| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 26.03.2002 |
| PATENT TITLE |
Peroxyketals derived from cyclic beta-keto esters |
| PATENT ABSTRACT |
This invention relates to peroxyketals derived from cyclic .beta.-keto esters and use of the same in the curing of resins, such as unsaturated polyester resins. The new peroxyketals were synthesized via an acid catalyzed reaction of cyclic .beta.-keto esters with aliphatic hydroperoxides. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | June 22, 2001 |
| PATENT CLAIMS |
What is claimed is: 1. A cyclic .beta.-ester peroxyletal having the general structure: ##STR12## wherein: R.sup.1 is C.sub.1 -C.sub.10 alkyl, cycloalkyl, alkaryl, or aryl which may be unsubstituted or substituted with one or more halogen or hydroxy; R.sup.2 and R.sup.3 are each independently C.sub.1 -C.sub.10 alkyl, cycloalkyl, or aralkyl; and n is 1, 2 or 3. 2. The peroxyketal of claim 1 wherein R.sup.1 is C.sub.1 -C.sub.5 alkyl and R.sup.2 and R.sup.3 are each independently C.sub.3 -C.sub.8 alkyl. 3. The peroxyketal of claim 2 wherein R.sup.1 is methyl. 4. The peroxyketal of claim 2 wherein R.sup.1 is ethyl. 5. The peroxyketal of claim 2 wherein R.sup.2 and R.sup.3 are the same substituent. 6. The peroxyketal of claim 5 wherein R.sup.2 and R.sup.3 are each t-butyl. 7. The peroxyketal of claim 5 wherein R.sup.2 and R.sup.3 are each t-amyl. 8. The peroxyketal of claim 5 wherein R.sup.2 and R.sup.3 are each cumyl groups. 9. The peroxyketal of claim 1 wherein n is 1. 10. The peroxyketal of claim 9 wherein R.sup.1 is ethyl and R.sup.2 and R.sup.3 are each independently t-butyl. 11. The peroxyketal of claim 9 wherein R.sup.1 is ethyl and R.sup.2 and R.sup.3 are each independently t-amyl. 12. The peroxyketal of claim 9 wherein R.sup.1 is methyl and R.sup.2 and R.sup.3 are each independently t-butyl. 13. The peroxyketal of claim 1 wherein n is 2. 14. The peroxyketal of claim 13 wherein R.sup.1 is ethyl and R.sup.2 and R.sup.3 are each independently t-butyl. 15. The peroxyketal of claim 13 wherein R.sup.1 is ethyl and R .sup.2 and R .sup.3 are each independently t-amyl. 16. The peroxyketal of claim 1 wherein n is 3. 17. The peroxyketal of claim 16 wherein R.sup.1 is methyl and R.sup.2 and R.sup.3 are each independently t-butyl. 18. A method for curing a resin comprising: contacting a curable cross-linkable resin with a cure-effective amount of a peroxyketal having the structure: ##STR13## wherein; R.sup.1 is C.sub.1 -C.sub.10 alkyl, cycloalkyl, alkaryl, or aryl which may be unsubstituted or substituted with one or more halogen or hydroxy; R.sup.2 and R.sup.3 are each independently C.sub.1 -C.sub.10 alkyl, cycloalkyl, or aralkyl; and n is 1, 2 or 3. 19. The method of claim 18 wherein R.sup.1 is C.sub.1 -C.sub.5 alkyl and R.sup.2 and R.sup.3 are each independently C.sub.3 C.sub.8 alkyl. 20. The method of claim 19 wherein R.sup.1 is methyl. 21. The method of claim 19 wherein R.sup.1 is ethyl. 22. The method of claim 19 wherein R.sup.2 and R.sup.3 are each independently t-butyl. 23. The method of claim 19 wherein R.sup.2 and R.sup.3 are each independently t-amyl. 24. The method of claim 18 wherein R.sup.2 and R.sup.3 are each independently cumyl groups. 25. The method of claim 18 wherein R.sup.1 is ethyl and R.sup.2 and R.sup.3 are each independently t-butyl. 26. The method of claim 25 wherein n is 1. 27. The method of claim 25 wherein n is 2. 28. The method of claim 18 wherein R.sup.1 is ethyl and R.sup.2 and R.sup.3 are each independently t-amyl. 29. The method of claim 28 wherein n is 1. 30. The method of claim 28 wherein n is 2. 31. The method of claim 18 wherein R.sup.1 is methyl and R.sup.2 and R.sup.3 are each independently t-butyl. 32. The method of claim 31 wherein n is 1. 