Structure and properties of the δ‐form and mesophase of syndiotactic polystyrene membranes prepared from different organic solvents

Syndiotactic polystyrene (sPS) membranes were prepared with different organic solvent systems and compared to get the information about the δ‐form complexing behavior of sPS. Further, the guest molecules included in the clathrate δ form of sPS are removed by stepwise extraction method. The conformational changes during the TTGG helical formation of sPS/organic solvent systems have been identified by FTIR spectroscopy, and it was concluded that the TTGG helices were constructed in regular sequences, which depends on the nature of the respective solvents. The TTGG content in the mesophase is found to be increased by removing the guest molecules. The structural changes of sPS/organic solvent systems have been characterized by WAXD analysis. Moreover, the different clathrate structures were found and showed the different crystalline reflections in the WAXD profiles, which are significantly changed with the kind of guest solvent included in sPS. The content of solvents in the clathrated sPS and the desorption temperatures were determined by thermal analysis. The resulted mesophase of sPS membrane contains the nanoporous molecular cavities that depend on the size of the guest molecule. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1873–1880, 2005     

Infrared linear dichroism as a tool to evaluate volatile guest partition between amorphous and nanoporous‐crystalline polymer phases

Desorption kinetics of ethene, propene, and butadiene from films exhibiting axially oriented nanoporous‐crystalline δ phases of syndiotactic polystyrene (s‐PS) have been followed by gravimetric and infrared linear dichroism measurements. The reported data can be rationalized by assuming that, after the initial desorption mainly involving molecules absorbed in the amorphous phase, most gaseous molecules are included as guest in the nanoporous‐crystalline phase. This allows establishing a simple method to evaluate guest partition between nanoporous‐crystalline and amorphous polymeric phases, which possibly can be applied for most volatile guest molecules. The described method also allows establishing the presence of one guest molecule (ethene, propene, or butadiene) per cavity of the nanoporous δ form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Disordered Nanoporous Crystalline Modifications of Syndiotactic Polystyrene

Disordered crystalline modifications formed by s(2/1)2 helices of syndiotactic polystyrene (s-PS) can be prepared by the removal of bulky guest molecules from intercalate as well as from triclinic δ clathrate forms. The X-ray diffraction pattern of the disordered crystalline modification is characterized from 2θ_CuKα < 12° by only a broad diffraction peak whose maximum is located in the 2θ_CuKα range between 8.7° and 9.8°. Films presenting disordered crystalline modifications have been used for the removal of an organic pollutant from dilute aqueous solutions. The sorption behavior of the disordered crystalline modifications are compared with that of the nanoporous-crystalline δ form as well as of the dense γ form. The disordered crystalline modifications of s-PS presents pollutant (1,2-dichloroethylene) uptake comparable to those of the nanoporous δ and ε forms and much higher than those obtained for the dense γ form. Moreover, FTIR data relative to sorption of 1,2-dichloroethane show that the guest sorption occurs essentially only in the crystalline phase. As a consequence, the obtained disordered crystalline modifications of s-PS can be fully considered disordered nanoporous-crystalline modifications.     

Structure and properties of the mesophase of syndiotactic polystyrene—III. Selective sorption of the mesophase of syndiotactic polystyrene

Syndiotactic polystyrene (sPS) has various crystalline forms such as α, β, γ, and δ forms, and a mesophase depending on the preparation method. In this study, we focused on the mesophase with the molecular cavity of sPS, which is obtained by step‐wise extraction of the guest molecules from the sPS δ form. To prepare the mesophase containing different shapes and sizes of the cavity, two kinds of the sPS δ form membrane cast from either toluene or chloroform solution were first prepared and then the guest molecules were removed by a step‐wise extraction method using acetone and methanol. We could succeed in the preparation of two kinds of mesophase with different shapes and sizes of the molecular cavity. Either toluene or chloroform vapor sorption to the sPS mesophase membranes was examined at 25 °C. Sorption analysis indicates that the mesophase with large molecular cavities can mainly sorb large molecules; on the other hand, the mesophase with small cavities can sorb only the small molecules, and is unable to sorb a large amount of large molecule because the cavity was too small to sorb the large molecules. Therefore, the sPS mesophase membrane has sorption selectivity based on the size of the molecular cavity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 238–245, 2004     

