Aromatic diamines having one or two benzene rings, two ar-N-methylamino substituents, and ar-alkyl substituents in all positions ortho to the amino substituents are novel compounds which can be used in the preparation of polyurethanes, polyureas, polyurethane-urea polymers, and epoxy resins.

FIELD OF INVENTION 
This invention relates to aromatic diamines and more particularly to 
sterically hindered secondary aromatic diamines which can be used in the 
preparation of polyurethane, polyurea, polyurethane-urea, and epoxy 
resins. 
BACKGROUND 
There are many polyfunctional compounds, including diols and aromatic 
diamines, which are known to be useful as chain extenders in the 
preparation of polyurethane, polyurea, and polyurethane-urea polymers 
and/or as curing agents for epoxy resins. None of these compounds has a 
reactivity such as to make it universally ideal, and many fail to provide 
satisfactory properties in the products made by their use. Thus, there is 
still a need to find other compounds capable of serving as chain extenders 
of curing agents. 
U.S. Pat. Nos. 4,806,616 (Baumann et al.) teaches the use of certain 
N,N'-dialkylphenylenediamines as chain extenders in preparing 
polyurethanes and polyureas by RIM processes. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide novel sterically hindered 
secondary aromatic diamines. 
Another object is to provide polyurethane, polyurea, polyurethane-urea, and 
epoxy resins prepared from such aromatic diamines. 
These and other objects are attained by (A) providing an aromatic diamine 
having one or two benzene rings, two ar-N-methylamino substituents, and 
ar-alkyl substituents in all positions ortho to the amino substituents and 
(B) when desired, using the aromatic diamine to prepare a polyurethane, 
polyurea, polyurethane-urea, or epoxy resin. 
DETAILED DESCRIPTION 
The aromatic diamines of the invention may be any of the aromatic diamines 
described in the preceding paragraph, including such diamines wherein the 
alkyl groups have rather long carbon chains, e.g., chains of up to about 
20 carbons. However, it is generally preferred that the compounds be 
aromatic diamines in which the ar-alkyl substituents are straight- or 
branched-chain alkyl groups of 1-6 carbons, e.g., methyl, ethyl, propyl, 
isopropyl, butyl, t-butyl, pentyl- hexyl, etc. These alkyl substituents 
may be the same or different. 
In a preferred embodiment of the invention, the aromatic diamine is a 
compound corresponding to the formula: 
##STR1## 
wherein R, R', and R" are independently selected from alkyl groups 
containing 1-6 carbons; and it is most preferably such a compound in which 
at least two of the alkyl substituents contain at least two carbons. Of 
these compounds, those particularly preferred are the 
N,N'-dimethyl-3,5-diethyl-2,4-diaminotoluene, 
N,N'-dimethyl-3,5-diethyl-2,6-diaminotoluene, and mixtures thereof. 
In another preferred embodiment of the invention, the aromatic diamine is a 
compound corresponding to the formula: 
##STR2## 
wherein Q, Q', T, and T' are independently selected from alkyl groups 
containing 1-6 carbons and Z is an alkylidene group containing 1-3 
carbons. A particularly preferred aromatic diamine of this type is 
N,N'-dimethyl-3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane. 
Regardless of the particular type of compound involved, the secondary 
aromatic diamines of the invention are prepared by reacting formaldehyde 
with the primary aromatic diamine corresponding to the desired secondary 
aromatic diamine (i.e., an aromatic diamine having one or two benzene 
rings, two primary amino groups attached to the ring or rings, and 
ar-alkyl substituents in all positions ortho to the amino substituents) 
and reducing the -N=CH.sub.2 groups of the resultant aromatic diimine. 
