimethylacrylamide) in a comonomer composition 1:1 is studied. The copolymers undergo short-range aromatic-aromatic interactions with methylene blue and rhodamine B, as a consequence of which their UV-vis monomer band is shifted to lower energies. As a result of their polyaromatic-anion behavior, methylene blue is easily dispersed on the polymeric domains. Moreover, the pK(a) of rhodamine B is shifted from 3.2 to 4.5-5 in the presence of these copolymers. This behavior is also observed in the presence poly(sodium 4-styrenesulfonate), but not in the presence of poly(sodium vinyl sulfonate), which are taken as reference polymers. Compared with poly(sodium 4-styrenesulfonate), a lower resistance to the cleaving effect of added NaCl on the interaction with methylene blue is found. A different influence on the reduction of 2,3,5-triphenyl-2H-tetrazolium chloride with ascorbic acid was found for the different polyelectrolytes.

Effect of vinyl pivalate/vinyl acetate comonomer composition on the self‐assembled morphology of poly(vinyl alcohol) prepared by in situ fibrillation: Preparation of PVA with a spherical morphology

AbstractThe photoinitiated copolymerization of vinyl pivalate (VPi) and vinyl acetate (VAc) was carried out in bulk. Varying monomer feed ratios of VPi/VAc (mol %/mol %) of 100/0, 90/10, 60/40, 50/50, and 30/70 were used. Polyvinyl alcohol (PVA) with s‐diad contents ranging from 61.8% to 55.7% was obtained. The morphology and thermal properties of the different PVA samples were investigated. PVA prepared from PVPi homopolymer resulted in PVA with a well‐aligned microfibrillar structure. With a decrease in the VPi content in the precursor polymer, the fibrous morphology was gradually lost, resulting in PVA with mixtures of fibrillar and spherical structures. When the PVPi content was 38.5 mol %, only spherical particles were observed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Comonomer Compositional Distribution, Physical Properties, and Enzymatic Degradability of Bacterial Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) Copolyesters

Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) (P(3HB-co-3H4MV)) was synthesized by using Ralstonia eutropha strain PHB(-)4 (PHA-negative mutant) harboring with the N149S/D171G double mutation of PHA synthase gene from Aeromonas caviae (PhaC(Ac) NSDG mutant) with 4-methylvaleric acid and fructose as the carbon sources. Because the microbially synthesized P(3HB-co-3H4MV) samples were found to have broad comonomer compositional distribution, P(3HB-co-3H4MV) samples with 3H4MV content of 7, 11, and 35 mol % were fractionated into several fractions with different comonomer composition ranging from 2 to 47 mol % by using a chloroform/n-hexane mixture. It was confirmed that a series of well-fractionated P(3HB-co-3H4MV) samples had a statistically random distribution. Physical properties and structure of the fractionated P(3HB-co-3H4MV) random copolymers were investigated. Both the melting temperature and glass-transition temperature of P(3HB-co-3H4MV) copolymers decreased with an increase in the 3H4MV composition. The degree of X-ray crystallinity of fractionated P(3HB-co-3H4MV) films decreased from 60 to 13% as the 3H4MV fraction increased from 0 to 39 mol %. Enzymatic degradation test for fractionated P(3HB-co-3H4MV) films was carried out at 37 degrees C in the presence of PHB depolymerase from Ralstonia pickettii T1. The rates of enzymatic erosion markedly increased with an increase in the 3H4MV composition to reach the highest one at 7 mol % of 3H4MV, followed by a decrease in erosion rate.

