Hexavalent Chromium-Thioacetamide Redox System Initiated Polymerization of Acrylonitrile

Polymerization of acrylonitrile initiated by the Cr⁶⁺/thioacetamide redox system was studied in nitrogen atmosphere in the temperature range 35–45°C. The rate of polymerization and the rate of Cr⁶⁺ ion disappearance were measured. The effect of certain water-miscible organic solvents, neutral electrolytes, and complexing agents on the rate of polymerization was investigated. Chromic acid alone did not initiate the polymerization under deaerated and undeaerated conditions. Depending on the results obtained, a suitable kinetic scheme was proposed and various rate parameters were evaluated.     

Polymerization of Methyl Methacrylate: Kinetics of the Reaction Initiated by the Mn(III)-1,2-Propanediol Redox System

Kinetics of polymerization of methyl methacrylate initiated by Mn³⁺/1,2-propanedlol has been investigated in aqueous sulfuric acid at the temperature range of 25–35°C. The rate of polymerization (R_p) and the rate of manganic ion disappearance (-R_Mn) have been computed. The effects of organic solvents, certain cationic and anionic detergents, added electrolytes on the initial rate of polymerization, and maximum conversion have been examined. Depending on the kinetic results, a reaction scheme has been suggested involving the formation of a complex between Mn³⁺ and the alcohol, which subsequently decomposed in an unimolecular step to generate the initiating free-radical which initiates polymerization and termination of the growing polymer chain by metal ion.     

Unexpected solute aggregation in water on dilution

Studies on cluster-cluster aggregation phenomena in aqueous solutions of fullerene-cyclodextrin conjugates, beta-cyclodextrin, sodium chloride, sodium guanosine monophosphate, and a DNA oligonucleotide revealed that there are larger aggregates existent in dilute aqueous solutions than in more concentrated solutions.     

Synthesis of poly(butyl acrylate)/sodium silicate nanocomposite fire retardant

Poly(butyl acrylate) (PBA)/sodium silicate (SS) nanocomposites were prepared via emulsifier-free emulsion technique in presence of Cu(II)/glycine chelate complex and ammonium persulfate (APS) initiator. The strongly hydrophobic PBA was intercalated into the hydrophilic SS layer. Since the interlayers of silicate were filled with sodium cations, the hydrophilic properties were enhanced and lead to high degree of swelling. The formation of the PBA/SS nanocomposite was confirmed by infrared spectra (IR). Furthermore, as evidenced by transmission electron microscopy (TEM), the composite so obtained was found to have nanoscale structure. X-ray diffraction (XRD) was used to characterize the nanoscale dispersion of the layer silicate and useful for measurement of d-spacing in interlayer system. It was found from thermogravimetric analysis that PBA/SS nanocomposites had more thermal stability as compared to raw PBA due to intercalation. Burning test of the nanocomposites performance exhibited a flame retardant property, which was also verified from cone calorimeter analysis. For its commercialization, the ecological friendly nature was studied via biodegradation and was found to have better biodegradability than the raw PBA.     

Pt3Te4 nanoparticles from tellurium nanowires

We report the synthesis of platinum telluride nanoparticles (Pt(3)Te(4) NPs) in the solution phase at room temperature using a template-assisted method. The dendrimeric aggregates formed are composed of several small units of Pt(3)Te(4) NPs of ～4 nm diameter. Tellurium nanowires (Te NWs) are used as the template and the reducing agent in the growth of NPs which occurs due to the galvanic replacement reaction between Te NWs and PtCl(6)(2-). Surface-enhanced Raman scattering (SERS) of the dispersed Pt(3)Te(4) NPs was studied using crystal violet (CV) as the analyte. SERS sensitivity up to 10(-8) M of CV was observed. The Raman enhancement factor (EF) of adsorbed CV on NP aggregates was calculated to be 1.74 × 10(5). The catalytic ability of the as-synthesized Pt(3)Te(4) NPs for the reduction of 4-nitrophenol (4-NP) was studied.     

Novel soluble thermally stable silane-containing aromatic polyimides with reduced dielectric constant

Bis(p-aminophenoxy)diphenylsilane (BPS), bis(m-aminophenoxy)diphenylsilane (BMS) and bis(5-amino-1-naphthoxy)diphenylsilane (BAS) as three silane-diamines were prepared by the reactions of 4-aminophenol, 3-aminophenol, and 5-amino-1-naphthol respectively, with dichlorodiphenylsilane in the presence of triethylamine. The related silane-containing polyimides were prepared by two-step polycondensation reactions of these diamines with three different aromatic dianhydrides. All the polymers were characterized and their physical and thermal properties were studied. The polymers showed high thermal stability while their solubility was greatly increased in polar aprotic solvents. Wide angle X-ray diffraction showed that all the polyimides were almost amorphous. Also their dielectric constants were decreased due to the incorporation of softening and low-polarizing siloxane units into the polymer backbone.     

