Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2002-11-12
2003-11-04
Ford, John M. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
C544S221000
Reexamination Certificate
active
06642382
ABSTRACT:
The subject of the present invention is a process for preparing polyisocyanates-polyisocyanurates by catalytic cyclotrimerization of polyisocyanate monomers. It relates more particularly to the cyclotrimerization of isocyanate functional groups carried by sp
3
-hybridized carbons of a particular kind. These carbons are carbons either in the neopentyl position, that is to say said carbon is linked to a tertiary radical such as tert-butyl, or said carbon is a secondary or tertiary carbon, preferably belonging to an aliphatic ring.
The cyclotrimerization of isocyanates has been known for several decades. Such trimerizations generally involve mechanisms which are basic by nature. These bases may be ionic by nature, such as hydroxides or salts of a strong base and strong acid. These bases may also be nonionic bases but may have a very accessible and highly basic electron pair.
The first trimerizations carried out were on aromatic isocyanates, that is to say on isocyanates carried by one of the member carbons of an aromatic ring. Such trimerizations do not pose any particular difficulty and suitable catalysts are readily found for easily carrying out trimerizations of aromatic isocyanates.
The problems inherent with aromatic isocyanates have led to the development of aliphatic isocyanates which have chemical and physical properties which are different and often much improved over aromatic isocyanates.
Most aliphatic isocyanates are too volatile to be used as such. It is therefore necessary to increase their molecular weights by producing either oligomers (biurets, trimers, etc.) or oligo-condensates with polyols.
The trimerization of linear-chain aliphatic isocyanates is now well controlled and there are available catalysts capable of carrying out trimerizations efficiently, that is to say with good yields and developing little coloration.
On the other hand, for reasons which are not fully elucidated, the trimerization of branched aliphatic isocyanates, and especially of cycloaliphatic isocyanates or those in the neopentyl position, remains difficult because, on the one hand, of the difficulty of finding catalysts giving satisfactory yields and satisfactory productivity and because, on the other hand, these derivatives have a strong propensity to develop within them undesirable coloration.
Coloration problems, as mentioned above, have already been treated in the case of linear aliphatic isocyanates such as HDI (hexamethylene diisocyanate), but the techniques used are not easily transposable to branched-type isocyanates, such as isocyanates in neopentyl, cycloaliphatic and tertiary positions, in particular because the reactivity of these branched isocyanates is very significantly less than that of linear isocyanates, with the result that the catalysts used for linear aliphatic isocyanates often give low, or even very low, yields in the case of branched isocyanates.
Thus, it has been proposed to use as basic anion a fluoride anion for carrying out cyclotrimerizations of linear aliphatics without coloration, but this technique cannot easily be used for cycloaliphatics since the yields are very significantly lower in their case.
The degassing of isocyanate monomers has also already been described for the purpose of cyclotrimerizing HDI.
Thus, EP 330 966 discloses a process for trimerizing HDI with the help of a quaternary ammonium hydroxide in which the starting HDI is stripped of carbon dioxide down to a residual content of less than 20 ppm by weight, so as to reduce the amount of catalyst to less than 0.03% by weight for the purpose of reducing the coloration of the final reaction mixture.
EP 524 501 discloses a process for preparing polyisocyanates comprising isocyanurate groups and allophanate groups from HDI by using, as catalyst, a trimethylbenzylammonium hydroxide or a quaternary ammonium hydroxide in which the substituents are C
1
-C
20
alkyl groups optionally substituted with hydroxyl groups. It is specified in that document that the starting HDI mixture contains less than 10 ppm CO
2
.
However, the catalysts illustrated in that document have in three cases methyl substituents, the fourth substituent being either a benzyl group, or a hydroxyalkyl group.
U.S. Pat. No. 5,232,988 discloses a process for preparing blocked polyisocyanates comprising a trimerization reaction on cyclic diisocyanates such as IPDI in the presence of quaternary ammonium carboxylates, phenolates or hydroxides in which the starting diisocyanate is treated by bubbling into it an inert gas.
U.S. Pat. No. 5,914,383 discloses the preparation of a polyisocyanate composition comprising trimers of the iminooxadiazine-dione type and optionally isocyanurate groups in the presence of a polyfluoride as catalyst.
That document discloses in particular the preparation of a composition of the aforementioned type from HDI and IPDI, in which, before the proper catalytic reaction, the gases dissolved in the starting isocyanate mixture are removed.
DE 19 754 748 and EP 927 731 disclose processes for preparing polyisocyanates from IPDI using starting monomers having low chlorine contents, obtained especially by what is referred to as the “urea” process.
On the other hand, EP 379 914 and U.S. Pat. No. 5,013,838 recommend the addition of carbon dioxide during trimerization of aliphatic and/or cycloaliphatic organic diisocyanates, using a catalyst consisting of an ammonium or phosphonium fluoride.
This is why one of the objectives of the present invention is to provide a process which allows branched isocyanate trimers to be obtained while preventing the development of undesirable coloration.
Another object of the present invention is to provide a process which allows good yields and good productivity to be achieved.
Another objective of the present invention is to provide a process which allows the trimerization of cycloaliphatic isocyanates and especially of IPDI (often referred to as isophorone diisocyanate).
Another objective of the present invention is to provide a process which allows the trimerization of cycloaliphatic isocyanates, by improving the reactivity of the catalytic system used for this purpose.
These objectives, and others which will appear later, are achieved by means of a process for trimerizing branched isocyanate functional groups by the action of a quaternary-ammonium- or quaternary-phosphonium-based catalyst, of which the sum of the carbons is at most equal to 30 and at least equal to 12; of which the counterion is chosen from anions corresponding to weak acids whose pK
A
is at least equal to 8, preferably 10 and more preferably 12; of which the substituents are aliphatic (that is to say they are linked to the atom carrying the positive charge via an sp
3
-hybridized carbon atom) and do not possess unsaturation in the beta position (as the benzyl, allyl or propargyl positions have); and in that said oniums comprise at most 2 radicals of more than 6, advantageously more than 10 and preferably more than 12 carbon atoms.
The subject of the invention is also a process for preparing polyisocyanates by cyclotrimerizing isocyanate functional groups carried by isocyanates having a branched hydrocarbon backbone, characterized in that it comprises the following steps:
a) supplying of starting isocyanate monomers;
b) removal of the reactive gases from said isocyanate monomers;
c) optionally, supplying of a starting reaction mixture comprising said starting isocyanate monomers;
d) addition of a cyclotrimerization catalyst consisting of a quaternary ammonium or phosphonium compound, as defined above;
e) reaction until the desired degree of conversion obtained; and
f) optionally, removal of the monomers that have not reacted;
the order of steps b) and c) not mattering.
Thus, removal of the reactive gases may take place on the starting isocyanates themselves or after these have been introduced into a possible reaction mixture comprising a suitable solvent.
It goes without saying that when the reaction is carried out with no solvent, directly in the mass of isocyanates, step c) may be omitted.
Advantageously, no subst
Bernard Jean-Marie
Dallemer Frédéric
Revelant Denis
Burns Doane Swecker & Mathis L.L.P.
Ford John M.
Rhodia Chimie
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