Sorption of Pollutant Traces by Nanoporous Crystalline Aerogels: Visualization by a Dye

Summary: The influence of the crystalline structure on the pollutant sorption properties of high porosity syndiotactic polystyrene (sPS) aerogels has been made visible by using azulene, a blue dye, capable to form a clathrate phase with sPS. The bluish coloration observed for aerogels with the nanoporous δ-form and the absence of coloration for aerogels with the densely-packed γ-form clearly establish that the crystalline nanopores play a key role for the removal of pollutant traces from water or air.     

Application of Fluorescence Depolarization Method to Monitor Free Volume in Gels of Stereoregular Polystyrene

Summary: A fluorescence depolarization technique was applied to get the information on free volume among polymer chains in gel form. Four fluorescent molecules with different molecular sizes were doped throughout the gels of syndiotactic polystyrene (sPS) and isotactic polystyrene (iPS) physical gel system, and their fluorescence anisotropy values were examined in detail for a range of polymer concentrations. Consequently, the free volume among sPS chains in sPS/chloroform gels is as large as the size of molecules smaller than 1,5-dimethylnaphthalene and is consistent with that of the cavity size in the δ-empty crystalline form of sPS solids. The cause to produce δ-empty crystalline form of sPS solids and to form cocrystals between sPS and guest molecules is discussed by comparing the molar size of guest molecules with the free volume among sPS chains in gel form.     

DGEBA monomer as a solvent for syndiotactic polystyrene

Syndiotactic polystyrene (sPS) has to be processed at high temperatures (i.e. >290°C due to its melting point of 270°C), which approaches its degradation temperature. We aim to facilitate the processing of sPS by lowering its melt temperature and viscosity with a curable epoxy/amine model system as reactive solvent, which will result in a thermoplastic-thermoset polymer blend. As a first step we therefore investigated the melting behaviour of sPS in epoxy monomer, established its phase diagram, and investigated the crystalline form of sPS in these mixtures. DGEBA epoxy monomer is found to be a solvent for syndiotactic polystyrene at temperatures above 220°C. The DGEBA-sPS phase diagram was established by means of DSC, on the basis of crystallization and melting peaks. The form of the curve in the phase diagram indicates that DGEBA is a poor solvent for sPS. In WAXS studies of blends only the β crystalline form was detected, not the δ form, thus no sPS-DGEBA polymer-solvent compounds (clathrates) were detected. However, DGEBA can still serve as a monomer for improved processing as it depresses the crystallization temperature by 20 to 60 K upon addition of 20 to 90 wt% DGEBA respectively, while a 16 to 45 K melting peak depression can be observed by adding 20 to 90 wt% DGEBA.     

Syndiotactic Polystyrene / Fullerene Composites: Elucidation of Structural Aspect

Summary: Syndiotactic polystyrene (sPS), an attractive polymer due to its wide range of application, forms polymer-solvent intercalates with a large variety of solvent molecules ranging from liquids to solids. Recently, it has been realized that sPS intercalate prepared from SPS/naphthalene gel is more promising of making mesoporous materials. Here, the composite of sPS/fullerene have been prepared by taking advantage of sublimation of naphthalene. The different techniques as like XRD, SEM, HRTEM, FT-IR, DSC, TGA etc have been employed to characterized sPS/fullerene composite. XRD investigation shows the presence of δ form sPS in the composite. SEM and HRTEM reveal the fibrillar network with fringe like structure in presence of fullerene only and the average diameter of fibril has increased as compared to pure sPS fibrils. The conductivities of these fibrils have been increased with increasing amount of fullerene.     

