Atomistic simulations of the surfaces of thin films of random copolymers

Amorphous thin films of styrene-butadiene and styrene-butadiene-acrylonitrile copolymers containing a small amount of acrylic acid are generated using molecular dynamics and energy minimization simulations. The structure of the films shows an interior region of bulk density and a thin outer surface layer where the density falls to zero. The surface layer over which the density changes is approximately 5 Å in thickness. The film mass density at its center of mass is close to the bulk values. The orientation function parameter of the backbone carbon-carbon bonds, averaged over the ensemble of representative cells, shows a random nature in the dense region and an inclination towards an orientation somewhat along the plane of the surface layer in the external parts of the film. The styrene rings are mostly located in the bulk region, with random spatial and orientation distributions. The polar groups in the acrylonitrile segment of the SBA films are mostly found in the surface region, where they contribute to the marked enhancement in the surface energy for SBA films compared to SB films. The surface energy values deduced from the models are systematically slightly lower than independent estimates.     

Metallo‐Supramolecular Block Copolymers

Supramolecular copolymers have become of increasing interest in recent years for the search of new materials with tunable properties. In particular, metallo‐supramolecular block copolymers—copolymers in which the blocks are linked together by a metal–ligand complex—have seen important progresses, allowing better control over the synthetic strategies for various architectures, and providing a better understanding of the parameters governing their self‐assembly. We review here recent developments on the synthesis and self‐assembly of such materials achieved in this field.     

Modern mass spectrometry for coatings

For the analysis of polymers soft ionization mass spectrometry, in which only molecular ions are observed, can provide the complete distribution of chains (length, composition, end-groups) in under ten minutes on microgram quantities of material. Moreover, molecular ion information of neat organic pigments or those present in crosslinked networks can also be furnished. No other analytical technique can supply these data in such a short time. The application of mass spectrometry to the characterization of materials used in today's high performance automotive coatings is presented. These include functional monomers, several acrylic copolymers, organic pigments and an epoxide prepolymer. While there are a variety of mass spectrometric techniques, in this paper we will highlight the techniques that we have found useful for the characterization of organic coating components. The selection of the mass spectrometric technique is dictated by the molecular weight of the material and to a lesser extent the chemical composition. We used potassium ionization of desorbed species (K⁺IDS) performed on a quadrupole mass spectrometer for materials under 1000 Daltons (Da). However, many of the ingredients used in current automotive finishes fall between 1000 and 10 000 Da. For these materials we used a Fourier transform mass spectrometer (FTMS) which is well suited for this mass range and boasts the highest resolution and mass accuracy available. Direct desorption/ionization using a carbon dioxide laser is our standard method of sample introduction. Recently, we coupled a gel permeation chromatograph to our FTMS using an electrospray ionization interface. This hyphenated technique offers one of the most powerful characterization methods for the coatings chemist.     

Synthesis and nonlinear optical properties of PMMA copolymers having novel benzoxazole chromophores attached with various electron-withdrawing groups

For improvements of thermal stability and nonlinear optical (NLO) activity of chromophores, we newly synthesized a series of NLO chromophores incorporating aromatic benzoxazole unit as a π-conjugated bridge with various electron-withdrawing groups, such as nitrophenyl, nitrothiophene, nitrofuran, dicyanovinylphenyl, and nitrophenylethenyl group. Polymethylmethacrylate copolymers (PMBz) containing these benzoxazole chromophores were synthesized and their properties were investigated by thermogravimetry and ultraviolet-visible spectroscopy. The PMBz copolymers exhibited better thermal and ultraviolet stabilities than the corresponding copolymer with general stilbene chromophores (PMSt). Moreover, temporal stability of nonlinear optical coefficient (d₃₃) of PMBz copolymer increased in comparison with that of PMSt. The copolymer with benzoxazole–nitrothiophene chromophores had the largest d₃₃ value of 153 pm/V (at 1.064 mm) and nonresonant d₃₃ calculated by the two-level model was 21.3 pm/V.     

Investigation on the polymer particle growth in ethylene polymerization with PS beads supported rac-Ph2Si(Ind)2ZrCl2 catalyst

The mechanism of polyethylene particle growth was investigated using poly(styrene-co-divinylbenzene) (PS beads) supported rac-Ph₂Si(Ind)₂ZrCl₂ catalyst. From the analysis of the resulting polyethylene particles by SEM (scanning electron microscopy) and EPMA (electron probe microanalysis), it was found that the active species are located on the surface layer of catalyst particles and that the catalytic species are uniformly distributed throughout the polymer particles, whereas the cores of PS beads, which lack a potential active species, were not disintegrated during polymerization. These results suggest that the PS beads supported catalyst also follows the fragmentation and replication process as frequently observed with the MgCl₂ supported Ziegler–Natta catalysts.     

