Organohalogen flame retardants, particularly brominated aromatics, are popular, effective, low cost, and widely used in the
plastics industry. However, an increasing concern about persistence in the environment and potential negative health effects
of these materials has generated intense interest in the development of alternatives. Ideally, these should have all the positive
attributes of the materials that will be replaced. In addition, it is desirable that the new materials be as “green” as possible,
e.g., based on renewable resources and be degradable to nontoxic products in the environment. A series of new, non-halogenated
flame retardants based on tartaric acid is being developed. Tartaric acid is a by-product of the wine industry and is readily
available locally on an annual basis (Michigan is the thirteenth largest producer of wine in the U.S.). It can be readily
converted to the corresponding diethyl ester. This ester may serve as the base for the development of a series of new, non-halogenated
flame-retarding agents. The presence of the reactive hydroxyl groups allows the introduction of a variety of phosphorus-containing
moieties. For example, treatment of diethyl tartrate with diphenylphosphinyl chloride generates diethyl 2,3-di(diphenylphosphinato)-1,4-butanedioate.
This material may serve as a monomer for the preparation of various phosphorus-containing polymers and oligomers via step-growth
transesterification. The thermal stability of this compound has been assessed by thermogravimetry.
General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of
polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of
the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer.
This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly
for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing
no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared
by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared
in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional
poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques.
A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition.
For a finite abelian group A, the ring End(A) is a maximal ring in the nearring M(A). In this paper we consider an analogous problem for finite semigroups, concentrating on commutative Clifford semigroups.
Authors:B. Howell, P. Chhetri, A. Dumitrascu and K. Stanton
Organoplatinum antitumor agents are very effective, broad-spectrum drugs used for the treatment of a variety of cancerous
conditions. The two most prominent of these, Cisplatin [cis-diamminodichloroplatinum(II)] and Carboplatin [diammino(1,1-cyclobutanedicarboxylato)platinum(II)], are large scale commercial
successes. The third, Oxaliplatin [((trans-1,2-diamminocyclohexane)oxalato)platinum(II)], is now commercially available. The administration of all these drugs is accompanied
by severe side effects. For Cisplatin, the most debilitating of these is kidney damage and extreme nausea. Several approaches
to generate drug-release formulations that might mitigate toxic side effects have been explored. Now, platinum(IV) compounds
which are more inert than platinum(II) compounds, and consequently less toxic, but which may be reduced to platinum(II) species
within the cell are being evaluated for effectiveness in the treatment of cancer. The thermal stability of several precursors
to compounds of this kind has been examined by thermogravimetry. In general, these materials lose ligands sequentially to
generate a residue of platinum. This behavior may be generally useful for the characterization of such materials.