The primary aromatic diamines used as starting materials are well known and 
include, e.g., 3,5-diethyl-2,4-diaminotoluene, 
3,5-diethyl-2,6-diaminotoluene,

A (a mixture of 
3,5-diethyl-2,4-diaminotoluene and 3,5-diethyl-2,6-diaminotoluene), 
1,3,5-triethyl-2,6-diaminobenzene, 3,5-diisopropyl-2,4-diaminotoluene, 
3,5-di-sec-butyl-2,6-diaminotoluene, 
3-ethyl-5-isopropyl-2,4-diaminotoluene, 3,3',5,5'- 
tetraethyl-4,4'-diaminodiphenylmethane (MBDEA), 
3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane, 
3,3'-dimethyl-5,5',-di- t-butyl-4,4'-diaminodiphenylmethane. 
Except for the use of such aromatic diamines, the formaldehyde/amine 
reaction is conducted by techniques known for converting amines to imines, 
e.g., the techniques disclosed in March, Advanced Organic Chemistry, 
Second Edition, McGraw-Hill (New York), page 817 (1977), and the 
references disclosed therein. It is generally preferred to employ 2-4 mols 
of formaldehyde per mol of aromatic diamine, to incorporate the 
formaldehyde in the form of paraformaldehyde, and to reflux a mixture of 
the reactants in toluene or other solvent which azeotropes with water in 
order to form the diimine, the water of reaction being removed during the 
course of the reaction. 
Actually, it is somewhat surprising both that the diimine intermediates can 
be prepared by this process and that they are stable and isolable. The 
literature indicates that formaldehyde is analogous to higher aldehydes 
and to ketones in the iminization of amines, but it has not been found 
possible to obtain imines from the aromatic diamines used to prepare the 
present diimines when attempts have been made to react those diamines with 
acetaldehyde or acetone in the presence or absence of catalysts. Also, 
even though March indicates that the presence of an aryl group on the 
nitrogen or carbon of the imine group makes an imine stable, more recent 
literature (e.g., Distefano et al., J. Chem. Soc. Perkin Trans. II, 1985, 
pp. 1623-1627) indicates that at least some of the compounds previously 
believed to be stable aromatic imines had been misidentified and were 
really polymers formed from unstable imines. 
The reduction of the diimine intermediates to the secondary diamines is 
accomplished by known techniques for reducing imino groups, e.g., the 
techniques taught by March on page 34. Of these known techniques, 
reduction with lithium aluminum hydride is preferred. 
When the sterically hindered secondary aromatic diamines are to be used as 
chain extenders in the preparation of polyurethane, polyurea, or 
polyurethane-urea polymers, they are simply substituted for the chain 
extenders that have previously been used in such processes or used in 
conjunction with the known chain extenders, e.g., primary aromatic 
diamines such as those mentioned above; the aromatic polyamines of U.S. 
Pat. Nos. 3,428,610 (Klebert), 4,218,543 (Weber et al.), 4,595,742 (Nalepa 
et al.), and 4,631,298 (Presswood), the teachings of all of which are 
incorporated herein in toto by reference; polyhydroxyalkanes containing 
2-6 carbons and 2-3 hydroxyl groups, such as ethylene glycol, the 1,2- and 
1,3-propylene glycols, the 1,4-, 1,2-, and 2,3-butanediols, 
1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, glycerol, 
1,2,4-butanetriol, 1,2,6-hexanetriol; and mixtures thereof. Thus, the 
chain extender or mixture of chain extenders is reacted with an organic 
polyisocyanate and an active hydrogen-containing organic compound or with 
a prepolymer thereof having a free -NCO content of at least 0.1% by weight 
to form the desired polymer. Exemplary of the isocyanates and active 
hydrogen-containing organic compounds that can be used are those taught in 
Nalepa et al. 
When the sterically hindered secondary aromatic diamines are to be used as 
curing agents for epoxy resins, they are just substituted for the curing 
agents that have previously been used to cure such resins or used in 
conjunction with the known curing agents, e.g., the aromatic polyamines 
and/or polyhydroxyalkanes described above as known chain extenders. The 
epoxy resin may be any epoxy resin, i.e., it may be saturated or 
unsaturated, aliphatic, cycloaliphatic, aromatic, or heterocyclic. 
Exemplary of such resins are those taught in Lee et al., Handbook of Epoxy 
Resins, McGraw- Hill (New York), 1967, the teachings of which are 
incorporated herein in toto by reference.