Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phosphorus-containing reactant
Reexamination Certificate
1999-06-14
2001-09-04
Tucker, Philip (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phosphorus-containing reactant
C528S108000, C428S209000, C428S901000
Reexamination Certificate
active
06284869
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to an adduct of an epoxy compound and a cyclic phosphite, the use of such an adduct in a resin formulation, in synthetic materials, and in particular in prepregs and electrolaminates, and to the synthetic materials, prepregs, and electrolaminates thus obtained.
Phosphorous, flame extinguishing, curable epoxy resins are known per se. Swiss patent application 456,949 discloses that such epoxy resins are obtainable by adding to the formulation a particular quantity of adduct prepared from a 1,2-epoxy-containing compound and dialkyl phosphite or dialkenyl phosphite. Examples of dialkyl phosphite and dialkenyl phosphite are dimethyl phosphite, diethyl phosphite, dipropyl phosphite or dibutyl phosphite, as well as diallyl phosphite or dibutenyl phosphite. In the formation of adducts use is made of epoxy resins having, on average, more than one epoxy function per molecule.
U.S. Pat. No. 3,971,813 describes adducts of hydantoin-containing epoxy resins and phosphites. These epoxy resins contain two or more glycidyl groups per molecule. Specifically, only acyclic phosphites are disclosed in this patent specification (i.e. dimethyl, diethyl, and di-n-butyl phosphite). The drawback to the examples described in this patent specification is that the adducts obtained are not in the pure form, and that volatile components are formed which have to be removed under low pressure on conclusion of the reaction.
The use of the dialkyl phosphite compounds mentioned in the examples results in the formation of oligomeric products of high viscosity. Said high viscosity is the result of the dialkyl phosphite compound being capable of both adding to an epoxy group and transesterifying with two hydroxy groups, which creates very large, branched molecules and may lead to gelling. The alcohol and any residual dialkyl phosphite compound have to be removed from the resulting crude adduct at elevated temperature and reduced pressure. The removal is especially hard when the resin is viscous or the alcohol is high-boiling. Residual alcohol is disadvantageous also because during the curing process, particularly at high temperatures, it will cause the release of yet more alcohol from the chemically bound alkoxy groups, which will interfere objectionably with the curing process or lead to blisters in the cured product.
Polymers prepared from compounds carrying two a-epoxy groups with spiro phosphites, such as 3,9-dioxo-3,9-diphospha-2,4,8, 10-tetraoxa-spiro[5,5]-undecane, have been disclosed in Japanese patent publication Sho 46-20824. However, the products concerned are high-molecular polymers which do not contain epoxy groups, and which are not cured and used for further processing into products with extra epoxy groups for application in electrolaminates.
SUMMARY OF THE INVENTION
Surprisingly, it was found in the present invention that the transesterification reaction can be avoided completely or virtually completely by having the epoxide compound react to an adduct with cyclic phosphites according to Formula 1:
wherein R
1
and R
2
may be the same or different and represent H or C
1-4
alkyl, R
3
-R
6
may be the same or different and represent H or C
1-4
alkyl, and m is 1.
Optionally, the adduct comprising epoxy groups is obtainable by condensation of an epoxy compound and a mixture of a cyclic phosphite according to Formula 1 wherein R
1
and R
2
may be the same or different and represent H or C
1-4
alkyl, and m is 1, and a bicyclic phosphite according to Formula 1 wherein R
1
and R
2
are absent, m is 2, and wherein R
3
-R
6
may be the same or different and represent H or C
1-4
alkyl.
For that reason, the invention pertains to an adduct comprising epoxy groups obtainable by condensation of an epoxy compound and at least a monocyclic phosphite according to Formula I, or, optionally a mixture of a monocyclic phosphite and a bicyclic phosphate according to Formula I.
