Structure and properties of the mesophase of syndiotactic polystyrene. I. Effect of casting conditions on the preparation of the mesophase

A syndiotactic polystyrene–toluene solution was cast under two different casting conditions to obtain the δ form. A systematic study of its conformational transition, thermal behavior, and structural transformation as functions of the annealing temperature and time was performed. Spectroscopic studies revealed the content of its helical conformations and its retention up to 190 °C. Thermal analyses showed a significant difference in the transformation from the γ form to the α form. The retention of the intermediate emptied clathrate form (mesophase) of the conformational order for a longer duration (from 120 to 180 °C) in a syndiotactic polystyrene membrane cast at room temperature was confirmed by X‐ray diffraction analysis. On the basis of the experimental results in this work, the transition mechanism is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 530–536, 2002; DOI 10.1002/polb.10120     

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     

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     

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     

Helical tubulate inclusion compounds

Abstract

The inclusion properties of the first helical tubuland diol hosts 1–5 have been surveyed and are reported. Bicyclic diol 1 forms helical tubulate inclusion compounds with most small solvent molecules, but with certain phenols hydrogen bonded co-crystalline materials are produced instead. Diol 2 yields helical tubulates with larger guest molecules, but if smaller solvents are used then an alternative host system is obtained. This has the guests trapped in ellipsoidal cavities located along constricted canals and is termed the ellipsoidal clathrate type. In some cases both inclusion types can be produced from 2 by varying the experimental conditions. The free volume present in the helical tubuland lattices of 3 and 5 is insufficient for guest inclusion. Diol 4 has the largest void space and can form inclusion compounds with large molecules such as ferrocene and squalene. X-ray crystal structures of representative examples of these compounds are discussed.     

Induced helix formation and stabilization of a meta‐linked polymer containing pyridine units

A new amphiphilic polymer containing pyridine units was synthesized and characterized. The solvent‐dependent conformational transition from extended transoid to helical cisoid was studied by absorption, fluorescence, and ¹H NMR measurements. The polar solvent promoted the formation of the helical structures. A metal ion or H⁺ could stabilize the ordered structure. Moreover, the solvophobically induced helical structure was stable to environmental stimuli. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1403–1412, 2007.     

Quantitative characterization of the optical properties of absorbing polymer films: Comparative investigation of the internal reflection intensity analysis method

Nondestructive, three‐dimensional refractive‐index measurements are used for the determination of both the crystallinity and orientation in thin polymer films. The prism wave‐guide coupler is particularly suited for three‐dimensional isotropic and anisotropic thin‐film studies because of the quantitative character of the information obtained and the ease of data acquisition. It has been limited, however, to determining only the refractive index of transparent or weakly absorbing thin‐film samples. On the basis of thin‐film optics, this study develops a new internal reflection intensity analysis (IRIA) method, which uses the intensity information rather than the conventional mode angle values to acquire both the refractive index and the extinction coefficient over a range of transparent to highly absorbing polymer films. Therefore, the IRIA method overcomes the limitations of this prism wave‐guide coupler technique, which can only measure the refractive index of a weakly absorbing sample. With a Metricon PC‐2010 as the skeletal framework, a prototype instrument has been developed to apply and test the IRIA method. A study comparing both the refractive index and extinction coefficient obtained with ellipsometry, ultraviolet–visible/near‐infrared reflectometry, and IRIA for solvent blue 59 dyed polystyrene films confirms that the IRIA method is effective for obtaining the three‐dimensional refractive indices and extinction coefficients of polymer films. In addition, the refractive index and extinction coefficient spectrum (400–800 nm) of solvent blue 59 have been determined with the effective media theory. Furthermore, the three‐dimensional complex refractive indices of highly absorbing black electrical tape, inaccessible to other optical measurement because of its surface character, has been determined by the IRIA method. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 842–855, 2003     

Prediction of infinite dilution solvent activity coefficient in rubbery polymer solutions using Engaged Species Induced Clustering (ENSIC) model

