Simulation of mechanical properties of oriented glassy polystyrene

Mechanical properties of processed polymers depend sensitively on their microstructure. In order to understand how different processing conditions affect the mechanical properties of polymers, one needs a means to describe the process-induced microstructure. Because the characteristic relaxation times of processed polymer chains often span several orders of magnitude, it is commonly the case that partial relaxation of the chains is frozen into the final product. We report results of molecular simulations by the Semi-Grand Canonical Monte Carlo (SGMC) method to study the orientation-dependent elasticity of glassy polystyrene as a function of both the system-average degree of orientation and the degree of relaxation of chain ends at a constant average orientation, in accord with the tube model of Doi and Edwards. Our simulations reproduce quantitatively the experimentally observed trends in the tensile modulus E₁₁ as a function both of the system-average orientation and of the inhomogeneity of the orientation along the chain due to rapid relaxation of chain ends. The results show that the partial relaxation of the polymer chains is sufficient to explain the observed variation of mechanical properties for samples that differ in processing history, yet have the same observed birefringence.     

Effects of orientation on mechanical properties of uniaxially oriented polystyrene films

Oriented samples of polystyrene have been produced by drawing at temperatures just above the glass transition range. Birefringence measurements have been used to characterise the degree of orientation. Mechanical measurements of elastic modulus and tensile yield stress have been made in the direction of drawing and it has been established that the birefringence value does not uniquely determine the mechanical properties—samples drawn to a high draw ratio at high temperatures have a higher modulus and yield stress than samples drawn at lower temperatures and lower draw-ratios to the same birefringence. The results are explained qualitatively by the convective constraint release theory of McLeish et al.     

Surface modification of polystyrene particles for specific antibody adsorption

Biospecific interactions between biological molecules such as antibodies and polymer particles bearing the chemical groups capable of mimicking natural bioactive sites were investigated. Polystyrene particles were substituted by various amino-acids and exposed to antiviral antibodies directed against two different enveloped viruses related to the Arbovirus group. Functionalization yields of polystyrene particles were found to depend on the nature of the amino-acid. The interactions between the functionalized latexes and the antiviral antibodies were systematically compared to the interactions with the ‘non-antiviral’ antibodies. Results indicated that the adsorption of antiviral antibodies depends on the chemical composition of the polystyrene particles surface, i.e. substituted amino acid, the amount of substitution and the surface charge density of the polymer particles. These differences are illustrated by variation in the immunoglobulin adsorption capacities and in the affinity constants. Therefore amongst the assessed polystyrene derivatives, some precise compositions were shown to display specificity to one antiviral antibody whereas other compositions displayed specificity to both antiviral antibodies but with different affinities.     

Reliability of molecular weight determination methods for oligomers investigated using certified polystyrene reference materials

Using polystyrene certified reference materials (CRMs) whose molecular weights range from 500 to 2400, we investigated the reliability of molecular weight determination by size-exclusion chromatography (SEC), SEC coupled with multi-angle light scattering detection (SEC-MALS), conventional static light scattering (SLS), matrix-assisted laser desorption/inonization time-of-flight mass spectrometry (MALDI-TOFMS), and ¹H NMR. Average molecular weights determined by these methods were compared with the certified values which were determined by supercritical fluids chromatography with relative standard uncertainty less than 1%. The comparison showed that recent SEC with calibration constructed by uniform polystyrenes can provide just the same average molecular weights as certified ones within the standard uncertainty. ¹H NMR was also found to be a powerful technique to determine number-average molecular weight accurately. Average molecular weights measured by SEC-MALS and SLS nearly agreed with certified values except for lower molecular weights. Although MALDI-TOFMS provided average molecular weights in agreement with certified values, the polydispersity given by MALDI-TOFMS were found to be very small for all the polystyrenes.     

Functionalized polystyrene latex particles as substrates for ATRP: Surface and colloidal characterization

In this work, the process for producing polystyrene particles surface functionalized with a thin shell of ATRP initiator polymerized alone or along with styrene and a crosslinker, is presented. Copolymerization of styrene and acrylic end-capped ATRP initiator to generate a thin shell on the fully polymerized core particles suffered from secondary nucleation owing to their possible incompatibility with the core particles and their own colloidal stability. One step functionalization processes, where the shell forming monomers are added directly to the 70% polymerized core particles, lead to significant changes in the resulting particle morphologies. The shot addition of these monomers led to a very uniform surface morphology without any secondary nucleation owing to quick coalescence of the secondary particles on the soft surface of the seed particles. Addition of crosslinker to the system helped in effectively eliminating the smaller particles generated due to secondary nucleation along with the chemical networking.     

