Catalyst for making polyurethanes

Polyurethane foams with excellent physical properties can be obtained by using a partial salt between N,N-dimethylaminopropane-1,3-diamine (DMAPA) and a branched octanoic acid.

DETAILED DESCRIPTION OF THE INVENTION 
Polyurethanes are widely used where rigid, semi-rigid or flexible foams are 
needed. Particularly, in formulations leading to flexible products and to 
some extent in the others, blowing agents are used to provide a cellular 
structure. While water can be used as the only blowing agent, most 
polyurethane foams are made by using fluorinated hydrocarbons such as 
those known as Freon.RTM. compounds. However, because of environmental 
considerations, fluorinated hydrocarbons are in current disfavor and may 
some dlay have to be replaced entirely in formulations used on large scale 
such as urethane manufacture. 
Unfortunately, the replacement of the fluorocarbons by other materials 
requires much more than just a subsitution thereof by other halogenated 
hydrocarbons; in fact, many foam formulations where the Freon has been 
substituted, for example, by methylene chloride, do not lead to usable 
polyurethanes. Methylene chloride would otherwise fit all of the needs of 
a blowing agent, having the right vapor pressure and other physical 
characteristics. 
Because methylene chloride cannot simply be substituted for a Freon, other 
adjustments need to be made in the urethane formulations. Obviously, it is 
not desirable to change the polyols or the polyisocyanates that have been 
manufactured in large scale in the past. The simplest adjustment therefore 
lies in the selection of a catalyst for the urethane reaction. 
Amine catalysts of all types have been used for many years in the urethane 
foam industry: primary amines, secondary amines, di- or tri-tertiary 
amines, combination of primary and tertiary amines, etc. with or without 
tin co-catalysts and any variation of mixtures of the above. A great many 
of these catalysts or mixtures thereof simply do not produce a useful 
urethane foam when methylene chloride is present. 
It has now been discovered that a partial salt between 
3-dimethylaminopropylamine (hereinafter referred to as DMAPA) and a 
branched octanoic acid produces excellent foams. The term "partial salt" 
must, for the purpose of this description, be interpreted as meaning a 
combination of 10 equivalents of DMAPA with 1 to 5 equivalents of a 
branched octanoic acid, and by no means is intended to identify the named 
combination as a true salt. Branched octanoic acid, for the purpose of 
this description, is intended to define a linear carbon chain of 7 carbons 
carrying the carboxylic acid group in a position other than the 1- or 
7-positions; for instance, dipropylacetic acid, 2-ethylhexanoic acid, 
2-methylheptanoic acid, with the 2-ethylhexanoic acid being the preferred. 
As mentioned before, the "salt" terminology would apply only to part of the 
new mixture since only 10 to 50 percent of the nitrogen functions of DMAPA 
are blocked by the branched octanoic acid. The two reactants are therefore 
just simply mixed in the desired proportion for use as a urethane 
catalyst, requiring no other manipulations than the physical combining of 
the appropriate portions thereof. This mixture can then be used in the 
formulation leading to polyurethane foams and is particularly effective, 
when methylene chloride is used as part of the blowing agent component. 
However, this invention is not limited to the use of the above partial 
salt between DMAPA and a branched octanoic acid in methylene chloride 
blown foams; it can also be used in some Freon blown foams, particularly 
in connection with tin or other amine co-catalysts. The new 
DMAPA/DMAPA-salt mixture, however, is of greatest use where methylene 
chloride is used in conjunction with water and/or other blowing agents, 
and, particularly in the presence of the commonly used diluent dipropylene 
glycol (DPG).

To show the effect of the new catalyst, reference is made to the following 
examples, which, however, are for illustration only and are not intended 
to limit this invention in any respect. All parts and percentages used are 
based on weight unless specified differently; all catalyst percentages are 
based on the amount of polyol used. 