Structure and properties of the mesophase of syndiotactic polystyrene. VIII. Solvent sorption behavior of syndiotactic polystyrene/p‐chlorotoluene mesophase membranes

A crystalline δ form of a syndiotactic polystyrene (sPS) membrane was prepared from a solution of sPS (1 wt %) and p‐chlorotoluene (p‐CT) by a solution‐casting method. The mesophase (δ empty form) of sPS was obtained by the extraction of the guest solvent from the δ form of sPS by a stepwise solvent‐extraction method. The sPS/p‐CT mesophase membrane [p‐CT (A‐M)] was used for the sorption of 1 mol % p‐CT for different times and for the sorption of different concentrations of p‐CT, chlorobenzene (CB), p‐xylene (p‐X), toluene, and chloroform for 48 h. The presence of solvents in the sPS membrane was confirmed by IR analysis. A thermal study revealed that the sorption amount of 1 mol % p‐CT increased with increasing immersion time, and the sorption amounts of different solvents increased with increasing solvent concentration. Differential scanning calorimetry results showed that the desorption peak temperature increased as the amount of the solvent increased in the clathrated sPS membrane. Wide‐angle X‐ray diffraction results showed that 2θ at 8.25° was slightly shifted toward 8°, and there was no change in the peak position at 10° for p‐CT (A‐M), which was immersed in different solvents (1 mol %); however, the intensity of 2θ at 10° was not similar for all the samples. Among the solvents used for the sorption studies at 1 mol %, p‐CT (A‐M) could sorb more p‐CT and CB than p‐X, toluene, and chloroform. The solvent sorption isotherm was the Langmuir sorption mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3439–3446, 2004     

Crystalline orientation and molecular transport properties in nanoporous syndiotactic polystyrene films

The orientation of the crystalline δ nanoporous phase in syndiotactic polystyrene films, obtained by different procedures, have been characterized. For both solution cast and biaxially stretched films a high degree of uniplanar orientation, corresponding to the tendency of the ac crystallographic planes, to be parallel to the film plane has been observed and rationalized. According to molecular dynamics simulations of diffusion of small molecules into the δ nanoporous phase, this uniplanar orientation would minimize the molecular diffusivity through the nanoporous crystalline phase.     

Molecular‐Complex Formation of Syndiotactic Polystyrene with Stable Radical Molecules

Summary: The formation of a molecular‐complex crystalline phase of syndiotactic polystyrene (sPS) that contains a stable nitroxide radical compound, 2,2,6,6‐tetramethylpiperidinyl‐N‐oxyl (TEMPO), is confirmed by IR and electron spin resonance (ESR) spectroscopy, X‐ray diffractometry, and thermogravimetric analysis. Through a guest exchange procedure assisted by a plasticizing agent, the original guest (chloroform) contained in the starting clathrate phase is completely replaced by TEMPO. Although the conformational regularity of the sPS helices in the resultant crystalline phase that contains TEMPO is similar to that in the starting clathrate phase, the host lattice expands in the 010 direction. The guest TEMPO molecules exhibit a significantly broadened ESR signal because of their highly concentrated state in the complex crystalline phase.

Thermogravimetric measurement of a powder sample of the sPS/TEMPO complex.     

1,2‐dichloroethane conformation and molecular organization in syndiotactic polystyrene gels

The conformational equilibrium of 1,2‐dichloroethane (DCE) in syndiotactic polystyrene (sPS)/DCE gels has been investigated by using Fourier transform infrared spectroscopy. Results show that the fraction of DCE in the trans conformation (X_T) increases with increasing polymer concentration. From these X_T values, by assuming that the crystalline phase in the gel presents the clathrate structure, the amount of DCE included in the crystalline phase and the fraction of polymer included in the crystalline phase were evaluated as a function of the gel composition.     

