Rigid urea-modified polyisocyanurate foams with improved dimensional stability and flame retardancy have densities of 0.5-20 p.c.f., a limiting oxygen index greater than 22 and dimensional changes at 100% R.H. and 70.degree. C. of less than 2% in any linear dimension and a method of making same. The method comprises reacting an organic polyisocyanate, a blowing agent and an N,N'-dialkyl aromatic diamine in the presence of a trimerization catalyst and, if water is used as the blowing agent, a blowing catalyst, wherein the N,N'-dialkyl aromatic diamine and an amine produced by water, if used, constitute the sole sources of active hydrogen.

FIELD OF THE INVENTION 
The present invention relates to rigid polymeric foams. Specifically, the 
invention relates to urea-modified isocyanurate rigid foams and a method 
for making such foams. 
BACKGROUND OF THE INVENTION 
Rigid polyurethane foams are recognized as excellent thermal insulation 
materials. Yet, they are not truly flame retardant. Isocyanurate foams are 
considerably more flame-retarding, but the unmodified foams made therefrom 
are highly cross-linked and are extremely brittle. Previous attempts have 
been made to reduce the brittleness of the isocyanurate foams by employing 
modifiers to reduce the amount of cross-linking. For example, 
flame-retardant urethane-modified polyisocyanurate rigid foams have been 
known since 1966 (Ashida, Polyisocyanurate Foams, Chap. 6, The Handbook of 
Polymeric Foams and Foam Technology, edited by D. Klempner and K. C. 
Frisch, Hauser Publishers, 1991, p 96); also amide-, carbodiimide- and 
imide-oxazolidone-modified polyisocyanurate foams. Ashida, ibid, p 97-8. 
Heat resistant and flame-retardant polyisocyanurate-polyurea foams 
prepared by reaction of diisocyanates with aqueous solutions of 
trimerization catalysts were disclosed in East German Patent 126,460. 
Urea-modified isocyanurate foams were disclosed in U.S. Pat. No. 
4,425,446. The disclosed foams were useful in retrofitting wall cavities 
with insulating material, in that the material was substantially 
completely risen before setting or gelling. The urea-linkages were formed 
by an initial reaction between water and a multifunctional isocyanate 
which causes early rising of the foam. Additionally, the patentee 
discloses further modification of the formulation by the addition of a 
primary or secondary terminated polyamine, to form additional urea 
linkages. The polyisocyanurates of the present invention have rise times 
which exceed their gel times and set times. 
Secondary amines have previously been proposed as curing agents for 
TDI-based flexible polyurethane foams, Gattuso et al Secondary Amine 
Extended Flexible Polyurethane-Urea Foams, Polyurethanes 88, Proceedings 
of the S.P.I. 31st Annual Technical/Marketing Conference, Oct. 19-21, 
1988. 
U.S. Pat. No. 3,846,351 describes the use of secondary phenylene diamines 
in combination with polyols as catalysts and chain extenders in the 
production of flexible polyurethane foams. More recently, it has been 
shown in U.S. Pat. No. 4,578,446 to House et al that N-alkylated 
methylenedianilines are suitable curing agents for urethane prepolymers, 
i.e., in elastomer production via non-RIM processes. In U.S. Pat. No. 
4,801,674 to Scott et al, N-alkylated methylene dianilines are disclosed 
as suitable curing agents for RIM applications. However, neither patent 
discloses the unexpected beneficial results achieved with the rigid 
polyisocyanurate foams of the present invention. 
SUMMARY OF THE INVENTION 
The invention relates to a rigid urea-modified polyisocyanurate composition 
with improved dimensional stability and flame retardency and a method for 
making the same. The method for making a dimensionally stable rigid 
urea-modified polyisocyanurate having a density of from 0.5-20 p.c.f., 
dimensional stability at 100% relative humidity (R.H.) and 70.degree. C. 
of less than 2% change in linear dimension in any direction and a limiting 
oxygen index (L.O.I) greater than 22 comprises reacting an organic 
polyisocyanate and an N,N'-disubstituted aromatic diamine having the 
structure 
##STR1## 
where R is selected from the group consisting of monovalent alkyl- or 
alkenyl moieties containing from 3 to about 20 carbon atoms and monovalent 
aromatic moieties containing from 6 to about 10 carbon atoms, and R.sub.2, 
R.sub.3 are independently selected from the group consisting of hydrogen 
and alkyl moieties containing 1 to 3 carbon atoms, and where the relative 
amount of polyisocyanate and aromatic diamine is such that the NCO/NH 
ratio is from 1 to 9. The reaction is effected in the presence of a 
catalytically effective amount of a first catalyst which catalyzes the 
blowing reaction between an isocyanate and water, if water is used as a 
blowing agent, and a second trimerization catalyst which catalyzes the 
formation of the isocyanurate ring, 
##STR2## 
The diamine and the amine produced by water, if used as a blowing agent, 
constitute the sole sources of active hydrogen. 
