Syndiotactic Polystyrene Research Articles

Etched Fibers of Syndiotactic Polystyrene with Nanoporous-Crystalline Phases

Nanoporous-crystalline (δ and e form) fibers of syndiotactic polystyrene (s-PS) have been prepared from melt-spun fibers by different guest-induced cocrystallization procedures. Their crystal structure, morphology, and uptake of volatile organic compounds (VOC) have been investigated. The use of chloroform, i.e., of a molecule being a suitable guest for both δ and e forms but also a strong solvent for s-PS, leads to nanoporous-crystalline fibers with VOC sorption kinetics much faster than for s-PS nanoporous-crystalline powders and films and comparable with those of nanoporous-crystalline s-PS aerogels. This unexpected phenomenon is due to etching of the melt-spun fibers by chloroform that exposes internal fibrils and markedly increases the surface area up to 165 m2/g. Etched δ form fibers are more effective for sorption of most pollutants while etched e form fibers are much more effective in sorption of long organic molecules, like n-decane. Outstanding sorption properties, simple preparation processes (...

Progressive Relaxation Behavior and Relaxation Dynamics of sPS Gels upon Controlled Heating.

Progressive relaxation behavior of syndiotactic polystyrene (sPS) chains in sPS gel was detected in the course of melting via the application of intrinsic fluorescence and fluorescence anisotropy techniques. The melting process included a dissociative process of the network at lower temperature and a relaxation process from helix to worm-like chains at higher temperature. The dynamics of structural relaxation behavior was discovered by intrinsic fluorescence technique, and an abrupt bend emerged at 58 °C on the Arrhenius plot. At temperatures lower than 58 °C, only the dissociation of the helical structure existed and the rate of relaxation from helix to worm-like conformation was negligible. At temperatures higher than 58 °C, the transition from helical chain to worm-like chain was the rate-determining step. The intrinsic fluorescence technique demonstrated its practicability in detecting kinetic processes of sPS/chloroform gel in the course of melting.

Effect of tacticity on the structure and glass transition temperature of polystyrene adsorbed onto solid surfaces.

We have carried out atomistic (all-atom) molecular dynamics simulations to investigate the effect of tacticity on the structure and glass transition temperature (Tg) of polystyrene (PS) thin films adsorbed on two distinct types of solid substrates. The systems consist of thin films made of atactic, isotactic, and syndiotactic PS chains supported by graphite or hydroxylated α-quartz substrates, which are known to be atomically flat but chemically and structurally different. We have observed a marked dependence of the film structure on substrate type as well as on tacticity. For instance, rings' orientation near substrate surfaces depends on substrate type for atactic PS and isotactic PS films, while no such dependence is observed for syndiotactic PS films whose interfacial structure seems to result from their propensity to adopt the trans conformation rather than their specific interaction with the substrates. Moreover, our results indicate that glass transition temperatures of substrate supported polystyrene films are higher compared to those of the corresponding free-standing films. More specifically, PS films on graphite exhibit larger Tg values than those on α-quartz, and we have noticed that syndiotactic PS has the largest Tg irrespective of the substrate type. Furthermore, the local Tg in the region of the film in contact with the substrates shows a strong tacticity and substrate dependence, whereas no dependencies were found for the local Tg in the middle of the film. Substrate-film interaction energy and chains' dynamics near substrate-film interfaces were subsequently investigated in order to substantiate the obtained Tgs, and it was found that films with higher Tgs are strongly adsorbed on the substrates and/or exhibit smaller interfacial chains' dynamics essentially due to steric hindrance.