The thermal, mechanical and viscoelastic properties of poly(butylene succinate-co-terephthalate) (PBST) copolyesters with high content of BT units

Poly(butylene succinate-co-terephthalate) (PBST) copolyesters, with rigid butylene terephthalate (BT) units varying from 50 to 70 mol%, were synthesized via direct esterification route. The chemical structure and comonomer composition were characterized by 1H NMR. The weight-average molecular weights (Mw) of the prepared products measured by GPC spanned a range of 1.39 × 105–1.93 × 105 with corresponding Mw/Mn value of 2.23–2.42. Based on the WAXD analysis, PBST copolyesters were identified to have the same crystal structure as that of poly(butylene terephthalate) (PBT). The researches on the thermal properties showed that the melting temperature and decomposed temperature of PBST copolyesters increased with the increasing content of rigid BT units through DSC and TGA measurement. Furthermore, the tensile test results presented that the copolyester with higher content of BT units had higher initial modulus, higher breaking strength but lower elongation at break. Additionally, the viscoelastic properties of the prepared PBST films were analyzed by DMA measurement. It was found that both storage modulus (E′) and loss modulus (E″) corresponding to the peak tended to heighten with the increase of BT units, indicating the copolyester with higher BT units content had the more prominent viscoelasticity. The peak of loss factor (tan δ) curve shifted to higher temperature as the content of rigid BT units increased due to the increasing of the glass transition temperature (Tg).

Thermoresponsive fluorescent water‐soluble copolymers containing BODIPY dye: Inhibition of H‐aggregation of the BODIPY units in their copolymers by LCST

Novel water-soluble copolymers containing 4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The copolymers with both number-average molecular weight between 5.0 × 103 and 5.8 × 103 and narrow molecular weight distribution (Mw/Mn < 1.19) were obtained by the copolymerization of (2-dimethylamino)ethyl methacrylate (DMAEMA) and BODIPY-based methyl methacrylate (1) with 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator in the presence of cumyl dithiobenzoate (CDB) as a chain transfer agent (CTA). The structures of the resulting copolymers were characterized by 1H, 13C, and 11B NMR spectroscopies, and the comonomer compositions were good consistent with the feed ratio. Characteristic optical properties of the obtained copolymers were investigated by UV-vis and PL spectroscopic methods. The copolymers composed of [DMAEMA]: [1] = 98.0:2.0 and 99.4:1.4 led to thermoresponsive polymers having phase separation temperatures at 32 °C and 40 °C, respectively, depending on the compositions of hydrophilic/hydrophobic balances. Further, the effective reversible decrease/increase of the emission intensity of the copolymers led to the reversible formation/inhibition of the H-aggregation between two BODIPY planes in the copolymers on heating and cooling across the border of LCST. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 627–634, 2010

Influence of the Linear Aromatic Density on Methylene Blue Aggregation around Polyanions Containing Sulfonate Groups

The aggregation of methylene blue around different polyelectrolytes is studied by diafiltration, UV-vis, and (1)H NMR spectroscopies. Poly(sodium acrylate-co-sodium maleate) induces the formation of higher-order aggregates, showing a typical polyelectrolyte behavior dominated by long-range electrostatic interactions with the dye which are highly dependent on the ionic strength. Poly(sodium 4-styrenesulfonate) presents a high dispersant ability of methylene blue, showing what we can call a typical polyaromatic-anion behavior characterized by the presence of short-range aromatic-aromatic interactions with the dye which are less dependent on the ionic strength. An intermediate behavior is found for the copolymers poly(sodium 4-styrenesulfonate-co-sodium maleate) at two different comonomer compositions, related to a different probability of the polymers to form and stabilize ion pairs in hydrophobic environments. Their behavior is a function of the linear aromatic density, which is related to the comonomeric structure.

Fabrication and characterisation of capillary polymeric monoliths incorporating continuous stationary phase gradients

Polymeric monoliths in capillary formats have been fabricated incorporating a gradient of charged functional groups along their length. Scanning capacitively coupled contactless conductivity detection (sC(4)D) was then used to measure the conductive response of the stationary phase and characterise the relative axial distribution of functional groups along the column length. Gradients of 2-acrylamido-2-methyl-1-propanesulphonic acid were prepared using either photografting methods or by filling a capillary column with segmented plugs of monomer mixtures each containing incrementally higher concentrations of the functional monomer. The utility of sC(4)D as a rapid and non-invasive tool for assessing the slope of a variety of gradient configurations is demonstrated. Repeatability of the sC(4)D measurements was <1.7% RSD. Columns with a gradient of covalently bonded iminodiacetic acid were also produced. Changes in the gradient slope were observed after chelation of copper on the stationary phase via a reduction of the conductive response. The effect upon the observed gradient profile of changing the co-monomer composition during column fabrication was studied.