EXAMPLE 1 
After mixing 100 parts of a polyoxyethylene-polyoxypropylene triol 
(marketed as Voranol.RTM.3010 by Dow Chemical), 3.5 parts of water, 12.0 
parts of methylene chloride, 1.2 parts of a silicone surfactant (sold as 
Tegostab.RTM.BF-2370 by Th. Goldschmidt AG), the shown amount of stannous 
octoate used as a 50% solution in dioctyl phthalate (DOP) and the 
specified amount of the partially blocked DMAPA salt, the appropriate 
amount (110% of theoretically calculated stoichiometry, or 110 index) of a 
toluene di-isocyanate (sold by Mondur.RTM.TD-80 by Mobay Chemical) is 
added and stirred at 3,000 rpm for 8 seconds with a 3-inch Conn mixer. The 
stirred mixture is poured into a corrugated cardboard box, 
17.times.17.times.15 inches, and allowed to rise, producing the results 
indicated below in Table I, using 2-ethylhexanoic acid for blocking: 
TABLE I 
__________________________________________________________________________ 
Amine type Mixture (A) DMAPA + 25% EHA 
DMAPA + 50% EHA 
__________________________________________________________________________ 
Amine level 
% 0.2 
0.3 
0.2 0.2 0.2 0.15 
0.15 
0.1 0.1 0.15 
0.2 
DPG % 0 0 0 0 0 -- 0.15 
0.1 0.1 0.15 
0.2 
Tin octoate/DOP 
% 0.6 
0.7 
0.8 1.0 1.2 0.7 0.7 0.7 0.7 0.7 0.7 
Cream time 
Sec 
18 13 17 15 15 15 16 17 16 13 12 
Rise time 
Sec 
(B) 
(C) 
(B) 115 106 135 142 137 135 130 130 
Gel time Sec 
-- -- -- 155 141 160 167 162 155 150 150 
Density pcf 
-- -- -- 1.16 
1.16 
1.28 
1.33 
1.24 
1.21 
1.23 
1.24 
Air flow scfm 
-- -- -- 7.43 
3.83 
5.0 5.6 5.5 4.7 5.5 5.5 
Compr. set 50% 
% -- -- -- -- 
-- -- 6.58 
6.93 
3.87 
5.08 
5.04 
4.88 
Compr set 90% 
% -- -- -- -- 
-- -- 22.07 
7.93 
4.84 
5.63 
5.33 
5.32 
__________________________________________________________________________ 
(A) 33% triethylenediamine in DPG + equal parts of 
N--methyldicyclohexylamine (this mixture thus contains 33.3% DPG) 
(B) Collapsed 
(C) Split 
The above table demonstrates that using 0.2% or more of a standard catalyst 
does not produce a foam; unless at least 0.5% of stannous octoate is used; 
on the other hand, perfectly good foams are obtained when using DMAPA 
blocked by 25 and 50%, respectively, of 2-ethylhexanoic acid starting with 
0.1% catalyst and 0.7% stannous octoate. 
EXAMPLE 2 
In order to show the use of the above new catalyst in conjunction with 
other amine catalysts, DMAPA is used with 25% 2-EHA blockage. The 
formulation shown in Example 1 is used; the co-catalyst is [Me.sub.2 
N(CH.sub.2).sub.3 ].sub.2 N-Me. As shown in Table II, good foams are 
obtained, particularly at lower tin catalyst levels. 
TABLE II 
______________________________________ 
Catalyst level 
% 0.15 0.15 0.15 0.125 
0.125 
0.125 
0.125 
DPG % 0.15 0.15 0.15 0.125 
0.125 
0.125 
0.125 
Co-Catalyst 
% -- -- -- 0.05 0.05 0.05 0.05 
level 
Sn(Oct).sub.2 
% 0.6 0.7 0.8 0.6 0.7 0.8 1.0 
level 
Cream time 
Sec 17 17 15 15 14 13 12 
Rise time 
Sec 150 140 125 140 130 116 102 
Gel time Sec 175 160 145 165 150 136 117 
Density pcf 1.29 1.24 1.23 1.24 1.21 1.29 1.18 
Air flow scfm 4.5 4.0 1.1 6.8 5.6 2.3 0.27 
50% Compr 
% 6.8 7.7 (D) 6.7 6.4 7.9 (D) 
set 
______________________________________ 
(D) flattened out; collapsed 
EXAMPLE 3 
In order to show the activity of the above catalyst in a low density foam, 
the formulation of Example 1 was changed by increasing the methylene 
chloride level to 18% and that of the surfactant to 1.8%. The same 
catalyst and tin co-catalyst was used as in Example 2 at levels indicated 
below. The DMAPA/2-EHA mixture again was used as a 50% solution in DPG, 
the combined amount being given. 