On critical assessment of the use of local and nonlocal damage models for prediction of ductile crack growth and crack path in various loading and boundary conditions

In this work, we have assessed the results of the local and nonlocal versions of Rousselier’s damage model, which have been used here for simulation of ductile crack growth. There are several issues regarding the accuracy of the results which has been addressed in this paper, e.g., accuracy in simulation of crack path, extent and width of the damaged region, fracture resistance behaviour in situations such as symmetric vs. non-symmetric boundary-value problems, mixed-mode loading vs. mode-I loading of the crack-tip, etc. It was also observed that the shape and orientation of the elements at the crack-tip, in addition to their size, influence the results of the local damage model. In this work, it was shown that the above issues can be resolved through the use of nonlocal damage models. The predictions of the nonlocal model are also consistent with the experimental observations unlike its local counterpart. Several examples were presented, where the results as obtained by both the local and nonlocal models were compared. From this experience, it is recommended that the local damage models should not be used blindly by the analysts for all kinds of mesh design, loading, boundary conditions, etc.     

Synthesis of poly(2‐vinyl pyridine)‐b‐poly(n‐hexyl isocyanate) amphiphilic coil‐rod block copolymer by anionic polymerization

A well‐defined amphiphilic coil‐rod block copolymer, poly(2‐vinyl pyridine)‐b‐poly(n‐hexyl isocyanate) (P2VP‐b‐PHIC), was synthesized with quantitative yields by anionic polymerization. A low reactive one‐directional initiator, potassium diphenyl methane (DPM‐K), was very effective in polymerizing 2‐vinyl pyridine (2VP) without side reactions, leading to perfect control over molecular weight and molecular weight distribution over a broad range of initiator and monomer concentration. Copolymerization of 2VP with n‐hexyl isocyanate (HIC) was carried out in the presence of sodium tetraphenyl borate (NaBPh₄) to prevent backbiting reactions during isocyanate polymerization. Terminating the living end with a suitable end‐capping agent resulted in a P2VP‐b‐PHIC coil‐rod block copolymer with controlled molecular weight and narrow molecular weight distribution. Cast film from a chloroform solution of P2VP‐b‐PHIC displayed microphase separation, characteristic of coil‐rod block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 607–615, 2005     

A finite element model for nonlinear behaviour of piezoceramics under weak electric fields

It has been experimentally observed that piezoceramic materials exhibit different types of nonlinearities under different combinations of electric and mechanical fields. When excited near resonance in the presence of weak e to a Duffinor such as jump phenomena and presence of superharmonics in the response spectra. There has not been much work in the litrature to model these types of nonlinearities. Some authors have developed one-dimensional models for the above phenomenon and derived closed-form solutions for the displacement response of piezo-actuators. However, the generalized three-dimensional (3-D) formulation of electric enthalpy, the variational formulation and the FEM implementation have not yet been addressed, which are the focus of this paper. In this work, these nonlinearities have been modelled in a 3-D piezoelectric continuum using higher order quadratic and cubic terms in the generalized electric enthalpy density function. The coupled nonlinear finite element equations have been derived using variational formulation. A special linearization technique for assembling the nonlinear matrices and solution of the resulting nonlinear equations has been developed. The method has been used for simulating the nonlinear frequency response of a lead zirconate titanate plate excited near its first in-plane vibration resonance frequency with sinusoidal excitations of different electric field strengths. The results have been compared with those of the experiment.     

Unprecedented control over polymerization of n-hexyl isocyanate using an anionic initiator having synchronized function of chain-end protection

The living anionic polymerization of isocyanates carried out using conventional initiators is associated with side reactions due to rapid initiation rates as well as back-biting by the growing chain, resulting in a lack of control on the molecular weight (MW) and molecular weight distribution (MWD) of the polymers. Successful control over the reaction was possible by using additives that could prevent back-biting. We find an initiator in sodium benzanilide (Na-BA), which has a slow initiation rate combined with additive function, so that use of an external additive is eliminated. The initiator has resulted in polymers with high yields and an unprecedented control over the MW and MWD. It is possible to introduce a number of functionalities at the termini of the polymer by using Na-BA derivatives as well as suitable terminating agents, leading to macromonomer, reactive and chiral polymers, and chiral macromonomer in approximately 100% yields. In the process, the finding has expanded the scope of polyisocyanates in diverse applications.