Sulfonation of polystyrene: Toward the “ideal” polyelectrolyte

Sulfonation of narrow polydispersity polystyrene, PS, standards remains the method of choice for generating polystyrene sulfonate, PSS, samples with defined composition. Although a variety of sulfonation techniques have been described, relatively little is reported on the material obtained, which is used for so many studies on the fundamental behavior of polyelectrolytes. Here, we show that powdered polystyrene treated with concentrated sulfuric acid (96%) at 90 °C without catalyst yields fully sulfonated PSS. Extensive characterization with ¹H and ¹³C NMR as well as size exclusion chromatography coupled with static and dynamic light scattering shows no evidence of sulfone crosslinking or chain degradation under the conditions used. Though mono‐sulfonated as soon as it dissolves in the acid, the PSS contains about 6% meta substitution. Sulfonation kinetics for this heterogeneous reaction depend strongly on particle size, sulfuric acid content and temperature. For preparing perdeuterated PSS from the corresponding PS it is essential to employ D₂SO₄, as about half of the aromatic units undergo H/D exchange during sulfonation. The remaining ortho H/D may be exchanged with extended exposure to the concentrated sulfuric acid, but the meta site is deactivated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2416–2624     

“Directional” membrane permeability in polymer–vapor systems

A theoretical study is presented of the dependence of the vapor permeability of suitable nonhomogeneous polymer membranes on the sense of flow This is based on a simple model of a binary membrane in which the component phases A, B are either intimately mixed, with the composition of the mixture varying continuously across the membrane, or formed into a laminate AB. The influence of various parameters (which represent either properties of the component phases or the experimental conditions) on the magnitude of these flow reversal effects has been investigated. The results have proved useful as an indication of the capability of such membrane valves and of the conditions for optimum performance, as well as for the understanding of the behavior of experimental systems.     

Synthesis,purification, and characterization of “perfect” star polymers via “Click” coupling

The copper (I)‐catalyzed azide‐alkyne cycloaddition “click” reaction was successfully applied to prepare well‐defined 3, 6, and 12‐arms polystyrene and polyethylene glycol stars. This study focused particularly on making “perfect” star polymers with an exact number of arms, as well as developing techniques for their purification. Various methods of characterization confirmed the star polymers high purity, and the structural uniformity of the generated star polymers. In particular, matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry revealed the quantitative transformation of the end groups on the linear polymer precursors and confirmed their quantitative coupling to the dendritic cores to yield star polymers with an exact number of arms. In addition to preparing well‐defined polystyrene and poly(ethylene glycol)homopolymer stars, this technique was also successfully applied to amphiphilic, PCL‐b‐PEG star polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The Coordination Number – an “Inorganic Chameleon”

The purpose of the present article is to describe the changing ambiguous character of the term “coordination number” and its present-day definition in structural chemistry, particularly of typical solids (assemblies of particles with short-range and long-range order). An effort is made at the same time to describe the crystal structure of solids as simply as possible while also taking long-range order into account, i.e. by determining “effective” coordination numbers by the geometrical “polyhedron method” or from MAPLE (Madelung Part of Lattice Energy) values.     

Microstructure and fracture behavior of semicrystalline polymer–clay nanocomposites

The relationships between the microstructure and the fracture behavior of three polymer/clay nanocomposites were studied. Two different polymer matrices were chosen, namely polyamide‐6 and polyethylene (compatibilized with PE‐g‐MA or PE‐g‐PEo), to reach very different clay dispersion states. The microstructure was characterized in terms of polymer crystallinity, orientation of the polymer crystalline lamellae, clay dispersion state, and orientation of the clay tactoids. The mechanical behavior was characterized by tensile tests. The essential work of fracture (EWF) concept was used to determine the fracture behavior of the nanocomposites. Both tensile and EWF tests were performed in two perpendicular directions, namely longitudinal and transversal. It is shown that the fracture behaviors of the matrices mainly depend on the polymer crystalline lamellae orientation. For the nanocomposites, the relationships between the matrix orientation, the clay dispersion states, the values of the EWF parameters (w_e and βw_p), and their anisotropy are discussed. The results show that the lower the average clay tactoid thickness, the lower is the decrease of fracture performance for the nanocomposite and the more consumed energy as longer the path of the crack. Besides, a linear dependence of the anisotropy of the EWF parameters of the nanocomposites on the average clay aspect ratio is found. The more exfoliated the structure is, the less pronounced the anisotropy of the EWF parameters. Interestingly, it is thought that the average clay aspect ratio is the parameter representing the clay dispersion state that governs the fracture anisotropy of the nanocomposites (as the elastic properties determined by tensile tests). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1820–1836, 2008     

Modulating catalytic activity of polymer‐based cuAAC “click” reactions

The copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction is used to synthesize complex polymer architectures. In this work, we demonstrate the control of this reaction at 25 °C between polystyrene (PSTY) chains through modulating the catalytic activity by varying the combinations of copper source (i.e., Cu(I)Br or copper wire), ligand (PMDETA and/or triazole ligand), and solvent (toluene or DMF). The fastest rate of CuAAC was found using Cu(I)Br/PMDETA ligand in toluene, reaching near full conversion after 15 min at 25 °C. For the same catalysts system, DMF also gave fast rates of “click” (95% conversion in 25 min). Cu(0) wire in toluene gave a conversion of 98% after 600 min, a much higher rate than that observed for the same catalyst system used in DMF. When the PSTY had a chemically bound triazole ring close to the site of reaction, the rate of CuAAC in toluene increased significantly, 97% in 180 min at 25 °C, in agreement with our previously published results. This suggests that rapid rates can be obtained using copper wire and will have direct applications to the synthesis of compound where air, removal of copper, and reuse of the copper catalyst are required. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of polymer nanocomposites with “ultrahigh” refractive index

Nanocomposites of lead sulfide and several polymers, especially poly(ethyleneoxide), were prepared by coprecipitation of lead sulfide and polymer, followed by a drying and pressing procedure. Such nanocomposites consist of ca. 90% w/w (or ca. 50% v/v) lead sulfide, of particle dimensions of 2–40 nm. The refractive index of these materials is on the order of 3 and therefore, to the authors' best knowledge, is the highest reported for any polymer composite.     