The adduct according to this invention has the advantage compared with the prior art that oligomerization, transesterification, and rapid gelling do not occur. Furthermore, the cyclic phosphites have greater thermal stability than acyclic phosphites, so that the reaction with the epoxide compound is less susceptible to high temperatures and long reaction times.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Particularly preferred are adducts obtained using phosphites wherein m is 1 and R
1
and R
2
may be the same or different and represent H or C
1-2
alkyl and wherein R
3
-R
6
represent H. More preferably still, R
1
and R
2
represent a methyl or ethyl group.
Other suitable phosphites are phosphites according to general formula I, wherein m is 1, R
1
, R
2
, R
3
and R
5
are H, and R
4
and R6 are methyl.
Particular preference is given to 5,5-dimethyl-1,3,2-dioxa-phosphorinane-2 oxide as derivative for adduct formation.
In the preparation of the adduct according to the invention use may be made of a di-, tri-, or polyepoxide, or mixtures thereof.
Suitable difunctional epoxy compounds include epoxy resins prepared by reacting aromatic dihydroxy compounds such as bisphenol A, bisphenol S (sulfone bisphenol) or bisphenol F (methylene bisphenol) with epichlorohydrin. As an example may be mentioned the diglycidyl ether of bisphenol A, which is commercially available under the name Epikote 828®.
Also suitable are cycloaliphatic bisepoxides such as 3,4-epoxy-cyclohexyl-methyl-3,4-epoxycyclohexanecarboxylate and aliphatic bisepoxides such as 1, 4-butanediol dig lycidyl ether.
Examples of polyepoxy resins of the phenol type which are suitable for use in the present invention are polyepoxy resins of phenol-formaldehyde novolak or cresol-formaldehyde novolak based on polyglycidyl ethers, polyepoxy resins based on the triglycidyl ether of tris-(p-hydroxyphenol)methane, or polyepoxy resins based on the tetraglycidyl ether of tetraphenylethane. Polyepoxy resins of the amine type such as the polyepoxy resins based on tetraglycidyl methylene diphenyl diamine and triglycidyl isocyanurate are likewise suitable for use. The term “epoxy resin” also encompasses the reaction products of an excess of epoxy-containing compound (e.g., of the aforementioned type) and aromatic dihydro compounds. These dihydroxy compounds can be halogen-substituted. Various other useful types of epoxy resins are described in Clayton A. May, Epoxy Resins, Marcel Dekker, Inc. (1998). Preferably, the epoxy compounds are not hydantoin derivatives containing glycidyl groups.
The adducts are prepared in a melt using an inert, high-boiling solvent such as dimethyl formamide, or in the absence of a solvent at temperatures in the range of 100 to 200° C. Any addition of small quantities of acid catalyst such as tetramethylammonium chloride or tetrabutylphosphonium bromide salts, basic catalysts such as imidazole, 2-ethyl4-methyl imidazole, or metallic sodium will accelerate the reaction.
The molar ratio of monofunctional cyclic phosphite: epoxy groups is smaller than 1 when m is 1 and smaller than 0.5 when m is 2. Adducts without epoxy groups are obtained when the number of epoxy groups and P-H groups is virtually stoichiometric. Such products are not encompassed within the scope of the instant invention. Since it is envisaged to produce adducts in which epoxy groups are present, it is advisable to employ a less than stoichiometric amount of cyclic phosphite. For instance, one mole of epoxy compound containing on average three epoxy groups per molecule in combination with one mole of cyclic phosphite will give an adduct containing on average two epoxy groups and one phosphorous group.
The forming of the adduct during synthesis can be followed by measuring the disappearance of the epoxy groups as a function of time via titration. It was found that the incorporation of cyclic phosphite is complete when per mole of phosphite used, 1 to 1.1 moles of epoxy groups have disappeared.
The disappearance of the phosphite is demonstrated by the disappearance of the characteristic P-H band at 2400 cm
−1
in the IR spectrum and of the
Buser Antonius Johannes Wilhelmus
Schutyser Jan Andre Jozef
Akzo Nobel N.V.
Dilworth & Barrese LLP
Tucker Philip
LandOfFree
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