The foams of the invention are commercially desirable because of their 
reduced flammability, lower friability, excellent insulating properties 
and dimensional stability compared to available polyisocyanurate foams. 
Also important is the greater isotropicity imparted to the rigid foams 
through the use of specific N,N'-di-sec-alkyl-substituted aromatic 
diamines, i.e., the greater uniformity of load-bearing properties between 
the directions, parallel to rise and perpendicular to rise. 
In a preferred embodiment the invention relates to a dimensionally stable, 
rigid urea-modified polyisocyanurate having substantially no urethane 
linkages and a density of 1.5-6 pounds per cubic foot. 
DETAILED DESCRIPTION OF THE INVENTION 
Although rigid foam polyisocyanurates modified only by urea linkages have 
been proposed for the application in retrofitting wall cavities with 
insulating material, a reaction in which the gel time is longer than the 
initial rise time is required. Moreover, there is no requirement for 
dimensional stability since the walls provide the necessary boundaries and 
warping or shrinking after installation is of relatively minor importance. 
On the other hand, it is essential to the production of uniform insulating 
panels for original building construction that the panels be dimensionally 
stable after their formation and not be subject to shrinkage or warping or 
aging. This latter objective is achieved by reacting a polyfunctional 
isocyanate composition primarily with a polyfunctional amine in the 
presence of a blowing catalyst and a trimerization catalyst to produce a 
rigid isocyanurate foam. A major amount of the urea linkages in the final 
rigid foam is derived from the polyfunctional amine, although if water is 
used as a blowing agent, alone or with other known blowing agents, it will 
react with the polyfunctional isocyanate to produce a primary amine which 
can subsequently react with an isocyanate moiety to afford additional urea 
linkages. In any case, it is important that the amines, and optionally 
water as a blowing agent, are the sole source of active hydrogen, i.e., 
the sole isocyanate-reactive materials in the reaction mixture to avoid 
the formation of other types of linkages in the final rigid foams, such as 
urethane linkages which arise via reactions with, e.g., polyols. A first 
catalyst, such as those known in the art as blowing catalysts, is 
incorporated in the reaction mixture if water is used as a blowing agent. 
A second catalyst known for promoting the trimerization reaction to 
produce an isocyanurate is also incorporated in the reaction mixture. 
Where water is present, the initial reaction taking place, catalyzed by 
the blowing catalyst, is between the water and the polyfunctional 
isocyanate to form a primary amine. The primary amine, if water is 
present, and the disecondary aromatic diamines of this invention react 
with additional polyfunctional isocyanate molecules to produce an 
isocyanate-capped substituted urea intermediate compound in the following 
manner: 
##STR3## 
and OCN--R.sub.4 --NCO is a polyisocyanate of this invention, and R, 
R.sub.2 and R.sub.3 are as defined hereinbefore. Another reaction which 
occurs, catalyzed by the trimerization catalyst, is formation of the 
isocyanurate ring according to the reaction, 
##STR4## 
The incorporation of water in the reaction mixture as the blowing agent is 
in an amount from about 0.1 up to about 6.0 parts per 100 parts isocyanate 
when used alone. The reaction of water and an isocyanate moiety leads to 
the formation of additional urea linkages in the final foam product and 
produces carbon dioxide to form the cells of the foam. Alternatively, part 
or all of the water may be replaced by a conventional blowing agent such 
as chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's), 
hydrofluoroalkanes (HFA), acetone, methylenechloride, methylchloroform, 
etc. "Handbook for Reducing and Eliminating CFC's in Flexible Polyurethane 
Foams", EPA Publication 21A-4002, April 1991, page 21 et seq. Where water 
is used only in part as the blowing agent it may be used in amounts as 
little as 0.1 parts per 100 parts isocyanate. 