Crystalline Phase of Isomorphic Poly(hexamethylene sebacate-co-hexamethylene adipate) Copolyester: Effects of Comonomer Composition and Crystallization Temperature

The crystalline phase of random poly(hexamethylene sebacate-co-hexamethylene adipate) (P(HSe-co-HA)) was studied by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS). From the quantitative analysis of the comonomer composition in the crystalline phase and the finding of the change both in the WAXD patterns and in the d-spacing values of some planes in the HA composition (CHA) of 60 mol % < CHA < 70 mol %, the occurrence of isodimorphism was confirmed for P(HSe-co-HA). As the secondary comonomer unit content in the crystalline phase decreased with increasing crystallization temperature, it was concluded that the cocrystallization of the HSe and HA units in the crystal of P(HSe-co-HA) is affected by kinetics. From SAXS analysis, the lamella thickness of P(HSe-co-HA) was found to rely on the comonomer unit inclusion behavior in the PHSe or PHA type crystal. Application of the Sanchez−Eby model ...

Swelling Properties of New Hydrogels Based on the Dimethyl Amino Ethyl Acrylate Methyl Chloride Quaternary Salt with Acrylic Acid and 2-Methylene Butane-1,4-Dioic Acid Monomers in Aqueous Solutions

Hydrogels of dimethylaminoethyl acrylate methyl chloride quaternary salt (Q9) have been synthesized with different monomer ratio by copolymerization of this poorly studied monomer either with acrylic acid or with 2-methylene bu-tane-1,4-dioic acid. Hydrogel swelling was measured as a function of the composition of the hydrogel and of the crosslinking agent ratio. High values of swelling have been obtained at very high crosslinking values (< 14 wt %) and the equilibrium swelling was reached at very low time (less than 15 minutes). The swelling isotherms consisted of a steep initial portion and then levelled off as asymptotically to the equilibrium swelling limit. The experimental data suggest clearly that the swelling process obeys second-order kinetics. According to this, the kinetics rate constant and the equilibrium water content were determined at different comonomer composition and crosslinker concentration. The calculated kinetic constants ranged from 0.48 to 3.76 × 10-2 min-1 for poly (acrylic acid-co-Q9) hydrogels and from 0.68 to 4.0 × 10-2 min-1 for poly (2-methylene butane-1,4-dioic acid-co-Q9) hydrogels depending on the hydrogels composition. The diffusion process was evaluated for each hydrogel showing a non-Fickian type diffusion. In all cases was observed a considerable increase in diffusion coefficient as Q9 content increases.

Proline-Based Block Copolymers Displaying Upper and Lower Critical Solution Temperatures

Novel dual thermoresponsive block copolymers displaying lower critical solution temperature (LCST) and upper critical solution temperature (UCST) were synthesized by reversible addition−fragmentation chain transfer (RAFT) polymerization of two proline-based monomers. Poly(N-acryloyl-l-proline methyl ester), poly(A-Pro-OMe), was selected as a thermoresponsive segment, whereas poly(N-acryloyl-4-trans-hydroxy-l-proline), poly(A-Hyp-OH), could be regarded as a water-soluble polymer. The block copolymer having suitable comonomer composition (A-Pro-OMe/A-Hyp-OH = 27/73) exhibited soluble−insoluble−soluble transition with lower (LCST = 19−21 °C) and upper (UCST = 39−45 °C) critical solution temperatures in acidic water. The comonomer composition of poly(A-Pro-OMe)-b-poly(A-Hyp-OH) and pH value in the aqueous solution were found to affect characteristic thermoresponsive behaviors. The temperature-dependent assembled structures and chiroptical properties were evaluated by dynamic light scattering (DLS) and circula...