It is extremely important to predict infinite dilution solvent activity coefficients in rubbery polymers in design and operation of polymer‐related processes. Many models have been developed to predict the activity coefficients. However, the accuracies of these models are not satisfactory. This article advances a method for predicting the infinite solvent dilution activity coefficients in the rubbery polymers, using the Engaged Species Induced Clustering (ENSIC) model. It elucidates the physiochemical significance and mathematical meaning of the parameters in the ENSIC model. In this article, the ENSIC approach has been proven to agree extremely well with the experimental data in both correlating the finite dilution solvent activity coefficient and predicting the infinite dilution solvent activity coefficient for rubbery polymer/solvent systems. In other words, both the ENSIC equation and its derivative at extremely low solvent concentration are in good agreement with the experimental data. In addition, the article indicates that the ENSIC model is much more accurate than another kind of empirical models‐ the F–H and related models in predicting the infinite dilution solvent activity coefficients in polymer solutions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1668–1675, 2006     

Design of a novel co‐electrospinning system with flat spinneret for producing helical nanofibers

A kind of biomimetic fibers of helical structures at nanoscale has attracted increasing interest. In this study, a novel co‐electrospinning setup with a designed flat spinneret, used for the fabrication of helical nanofibers, is reported in this study. Poly(m‐phenylene isophthalamide) (Nomex) and Thermoplastic polyurethane (TPU) are chosen as the two components in co‐electrospinning. To display the efficiency for producing helical fibers, a generally used core–shell needle spinneret is used for comparison. The effect of the uniformity of electric field distribution created by these two types of spinnerets on the jet motion and the resultant helical fibers is developed, with systematical simulation and experimental research. The results showed that the co‐electrospinning system with the newly designed flat spinneret can produce helical nanofibers efficiently. Compared with the needle spinneret, the flat spinneret created more uniform electric field, leading to better morphology and structure of the resultant helical fibers. In addition, an approach to achieve the scale‐up of this co‐electrospinning system is developed. This novel design is expected to provide a promising method to fabricate nanofiber materials with helical structures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1496–1505     

Measurements of freezing‐point depression to evaluate rubber network structure. Crosslinking of natural rubber with dicumyl peroxide

An experimental approach based on the freezing‐point depression of a solvent in a swollen gel has been developed to characterize the structure of rubber networks. This property depends on the conditions required for the formation of crystalline nuclei, which are limited by the elastomer network restrictions. Information about the functionality, spatial distribution, and number of crosslinks can be obtained by the use of this easy and ready experimental method. Application of the tube model of rubber elasticity in the uniaxial stress–strain experiments of natural rubber samples vulcanized with dicumyl peroxide yields the characteristic parameters of the rubber networks, which are in concordance with the network structures predicted by the freezing point method. Finally influence of vulcanization conditions in network structure and its relationship with the mechanical properties was evaluated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 544–556, 2007     

Emulsion copolymerization of substituted acetylenes for constructing optically active helical polymer nanoparticles. Synergistic effects and helicity inversion

Copolymerizations of substituted acetylenes have been intensively studied in solution polymerization for constructing chirally helical polymers, while emulsion copolymerizations of the kind of monomers have been only scarcely reported. In the present study, chiral substituted acetylene monomer containing cholic acid group underwent emulsion copolymerizations with an achiral acetylenic monomer in the presence of rhodium catalyst, providing optically active helical copolymer nanoparticles. Synergistic effects were found in the resulting helical copolymers, enabling one certain copolymer to show the maximum CD signal intensity. Moreover, the helicity of the helical copolymers in nanoparticle state was opposite to that in solution state. This is the first demonstration that synergistic effects and helicity inversion simultaneously occurred in helical copolymers prepared by emulsion copolymerization process. To deepen the understanding of the unique phenomena, corresponding solution copolymerization and emulsification process were also investigated. Different from “Sergeant and Soldiers rule” approach, the present study provides a new strategy for preparing chirally helical polymer particles by making full use of achiral monomers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1679–1685     

Spectroscopic studies of the conformational properties of naphthoyl chitosan in dilute solutions