Structure and morphology of model polymer electrolyte membranes based on sulfonated syndiotactic-polystyrene in the δ co-crystalline phase resolved by small-angle neutron scattering

Syndiotactic polystyrene (s-PS) is able to form different kinds of co-crystalline phases with guest molecules of different size, shape and property. Several advanced materials have been produced starting from s-PS co-crystalline films. In particular, sulfonated s-PS (s-sPS) can be used as proton-conductive membrane in some fuel cells applications, as it presents high proton conductivity (comparable with Nafion). Besides, it shows a high chemical and thermo-mechanical stability and a low cost. The morphology of different s-PS clathrates and the structural behavior of s-sPS upon hydration can be thoroughly understood by SANS. In fact, exploiting the neutron contrast variation between various hydrogenated and deuterated components of s-PS and s-sPS clathrates, additional and unique information about the distribution of guest molecules in the crystalline and amorphous regions and about the hydrated domains of the polymer were obtained. Moreover, using uni-axially deformed films the occurrence and distribution of scattering features from typical morphologies on specific directions and sectors of detection plan enable an accurate structural study of such complex polymeric systems. We report in the present paper a detailed SANS investigation of s-PS films, starting from their crystallization with guest molecules to the subsequent sulfonation and hydration. FT-IR, neutron PGAA, WAXD and cryo-TEM were used complementary to SANS to check the state of the samples after each step of the treatment process and to obtain additional structural information as support for the understanding of the SANS data. The current experimental analysis has highlighted that the morphology of these polymeric films is characterized by hydrated channels in the bulk amorphous phase alternated to stacks of crystalline lamellae, oriented along the stretching direction.

Functionalization of Syndiotactic Polystyrene via Superacid-Catalyzed Friedel–Crafts Alkylation

Crystalline syndiotactic polystyrene (sPS) was functionalized by superacid-catalyzed Friedel–Crafts alkylation. Once a tertiary carbocation is generated by the reaction of tertiary alcohols and triflic acid, it subsequently reacted with aromatic ring of sPS, forming alkyl functionalized sPS. Various functional groups were incorporated into the phenyl ring of sPS using different substrates of tertiary alcohols including tertiary butanol, 2-methyl-2-butanol, and 2-methyl-2-hexanol. Degree of functionalization was conveniently tunable by changing the ratio of tertiary alcohol to styrene unit, and a maximum 80% of styrene rings was functionalized. Thermal properties of the functionalized sPSs were investigated by differential scanning calorimetry. Glass transition temperature and melting temperature of sPS were reduced after the modification.

Synthesis, characterization and reactivity of rare-earth metal amide complexes supported by pyrrolyl-substituted cyclopentadienyl ligand

Absaact Amine elimination between rare-earth metal tris(amide) complexes Ln [N(SiHMe2)2]3 (THF)x and 1 equiv. of pyrrolyl-substituted cyclopentadienyl ligand C4H4NSiMe2C5Me4H was investigated. Reaction of C4H4NSiMe2C5Me4H and Ln [N(SiHMe2)2]3 (THF)x with small metals afforded the half-sandwich rare-earth metal bis(silylamide) complexes (C4H4NSiMe2C5Me4)Ln [N(SiHMe2)2]2 (Ln = Sc (1), Y (2)), while the same reaction using La [N(SiHMe2)2]3 (THF)2 isolated lanthanum mono-silylamide complex [C5Me4SiMe2N(SiHMe2)2]La [N(SiHMe2)2](C4H4N) (3). These complexes were characterized by elemental analysis and NMR spectroscopy. 1 and 3 were structurally authenticated by single crystal X-ray diffraction. The ternary catalyst systems of 1 or 2/AliBu3/[Ph3C][B(C6F5)4] showed activity towards styrene polymerization to give pure syndio-tactic polystyrenes (rrrr > 99%).