Sulfonated syndiotactic polystyrene: sorption of ionic liquid in the amorphous phase and of organic guests in the crystalline phase

Fourier Transform Infrared spectroscopy (FTIR) and Wide‐Angle X‐Ray Diffraction (WAXD) measurements have clearly established the occurrence of a dual sorption ability of sulfonated syndiotactic polystyrene samples, which exhibit the nanoporous δ crystalline phase. In fact, large uptake (up to 20–30 wt%) of ionic liquid (IL; e.g. 1‐ethyl‐3‐methylimidazolium dicyanamide) occurs only in the hydrophilic amorphous sulfonated phases and does not disturb the hydrophobic nanoporous crystalline δ phase. On the other hand, a large uptake of organic guests (e.g. naphthalene) occurs prevailingly in the nanoporous hydrophobic crystalline phase, independently of the presence of the IL in the amorphous phase, eventually leading to the formation of syndiotactic polystyrene co‐crystalline phases. The thermal stability of IL can be largely increased by their inclusion in the amorphous phase of sulfonated syndiotactic polystyrene films. Copyright © 2012 John Wiley & Sons, Ltd.     

Complexation of Syndiotactic Polystyrene with 12‐Crown‐4

Solid‐state complexation of syndiotactic polystyrene (sPS) with a crown ether compound, 1,4,7,10‐tetraoxa‐cyclododecane (12‐crown‐4), took place when a film of sPS/chloroform clathrate was subjected to a guest exchange procedure assisted with a plasticizing agent. The new guest 12‐crown‐4 molecules were incorporated into the crystalline region of the sPS film, without causing a large conformational change of host sPS helices. X‐ray diffraction and thermogravimetric investigations showed that sPS/12‐crown‐4 complex had a clathrate complex structure which contained four 12‐crown‐4 molecules per unit cell. IR and Raman data suggested that 12‐crown‐4 took a C_i‐type conformation in the sPS complex phase.

     

Thermally-Induced Phase Transitions in the Uniaxially-Oriented δ Form of Syndiotactic Polystyrene

The empty δ (δ_e) form of uniaxially-oriented syndiotactic polystyrene (sPS) samples were obtained by extracting the solvent molecules from the δ form of sPS and solvent complex in acetone and methanol. Temperature dependence of the X-ray fiber diagrams starting from the uniaxially-oriented δ_e and δ form has been measured successfully at various temperatures for the first time. The transition behavior was traced clearly by separating the equatorial and layer line reflections. The δ_e form transformed to the γ form via an intermediate form. The intermediate form is speculated to take disordered structure due to the empty cavities present in the δ_e form. Calorimetric studies showed an endotherm followed by an exotherm during this phase transition, which is consistant with such a speculation. On the other hand the δ form transformed to the γ form directly without passing through the intermediate form or δ_e form. During the δ to γ phase transition the solvent molecules evaporate through the columnar structure in a broad range of temperature, allowing the transition to occur smoothly.     

Study on δ‐form complex in syndiotactic polystyrene–organic molecules systems. IV. Formation of complexes with a mixture of solvents and structural changes during the sorption of solvents by syndiotactic polystyrene mesophase membranes

The syndiotactic polystyrene (sPS) δ form was crystallized from mixtures with different compositions of p‐chlorotoluene–chlorobenzene (p‐CT–CB) and p‐chlorotoluene–1,1,2‐trichloroethane (p‐CT–TCE). The presence of the δ form and TTGG helical conformation was confirmed by Fourier transform infrared and wide‐angle X‐ray diffraction (WAXD) analyses. In sPS/p‐CT–CB and sPS/p‐CT–TCE δ‐form membranes, the relative absorbance (RA) of the p‐chlorotoluene (p‐CT) solvent peak was very high even at very low concentrations of p‐CT in comparison with the RA of higher concentrations of chlorobenzene (CB) or 1,1,2‐trichloroethane (TCE) in the mixtures. However, the RAs of both CB and TCE solvent peaks decreased with decreasing concentrations of CB and TCE in the mixtures. A negligible decrease in the RA of the TTGG helical content was observed with a decreasing concentration of CB or TCE. The WAXD results showed that the 2θ peak positions of the [010] and [ 10] planes of the sPS/p‐CT–CB and sPS/p‐CT–TCE δ‐form membranes appeared in the same position and were almost equal to those of the sPS–p‐CT δ‐form membrane. The mesophases of the sPS–p‐CT [p‐CT (A‐M)] and sPS–TCE [TCE (A‐M)] membranes were used for the sorption studies with different concentrations of various solvents. The sorption amount of aromatic solvents by both p‐CT (A‐M) and TCE (A‐M) mesophase membranes was higher than that of aliphatic solvents, regardless of the size, shape, and nature of the molecular cavity. The 2θ peak of the [010] plane of the sPS membranes slowly approached the original δ‐form value when the sPS mesophase membranes were immersed in various solvents of different concentrations for 48 h. The shifting of the 2θ peak of the [010] plane to the original δ form depended on the nature and concentration of the immersion solvents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2380–2387, 2005     

