Compositions – Preservative agents – Anti-oxidants or chemical change inhibitants
Reexamination Certificate
1999-04-28
2003-03-25
Teskin, Fred (Department: 1713)
Compositions
Preservative agents
Anti-oxidants or chemical change inhibitants
C252S182290, C252S183120, C252S397000, C252S399000, C252S400300, C252S404000, C252S405000, C252S406000, C560S002000
Reexamination Certificate
active
06537467
ABSTRACT:
The present invention relates to immobilized free radical captors, to their preparation and to their use. More specifically, the present invention relates to:
immobilized free radical captors, and especially immobilized radical polymerization inhibitors or retarders;
a method of preparing them; and
a method of stabilizing, at least temporarily, molecules or mixtures of molecules, which makes use of said immobilized captors.
According to prior art, free radical captors are used per se in various contexts for protecting molecules which are sensitive to free radicals, from said free radicals. They are suitable, for example:
as stabilizers or preservatives: placed in the presence of sensitive molecules, such as biological molecules (for example, polyunsaturated lipids, vitamins), they minimize the degradation of the sensitive molecules by said radicals;
as radical polymerization inhibitors or retarders: dispersed within monomers, they prevent any uncontrolled and/or premature polymerization thereof (especially during phases of storage and transport of said monomers). Such radical polymerization inhibitors or retarders (methoxyphenol, phenothiazine, para-benzoquinone, 2,2-diphenyl-1-picrylhydrazyl (DPPH), metal salts) and their mechanisms of action (in the presence of monomers such as acrylic acid, butyl acrylate, acrylonitrile, styrene, even more generally, acrylates and methacrylates) have notably been described:
by L. B. Levy in Journal of Polymer Science; Polymer Chemistry, 23, 1505 (1985) and 30, 569 (1992) (methoxyphenol, phenothiazine, acrylic acid monomer);
by L. B. Levy in Journal of Applied Polymer Science, 60, 2481 (1996) (methoxyphenol, butyl acrylate);
by S. S. Cutié, D. E. Henton, C. Powell, R. E. Reim, P. B. Smith, T. L. Staples, in Journal of Applied Polymer Science, 64, 577 (1997) (methoxyphenol, acrylic acid); and
in Encyclopaedia of Polymer Science and Engineering, 2
nd
edition, vol. 13, p. 729-735, Ed Wiley Interscience (1988) (para-benzoquinone, DPPH, metal salts, acrylates, methacrylates, acrylonitrile, styrene . . . ).
Thus, the commercially available liquid monomers, especially those of the vinylic type (acrylates, or styrene, for example) usually contain 50 to 1,500 ppm of dissolved inhibitor(s) or retarder(s). Said inhibitor(s) or retarder(s) rapidly react with any free radical which is spontaneously generated at ambient temperature and/or under the action of light.
According to a first variant, such molecules prevent any efficient polymerization, and it is imperative to get rid of them when it is desired to initiate said polymerization. Their prior and compulsory removal, by distillation or chromatography, is a relatively difficult technique to carry out, especially on an industrial scale. The complete removal is in any case only with difficulty.
According to a second variant, molecules of this type are only active as inhibitors or retarders up to a certain temperature threshold and/or up to a certain irradiation threshold. It is necessary to, pass over this threshold in order to initiate the polymerization desired in the presence of said molecules. In such a context, said polymerization, deferred with time, is slower to carry out, more difficult to control and, in any case, it generates a polymer which contains said molecules as impurities.
The presence of these molecules in the monomers is furthermore cumbersome or restricting, for various reasons. Thus
in order to maintain a certain constancy in the process of polymerization, especially in its kinetics, it proves to be compulsory to keep the concentration of said molecules constant. The latter, obviously, decreases with time: the longer the storage time is, the more significant the amount of inhibitor(s) or retarder(s) consumed is. Maintaining said amount constant is a real constraint;
certain inhibitors or retarders, such as hydroquinone or methoxyphenol, only react with the free radicals in the presence of oxygen. It is however difficult to ensure a homogeneous dissolved oxygen content within a mixture of monomers. Failing this, the polymer obtained by polymerization of said mixture will not have a perfect homogeneity. The Applicant is especially confronted with this technical problem during the preparation of photochromic or non-photochromic lenses; the leaktightness at the joint of the lens mould is never perfect;
said inhibitor molecules may induce parasitic reactions with various types of other molecules (photochromic or non-photochromic colorants, chromophores . . . ), which may be present in the mixture to be polymerised;
said inhibitor molecules can also directly influence the final properties of the polymer prepared. Thus, they may alter the optical properties thereof. For a typical concentration of 100 ppm of said inhibitor molecules in the mixture to be polymerised, said molecules, which contain C—H and C—OH groups, increase the loss of transmission at 1.55 &mgr;m, by about 0.1 dB/cm in the polymerised material . . .
Upon considering all the problems set forth above, the Applicant desired developing an alternative to the use in accordance with prior art of dissolved free radical captors. The Applicant proposes to no longer use said dissolved free radicals captors per se, but to make them immobilized on a solid support. Thus, whatever their nature and the context of their use may be, they can be easily manipulated, in general got rid of, prior to the implementation of the polymerization, in the particular case of radical polymerization inhibitors or retarders.
Thus, according to a first object, the presently claimed invention relates to free radical captors, especially radical polymerization inhibitors or retarders within the sense of the prior art which, characteristically, are immobilized on a solid support.
Said free radical captors, especially of the stabiliser type (preservative type) or polymerization inhibitor or retarder are, according to the invention, fixed in a stable manner onto a solid support.
Advantageously, the radical polymerization inhibitors or retarders are selected from:
phenol derivatives, and especially:
alkylphenols, such as 2,6-di-tert-butyl-4-methylphenol,
hydroquinone,
alkoxyphenols, such as methoxyphenol,
catechol and derivatives thereof, such as 4-tert-butylcatechol;
quinones and especially benzoquinone;
phenothiazine;
organic radicals known as stable organic radicals, and especially:
nitroxy radicals, such as 2,2,6,6-tetramethylpiperidinooxy (TEMPO),
2,2-diphenyl-1-picrylhydrazyl (DPPH);
nitro derivatives, and especially:
nitromethane,
nitrobenzene;
metal salts, and especially:
CuBr
2
,
FeCl
3
, both used in solution, advantageously in dimethylformamide (DMF);
sulphur derivatives, used in iniferter systems.
These radical polymerization inhibitors or retarders are known per se. Within the context of the present invention, it is proposed to use them in an original manner, i.e. immobilized on a support.
The most-used radical polymerization inhibitors or retarders to this day are phenol derivatives and stable organic radicals. According to a preferred variant, the free radical captors, immobilized in the sense of the invention, consist of said phenol derivatives or said stable organic radicals.
The solid support which intervenes can be of any nature. Obviously, it must be suitable for the stable immobilization of the captor on its surface, as well as for the further use of said immobilized captor. Generally, it is a mineral and/or organic support, more frequently a mineral or organic support, and, preferably, a mineral support.
An organic support, either by nature or after chemical modification of its surface, possesses on said surface numerous reactive functions, notably of the alcohol-, amine-, carboxylic acid-, halide-, ester-, amide-type . . . These reactive functions are advantageously used for the immobilization (coupling), generally by chemical grafting, of the captors.
The intervention of a:
silica support or silica-based glass support (containing more than 50% by weight of silica);
an alumina support, or
an iron oxide support, titanium oxide support . . .
Beall Thomas R.
Corning Incorporated
Nwaneri Angela N.
Rogalskyj Peter
Teskin Fred
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