Fabrication and photocatalytic performance of Sn-doped titania hollow spheres using polystyrene as template

Sn-doped anatase hollow spheres were fabricated using a template method involving polystyrene spheres as core and anatase coating as shell. The synthesis route included the preparation of PS spheres, followed by their coating by Sn-doped TiO₂ sol-gel precursor and subsequent removal of the PS cores by pyrolysis and recrystallization at 500 °C for 2 h. The observation of minor amounts of rutile suggests that Sn promotes the anatase → rutile phase transformation. At doping levels of ≤ 1.0 mol% Sn, the unsaturated solubility and increasing defect densities enhanced nucleation. At 1.0–2.0 mol% Sn, the solubility remained unsaturated but increasing Sn incorporation reduced crystallinity owing to lattice deformation and partial amorphization. At 2.0–3.0 mol% Sn, solid solution saturation occurred, resulting in excess dopant precipitation, leading to grain boundary pinning and partial blockage of surface-active sites. Ionic radii, thermodynamic, phase equilibria, intervalence charge transfer, and defect chemistry considerations suggest that Sn⁴⁺ exhibits substitutional solid solubility in the TiO₂ lattice. The photocatalytic performance was in the order 1.0 > 1.2 > 1.5 ≈ 0.7 > 2.0 > 0.0 > 3.0 mol% Sn. This ranking is consistent with the dominant role of crystallinity such that, at ≤ 1.0 mol% Sn, the performance increased owing to enhanced nucleation from low defect density and increasing crystallinity while, at 1.0–2.0 mol% Sn, the performance decreased from increased lattice strain and effective partial amorphization, and, at 2.0–3.0 mol% Sn, it decreased from maximal lattice strain and blockage of active sites.     

A novel route for synthesis of cross-linked polystyrene copolymer beads with tunable porosity using guar and xanthan gums from bioresources as alternative synthetic suspension stabilizers

Cross-linked polymer beads with different cross-linking agent loading were prepared by carrying out cross-linking suspension copolymerization of styrene-divinylbenzene (St- DVB) monomers using guar gum (GG) and xanthan gum (XG) from bioresources as eco-friendly suspension biopolymer stabilizers in the presence of non reactive diluents. The effects of GG and XG as suspension biostabilizers on the characteristics of the styrene copolymer beads were investigated regarding thermal properties, porosity characteristics, solvent swelling ratio, and surface morphologies using TGA, DSC, XRD, SEM, BET analyses. Spherical and regular beads with smooth surface were produced and the average particle size was in the range 170–290 μm (50–80 mesh size). The porosity characteristics of the produced beads including surface area and pore volume were in range 0.45 m²/g and 32–45 ml/g, respectively. Overall, the present article provided a novel route to prepare cross-linked polystyrene copolymer beads with tunable porosity suitable for catalyst support.     

Effect of carbon coating on low temperature electrochemical performance of LiFePO4/C by using polystyrene sphere as carbon source

Carbon perfectly coated LiFePO₄ cathode materials are synthesized by carbon-thermal reduction method using polystyrene (PS) spheres as carbon source. The PS spheres with diameters of 150–300 nm used for the pyrolysis reaction not only inhibit the particle growth but also lead to uniform distribution of carbon coating on the surface of LiFePO₄ particles. Rate capability and cycling stability of LiFePO₄/C with the carbon contents ranging from 1.4 wt% to 3.7 wt% are investigated at −20 °C. The LiFePO₄/C with 3.0 wt% C exhibits excellent electrochemical capability at low temperature, which delivers 147 mAh g⁻¹ at 0.1 C. After 100 cycles at a charge–discharge rate of 1 C, there is still 100% of initial capacity retained for the LiFePO₄/C electrode at −20 °C. According to the transmission electron microscope analysis and cyclic voltammetry measurement, this can be attributed to the good carbon coating morphology and optimal carbon coating thickness.     

Supramolecular Chemistry in Solid State Materials such as Metal-Organic Frameworks

