Vinylidene chloride polymers containing comonomer
units capable of consuming evolved hydrogen chloride to expose good radical-scavenging
sites might be expected to display greater thermal stability than similar
polymers containing simple alkyl acrylates as comonomer. Incorporation of
a comonomer containing the phenyl t-butyl
carbonate moiety into a vinylidene chloride polymer has the potential to afford
a polymer with pendant groups which might interact with hydrogen chloride
to expose phenolic groups. Copolymers of vinylidene chloride with [4-(t-butoxycarbonyloxy)phenyl]methyl acrylate have been
prepared, characterized, and subjected to thermal degradation. The degradation
has been characterized by thermal and spectroscopic techniques. The degradation
of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl
acrylate copolymers is much more facile than the same process for similar
copolymers containing either [4-(isobutoxycarbonyloxy)phenyl]methyl acrylate
or methyl acrylate, a simple alkyl acrylate, as comonomer. During copolymer
degradation, [4-(t-butoxycarbonyloxy) phenylmethyl
acrylate units are apparently converted to acrylic acid units by extensive
fragmentation of the sidechain. Thus, the phenyl t-butyl
carbonate moiety does function as a labile acid-sensitive pendant group but
its decomposition in this instance leads to the generation of a phenoxybenzyl
carboxylate capable of further fragmentation.
Fully substituted 1,3-dioxa-2-siloles contain a strained carbon–carbon bond that will undergo thermolysis at modest temperatures to generate a diradical capable of initiating vinyl polymerization. If the substituents contain flame-retarding moieties, e.g., halogen or phophorus-containing groups, the use of such compounds as initiators serves to incorporate a flame-retarding unit into the polymer mainchain. Both 2,2-dialkyl- and 2,2-diaryl-4,4,5,5-tetra(3,5-dibromophenyl)-1,3-dioxa-2-siloles may be prepared from the appropriate tetra(bromoaryl)-1,2-ethanediol and are obtained as white solids. Thermal decomosition (thermogravimetry) of these materials occurs in two stages. Initial decomposition is observed at about 250 °C and corresponds to the loss of nearly half of the initial sample mass.
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.