Vitronectin activity on polymer substrates with controlled -OH density

Vitronectin (VN) adsorption on a family of model substrates consisting of copolymers of ethyl acrylate and hydroxyl ethylacrylate in different ratios (to obtain a controlled surface density of -OH groups) was investigated by Atomic Force Microscopy (AFM). It is shown that the fraction of the substrate covered by the protein depends strongly on the amount of hydroxyl groups in the sample and it monotonically decreases as the -OH density increases. Isolated globular-like VN molecules are observed on the surfaces with the higher OH density. As the fraction of hydroxyl groups decreases, aggregates of 3-5 VN molecules are observed on the sample. Overall cell morphology, focal adhesion formation and actin cytoskeleton development are investigated to assess the biological activity of the adsorbed VN on the different surfaces. Dermal fibroblast cells show excellent material interaction on the more hydrophobic samples (OH contents lower than 0.5), which reveals enhanced VN activity on this family of substrates as compared with other extracellular matrix proteins (e.g., fibronectin and fibrinogen).     

Electrochemical synthesis and spectroelectrochemical behavior of poly(diphenylamine-co-4,4′-diaminodiphenyl sulfone)

The electroactive copolymer of diphenylamine (DPA) and 4,4′-diaminodiphenyl sulfone (DADPS) was synthesized electrochemically in 4 M H₂SO₄ and ethanol medium. Both electrochemical synthesis and characterization of the copolymer deposited on a glassy carbon electrode (GCE) were carried out using cyclic voltammetry. The voltammograms exhibited different patterns of behavior with different feed concentrations of DPA. Equimolar concentrations of DPA and DADPS demonstrated very efficient growth of the copolymer film on the surface of the GCE. The copolymer exhibited high solubility in dimethyl sulfoxide (DMSO). The scan rate exerted little-effect on this GCE copolymer film, revealing the film's excellent electroactive adherent properties. The effect of pH on the copolymer film showed that the polymer was electrochemically active up to pH 7.0. Spectroelectrochemical analysis of the copolymer film, carried out on an indium tin oxide (ITO) plate, showed multicolor electrochromic behavior when the applied potential was changed. The copolymer was characterized by FTIR and ¹H NMR spectral data. The surface morphology was studied using SEM analysis, the grain size of the copolymer was measured using XRD studies and was found to be 56 nm. The electrical conductivity of the copolymer was 2.65 × 10⁻² S cm⁻¹, as determined using a four-probe conductivity meter.     

Copolymers—A refined way to tailor intrinsically conducting polymers

An overview is given on electrochemically prepared intrinsically conducting copolymers, their preparation, their properties, potential applications and significant differences from the respective homopolymers. Particular attention is paid to verification of the formation of true copolymers and their characteristic features in comparison to mixtures of homopolymers.     

Preparing phenolic resins using pulping spent liquor

The method of using spent liquor (SL) obtained from the chemical pretreatment stage of wheat straw semi-chemical pulping to prepare spent liquor phenolic resins (SLPR) was investigated in the present work. In this work spent liquor was modified with phenol, and then the modified spent liquor was further synthesized with phenol and formaldehyde under appropriate conditions. Experimental data shows that the substitution mass fraction of spent liquor for phenol, the mole ratios of formaldehyde and sodium hydroxide to phenol, temperature and duration time of addition and condensation reaction all show significant influence on the properties of SLPR. SLPR and pure phenolic resins (PR) exhibited almost the same macromolecular structures characterized by FT-IR, and the main properties of the SLPR such as free formaldehyde content, gel time and bonding strength demonstrated superiority to that of PR.     

HIGH WATER ABSORBENTS FROM LIGNOCELLULOSES. I. EFFECT OF REACTION VARIABLES ON THE WATER ABSORBENCY OF POLYMERIZED LIGNOCELLULOSES

Hydrogels of 350 water-absorbency (g H₂O₂/g sample) and 900 water-keeping capacity (mL H₂O₂/g sample) were prepared from local lignocellulosic wastes. The wastes used are rice straw, sugar-cane bagasse, and cotton stalks. These hydrogels were prepared via graft–polymerization reaction using some vinyl monomers, followed by alkali hydrolysis. The effects of grafting parameters (concentration of both initiator and monomer, temperature, and time), purity of lignocellulose sample, type of monomer, pretreatment of lignocellulose, and manner of saponification reaction were examined.

The application of such polymeric materials as soil conditioners, by following the pore size distribution of sand soil, in comparison with conventional soil conditioners (e.g., natural organic fertilizer and clay), were also evaluated.