The Effects of Compatibilizers on the Morphological, Mechanical, and Optical Properties of Biaxially Oriented Poly(ethylene terephthalate)/Syndiotactic Polystyrene Blend Films

In this study, the effects of three different types of compatibilizers on the morphological, mechanical, and optical properties of poly(ethylene terephthalate) (PET) and syndiotactic-polystyrene (s-PS) (70/30, wt%) blends and biaxially oriented blend films of the two polymers were investigated. The morphological results of the PET/s-PS (70/30) blends revealed that when the 5 phr polystyrene-g-oxazoline (PS-g-OXA) was used as a compatibilizer, the domain size showed minimum. The mechanical studies of the PET/s-PS (70/30) blends showed that when 5 phr PS-g-OXA was used, increased tensile strength was obtained. The transmittance of the blend film showed the highest value (83.7%) for the biaxially oriented PET/s-PS (70/30) blend films with the PS-g-OXA (5 phr), compared with that of the blends without compatibilizer (70.8%), or with the styrene-co-maleic anhydride as a compatibilizer, at the wavenumber of 600 nm. The tensile strength of the biaxially oriented PET/s-PS (70/30) blend films also showed the highest value when PS-g-OXA (5 phr) was used as a compatibilizer. The morphological, optical, and mechanical results of the PET/s-PS (70/30) blends and biaxially oriented blend films of the two polymers showed that PS-g-OXA was the most effective compatibilizer, and that the optimum compatibilizer content was 5 phr.

Removal of phenol in aqueous media by N-doped TiO2 based photocatalytic aerogels

In this work, composite monolithic aerogels based on syndiotactic polystyrene (s-PS) and N-doped TiO2 (NdT) photocatalyst characterized by high surface areas (up to 280 m2/g) and low density (0.1 g cm−3) are presented. These aerogels are obtained by supercritical carbon dioxide extraction of NdT/s-PS gels prepared by s-PS dissolution with NdT in suitable organic solvent. X-ray diffraction measurements and SEM analysis showed that a highly efficient dispersion of NdT nanoparticles can be achieved in the composite aerogels avoiding thus the aggregation phenomena that typically occur when the photocatalyst is used in slurry reactors. The optimization of NdT amount dispersed in s-PS was evaluated using phenol as model pollutant both under UV and visible light irradiation. The photoactivity of NdT/s-PS samples increased with increase of the amount of NdT dispersed in aerogel matrix up to NdT/s-PS weight ratio equal to 10/90 (10NdT/s-PS), for which the highest phenol degradation and TOC removal were achieved both under UV and visible light irradiation. Moreover, the photocatalytic activity of the optimized photocatalyst 10NdT/s-PS did not change significantly after several reuses underlining that any NdT particles are removed from the polymeric matrix.

Packaging technology for improving shelf‐life of fruits based on a nanoporous–crystalline polymer

ABSTRACTThe ability of films with an active layer of nanoporous–crystalline syndiotactic polystyrene (s‐PS) to prolong shelf‐life, not only of climacteric but also of non‐climacteric fruits, is discussed. Studies on oxygen and carbon dioxide concentrations in the environment of packaged fruits as well as in s‐PS active layers have been combined. Reported results indicate that prolonged shelf‐life can be associated with large increases and decreases of carbon dioxide and oxygen concentrations inside the package, respectively. These data are consistent with a higher barrier offered to both gases by nanoporous–crystalline s‐PS layers. This barrier phenomenon is due to reduction of gas diffusivity typical of nanoporous–crystalline polymer films, which is further enhanced by orientation, parallel to the film plane, of crystalline planes of closely packed s‐PS helices. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46256.

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene γ Form

The crystallization behavior of syndiotactic polystyrene (sPS) γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl’s crystallization theory. On the basis of the differential scanning calorimetric results, it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness, which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization. Further temperature dependent small-angle X-ray scattering (SAXS) measurement revealed the evolution of the γ form lamellae upon heating until phase transition, involving three different regimes: lamellae stable region (25−90 °C), melt-recrystallization region (90−185 °C) and pre-phase transition region (185−195 °C). As a result, recrystallization line, equilibrium recrystallization line and melting line were developed for the sPS γ form crystallization process. Since the melt of γ form involved a γ-to-α/β form phase transition, the melting line was also denoted as the phase transition line in this special case. Therefore, the equilibrium crystallization temperature and melting (phase transition) temperatures were determined at around 390 and 220 °C on the basis of the thermodynamic phase diagram of the sPS γ form.