Thermoresponsive fluorescent water‐soluble copolymers containing BODIPY dye: Inhibition of H‐aggregation of the BODIPY units in their copolymers by LCST

AbstractNovel water‐soluble copolymers containing 4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) dyes were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The copolymers with both number‐average molecular weight between 5.0 × 103 and 5.8 × 103 and narrow molecular weight distribution (Mw/Mn &lt; 1.19) were obtained by the copolymerization of (2‐dimethylamino)ethyl methacrylate (DMAEMA) and BODIPY‐based methyl methacrylate (1) with 2,2′‐azobis(isobutyronitrile) (AIBN) as an initiator in the presence of cumyl dithiobenzoate (CDB) as a chain transfer agent (CTA). The structures of the resulting copolymers were characterized by 1H, 13C, and 11B NMR spectroscopies, and the comonomer compositions were good consistent with the feed ratio. Characteristic optical properties of the obtained copolymers were investigated by UV‐vis and PL spectroscopic methods. The copolymers composed of [DMAEMA]: [1] = 98.0:2.0 and 99.4:1.4 led to thermoresponsive polymers having phase separation temperatures at 32 °C and 40 °C, respectively, depending on the compositions of hydrophilic/hydrophobic balances. Further, the effective reversible decrease/increase of the emission intensity of the copolymers led to the reversible formation/inhibition of the H‐aggregation between two BODIPY planes in the copolymers on heating and cooling across the border of LCST. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 627–634, 2010

Poly(hexamethylene terephthalate- co-caprolactone) copolymers: Influence of cycle size on ring-opening polymerization

Poly(hexamethylene terephthalate) was cyclo-depolymerized in solution by heating to yield a fraction of cyclic oligomers of hexamethylene terephthalate ( c(HT) 2–5) with a content around to 95% in dimer to pentamer. Ring-opening polymerization in the melt of c(HT) 2–5, either neat or in mixtures with ε-caprolactone (CL) covering a range of HT/CL ratios from 9/1 to 1/9 was carried out to produce polyesters with molecular weights above 30,000 in high yields. The copolyesters had a comonomer composition according to the feed and the microstructure evolved from random to blocky as the content in CL increases. The thermal and mechanical properties of the copolyesters were evaluated for a variety of compositions. Results obtained in this work were compared to those previously obtained by us in the ring-opening copolymerization of CL with a cyclic oligomeric fraction enriched in hexamer and heptamer ( c(HT) 6–7). Although the polyesters resulting from the use of these two fractions were similar, significant differences were found in polymerization rate evidencing a lower reactivity of c(HT) n with decreasing values of n.

Antistatic coating material consisting of poly (butylacrylate-co-styrene) core-nickel shell particle

A transparent and antistatic coating material consisting of polymer core-metal shell particle was prepared. As a polymer core, poly(butylacrylate-co-styrene)s ([P(BA-co-sty)s]) with various compositions of butylacrylate and styrene were synthesized by emulsion polymerization. And the effect of comonomer composition on the thermal property of polymer core particle was investigated. By electroless plating method, the nickel particles were formed and deposited on the surface of P(BA-co-Sty) particles to form P(BA-co-Sty) core-nickel shell composite particles. SEM observation confirms that the nickel particles with size of 15 nm are distributed on the surface of the polymer core particles. The surface resistance of P(BA-co-Sty) core-nickel shell composite is 0.8×10 8 Ω/cm 2, enough to act as antistatic coating material.

