Media effects on the kinetics of anthracene photo-oxidation in polymers

An improved quantitative analysis of the photochemical reaction of diphenylanthracene (DPA) in thin films of poly(ethyl methacrylate) (PEMA) is reported. This analysis confirms the previous suggestion (J.R. Sheats, J. Phys. Chem., 94 (1990) 7194) that the rate of reaction between singlet oxygen and DPA decreases as the reaction proceeds, consistent with the hypothesis that the free volume is decreased by endoperoxide formation. For [DPA]≈30 wt.%, the rate constant decreases by approximately 50% for complete conversion. The initial value is 25-fold smaller than in fluid solution, and decreases slightly as [DPA] is increased.     

Trapping an elusive intermediate in manganese-oxo cubane chemistry

A new member of the Mn-oxo cubane core complex family [Mn2III,2IV4O4L6] (1), where L = (p-MeOPh)2PO2-, has been synthesized and characterized. Compound 1 possesses structurally inequivalent MnIII and MnIV with clear valence electron localization in the crystal phase, quite unlike the structurally equivalent sites, tetrahedral core symmetry, and delocalized valence of its analogue where L = Ph2PO2-. Compound 1 exhibits appreciable positive shifts (0.1-0.3 V) of both the oxidation and reduction electrochemical potentials, attributable to the remote electron donating p-MeO groups. Reduction of 1 by methanol yields a novel core complex [MnIII4O2(OMe)2(MeOH)[(p-MeOPh)2PO2]6] (2). Each MnIII of 2 is tetragonally distorted due to the Jahn-Teller effect with elongated Mn-O bonds that are directed at the two micro3-MeO bridges and neither of the two micro3-oxos. These electronically driven distortions provide a structural rationale for the greater basicity of the former sites and explain why 2 of the 4 corner oxos are preferentially reduced to water molecules.     

Synthesis and characterization of polymers and copolymers of vinylruthenocene

Homopolymers of vinylruthenocene and its copolymers with methyl acrylate, styrene, and n-vinylpyrrolidinone have been prepared by free-radical polymerization. No evidence for the electron transfer termination mechanism postulated for polymerization of vinylferrocene was observed. Yields of soluble polymers were 40–90% with M _w (4–25) × 10³ and M _w/M _n = 3.0–13.2. TGA analysis showed little weight loss up to 300°C but rapid decomposition above 300°C. Polyvinylruthenocene is a highly brittle material with T_g above 250°C. Torsional braid analysis of the copolymer samples showed T_g in the range 90–130°C which in some samples increased upon cooling and reheating. Several samples showed weak thermal transitions occurring prior to or following T_g. The rise in T_g upon cooling and reheating is indicative of possible decomposition, crosslinking, or realignment of the polymer chains.     

Inorganic and organometallic polymers – an overview

The need for new materials with lower density, higher strength, ability to withstand extremes of temperature and electrical conductivity ranging from semiconductors to superconductivity has stimulated research in polymer science.¹ The polymers chosen for these applications are often organometallic or metal‐containing organic polymers. These materials combine the low density and great variety of functional groups and structural variation of organic materials with the ease of achieving multiple oxidation states and electrical conductivity and the high temperature stability characteristic of inorganic compounds. In order to keep abreast of this rapidly expanding field, PMSE, sometimes jointly with the Polymer and Inorganic Divisions of the A.C.S., has sponsored symposia in 1971, 1977, 1979, 1985, 1989, and 1994. The authors of this paper have organized these symposia. A new journal, The Journal of Inorganic and Organometallic Polymers, is now completing its eighth year. Our goal in this review is to discuss developments in five areas – Silanes, Germanes and Stannanes, Poly(silsequioxanes), Polyphosphazenes, Metallocene Polymers, and Condensation Polymers and to discuss potential applications of these materials. We are seeking several scientists in these fields from outside of the United States to help us to continue this series of symposia and to support the Journal of Inorganic and Organometallic Polymers.