On the “Wolfsberg–Helmholz Conjecture” of “Extended‐Hückel Theory”

After having reviewed some pioneer integral approximations closely related to Rüdenberg's expansions of one‐ and two‐electron orbital products, we apply the previously described “Implicit Multi‐Center Integration” techniques on Roothaan's “restricted” Fock‐matrix components over standard atomic orbital bases. The resulting compact forms are very similar to the well‐known “Wolfsberg–Helmholz Conjecture” of “Extended‐Hückel Theory,” which relates the various off‐diagonal matrix elements of “restricted” Fock‐type to their corresponding diagonal counterparts. In this way, a “nonempirical Extended‐Hückel Theory” can be created. © 2012 Wiley Periodicals, Inc.     

Synthesis and characterization of “umbrella” shaped polymers

A new strategy has been developed to prepare umbrella polymer, i.e. star polymers with one heteroarm. The synthesis uses living anionic polymerization to prepare a short segment of 1,2-polybutadiene at the end of a linear polystyrene. The vinyl groups of 1,2-polybutadiene are hydrosilylated with dichloro(methyl)silane. The umbrella polymer is then formed by nucleophilic displacement of the silicon-chlorine with 1,4-polybutadienyllithium. An umbrella polymer with poly(2-vinylpyridine) arms is prepared in the same way after hydrosilylation with chlorodimethylsilane. The umbrella polymers are characterized by light scattering, size-exclusion chromatography (SEC), ultraviolet/visible spectroscopy (UV/vis), nuclear magnetic resonance (NMR) and intrinsic viscosity.     

Concept of the “stability” of the quantum mechanical state

A new concept of the “stability” of the quantum mechanical state is presented. This concept is closely related to the hydrodynamical theory of quantum mechanics. For charged particles, the “stability” against the application of the external electromagnetic field is examined. Under a nonlinear interaction, a new type of the solitonlike phenomenon is shown as a novel, illustrative example of the “stable” state. An extension for the relativistic treatment is also examined.     

Recent developments in rubber processing,leading to new applications such as the “green tyre”

Rubber articles derive most of their mechanical properties from the admixture of reinforcing fillers. Most commonly, carbon black is used as reinforcing filler. If silica is used instead, tyres made with such rubber compounds may exhibit a rolling resistance reduction by ca. 30%, which translates in substantial fuel savings of a car. Such silicas are far more difficult to mix with rubber than carbon black. Coupling agents are used as a surface modification of the filler to enhance compatibility with the polymer. Additionally they improve the ease of mixing with the rubber. The development of proper coupling agents combined with improved mixing techniques has contributed to the final break-through of the silicareinforced “Green Tyre”.     

“Superpermeability” and “pumping” of atomic hydrogen through palladium membranes

Permeation of atomic as well as molecular hydrogen through palladium membranes has been investigated experimentally in the temperature range from room temperature to 200 °C and at a higher incident flux of hydrogen atoms on palladium surface than in previous studies. The results demonstrate that phenomena of ‘superpermeability’ and ‘pumping’ of atomic gases through metal membranes are of a common nature. A theoretical model based on chemical thermodynamics and diffusion theory adequately describes the quantitative relationships observed in experiments. It was found that permeability of atomic hydrogen depends strongly on the magnitude of surface incident flux and membrane temperature.     

Transformation of “living” carbocationic and other polymerizations to controlled/“living” radical polymerization

Transformation of “living” carbocationic polymerization of styrene and isobutene to controlled atom transfer radical polymerization (ATRP) is described and formation of the corresponding AB and ABA block copolymers with styrene (St), methyl methacrylate (MMA, methyl acrylate (MA) and isobornyl acrylate (IBA) was demonstrated. A similar approach was applied to the cationic ring opening polymerization of tetrahydrofuran leading to the AB and ABA block copolymers with St, MMA and MA using ATRP. Site transformation approach was also used for the ring opening metathesis polymerization of norbornene and polycondensation systems using polysulfone as an example. In both cases, AB and ABA block copolymers were efficiently formed with styrene and acrylates.     

Preparation of the polymer–clay nanocomposites in exfoliated state by interface stabilization

To suppress the repulsive interfacial energy between hydrophilic clay and a hydrophobic polymer matrix for polymer–clay nanocomposites, a third component of amphiphilic nature such as poly(?‐caprolactone) (PCL) was introduced into the styrene–acrylonitrile copolymers (SAN)/Na‐montmorillonite system. Once ?‐caprolactone was polymerized in the presence of Na‐montmorillonite, the successful ring‐opening polymerization of ?‐caprolactone and the well‐developed exfoliated structure of PCL/Na‐montmorillonite mixture were confirmed. Thereafter, SAN was melt‐mixed with PCL/Na‐montmorillonite nanocomposite, and the SAN matrix and PCL fraction were completely miscible to form a homogeneous mixture with retention of the exfoliated state of Na‐montmorillonite, exhibiting that PCL effectively stabilizes the repulsive polymer–clay interface and contributes to the improvement of the mechanical properties of nanocomposites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 246–252, 2004