The product is a rigid urea-modified isocyanurate foam having substantially 
no urethane linkages, excellent insulating properties, is non-friable and 
exhibits flame retardance, dimensional stability on aging and a density of 
0.5 to 20 p.c.f., usually 1 to 12 p.c.f., preferably 2 to 8 p.c.f. and 
most preferably 1.5 to 6 p.c.f. 
Flame retardancy, as measured by the Butler Chimney Test, is excellent and 
is in the range 71% to 98%. 
Multi-functional isocyanates which can be used in the invention are well 
known in the production of polyurethanes and polyureas and include 
monomers and polymers containing at least two isocyanate groups. Thus, 
diisocyanates and higher functionality polyisocyanates are intended and 
include both aliphatic and aromatic multifunctional isocyanates such as 
2,4- and 2,6-toluene diisocyanate and mixtures thereof (inclusively 
referred to sometimes as TDI); diphenylmethane diisocyanate (MDI), 
polymeric MDI (PAPI-27) and modified MDI. 
Blowing catalysts are well known in the art and need not be discussed at 
length herein. It is important that catalysts used in the present 
invention provide a reaction profile such that the blowing reaction of 
water and the multifunctional isocyanate is more rapid than the 
trimerization reaction and is substantially complete prior to the 
formation of the isocyanurate. Blowing catalysts meeting this criterion 
also are well known to those in the art and include bis-dimethyl 
aminoethyl ether (NIAX A-1 sold by Union Carbide), 
dimethylaminoethoxylethanol, N,N-dimethyl-3-[2-dimethyl amino ethoxy] 
propylamine, (Thancat DD sold by Texaco), and triethylene diamine (Dabco 
33LV). 
Trimerization catalysts are also well known. In the present invention, the 
formation of isocyanurates takes place after the urea reaction has been 
substantially completed. Any of the conventional trimerization catalysts 
well known in the art can be used in the invention including as 
representative examples TMR-2 from Air Products, substituted triazines, 
such as Polycat 41 from Air Products, alkali metal salts of organic acids 
such as sodium or potassium octanoate, hexanoate, or laurate, and 
phospholines, etc. 
The sole isocyanate-reactive component (i.e., sole source of active 
hydrogen), except when water is used as the blowing agent, is an 
N,N'-disubstituted aromatic secondary diamine of the following structure, 
##STR5## 
where R is selected from the group consisting of a monovalent alkyl or - 
alkenyl moieties containing from 3 to about 20 carbon atoms or a 
monovalent aromatic moiety containing from 6 to about 10 carbon atoms, and 
each of R.sub.2 and R.sub.3 is H or an alkyl moiety having 1 to 3 carbon 
atoms. The amount of diamine added to the multi-functional isocyanate is 
determined by the isocyanate/amine ratio, NCO/NH, and can be from about 1 
to about 9, and is preferably 3-7. 
Preferred R groups are secondary alkyl and, of these, the secondary butyl 
group is especially preferred. Examples of secondary and tertiary alkyl 
groups which may be used in the practice of this invention include 
iso-propyl, -sec-butyl, sec-pentyl, sec-hexyl, sec-heptyl, sec-octyl, 
sec-nonyl-sec-decyl, sec-undecyl, sec-dodecyl, sec-tridecyl, 
sec-tetradecyl, sec-pentadecyl, sec-hexadecyl, sec-heptadecyl, 
sec-octadecyl, sec-nonadecyl, and sec-eicosyl moieties. Examples of 
secondary alkenyl groups are the unsaturated counterparts of the 
aforementioned alkyl groups. Tertiary alkyl or alkenyl groups, i.e., those 
which are fully substituted at the carbon atom bound to the nitrogen may 
be useful in the practice of this invention, but there is the risk that 
the size and/or shape of the molecule may prevent the reaction or slow it 
down due to hindrance. 
Additionally, the diamines can be blends of the above diamines or can be 
blended with another secondary diamine having a single aromatic ring with 
the following structural formula 
##STR6## 
where R is selected from the group consisting of a monovalent alkyl- or 
alkenyl moiety containing from 3 to about 20 carbon atoms or a monovalent 
aromatic moiety containing from 6 to about 10 carbon atoms. Exemplary 
compounds useful in blends, in addition to the previously mentioned 
dianiline compounds are N,N'-di-sec-butyl-p-phenylene diamine and 
N,N'-di-sec-octyl-p-phenylene diamine. 