A naphthoyl chitosan derivative was prepared, and its conformations in dilute solutions were characterized with spectroscopic methods, including circular dichroism (CD) spectroscopy and fluorescence emission spectroscopy. The CD spectrum of this polymer showed a negative band at about 295 nm in dimethyl sulfoxide (DMSO), indicating that the polymer adopted a helical secondary structure. A helix reversion occurred at concentrations greater than 1 mg/mL. The intensity of the CD signal decreased with the addition of water to the solution, and this suggested a change from a helical conformation to a looser one as a result of the collapse of intramolecular hydrogen bonds. In the fluorescence emission experiments, two kinds of excimer emission bands were detected at 375 and 425 nm, and they were assigned to a partially overlapped dimer with a twisted geometry and a fully overlapped dimer with a sandwichlike geometry, respectively. Adding water to a solution of naphthoyl chitosan in DMSO resulted in a gradual reduction of the emission intensity at 375 nm, and this implied that the twisted arrangement of the chromophore was destroyed by the presence of water. The relative intensity (i.e., the ratio of the intensity of the excimer emission at 425 nm to that of the excimer emission at 375 nm) depended on the solvent (DMSO, N,N‐dimethylformamide, N,N‐dimethylacetamide, and 1‐methyl‐2‐pyrrolidinone), and this indicated that the conformation of naphthoyl chitosan was solvent‐dependent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2747–2758, 2004     

Molecular dynamics simulation of poly(3‐hexylthiophene) helical structure In Vacuo and in amorphous polymer surrounding

The stability of poly(3‐hexylthiophene) (P3HT) helical structure has been investigated in vacuo and in amorphous polymer surrounding via molecular dynamics‐based simulations at temperatures below and above the P3HT melting point. The results show that the helical chain remains stable at room temperature both in vacuo and in amorphous surrounding, and promptly loses its structure at elevated temperatures. However, the amorphous surrounding inhibits the destruction of the helix at higher temperatures. In addition, it is shown that the electrostatic interactions do not significantly affect the stability of the helical structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2448–2456     

Development of synthetic double helical polymers and oligomers

There is growing interest in the design and synthesis of artificial helical polymers and oligomers, in connection with biological importance as well as development of novel chiral materials. Since the discovery of the helical structure of isotactic polypropylene, a significant advancement has been achieved for synthetic polymers and oligomers with a single helical conformation for about half a century. In contrast, the chemistry of double helical counterparts is still premature. This short review highlights the recent advances in the synthesis, structures, and functions of double helical polymers and oligomers, featuring an important role of supramolecular chemistry in the design and synthesis of double helices. Although the artificial double helices reported to date are still limited in number, recent advancement of supramolecular chemistry provides plenty of structural motifs for new designs. Therefore, artificial double helices hold great promise as a new class of compounds. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5195–5207, 2009     

Solvent‐tunable colors in imprinted helical structures on polymer template via multiple UV‐induced polymerization

A solvent tunable single‐layer polymer film with a multipitched photonic structure as a new photonic band gap material has been developed by imprinting the helical structures on polymer matrices through multiple photocrosslinking in an induced chiral nematic mesophase. Here, the polymer matrices themselves served as a chiral template, which exhibited Bragg reflections in the absence of both a chiral dopant and anisotropic materials because of the memory effects of the polymer network. Tuning of colors was achieved by making a refractive index contrast in the two periodic media of imprinted solid helical structure and the isotropic liquids that fill it. On incorporation of various isotropic liquids in the imprinted matrices, a sharp peak in the reflection spectrum shifted drastically, which indicated that the wavelength shifts strongly depended on the sort of liquids that filled the matrices. The effects of temperature on the imprinted polymer template feeding the various liquids were studied through the reflectance spectra. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Influence of solvents on the formation of ultrathin uniform poly(vinyl pyrrolidone) nanofibers with electrospinning