Lamellar Thickness Dependence of Crystal Modification Selection in the Syndiotactic Polystyrene γ-to-α/β Phase Transition Process

The syndiotactic polystyrene (sPS) γ-to-α/β phase transition was investigated using temperature-dependent synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurement. The sPS γ form samples, which were obtained from acetone solvent induced crystallization followed by annealing at various temperatures (Ta), exhibited a regular manner on the selection of the α or β crystal modification during the phase transition process. As the Ta was increased from 25 to 150 °C, the weight fraction of β form in bulk sPS decreased from 55% to 0%, but that of the α form increased from 45% to 100%. In other words, the α form became the dominating crystalline modification at higher Ta. The lamellar thickness (dc) of the γ form at the initial state (before heating) ranged from 4.4 to 5.8 nm, and the weight crystallinity (Xc) was between 0.52 and 0.64. However, the dc values of the γ form at the final state (before γ-to-α/β phase transition) were very close for the samples pretreated at d...

Aerogels of hierarchically porous syndiotactic polystyrene with a dielectric constant near to air

Syndiotactic polystyrene aerogels with hierarchical micro, meso and macroporosity possess an ultra low dielectric constant very near to air.

Convenient synthesis of versatile syndiotactic polystyrene materials containing pendant alkenyl groups with a scandium catalyst system

The syndioselective copolymerization of styrene with five alkenyl functionalized styrenic monomers, with the use of a scandium catalyst, produced a new family of versatile syndiotactic polystyrene materials with pendant alkenyl groups.

Blocky bromination of syndiotactic polystyrene via post-polymerization functionalization in the heterogeneous gel state

This work demonstrates the successful blocky bromination of syndiotactic polystyrene (sPS-co-sPS-Br) copolymers containing 6–30 mol% p-bromostyrene units, using a post-polymerization functionalization method conducted in the heterogeneous gel state.

Thermal effects on the strain-induced β to α form crystalline structural transition of solid-state syndiotactic polystyrene

Thermal effects on the strain-induced structural transition from β-form to α-form crystals of syndiotactic polystyrene (sPS) were investigated by changing the stretching temperature and the annealing temperature. When sPS was stretched at lower temperature (near the glass transition temperature (Tg) of sPS (∼130 °C)), the crystalline structural transition was incomplete, producing fragmented β-form and mesomorphic α-form crystals. Stretching at higher temperature facilitated the crystalline structural transition from β to α. For the sPS specimen stretched at 130 °C, the β-form crystals broke into small pieces, simultaneously creating mesomorphic α-form crystals. After annealing, the fragmented β-form crystals and the mesomorphic α-form crystals were reorganized to become complete crystals. The reorganization became more pronounced as the annealing temperature increased. The main role of the mechanical strain and the heat, therefore, could be the destruction of β-form crystals to produce fragmented β-form crystals and mesomorphic α-form crystals, and the formation of complete crystals, respectively.

Syndiotactic polymerization of styrene and copolymerization with ethylene catalyzed by chiral half-sandwich rare-earth metal dialkyl complexes

The syndiotactic polymerization of styrene (St) and the copolymerization of St with ethylene (E) were carried out by using a series of chiral half-sandwich rare-earth metal dialkyl complexes (Cp x *) as the catalysts. The complexes are Ln(CH2SiMe3)2(THF) (1−4: Ln = Sc (1), Ln = Lu (2), Ln = Y (3), Ln = Dy (4)) bearing chiral cyclopentadienyl ligand containing bulky cylcohexane derivatives in the presence of activator and Al i Bu3. For the St polymerization, a high activity up to 3.1 × 106 g of polymer molLn−1·h−1 and a high syndiotactic selectivity more than 99% were achieved. The resulting syndiotactic polystyrenes (sPSs) have the molecular weights (Mn) ranging from 3700 g·mol−1 to 6400 g·mol−1 and the molecular weight distributions (Mw/Mn) from 1.40 to 5.03. As for the copolymerization of St and E, the activity was up to 2.4 × 106 g of copolymer molSc−1·h−1·MPa−1, giving random St-E copolymers containing syndiotactic polystyrene sequences with different St content in the range of 15 mol%−58 mol%. These results demonstrate that the bulky cyclopentadienyl ligands of the chiral half-sandwich rare-earth metal complexes effectively inhibit the continued insertion of St monomers into the (co)polymer chain to some extent in comparison with the known half-sandwich rare-earth metal complexes.