33. The method of claim 31 wherein n is 3. 34. The method of claim 18 wherein the resin is selected from the group consisting of unsaturated polyester resins, epoxy vinyl ester resins, elastomers, thermoplastics, and rubbers. 35. The method of claim 18 wherein the peroxyketal is present in an amount from about 0.5 to about 3.0 phr. 36. The method of claim 35 wherein the peroxyketal is present in an amount from about 1.0 to about 1.5 phr. |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to peroxyketals; more specifically to a class of peroxyketals derived from cyclic .beta.-keto esters. Among other things, the peroxyketals of the present invention provide for improved curing of various resins, such as polyesters, than heretofore obtainable. In another aspect, the invention relates to the curing of resins using such peroxyketals. 2. Description of the Prior Art Organic peroxides have multifarious commercial applications, many of which predominate in the polymer industry. There, organic peroxides are used inter alia to cure various resins, such as unsaturated polyesters, and epoxy vinyl esters; and to crosslink homo- and co-polymers of ethylene and various rubbers. They are also used to polymerize vinyl monomers such as vinyl chloride, styrene, etc. It is necessary for organic peroxides having uses in commercial and industrial applications in the polymerization and copolymerization of polyesters to be readily reactable and of low cost. The more cost effective the organic peroxide the more applicable the material will be to the industry. One means of decreasing the cost associated with such a material is by decreasing the resin cure time, thus enabling more polymerizations to be conducted over a given period of time. Peroxyketals have been the subject of several disclosures in the prior art. For example, U.S. Pat. No. 2,455,569 first disclosed peroxyketals obtained from the reaction of tertiary organic hydroperoxides and carbonyl-containing compounds. 2,2-Bis(tertiary butylperoxy)butane is disclosed in U.S. Pat. No. 2,650,913 to be a catalyst for the polymerization of ethylene. U.S. Pat. Nos. 2,656,334 and 2,692,260 report the use of 2,2-di-(tertiarybutylperoxy)butane as one part of a two component catalyst system useful for polymerization of vinyl compounds. A series of patents (Great Britain 1,047,830; U.S. Pat. Nos. 4,052,543; 4,328,360; 4,365,086) disclose compounds such as n-butyl 4,4-bis(t-butylperoxy)valerate and ethyl 3,3-bis(t-butylperoxy)butyrate. U.S. Pat. No. 3,296,184 discloses a series of peroxyketals used to vulcanize polymers and copolymers. U.S. Pat. No. 3,344,125 discloses a series of substituted cyclohexane peroxyketals. Esters of 4,4-ditert-butylperoxy pentanoic acid are reported in U.S. Pat. No. 3,433,825 as useful for the crosslinking of copolymers of ethylene and monomers containing terminal vinyl groups. U.S. Pat. No. 3,763,275 discloses the polymerization of ethylenically unsaturated monomers and the curing of unsaturated polyester resins and elastomers using .beta.-substituted diperoxyketals. U.S. Pat. No. 4,032,596 reports the use of quaternary ammonium salts as cure accelerators for unsaturated polyester resins containing peroxyketal initiators. Notwithstanding the teachings of the peroxide materials reported by these printed publications, the prior art is deficient with respect to improved gel times and amelioration of exothermic behavior. Clearly there still remains a need for providing new and improved organic peroxides for use in the polymerization and copolymerization of polyesters. Moreover, there is a need for providing a cost effective organic peroxide which is both thermally stable and which increases the speed with which it polymerizes or copolymerizes a material being acted upon. Such an organic peroxide preferably decreases the gel time of resins which it acts upon and may preferably decrease the exothermic temperature of the reaction as a whole. SUMMARY OF THE INVENTION The present invention is directed to a class of peroxyketals derived from cyclic .beta.