The urea-modified polyisocyanurates are obtained by the following 
procedure. The reactants, including auxiliaries, are mixed in a 
conventional manner by bringing the "A-side", comprising the 
multi-functional isocyanate, into contact with the "B-side", comprising 
the remaining reactants, catalysts, curing agents, blowing gents, 
combustibility modifiers, surfactants, etc., into contact in a nozzle and 
directed onto a conveyor or into a mold. The foam cures in from about 12 
to 18 hours and, preferably overnight at ambient temperatures. 
The mixture of isocyanate-reactive components also may contain other 
materials, such as surfactants, combustibility modifiers, curing agents, 
etc. Examples of surfactants include the sodium salts of sulfonates or of 
fatty acids, amine salts of fatty acids, alkali metal or ammonium salts of 
sulfonic acids, polyether siloxanes, and the like. The component mixture 
also may contain pigments, dyes, flame retardants, stabilizers, 
plasticizers, fungicides and bactericides, and fillers. 
The composition of the foams of this invention result from several 
reactions, and although the chemistry of each reaction is basically quite 
simple the multiplicity of reaction paths makes formulation of the 
resulting foam quite complicated. What we shall do below is to express 
separately the various reactions which can occur, which ultimately will 
permit some formulation of the resulting foam. 
In the first instance let us deal with that branch of our invention where 
water is not used as the blowing agent, i.e., the secondary amines of our 
invention are the sole source of active hydrogen. The polyisocyanate is 
represented for convenience as a diisocyanate, OCN-R.sub.4 -NCO, and the 
aromatic diamine is represented as RNH-R.sub.5 -NHR. 
A. Reaction of isocyanate with aromatic diamine; product I 
##STR7## 
B. Reaction of aromatic diamine with product I; product II 
##STR8## 
C. Reaction of isocyanate with product I; product III 
##STR9## 
D. Trimerization of isocyanate; product IV 
##STR10## 
E. Trimerization of I; product V 
##STR11## 
F. Reaction of IV with aromatic diamine; products V-VII 
##STR12## 
G. Chain extension; reaction of IV+V as representative 
##STR13## 
H. Chain extension; reaction of isocyanate with II 
##STR14## 
From the foregoing it can be seen that chain extension via path H leads to 
a polymer 
##STR15## 
Where the repeating unit is the structure within brackets, and the 
end-capping unit E is OCN-- or RNHR.sub.5 N(R)C(O)NH-- and F is --R.sub.4 
NCO or --R.sub.4 NHC(O)N(R)R.sub.5 NHR. 
Similarly, but rather more complicatedly, is the chain extension via G, 
##STR16## 
where the repeating unit is the structure within brackets. The third 
nitrogen in IX also may participate in chain extension, - a branch leading 
to crosslinking - or it may be capped by structures such as --R.sub.4 NCO 
and R.sub.4 NHC(O)N(R)R.sub.5 NHR. 
Since IV and V are trifunctional, ample opportunities for crosslinking 
occur. That is, reaction between functional groups carried on different 
polymer chains links the chains, which is precisely the meaning of the 
term crosslinking. 
In the instance when water is used as the blowing agent the structural 
representation of the final product becomes even more complicated, because 
the aromatic diamine RNHR.sub.5 NHR is no longer the sole source of active 
hydrogen, and because other amines which may form contain primary amino 
moieties, each one of which may react with more than one isocyanate 
moiety. The primary amines are generated by reaction of water with the 
isocyanate moiety according to the following representative (but not 
exhaustive) equations. 
##STR17## 
Each of the aforegoing amines also can react with any reactant or product 
bearing an isocyanate group, which can be readily appreciated to greatly 
increase the number and diversity of polymeric products. However, since 
only a small amount of water is used relative to aromatic diamine, in fact 
only few structural units arise which are attributable to reactions with 
primary amino moieties. 
In summary, then, the polyureas of this invention are characterized by the 
presence of repeating units VIII and IX, where OCN--R.sub.4 --NCO is 
selected from the group consisting of 2,4-toluenediisocyanate, 
2,6-toluenediisocyanate, 4,4'-diisocyanatodiphenylmethane (diphenylmethane 
diisocyanate, or MDI), the 2,4'-and 2,2'-isomers of MDI, polymeric MDI and 
modified MDI (see "The ICI Polyurethanes Book", J. Wiley and Sons, 1987, 
pp. 29-34).