TABLE III 
______________________________________ 
Catalyst level 
% 0.40 0.50 0.33 0.42 
Co-Catalyst level 
% -- -- 0.07 0.08 
Sn(Oct).sub.2 level 
% 0.8 0.8 0.8 0.8 
Cream time Sec 14 14 13 11 
Rise time Sec 150 135 132 125 
Gel time Sec 170 155 152 145 
Density pcf 1.09 1.10 1.08 1.08 
Air flow Scfm 5.3 3.3 7.2 7.1 
______________________________________ 
The above results show that even low density foams can be made 
successfully, using the new catalyst. This was heretofore not possible 
when methylene chloride was the blowing agent. 
EXAMPLE 4 
The method and materials of Example 1 were used to determine the effect of 
varying amounts of blocking of DMAPA with octanoic acids. In all runs, 
0.3% of a 50% solution of DMAPA or DMAPA/acid combination in DPG was used, 
together with 0.7% of a 50% stannous octoate solution in DOP. The results 
are shown in Table IV which includes an experiment using DMAPA partially 
blocked by valproic acid (V.A.). 
TABLE IV 
______________________________________ 
Acid % -- 2-EHA 2-EHA 2-EHA V.A. 
Blockage % 0 50 10 5 25 
Cream time 
Sec 10 16 16 14 17 
Rise time Sec 105 145 140 132 137 
Gel time Sec 145 188 184 172 177 
Health bubbles 
no no yes yes no yes 
Evaluation split good good split good 
Density Pct -- 1.22 1.20 -- 1.27 
Air flow Scfm -- 4.1 7.9 -- 4.1 
Comp. set 50% 
% -- 5.7 4.6 -- 5.6 
Comp. set 90% 
% -- 6.9 5.0 -- 13.0 
______________________________________ 
Table IV shows that branched octanoic acids other than 2-ethylhexanoic acid 
can be used with equally good foams resulting therefrom. Also demonstrated 
is the fact that more than 5% of a branched octanoic acid is needed to 
produce an acceptable foam as 5% or less yields an unacceptable, split 
foam. Best results are seen using 20-30% equivalent of the above acid. 
Since process times increase expectedly by blocking pars of the active 
catalyst, the use of more than 50% blocked DMAPA becomes uneconomical, 
although good foams may be obtained with 60-75% blocked DMAPA. 
Since catalyst mixtures usually are provided in liquid form, it is 
particularly noteworthy that the new salts are also conveniently soluble 
in DPG, a solvent frequently ued for free amine catalysts for urethane 
reactions. DPG is a favored solvent because it is a reactive participant 
in the fashion of the polyol used. Excellent catalyst compounds are 
therefore those where DMAPA is blocked by 10-50 equivalent % with a 
branched octanoic acid and the mixture is dissolved in 50-200% DPG. A very 
practical and suitable solution contains one part of DMAPA/DMAPA-salt to 
one part of DPG, said salt representing 10-50% of the total catalyst 
content. 
The preferred process of the invention is the preparation of a polyurethane 
foam from a polyisocyanate and a polyol in the presence of methylene 
chloride, DMAPA partially blocked by a branched octanoic acid and an 
amount of DPG equivalent to the weight of said partially blocked DMAPA. 
Other catalysts such as tin salts or other primary, secondary or tertiary 
amines may be added to said reaction and other blowing agents may be used 
in conjunction with said methylene chloride. These additional materials 
would preferably be selected by the processor to best suit his individual 
needs. Thus, the preferred catalyst solution according to this invention 
may include 0.1-0.4% of a tin salt. 
The compounds of the present invention are usable with all types of polyols 
and polyisocyanates. A representative list of these can be found in U.S. 
Pat. No. 4,212,952, col. 2, line 60 to col. 3, line 9 and col. 2, lines 
30-59, respectively.