NOPR Collection:

Magnetic field effect on polymers and polymerization

Fri, 01 Sep 1995 00:00:00 GMT

Title: Magnetic field effect on polymers and polymerization Authors: Maiti, Sukumar; Bag, Dibyendu S Abstract: The influence of magnetic field on polymerization reaction, polymer structure and properties has been discussed in the light of the radical pair theory and the cage effect to explain the kinetics of polymerization and crosslinking reactions. The rate of polymerization and crosslinking increases due to the singlet () triplet intersystem crossing mechanism. While the molecular weight increases, the molecular weight distribution decreases under magnetic field. The polymer microstructure viz., tacticity, copolymer composition and monomer sequence in the copolymer chain are also affected by the magnetic field. Polymerization of liquid crystal monomers under magnetic field results in highly oriented liquid crystal polymers. As a result, the polymer properties like crystallinity, chain flexibility, solubility, thermal behaviour are also changed. Conducting polyacetylene and magnetic polymers prepared under magnetic field also exhibit higher conductivity and magnetic properties respectively. Studies on biopolymers, solid state and plasma polymerization under magnetic field have also been reported. Page(s): 673-687

Some properties of Calvin's model of spontaneous chiral amplification

Fri, 01 Sep 1995 00:00:00 GMT

Title: Some properties of Calvin's model of spontaneous chiral amplification Authors: Gutman, Ivan Abstract: The kinetic scheme for spontaneous chiral amplification, put forward by Calvin, is examined and some of its general properties are established. Analytical solutions of Cailvin's model are found in two important limiting cases, namely, when the system is open and the concentration of the substrate is constant, and when the system is closed. Page(s): 688-691

Electron addition to triethylphosphite induced by ionising radiation: An ESR study

Fri, 01 Sep 1995 00:00:00 GMT

Title: Electron addition to triethylphosphite induced by ionising radiation: An ESR study Authors: Rai, U S Abstract: With a view to obtain [°P(OEt)₃]^- radical anions and to establish their preferred structure, solutions of triethylphosphite in different solvents have been exposed to ⁶⁰CO -rays at 77K and studied by ESR spectroscopy. Two phosphorus centred radicals suggested are parent radical anion and .P(OEt)₂ formed by dissociative electron capture. In methyltetrahydrofuran an electron adduct with A = 264G and small value of A is assigned to the primary radical anion having a planar T structure with SOMO on 3p of phosphorus, normal to the radical plane. In a methanolic solution, the same radical anion with extensive protonation having a phosphoranyl type radical with large ¹H and ³¹P hyperfine splitting is formed. The well defined triplets due to ²H adduct, obtained in CD₃OD glasses, confirm this assignment. Other phosphorus centred radicals are MeO-P(OEt)₃and the cation dimer (EtO)₃P—P(OEt). Page(s): 692-695

Studies on photoelectroactive (CdHg)Se films

Fri, 01 Sep 1995 00:00:00 GMT

Title: Studies on photoelectroactive (CdHg)Se films Authors: Singh, Kehar; Tanveer, Md. Rashid Abstract: (CdHg)Se films prepared by electrochemical deposition have been subjected to thermal treatment and tested for their photoresponsiveness. These studies in conjunction with capacitance measurements show that all (CdHg)Se films are endowed with n-type semiconductivity in contradiction to p-type semi-conductivity behaviour exhibited by some of the untreated preparations. Electrochemical impedance studies have also been carried out for the examination of corrosion characteristics of (CdHg)Se films. Page(s): 696-699