Stereoselective Copolymerization of Styrene with Terpenes Catalyzed by an Ansa-Lanthanidocene Catalyst: Access to New Syndiotactic Polystyrene-Based Materials

The copolymerization of bio-renewable β-myrcene or β-farnesene with styrene was examined using an ansa-neodymocene catalyst, affording two series of copolymers with high styrene content and unprecedented syndioregularity of the polystyrene sequences. The incorporation of terpene in the copolymers ranged from 5.6 to 30.8 mol % (β-myrcene) and from 2.5 to 9.8 mol % (β-farnesene), respectively. NMR spectroscopy and DSC analyses suggested that the microstructure of the copolymers consists of 1,4- and 3,4-poly(terpene) units randomly distributed along syndiotactic polystyrene chains. The thermal properties of the copolymers are strongly dependent on the terpene content, which is easily controlled by the initial feed. The terpolymerization of styrene with β-myrcene in the presence of ethylene was also examined.

Open Cell Aerogel Foams via Emulsion Templating.

The water-in-oil emulsion-templating method is used in this work for fabrication of open cell aerogel foams from syndiotactic polystyrene (sPS). A surfactant-stabilized emulsion is prepared at 60-100 °C by dispersing water in a solution of sPS in toluene. sPS gel, formed upon cooling of the emulsion to room temperature, locks the water droplets inside the gel. The gel is solvent exchanged in ethanol and then dried under supercritical condition of carbon dioxide to yield the aerogel foams. The aerogel foams show a significant fraction of macropores with a diameter of a few tens of micrometers, defined as macrovoids that originated from the emulsified water droplets. In conjunction, customary macropores of diameter 50-200 nm are derived from sPS gels. The macrovoids add additional openness to the aerogel structures. This paper evaluates the structural characteristics of the macrovoids, such as diameter distribution, macrovoid interconnect density, and skin layer density, in conjunction with the final aerogel foam properties.

Circularly polarized luminescence of syndiotactic polystyrene

Syndiotactic polystyrene (s-PS) films, when crystallized from the amorphous state by temporary sorption of non-racemic guest molecules (like carvone) not only exhibit unusually high optical activity, both in the UV–Visible and Infrared ranges, but also present circularly polarized luminescence (CPL) with high dissymmetry ratios (g = ΔI/I values in the range 0.02–0.03). Experimental evidences provide support, rather than to the usual molecular circular dichroism, to a supramolecular chiral optical response being extrinsic to the site of photon absorption and emission, possibly associated with a helical morphology of s-PS crystallites.

Polymerization of Aniline in Tubular Cavities of the Crystalline Phase of Syndiotactic Polystyrene: Proposal of a Preparation Method of Sophisticated Polymer Composites.

Syndiotactic polystyrene (SPS) has a unique crystalline phase, named ε, that has a tubular cavity inside. We connected these cavities by optimizing the solvent used to process the films and to polymerize aniline within these channeling cavities only by immersing the films in degassed hydrochloric acid solutions of ammonium persulfate. We succeeded in fixing pentameric to octameric oligoaniline in the cavities of the SPS ε crystalline phase. This is a new and sophisticated preparation method of polymer composites between SPS and linear oligomers/polymers within its long-connected tubular cavities.