Diamine compounds having the structural formula: ##STR1## wherein R.sup.1 and R.sup.2 are independently methyl, ethyl or isopropyl groups, can be used in preparing various polymers which are useful in gas separation membranes. The combined effect of alkyl substituents ortho to the amino groups along with the specific bridging group imparts useful properties to polymeric membranes formed with these diamines.

TECHNICAL FIELD 
The present invention relates to ortho-alkylated bisanilines which are 
useful in polymer preparations for gas membrane applications. 
BACKGROUND OF THE INVENTION 
There is a need for improved polymeric materials that are highly permeable, 
yet may under certain circumstances, provide selective separation of 
various gas combinations. Such materials would especially be useful in 
commercial, non-cryogenic gas separation processes. 
The commercial application for gas separation devices based on polymeric 
materials relies, in part, on maximizing the overall gas flux through the 
membrane. P. H. Kim, et al., J. Appl. Poly. Sci., 34 1761 (1987), reported 
that the gas flux for a membrane is relatable to the average space between 
the polymer chains. In addition, they indicated that the density of the 
polymer is also related to the overall gas flux. The problem, in part, for 
these commercial applications is to identify polymers with very high flux 
and with good thermo-mechanical properties. It has generally been observed 
that to achieve high overall flux requires having a polymer with low 
chain-chain interactions. This can be exemplified by polymers such as 
poly(dimethylsiloxane) or poly(4-methyl-1-pentene). These materials have 
rather high gas flux values. These high flux materials have, because of 
their low chain-chain interaction, low glass transition temperatures (Tg). 
As a consequence, these materials require either special processing 
conditions to build in chemical and physiochemical crosslinking or they 
can be used only at rather low application temperatures. By contrast, 
polymers with strong chain-chain interactions have rather high Tg values 
and have usually exhibited rather low gas flux. 
Polyimides, which generally have strong chain-chain interactions and have 
high Tg values, have been reported to have good gas flux values for 
certain specific structures. Specifically, U.S. Pat. No. 3,822,202 (1974), 
U.S. Pat. No. Re. 30,351 (1980) discloses a process for separating fluids 
using a semipermeable membrane made from polyimides, polyesters or 
polyamides. The repeating units of the main polymer chain of these 
membranes are distinguished in that such repeating units have at least one 
rigid divalent subunit, the two main chain single bonds extending from 
which are not colinear, is sterically unable to rotate 360.degree. around 
at least one of these bonds, and has 50% or more of its main chain atoms 
as members of aromatic rings. 
U.S. Pat. No. 4,705,540 discloses a highly permeable aromatic polyimide gas 
separation membrane and processes for using said membrane. The membrane is 
an aromatic polyimide membrane in which the phenylenediamines are rigid 
and are substituted on a essentially all of the positions ortho to the 
amino substituents, and the acid anhydride groups are essentially all 
attached to rigid aromatic moieties. 
U.S. Pat. Nos. 4,717,393 and 4,717,394 teach polymeric membranes and 
processes using the membranes for separating components of the gas 
mixture. The membranes disclosed in both of these patents are 
semi-flexible, aromatic polyimides, prepared by polycondensation of 
dianhydrides with phenylenediamines having alkyl substituents on all ortho 
positions to the amine functions, or with mixtures of other, non-alkylated 
diamines, some components have substituents on all positions ortho to the 
amine functions. It is taught that the membranes formed from this class of 
polyimides exhibit improved environmental stability and gas permeability, 
due to the optimization of the molecular free volume in the polymer. It is 
also taught that such membranes can be photochemically crosslinked, which 
in some instances results in a better performing membrane. 
U.S. Pat. No. 4,378,400 discloses gas separation membranes formed from 
aromatic polyimides based upon biphenyltetra-carboxylic dianhydride for 
separating various gas mixtures. Japanese patent application 62-112372 
discloses a polymeric membrane with an aromatic condensed polyimide as the 
film material. 
M. Salame in Poly. Eng. Sci., 26 1543 (1986}developed a predictive 
relationship for oxygen permeability coefficient [(PO.sub.2)] and polymer 
structure. In the publication he demonstrates the group contributions of 
various structural portions of a polymer to P(O.sub.2) values. In 
particular he indicates the presence of an aromatic group, such as phenyl, 
in place of a methylene (--CH.sub.2 --) decreases the P(O.sub.2) values 
for a pair of comparative polymers. 
U.S. Pat. No. 4,769,399 discloses an adhesive composition which is the 
reaction product of an admixture of an effective amount of a phenoxy 
resin, at least one epoxy resin and a fluorene curative. Additionally, 
European patent application 203828 (1986) also discloses a fluorene 
compound for use in adhesives. 
W. D. Kray and R. W. Rosser in an article entitled "Synthesis of 
Multifunctional Triarylfluoroethanes .1. Condensation of Fluoro Ketones" " 
J. Org. Chem. 42 No.7 (1977) 1186-9 teach a synthesis technique for making 
compounds having the structural formula: 
##STR2## 
SUMMARY OF THE INVENTION 
Novel alkylated 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethanes have 
been found which are useful in preparing various polymers for gas 
separation membranes. These diamine compounds can be represented by the 
structural formula: 
##STR3## 
wherein R.sup.1 and R.sup.2 are independently methyl, ethyl or isopropyl 
groups. 
The presence of the optimum combination of a 
1-phenyl-2,2,2-trifluoroethylidene bridging group and the steric effects 
of specific alkyl groups ortho to the amine function, impart desirable 
properties to membranes formed from polymers prepared from these diamines. 
