Polymerization of acrylonitrile initiated by a manganese(III) acetate glycerol redox system

The kinetics of polymerization of acrylonitrile(AN) initiated by manganese(III) acetate in the presence of glycerol was investigated in the temperature range of 30–40°C. The effect of varying the concentrations of glycerol, sulfuric acid, acetic acid, metal ion, and monomer on the rate was studied. A suitable reaction scheme and rate expression have been proposed. Termination was mutual and was caused by the combination of two growing polymer radicals.     

Modeling diffusion in miscible polymer blend films

Recent experiments designed to probe polymer transport in the bulk and in the vicinity of surfaces have examined the interdiffusion of multilayer sandwiches of isotopically labeled polymers. The measured time dependent concentration profiles normal to the surface are typically fit to Fick's law, with a single fitting parameter, the mutual binary diffusion coefficient (MBDC). The resulting MBDCs are found to vary over a broad range of film thicknesses and time, with the time dependence being viewed as a unique signature of the reptation mechanism of long chain motion, and the thickness dependence being attributed to the slowing down of chain dynamics near surfaces. Since the experiments are conducted at finite concentration, the MBDC, which is a product of the bare mobility and the concentration derivative of the chemical potential, could be dominated by the time and thickness dependence of this second term (which is ignored in Fick's law). To quantify this conjecture we consider the more rigorous Cahn formulation of the diffusion problem in terms of chemical potential gradients. We use square gradient theory to evaluate chemical potentials, and fit the resulting time dependent concentration profiles to the analytical solution of Fick's law. By thus mimicking the experimental analysis we find that the apparent MBDCs vary with time as t(-1/2) at short times, in good agreement with existing experiments. We show that this time dependence reflects the system's desire to minimize concentration gradients, a fact ignored in Fick's law. Since these arguments make no reference to the mechanism of chain motion, we argue that the time dependence of MBDC derived from interdiffusion experiments does not provide unequivocal support for the reptation mechanism of long chain transport. The MBDC values, which also vary with the degree of confinement, are predicted to increase with decreasing thickness for model parameters corresponding to experimental systems. In contrast, since the experimental fits yield an opposite trend, we suggest that the bare mobility of the chains decreases strongly with decreasing thickness. These findings strongly support the idea that the chains are "pinned" irreversibly to the surfaces, in good agreement with other, independent experiments.     

Dynamics of (H(-), H(2)) collisions: a time-dependent quantum mechanical investigation on a new ab initio potential energy surface

A global analytical potential energy surface for the ground state of H(3)(-) has been constructed by fitting an analytic function to the ab initio potential energy values computed using coupled cluster singles and doubles with perturbative triples [CCSD(T)] method and Dunning's augmented correlation consistent polarized valence triple zeta basis set. Using this potential energy surface, time-dependent quantum mechanical wave packet calculations were carried out to calculate the reaction probabilities (P(R)) for the exchange reaction H(-)+H(2)(v, j)-->H(2)+H(-), for different initial vibrational (v) and rotational (j) states of H(2), for total angular momentum equal to zero. With increase in v, the number of oscillations in the P(R)(E) plot increases and the oscillations become more pronounced. While P(R) increases with increase in rotational excitation from j=0 to 1, it decreases with further increase in j to 2 over a wide range of energies. In addition, rotational excitation quenches the oscillations in P(R)(E) plots.     

Structural and bonding investigation of an unbridged donor-acceptor complex 1-(2,2′-bipyrimidine)-1-(t-butyl)-2, 3-bis(trimethylsilyl) -2,3-dicarba-1-galla-closo-heptaborane(6)

The reaction between thecloso-gallacarborane, 1-(t-C₄H₉)-1-Ga-2,3-(SiMe₃)₂-2,3-C₂B₄H₄ (1), and 2,2-bipyrimidine in a molar ratio of 11 in dry benzene produced the unbridged donor-acceptor complex 1-(2,2-C₈H₆N₄)-1-(t-C₄H₉)-1-Ga-2,3-(SiMe₃)₂-2, 3-C₂B₄H₄ (2) as a pale-yellow crystalline solid in 81% yield. The spectroscopic data of2 are almost identical to those of the bridged species 1,1-(2,2-C₈ H₆N₄)-[1-(t-C₄H₉)-1-Ga-2,3-(SiMe₃)₂-2,3-C₂ B₄H₄]₂ (3). However, the single-crystal X-ray structure of2 reveals that the complex consists of only one distorted gallacarborane unit and a bipyrimidine molecule, that acts as a bidentate ligand. The apical gallium in2 is displaced further away from the centroidal position above the carborane than it is in 1. Despite the steric hindrance imposed by the bulky trimethylsilyl groups on the cage carbons, the Ga-C_(t-buty) bond is tilted toward the cage carbon atoms. Complex2 crystallizes in the monoclinic space groupP2₁ witha=11.279 (3),b=10.060 (3),c=11.911 (3) Å,=94.94 (2)°,V=1346.5 (6) ų,Z=2,D _x=1.24g cm^–3, (MoK) F(000)= 528, andT=220 K. Full-matrix least-squares refinement for2 converged at R=0.036 andRw= 0.045 for 3032 observed reflections. Molecular orbital calculations showed that antibonding interactions between the gallium and carborane cage carbons, induced by base complexation, are a contributing factor to the gallium's slip distortion that is found in2.     

Schur-type stability properties and complex diagonal scaling

We introduce new classes of n-by-n matrices with complex entries which can be scaled by a diagonal matrix with complex entries to be normal or Hermitian and study the Schur-type stability properties of these matrices.     

Functional polyethylene glycol derivatives nanostructured thin films synthesized by matrix-assisted pulsed laser evaporation

We report the thin film deposition by matrix-assisted pulsed laser evaporation (MAPLE) of a polymer conjugate with an hydrophilic sequence between metronidazole molecules that was covalently attached to both oligomer ends of carboxylate poly(ethylene glycol) (PEG 1.5-metronidazole). A pulsed KrF* excimer laser was used to deposit the drug-polymer composite films. Fourier transform infrared spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical properties similar to the starting materials. The dependence of the surface morphology on incident laser fluence is given.     

Processing of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80 (P(CPP:SA)20:80) by matrix-assisted pulsed laser evaporation for drug delivery systems

We have demonstrated successful thin film growth of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) by matrix-assisted pulsed laser evaporation using a KrF* excimer laser (λ = 248 nm, τ = 25 ns, ν = 10 Hz). The deposited thin films have been investigated by Fourier transform infrared spectroscopy, and atomic force microscopy. We have demonstrated that the main functional groups of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) are present in the deposited film. The effect of matrix on both thin film structure and surface morphology was also examined. The goal of this work is to explore laser processing of this material to create suitable constructs for drug delivery applications.