Photopolymerization of methyl methacrylate initiated by sulphur dioxide

In catalytic concentrations (10^?5?10^?4 mol l^?1) sulphur dioxide induces polymerization of MMA, particularly on photoactivation. The effective initiating species appears to be the monomer-SO₂ complex rather than free SO₂. A mechanism involving biradical initiation by decomposition of the initiating species, linear propagation in two directions, and significant termination of growing chains by chain transfer with initiating species has been suggested. The initiator transfer constant is 1.6 at 40°.     

Studies on the kinetics of polymerization of vinyl acetate by benzoyl peroxide at 60° using pyridine as solvent

Kinetics of Bz₂O₂-initiated polymerization of VAC in pyridine at 60° were investigated. The polymerization was significantly retarded by pyridine. The monomer exponent decreased from 2.5 at a relatively low [Bz₂O₂] (1.0 × 10^?2 M) to 2.0 at [Bz₂O₂] ? 4.0 × 10^?2 M. The observed kinetic features were explained on the basis of degradative chain transfer and copolymerization with pyridine.     

Use of cluster expansion techniques in quantum chemistry. A linear response model for calculating energy differences

In this paper we have reviewed the theoretical framework of the coupled-cluster (cc) based linear response model as a tool for directly calculating energy differences of spectroscopic interest like excitation energy (ee), ionisation potential (ip) or electron affinity (ea). In this model, the ground state of a many-electron system is described as in a coupled cluster theory for closed shells. The electronic ground state is supposed to interact with an external photon field of frequencyw, and the poles of the linear response function as a function ofw furnish with the elementary excitations of the system. Depending on the general form of the coupling term chosen, appropriate difference energies like ee, ip or EA may be generated. Pertinent derivations of the general working equations are reviewed, and specific details as well as approximations for ee, ip or ea are indicated. It is shown that the theory bears a close resemblance to the equation of motion (eom) method but is superior to the latter in that the ground state correlation is taken to all orders and may be looked upon as essentially a variant of renormalisedtda. A perturbative analysis elucidating the underlying perturbative structure of the formulation is also given which reveals that the theory has a hybrid structure: the correlation terms are treated akin to an open shellmbpt, while the relaxation terms are treated akin to a Green function theory. A critique of the methodvis-a-vis other cc-based approaches for difference energies forms the concluding part of our review.     

A zero differential overlap study of chemical binding in ammonia-borane and carbony l-borane

A cndo/2D study of the charge distribution obtained through Mulliken population analysis in the ground state of the title compounds shows that the features of charge distribution found by severalab initio calculations are fairly well reproduced by this method. The one-particle density, the interference density at the mid-point of the bond axis and the kinetic part of the interference energy calculated through the deorthogonalized density matrices over a wide range of intermolecular separation between the donor and the acceptor show that the one-particle density and the interference density steadily grow with decreasing internuclear separation, while the kinetic interference energy starts with negative value at large distance, then decreases and passes through a minima near but above the equilibrium distance and then increases rapidly below it conforming to the characteristic general behaviour of the kinetic component of Morse curve. The orbital pairwise interference density and the corresponding kinetic energy components reveal that the orbitals involved in the covalent binding are σ_2p AO of B and 2S and σ_2p AO of N and C atoms in H₃B-NH₃ and H₃B-CO respectively.     

Studies on vinyl photopolymerization using a macromolecular C.T. Complex between poly(N-vinyl carbazole) and bromine as the photoinitiator

Photopolymerization of methyl methacrylate (MMA) was studied at 40°C using a macromolecular C.T. Complex between poly(N-vinyl carbazole) and bromine, expressed in brief as (PNVC–Br₂) complex, as the photoinitiator. Initiator exponent was 0.40 for [PNVC–Br₂] ≤ 2.5 × 10^?3 mol L^?1 and practically zero for [PNVC–Br₂] > 2.5 × 10^?3 mol L^?1. Monomer exponent in different diluent systems such as benzene, carbon tetrachloride, and acetone was close to 1.0. Low initiator exponent (<0.5) is explained on the basis of an initiator-dependent termination mechanism, in addition to the usual bimolecular termination. Analysis of kinetic data indicates that the initiator-dependent termination is primarily due to degradative initiator transfer and that due to primary radicals is considered inconsequential in view of monomer exponent being close to unity. The non-ideal termination process assumes over-whelming prominence at high [PNVC–Br₂].     

Laser photolysis of 2-phenylheptamethyltrisilane

Two transient absorptions have been detected in the 266 nm laser photolysis of 2-phenylheptamethyltrisilane in cyclohexane solution at room temperature, and their time evolution was recorded in the presence and absence of air and added trapping agents. The shorter-lived 440 nm transient (t1/2 < 20μs) is tentatively assigned to the silylene :SiMePh and the more persistent 380 nm transient to the disilene MePhSiSiMePh. The reactivity of this silylene is much lower than had been expected.     

Studies in the metathesis of beryllium chloride and sodium silicate solutions

Summary From the conduotometrio and electrometric studies of the metathesis between beryllium chloride and sodium silicate, it has been concluded that two silicates of beryllium are formed along with the formation of beryllium hydroxide and silicic acid. It has been further concluded that the hydrolysis of beryllium chloride is not so great as that of chlorides of iron and chromium.

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Zusammenfassung Aus Leitf?higkeitsmessungen und elektrometrischen Untersuchungen an Reaktionsprodukten aus Berylliumchlorid und Natriumsilikat wird auf Entstehung von zwei Berylliumsilikaten geschlossen, gleichzeitig auf Bildung von Berylliumhydroxyd und Kiesels?ure. Die Hydrolyse von Berylliumchlorid ist nicht so stark wie die von Eisen- und Chromchlorid.

     

A Novel Method for Permeability Estimation from Micro-tomographic Images

Transport in Porous Media - A methodology has been developed to create a pore network model (PNM) from the geometrical/topological information extracted from the micro-tomographic images of a...