-keto esters and the use of such peroxyketals in the curing of unsaturated polyester resins. Particularly the present invention provides a peroxyketal comprising the general structure: ##STR1## wherein; R.sup.1 is C.sub.1 -C.sub.10 alkyl, cycloalkyl, alkaryl, or aryl which may be unsubstituted or substituted with one or more halogen or hydroxy; R.sup.2 and R.sup.3 are each independently C.sub.1 -C.sub.10 alkyl, cycloalkyl, or aralkyl; and n is 1,2 or 3. As will be made clearer herein, the peroxyketals of the instant invention unexpectedly manifest significantly reduced gel times as compared to the organic peroxides of the prior art. Reduced gel time in this regard will be appreciated as enabling an increased speed of polymerization or copolymerization. In accordance with another aspect of the present invention, a method of curing a resin is provided wherein a curable cross-linkable resin is contacted with a cure-effective amount of a peroxyketal having the structure: ##STR2## wherein; R.sup.1 is C.sub.1 -C.sub.10 alkyl, cycloalkyl, alkaryl, or aryl which may be unsubstituted or substituted with one or more halogen or hydroxy; R.sup.2 and R.sup.3 are each independently C.sub.1 -C.sub.10 alkyl, cycloalkyl, or aralkyl; and n is 1, 2 or 3. Another benefit provided by the practice of the present invention is a lessening of the exothermic nature of the underlying polymerization reactions which may be found useful in some applications, compared to the prior art. Beneficially, when the curing reaction generates less heat overall, there is a lessening of the development of internal stresses in the cured resin. This in turn will lessen the likelihood of the cured part developing cracks. Product cracking occurs when the heat of exotherm cannot be dissipated satisfactorily, typically during the heating or cooling processes. Product cracking in polymerized and copolymerized reactions potentially results in a total loss of product. DETAILED DESCRIPTION OF THE INVENTION As stated above, the present invention is directed to a class of peroxyketals derived from .beta.-keto esters. The peroxyketals of the present invention comprising the general structure: ##STR3## wherein; R.sup.1 is C.sub.1 -C.sub.10 alkyl, cycloalkyl, alkaryl, or aryl which may be unsubstituted or substituted with one or more halogen or hydroxy; R.sup.2 and R.sup.3 are each independently C.sub.1 -C.sub.10 alkyl, cycloalkyl, or aralkyl; and n is 1, 2 or 3. The substituents referred to are defined herein as follows: The C.sub.1 -C.sub.10 alkyl group may be either normal or branched; preferably R.sup.1 is of the lower alkyl groups in the range from C.sub.1 -C.sub.5, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, t-amyl, pentyl, and the like. The cycloalkyl group is C.sub.5 -C.sub.7, preferably cyclohexane (C.sub.6). Each aryl group consists of one or more aromatic rings of C.sub.6 -C.sub.10, including phenyl (C.sub.6) and .alpha.- and .beta.