Supramolecular chemistry has enriched the scientific research for more than fifty years reaching one of its summits in 2016, when the Chemistry Nobel Prize was awarded for the design and synthesis of molecular machines, in which host-guest chemistry plays a fundamental role. Recently, the groups of Omar Yaghi and Fraser Stoddart, among others, have demonstrated that this chemistry can be extended to the pores of metal-organic frameworks (MOFs). This heterogenization of supramolecular chemistry can be achieved through the incorporation of macrocycles to the organic struts of these highly porous and crystalline materials. Throughout this short review we summarize interesting examples of selective recognition by naturally occurring and synthetic macrocycles in solution and solid state; and later we survey important milestones to achieve specific recognition sites and develop host-guest chemistry at the pores of MOFs. This summary contains examples of different synthetic strategies to incorporate macrocycles to solid state materials, and in particular, to prepare supramolecular MOFs with particular properties and related applications. Specifically, the revised research includes the incorporation of both naturally occurring and synthetic macrocycles to solid state materials such as polymers, metal nanoparticles, etc., as prelude of the solid phase recognition studied in MOFs. An important number of the contributions presented here feature porous solids with smooth access to the host's cavity incorporated in the pores, allowing specific recognition of guest molecules. This smooth access to those active recognition sites in materials with extremely high surface area such as MOFs, open the possibility to develop the next generation of frontier materials with application in fields such as selective capture of water toxins and heterogeneous catalysis, among others.     

Imidazole-based dithienylethenes as a selective chemosensors for iron(III) ions

Four novel imidazole-based dithienylethenes have been successfully synthesized in good yields. Their structures have been confirmed by NMR spectrometry, mass spectrometry, and elemental analyses. UV/Vis absorption spectra indicated that these dithienylethenes can easily isomerize between the open-ring and closed-ring isomers upon irradiation with UV or visible light in solution, and that the respective closed-ring isomers show decreased fluorescence properties compared with the open-ring isomers. Moreover, the open-ring and closed-ring isomers display high selectivity toward Fe³⁺, such that the addition of Fe³⁺ obviously suppresses their fluorescence intensity.     

Designing a C84 fullerene as a specific voltage-gated sodium channel blocker

Fullerene derivatives demonstrate considerable potential for numerous biological applications, such as the effective inhibition of HIV protease. Recently, they were identified for their ability to indiscriminately block biological ion channels. A fullerene derivative which specifically blocks a particular ion channel could lead to a new set of drug leads for the treatment of various ion channel-related diseases. Here, we demonstrate their extraordinary potential by designing a fullerene which mimics some of the functions of μ-conotoxin, a peptide derived from cone snail venom which potently binds to the bacterial voltage-gated sodium channel (Na_vAb). We show, using molecular dynamics simulations, that the C₈₄ fullerene with six lysine derivatives uniformly attached to its surface is selective to Na_vAb over a voltage-gated potassium channel (Kv1.3). The side chain of one of the lysine residues protrudes into the selectivity filter of the channel, while the methionine residues located just outside of the channel form hydrophobic contacts with the carbon atoms of the fullerene. The modified C₈₄ fullerene strongly binds to the Na_vAb channel with an affinity of 46 nM but binds weakly to Kv1.3 with an affinity of 3 mM. This potent blocker of Na_vAb may serve as a structural template from which potent compounds can be designed for the targeting of mammalian Nav channels. There is a genuine need to target mammalian Nav channels as a form of treatment of various diseases which have been linked to their malfunction, such as epilepsy and chronic pain.     

Cu(II)‐incorporated,histidine‐containing,magnetic‐metal‐complexing beads as specific sorbents for the metal chelate affinity of albumin

N‐Methacryloyl‐(L )‐histidine methyl ester (MAH) was synthesized from metharyloyl chloride and histidine. Spherical beads with an average size of 150–250 μm were obtained by the suspension polymerization of ethylene glycol dimethacrylate and MAH in an aqueous dispersion medium. Magnetic poly(ethylene glycol dimethacrylate‐co‐N‐Methacryloyl‐(L )‐histidine methyl ester) [m‐p(EGDMA‐co‐MAH)] microbeads were characterized with swelling tests, electron spin resonance, elemental analysis, and scanning electron microscopy. The specific surface area of the beads was 80.1 m²/g. m‐p(EGDMA‐co‐MAH) microbeads with a swelling ratio of 40.2% and 43.9 μmol of MAH/g were used for the adsorption of bovine serum albumin (BSA) in a batch system. The Cu(II) concentration was 4.1 μmol/g. The adsorption capacity of BSA on the Cu(II)‐incorporated beads was 19.2 mg of BSA/g. The BSA adsorption first increased with the BSA concentration and then reached a plateau, which was about 19.2 mg of BSA/g. The maximum adsorption was observed at pH 5.0, which was the isoelectric point of BSA. The BSA adsorption increased with decreasing temperature, and the maximum adsorption was achieved at 4°C. High desorption ratios (>90% of the adsorbed BSA) were achieved with 1.0M NaSCN (pH 8.0) in 30 min. The nonspecific adsorption of BSA onto the m‐p(EGDMA‐co‐MAH) beads was negligible. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2669–2677, 2004