Acrylamide Copolymers에 의한 Liquid Crystal Emulsions의 안정성에 관한 연구

PDLC 필름을 제작하는 데는 여러 방법들이 있으나 그중 하나로서 에멀젼 기술에 기반을 둔 NCAP필름 제조방법이 있다. 이러한 에멀젼 기술은 물에 부분적으로 용해될 수 있는 PVA, PVP와 같은 고분자로 NCAP를 제조할 수 있고, 또한 안정제 없이도 안정한 액정 에멀젼을 형성할 수 있다. 본 연구에서는 물에 녹는 것과 물에 녹지 않는 부분을 가지고 있는 분자로 구성된 공중합체에 대하여 에멀젼의 안정성과 계면장력, 표면장력이 공중합체의 구성, 농도, 소수성 체인 등에 의존한다는 것도 연구하였다. Acrylamide-styrene(AA-ST)계 공중합체는 같은 농도조건에서 사용한 다른 공중합체보다 낮은 계면장력을 나타낸다. 낮은 계면장력 때문에 AA-ST 공중합체는 액정분자들과 좋은 친화성을 갖는다. 또한 액정표면에 쉽게 흡수되는 분자들이 액정 에멀젼 시스템을 더 안정화하다는 것과 형태학적 분석을 통한 액정의 안정성도 논의하였다. There are several methods to fabricate Polymer Dispersed Liquid Crystal(PDLC) films. One of them, so-called Nematic Curvilinear Aligned Phase(NCAP) film, is based on emulsion technology. To produce NCAP systems various water soluble polymers, such as partially hydrolyzed polyvinylalcohol(PVA) and polyvinyl pyrrolidone(PVP), which can form stable emulsion of liquid crystal(LC) without any stabilizers were used. In this work, we studied the dependence of emulsion stability on nature and composition of copolymers composed of water-soluble and water-insoluble moiety. We found that interfacial surface tension depends on the composition of comonomer, the copolymer concentration in the water, and the nature of hydrophobic chain. The Acrylamide -styrene(AA-ST) copolymer showed the lowest interfacial surface tension among the tested copolymers at the same concentration. Since the interfacial surface tension decreases with increasing the compatibility of copolymer with LC phase the AA-ST copolymer has the best compatibility with LC molecules. It is believed that molecules adsorbing easily on the surface of LC droplets allows the LC emulsion system to be more stable.

The effect of copolymer composition on the surface properties of perfluoroalkylethyl acrylates

AbstractThe surface properties of two perfluoroalkylethyl acrylic copolymers—aqueous, Zonyl®329 and solvent‐based, Zonyl®225—were studied. Zonyl®329 is a water‐based dispersion and Zonyl®225 a solvent‐based copolymer solution; both polymers have the same perfluoroalkyethyl side chains [F(CF2)nCH2CH2] but have different comonomer compositions. Thin films, prepared by dip coating onto mica and quartz, with and without annealing, were characterized by contact angle and by X‐ray photoelectron spectroscopy (XPS). The contact angle measurements showed little variation with polymer and with substrate, consistent with the supposition that the perfluoroalkylethyl chains aggregate on the surface and thus dominate surface properties, irrespective of the composition of the rest of the polymer. XPS revealed only small variations in surface chemistry for studied films. Annealed films showed improved segregation for solvent‐based Zonyl®225, which has both hydrocarbon alkyl and perfluoroalkylethyl side chains; the presence of hydrocarbon alkyl chains enables the perfluoroalkylethyl chains to reorganize after annealing. Depending on the external conditions, this thermal treatment can enable more perfluoroalkylethyl chains to reach the film surface (solid/air interface), leading to a reduction in the dispersive‐dominant surface and enhancement in perfluoroalkylethyl segregation. This suggested that perfluoroalkylethyl side chains dominate the surface properties, which are thus not dependent on substrate, backbone composition, or formulation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Polymorphic crystallization of fractionated microbial medium-chain-length polyhydroxyalkanoates

Abstract By focusing on a range of fractions of medium-chain-length polyhydroxyalkanoates (mcl-PHA), a more in-depth understanding of the thermal properties and the crystalline structure has been gained. Dual-mode melting was observed for all the fractionated samples. Further DSC analysis revealed that such phenomenon was due to the presence of two crystalline phases (phase I and phase II), forming at different temperatures. As noted, for the samples with higher 3-hydroxytetradecanoate (HTD) comonomer composition, the crystallization rate of phase II was much depressed, which made phase I dominant. The WAXD and FTIR results indicate that the two phases differ in the crystalline structure. The in situ IR and WAXD registrations indicate that phase I would transform into phase II through a melting-recrystallization process during heating. The high similarity of IR spectra in the range of 1500–900 cm−1 between phases I and II excludes the possibility of adopting different conformation. It is suggested that major differences between the two crystalline phases lie in the molecular packing.