-naphthyl (C.sub.10). Each aryl group may be unsubstituted or substituted with one or more halogen or hydroxy groups. Each alkaryl group contains up to twenty carbon atoms where each aryl group is C.sub.6 -C.sub.10 substituted with one or more C.sub.1 -C.sub.10 alkyl groups. Preferably the aryl group is phenyl (C.sub.6). Each alkyl group is in the normal or branched configuration and is preferably C.sub.1 -C.sub.3. Each aralkyl group contains up to twenty carbon atoms where each alkyl group is C.sub.1 -C.sub.10 and is substituted with one or more aryl groups; each alkyl group is in the normal or branched configuration and is preferably C.sub.1 -C.sub.4 ; C.sub.3 being most preferred. Each aryl group is C.sub.6 -C.sub.10. In addition, each aryl group may be unsubstituted or substituted with one or more alkyl groups of C.sub.1 -C.sub.3 ; a preferred aryl is phenyl (C.sub.6). A preferred aralkyl is cumyl. In a first preferred embodiment of the invention, R.sup.1 is methyl; in a second preferred embodiment, R.sup.1 is ethyl. Preferably, R.sup.2 and R.sup.3 are each independently C.sub.3 -C.sub.8 alkyls, more preferably they are each independently C.sub.3 -C.sub.6 alkyls, such as propyl, isopropyl, butyl, isobutyl, t-butyl, t-amyl, pentyl, hexyl, and the like. In a preferred practice, R.sup.2 and R.sup.3 are each independently branched alkyls, including more preferably t-butyl or t-amyl. In a most preferred embodiment, R.sup.2 and R.sup.3 are the same substituents, e.g. R.sup.2 and R.sup.3 each are t-butyl or t-amyl. In a preferred practice, n is 1 or 2. In yet another preferred embodiment, R.sup.2 and R.sup.3 are both aralkyls. Preferably the aralkyls are cumyl groups. Specific examples of peroxyketals contemplated by the present invention include, but are not limited to, ethyl 2,2-di(tertiary-butylperoxy)-1-cyclohexane carboxylate, ethyl 2,2-di(tertiary-butylperoxy)-1-cyclopentane carboxylate, ethyl 2,2-di(tertiary-amylperoxy)-1-cyclohexane carboxylate, ethyl 2,2-di(tertiary-amylperoxy)-1-cyclopentane carboxylate, methyl 2,2-di(tertiary-butylperoxy)-1-cyclopentane carboxylate, methyl 2,2-di(tertiary-butylperoxy)-1-cycloheptane carboxylate, and the like, for example. In another aspect, the present invention provides a method of curing a resin comprising contacting a curable or cross-linkable resin with a cure-effective amount of a peroxyketal having the structure: ##STR4## wherein; R.sup.1 is C.sub.1 -C.sub.10 alkyl, cycloalkyl, alkaryl, or aryl which may be unsubstituted or substituted with one or more halogen or hydroxy; R.sup.2 and R.sup.3 are each independently C.sub.1 -C.sub.10 alkyl, cycloalkyl, or aralkyl; and n is 1, 2 or 3. Without limitation, curable or cross-linkable resins contemplated by the method of the invention include, for example, unsaturated polyesters including orthophthalic resins, isophthalic resins, dicyclopentadiene resins; epoxy vinyl ester resins including epoxy novolac-based vinyl ester resins; elastomers including ethylene-propylene copolymers; thermoplastics such as polyethylene; and rubbers such as silicone rubber and styrene-butadiene rubber; or the like. In the practice of this invention the peroxyketals described aforesaid may be utilized in cure effective amounts. While not being limited to particular quantities, a cure effective amount is determinable relative to the subject resin. Exemplary cure effective amounts are within the range of about 0.5 to about 3.0 peroxyketal parts per hundred parts of resin (phr); preferably about 1.0 to about 1.5 phr. The peroxyketals of the present invention may be prepared as physical mixtures in the form of liquids, granules, powders or flakes. A physical mixture in accordance with the present invention may be prepared by mixing a peroxyketal with the desired amount of solvent to retain reactivity and usefulness in polymerizations and copolymerizations. Suitable organic solvents include those normally employed for such peroxides, such as esters of phthalic acid, and aliphatic and aromatic hydrocarbons and mixtures of such hydrocarbons, examples of which include hexane, mineral oil, benzene, toluene, xylene and (iso)paraffins. Other suitable solvents will be familiar to one of ordinary skill in the art. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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