The thermal polymerization of styrene is a long-known
and well-practiced phenomena. While the mechanism of the thermal initiation
event has been the subject of several investigations, it is not yet well understood.
In an attempt to gain further insight as to the details of possible initiation
from styrene dimer, analogous stable cycloadducts (maleic anhydride, tetracyanoethylene)
of 1- and 2-vinylnaphthalene have been synthesized, fully characterized spectroscopically,
and subjected to thermal decomposition. In the main, the major thermal event
observed for these styrene dimer mimics is retro cycloaddition. This process
is characterized by an activation enthalpy of approximately 30 kcal mol–1.
Aminor process which accompanies the major reaction is the homolysis of a
carbon–hydrogen bond to generate a carbon radical which may be trapped
as a stable adduct of the 2,2,6,6-tetramethylpiperinyloxy (TEMPO) radical.
multivalent platinum drug based on a poly(amidoamine) [PAMAM] dendrimer (generation
4.5, carboxylate surface) has been synthesized and fully characterized using
a variety of spectroscopic, chromatographic and thermal methods. Treatment
of the dendrimer with an aqueous solution containing an excess diaquo(cis-1,2-diaminocyclohexane)platinum(II) produces
a conjugate containing approximately forty (diaminocyclohexane)platinum(II)
moieties at the surface of the dendrimer. This material undergoes smooth two-stage
thermal decomposition to provide residual platinum oxide reflecting the platinum
loading in the drug.
The thermal degradation of a series of 1,1,2,2-tetraaryl-1,2-ethanediols has been examined using thermogravimetry (TG) and gas chromatography/mass spectrometry (GC/MS). These compounds are smoothly converted to the corresponding diaryl ketone and diaryl carbinol, i.e., the compounds undergo disproportionation arising from homolytic cleavage of the central carbon–carbon bond. Presumably, cleavage of the carbon–carbon bond generates a radical pair which disproportionates to provide the observed products.
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.
Authors:B. A. Howell, H. Dangalle, and M. Al-Omari
A difunctional imide monomer may be produced from 4-nitrophthalic anhydride and m-phenylenediamine. The requisite anhydride may be generated by nitration of phthalimide followed by hydrolysis to the corresponding acid and dehydration. All intermediate compounds have been fully characterized using spectroscopic and thermal methods.
Authors:B. Howell1, M. Johnson, D. Player, L. Hahnfeld, S. Kling, and M. Mounts
standard vinylidene chloride copolymers, the first containing approximately
9 mass% methyl acrylate and the second containing vinyl chloride at a nominal
15 mass% were prepared by radical suspension techniques using a series of
peroxide and azo initiators (all of approximately the same half-life temperature
The nature of the initiator could impact the
stability of the resulting polymer in two ways. Instability could be introduced
either via end-group effects or by attack of residual initiator fragments
on the finished polymer during isolation and residual monomer stripping. In
this case, the relative thermal stability of the resins produced was assessed
by exposing samples to heat and shear in an air environment in a two-roll
mill (Brabender Prep-Mill). The rate and extent of degradation was most readily
apparent from color development during this treatment. The more thermally
stable polymers were produced using initiator radicals that did not attack
the polymer during isolation/stripping processes.