Compositions – Preservative agents – Anti-oxidants or chemical change inhibitants
Reexamination Certificate
1999-08-04
2003-03-25
Mulcahy, Peter D. (Department: 1713)
Compositions
Preservative agents
Anti-oxidants or chemical change inhibitants
C252S400620, C252S400540, C252S402000, C252S406000, C524S110000, C524S392000
Reexamination Certificate
active
06537466
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to stabilizer compositions comprising degradation products of a blocked mercaptan present during processing of the composition at an elevated temperature, said products including a free mercaptan. This invention also relates to polymer compositions containing a polymer normally susceptible to heat-induced deterioration and the degradation products of a blocked mercaptan present during processing of the composition at an elevated temperature, said products including a free mercaptan. It also relates to such polymer compositions further containing a metallic-based heat stabilizer. This invention also relates to articles of manufacture, e.g. pipe, film, and window profile, made from stabilized polymer compositions containing a polymer normally susceptible to heat-induced deterioration, the degradation products of a blocked mercaptan present during processing of the composition at an elevated temperature, said—based heat stabilizer. Another aspect of this invention is the development of a novel reaction scheme which, although crude, affords latent mercaptans which need no purification to be highly active PVC heat stabilizers at low use levels.
This invention also relates to latent mercaptans which are substantially free of the offensive odor typical of mercaptans and which may be used as anti-oxidants, odorants, anti-microbial agents, chelating agents and photostabilizers; and as intermediates for the preparation of anti-oxidants and primary heat stabilizers. It also relates to such anti-oxidants and primary heat stabilizers.
BACKGROUND OF THE INVENTION
It is well known that the physical properties of various organic polymers deteriorate and color changes take place during processing of the polymer and during exposure of formed polymer products to certain environments. The prime examples of polymers which are susceptible to degradation during processing are the halogen-containing polymers such as the vinyl and vinylidene polymers in which the halogen is attached directly to carbon atoms. Poly (vinyl chloride) or PVC, copolymers of vinyl chloride and vinyl acetate, and poly (vinylidene chloride), the principal resin in self-clinging transparent food wraps, are the most familiar polymers which require stabilization for their survival during fabrication into pipes, window casings, siding, bottles, and packaging film, etc. When such polymers are processed at elevated temperatures, undesirable color changes often occur within the first 5 to 10 minutes as well as during later stages of the processing. Haziness, which sometimes accompanies the color changes, is particularly undesirable where clear products are needed. The addition of heat stabilizers to such polymers has been absolutely essential to the wide-spread utility of the polymers. From a great deal of work in the development of more and more effective heat stabilizers there has emerged two principal classes: organotin compounds and mixed metal combinations. Organotin-based heat stabilizers are the most efficient and widely used PVC stabilizers. Synergistic combinations of alkyltin mercaptides and free mercaptans are particularly efficient heat stabilizers for PVC during extrusion. They have not been entirely satisfactory, however, because of several failings on the part of the mercaptan synergist. Many mercaptans give off an offensive odor even at room temperature and the odor grows worse at PVC, processing temperatures. The oxidative stability of the mercaptans is very often very poor. Oxidation of the free mercaptans diminishes the synergism. Thus, a combination having an enhanced synergism would be welcomed by the PVC industry. Also, because of the end-use of articles made from some polymers, many polymeric compositions require the presence of both biocides and heat stabilizers but the use of the organotin mercaptide/mercaptan combination in such a composition is often frustrated by the tendency of the free mercaptan to deactivate a biocide such as the much used OBPA (10, 10′-oxybisphenoxarsine).
In U.S. Pat. No. 3,660,331, Ludwig teaches the stabilization of vinyl halide resins by certain thioethers and thioesters of tetrahydropyran. Better heat stabilizer compositions are still needed, however. The thioethers of this invention satisfy that need.
SUMMARY OF THE INVENTION
It is an object of this invention, therefore, to provide a heat stabilizer composition having the synergy of a mercaptan plus improved oxidative stability.
It is another object of this invention to provide a latent mercaptan-containing heat stabilizer composition which is substantially free from the offensive odor typically associated with mercaptans.
It is a related object of this invention to provide a latent mercaptan-containing heat stabilizer composition which has a decidedly pleasant odor.
It is a further object of this invention to provide an improved polymeric composition containing a biocide and a latent mercaptan-containing heat stabilizer.
It is a related object of this invention to provide a polymeric composition containing a heat stabilizer combination having the synergy of a mercaptan plus improved oxidative stability.
It is still another object of this invention to provide latent mercaptans as intermediates for the preparation of anti-oxidants, anti-microbial agents, photostabilizers, and primary heat stabilizers.
These and other objects of the invention which will become apparent from the following description are achieved by incorporating into a polymeric composition containing a polymer normally susceptible to heat-induced deterioration a blocked mercaptan which degrades during processing of the composition at an elevated temperature to liberate a free mercaptan. The latent mercaptan may act as the sole heat stabilizer but the free mercaptan may also synergize the activity of other heat stabilizers in the composition. Other products of the degradation of the blocked mercaptan are believed to include carbocations of the blocking moiety which are stabilized by a molecular structure in which the electron deficiency is shared by several groups. Resonance stabilization and neighboring group stabilization are two of the possible mechanisms by which the carbocations may be stabilized. The carbocations act as intermediates in the formation of stable compounds early in the hot processing of halogen-containing polymers. Although such mechanisms and the resultant carbocations are believed to be an impetus for the liberation of the active free mercaptan, this invention is in no way limited by the foregoing attempt to explain the working of the invention. Those skilled in the art will see the resonance stabilization and neighboring group stabilization that are possible in the following structures of the blocked mercaptan; other mechanisms may be at work in other blocked mercaptans represented by these structures that also liberate an active free mercaptan upon thermal and/or chemical degradation during processing of polymeric compositions containing such blocked mercaptans. For the purposes of this invention, the terms “blocked mercaptan” and “latent mercaptan” are used interchangeably to mean a thioether which degrades during processing of the composition at an elevated temperature to liberate a free mercaptan.
The stabilizer compositions of the present invention may comprise a metal-based stabilizer and such a latent mercaptan or mixture of latent mercaptans.
DETAILED DESCRIPTION OF THE INVENTION
As used herein: the terms “group” and “radical” are used interchangeably, a mono-valent radical has but one valence available for combining with another radical whereas a di-valent radical may combine with two other radicals; the term alkyl represents monovalent straight or branched chain hydrocarbon radicals containing, for example, 1 to 20 carbon atoms; the term alkylenyl represents divalent, trivalent, and tetravalent straight or branched chain hydrocarbon radicals containing, for example, 1 to 20 carbon atoms; the term aryl represents monovalent C
6
-C
10
aromatic rings such as benzene and naphthalene;
Adams Paul B.
Duvall Tod C.
Norris Gene K.
Mulcahy Peter D.
Rohm and Haas Company
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