Specifically, such polymer membranes typically exhibit increased oxygen 
permeance, increased average main chain spacing and decreased average 
polymer density compared to membranes formed from similar polymers without 
these specific diamines.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is drawn to novel alkylated 
1,1-bis{4-aminophenyl}-1-phenyl-2,2,2-trifluoroethanes represented by the 
structural formula: 
##STR4## 
wherein R.sup.1 and R.sup.2 are independently methyl, ethyl or isopropyl 
groups. 
The above diamines are prepared by the acid-catalyzed condensation of the 
appropriately substituted aniline with 1,1,1-trifluoroacetophenone, and 
when polymerized with appropriate dielectrophiles, provide polymers which 
are useful as gas separation membranes. These diamines can be described as 
ortho-alkylated bisanilines wherein the bridging group is a 
1-phenyl-2,2-trifluoroethylidene moiety. The combined effect of the 
specific substituents ortho to the amino groups along with the particular 
bridging group results in diamine monomers which are extremely useful in 
polymer preparations for gas membrane applications. Polymers, such as 
polyimides, prepared from these diamines are effective as high flux gas 
separation membranes, in part, due to restricted rotation and/or low Van 
der Waal energy for the bridging group and the steric bulk of the alkyl 
groups ortho to the diamine functional groups. These physical properties 
result in polymer membranes which exhibit high oxygen permeability, high 
average main chain spacing and decreased average polymer density when 
compared to similar polymers made from prior art diamines. 
In the diamine structure, both ortho positions to each amino group are 
alkyl groups selected from methyl, ethyl and isopropyl. In a preferred 
embodiment, at least one ortho position to each amino group is isopropyl 
and most preferably all four ortho positions are isopropyl. Accordingly, 
the preferred diamine of this invention is 
1,1-bis(3,5-diisopropyl-4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane. A 
key feature of this invention is the presence of alkyl groups at both of 
the ortho positions to each amino group. It has been shown that if 
hydrogen is substituted for an alkyl group at any of these ortho 
positions, the diamine does not exhibit the desired properties. While 
these diamines are useful in forming polyimide gas separation membranes, 
they are also useful in forming other polymers for membrane and other 
applications, as well as for other uses, such as in adhesive compositions. 
EXPERIMENTAL 
Preparation of 1,1-Bis(4-aminoaryl)-1-phenyl-2,2,2-trifluoroethanes 
The following general procedure was used to prepare the 1,1-bis 
(4-aminoaryl)-1-phenyl-2,2,2-trifluoroethanes. Specific product yields and 
physical properties, along with the specific diamines synthesized are 
outlined in Table 1. All compounds provided satisfactory spectral and 
elemental analysis. 
A 50.00 g (0.333 mol) portion of trifluoromethanesulfonic acid was slowly 
added to 1.75 moles of an arylamine, corresponding to the desired 
bisaniline product, contained in a one liter, three necked flash with 
mechanical stirring. After thorough mixing had occurred. 43.53g (0 250 
mol) of 1,1,1-trifluoroacetophenone was added. The mixture was then heated 
to 155.degree. C. for 17 hrs. under an atmosphere of nitrogen with 
continuous stirring. After which time, the reaction vessel was fitted with 
a Claisen distillation head and the excess arylamine along with some of 
the acid were removed via vacuum distillation. The residual product was 
cooled below 80.degree. C. then neutralized with a solution of 40.0 g 
(1.00 mol) of sodium hydroxide in 200 ml of water. A 800 g portion of 
toluene was then added with vigorous stirring. After 5 min., stirring was 
discontinued and the layers were separated. The organic layer was dried 
over anhydrous magnesium sulfate then the toluene was evaporated. Polymer 
grade diamine was obtained from the residue after recrystallization 
followed by vacuum drying at 80.degree.-100.degree. C./5 mm Hg for 24 
hours. 
TABLE 1 
______________________________________ 
Preparation of 1,1-Bis(4-aminoaryl)-1-phenyl-2,2,2-trifluoroethanes 
##STR5## 
##STR6## 
Diamine % Isolated 
Sample R.sup.1 R.sup.2 Solvent Yield mp .degree.C. 
______________________________________ 
1* H H toluene/hexane 
80.0 214-216 
2 CH.sub.3 
CH.sub.3 
toluene/hexane 
64.5 171-173 
3 CH.sub.3 
i-C.sub.3 H.sub.7 
toluene 44.6 160-162 
4 i-C.sub.3 H.sub.7 
i-C.sub.3 H.sub.7 
toluene/hexane 
66.0 182-185 
______________________________________ 
*Comparative sample 
EXAMPLES 1-4 
The diamine compounds synthesized above were reacted with 6F-dianhydride to 
form polyimides in accordance with the procedures set out in U.S. patent 
application Ser. No. 07/316,214. The resultant polyimides were cast as 
thin film membranes and tested for oxygen permeance (Po.sub.2) and O.sub.2 
/N.sub.2 selectivity (.alpha.O.sub.2 /N.sub.2). The results of these 
tests, along with the specific polyimide structures are set out in Table 2 
below. 
TABLE 2 
__________________________________________________________________________ 
##STR7## 
Example R.sup.1 R.sup.2 .sup.--P.sub.O2 
.alpha.(O.sub.2 N.sub.2) 
__________________________________________________________________________ 
1* H H 3.83 
5.0 
2 CH.sub.3 CH.sub.3 25.5 
3.0 
3 CH.sub.3 i-C.sub.3 H.sub.7 
57.2 
3.5 
4 i-C.sub.3 H.sub.7 
i-C.sub.3 H.sub.7 
80.0 
3.22 
__________________________________________________________________________ 
*Comparative example 
From the results reported in Table 2 above, it is clearly shown that the 
diamines of the present invention can be used to form polyimide membranes 
which exhibit significantly higher oxygen permeance than polyimides formed 
from prior art diamines. 
Having thus described the present invention, what is now deemed appropriate 
for Letters Patent is set out in the following appended claims.