Molecular conformation of syndiotactic polystyrene gel from octadecyl benzoate solution

The molecular chain conformation of the dried gel of syndiotactic polystyrene (sPS) in octadecyl benzoate solution was investigated. sPS gels form rapidly through solid-liquid phase separation. The obtained sPS chains are in the highly ordered all-trans TT skeletal conformation which is different from a twofold TTGG helical conformation that sPS assumes in normal solvents. The size of the solvent molecule is considered to play an important role in the formation of the conformation of sPS in solution.     

Preparation and characterization of the crystalline inclusion complexes between cyclodextrins and poly(1,3-dioxolane)

The preparation and characterization of the crystalline inclusion complexes between a polymeric guest, poly(1,3-dioxolane) (PDXL), and small-molecular hosts, cyclodextrins (CDs) are reported. It is observed that the polymer guest can form crystalline inclusion complexes with three kinds of cyclodextrins, which may be attributed to the high oxygen atom density in PDXL chain. The crystalline inclusion complexes were characterized with FTIR , TGA, X-ray diffraction, SEM, 1H NMR and 13C CP/MAS NMR spectroscopes. It was found that the crystalline inclusion complexes have higher temperature stability than the pure CDs. The X-ray powder diffraction patterns of the crystalline inclusion complexes proved that they have columnar structures. 13C CP/MAS NMR spectra of the crystalline inclusion complexes indicate that CDs adopt a more symmetrical conformation in the complexes, while pure CDs assume a less symmetrical conformation in the crystal without a guest inside their cavities. The morphology of the crystal was     

A clear-cut experimental method to discriminate between in-plane and out-of-plane molecular transition moments

A new method to orient organic molecules, based on their absorption as guest of the crystalline nanoporous delta phase of uniaxially stretched syndiotactic polystyrene films, is presented. This molecular alignment method not only allows high degrees of guest orientation to be attained but also orients the planar guest molecules with their smallest cross section nearly parallel to the stretching direction (B) rather than perpendicular (A, as usual for absorption in amorphous polymeric phases). As a consequence, in-plane and out-of-plane transition moment vectors maximize their absorption intensities for light polarization nearly perpendicular and parallel to the stretching direction, respectively. Hence, simple linear dichroism measurements by polarized spectra can allow an easy and clear-cut discrimination between in-plane and out-of-plane guest transition moment vectors.     

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

X‐ray diffraction methods were used in an investigation of the structural changes in syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay was prepared by the intercalation of sPS polymer into layered montmorillonite. Both X‐ray diffraction data and transmission electron microscopy micrographs of sPS/clay nanocomposites indicated that most of the swellable silicate layers were exfoliated and randomly dispersed in the sPS matrix. The X‐ray diffraction data also showed the presence of polymorphism in the sPS/clay nanocomposites. This polymorphic behavior was strongly dependent on the thermal history of the sPS/clay nanocomposites from the melt and on the content of clay in the sPS/clay nanocomposites. Quenching from the melt induced crystallization into the α‐crystalline form, and the addition of montmorillonite probably increased heterophase nucleation of the α‐crystalline form. The effect of the melt crystallization of sPS and sPS/clay nanocomposites at different temperatures on the crystalline phases was also examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 736–746, 2002