Although there have been many reports on the preparation and applications of various polymer nanofibers with the electrospinning technique, the understanding of synthetic parameters in electrospinning remains limited. In this article, we investigate experimentally the influence of solvents on the morphology of the poly(vinyl pyrrolidone) (PVP) micro/nanofibers prepared by electrospinning PVP solution in different solvents, including ethanol, dichloromethane (MC) and N,N‐dimethylformamide (DMF). Using 4 wt % PVP solutions, the PVP fibers prepared from MC and DMF solvents had a shape like a bead‐on‐a‐string. In contrast, smooth PVP nanofibers were obtained with ethanol as a solvent although the size distribution of the fibers was somewhat broadened. In an effort to prepare PVP nanofibers with small diameters and narrow size distributions, we developed a strategy of using mixed solvents. The experimental results showed that when the ratio of DMF to ethanol was 50:50 (w/w), regular cylindrical PVP nanofibers with a diameter of 20 nm were successfully prepared. The formation of these thinnest nanofibers could be attributed to the combined effects of ethanol and DMF solvents that optimize the solution viscosity and charge density of the polymer jet. In addition, an interesting helical‐shaped fiber was obtained from 20 wt % PVP solution in a 50:50 (w/w) mixed ethanol/DMF solvent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3721–3726, 2004     

Synthesis of helical poly(phenylacetylene)s bearing cinchona alkaloid pendants and their application to asymmetric organocatalysis

Four novel dynamic helical poly(phenylacetylene)s bearing cinchona alkaloids as pendant groups were synthesized starting from the commercially available cinchona alkaloids, cinchonidine, cinchonine, quinine, and quinidine, by the polymerization of the corresponding phenylacetylene monomers with a rhodium catalyst. These polymers exhibited an induced circular dichroism (ICD) in the UV–visible region of the polymer backbones in solution, resulting from the preferred‐handed helical conformation induced by the optically active cinchona alkaloid pendants. In response to the solvent used, their Cotton effect patterns and intensities were significantly changed accompanied by the changes in their absorption spectra probably due to the changes in their helical conformations, such as the inversion of the helical sense or helical pitch of the polymers. When these helical polymers were used as polymeric organocatalysts for the asymmetric conjugated addition and Henry reactions, the optically active products with a modest enantiomeric excess were obtained whose enantioselectivities were comparable to those obtained with the corresponding cinchona alkaloid‐bound monomers as the catalysts. However, we observed a unique enhancement of the enantioselectivity and a reversal of the stereoselectivity for some helical polymers, suggesting the important role of the helical chirality during the asymmetric organocatalysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Crystalline Organization in Syndiotactic Polystyrene Gels and Aerogels

The crystalline structure of syndiotactic polystyrene gels and aerogels has been investigated by using x-ray diffraction. Results show that, depending on the solvent, the crystalline structure of the junction zones of the gels is a clathrate phase or the solvent free orthorhombic β-form. For aerogels obtained from gels with a clathrate phase, the aerogel crystalline phase consists of the nanoporous δ-form while for aerogels obtained from gels with the β-form, the original crystalline structure is maintained.     

Plasticized microporous poly(vinylidene fluoride) separators for lithium‐ion batteries. I. Swelling behavior of dense membranes with respect to a liquid electrolyte—Characterization of the swelling equilibrium

Some poly(vinylidene fluoride) (PVdF) microporous separators for lithium‐ion batteries, used in liquid organic electrolytes based on a mixture of carbonate solvents and lithium salt LiPF₆, were characterized by the study of the swelling phenomena on dense PVdF membranes. We were interested in the evolution of the swelling ratios with respect to different parameters, such as the temperature, swelling solution composition, and salt concentration. To understand PVdF behavior in microporous membranes and, therefore, to have a means of predicting its behavior with different solvent mixtures, we correlated the swelling ratios in pure solvents and in solvent mixtures to the solvent–polymer interaction parameters and solvent–solvent interaction parameters. We attempted a parametric identification of swelling curves with a very simple Flory–Huggins model with relative success. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 532–543, 2004     

Optically active helical polymer from radical polymerization of menthyl vinyl ketone

Menthyl vinyl ketone (MVK) was radically polymerized to obtain a polymer with excess of one‐handed helical sense. Like as the anionically polymerized poly‐MVK, the radically polymerized poly‐MVK also kept stable one‐handed helical conformation in solvent. The optical rotation and the circular dichroism signal intensity of the radically polymerized poly‐MVK were larger than that of the anionically polymerized poly‐MVK. The molecular weight of the radically polymerized poly‐MVK was much larger than that of the THF‐soluble part of the anionically polymerized poly‐MVK. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010