A process of endcapping a polyimide system with an endcapping agent in order to achieve a controlled decrease in molecular weight and melt viscosity along with predictable fracture resistance of the molded products is disclosed. The uncapped system is formed by combining an equimolar ratio of 4,4'-bis (3,4-dicarboxyphenoxy) diphenylsulfide dianhydride (BDSDA) and 1,-bis (aminophenoxy) benzene (APB) dissolved in bis (2-methoxyethyl)ether. The endcapped system is formed by dissolving APB in bis-(2-methoxyethyl)ether, adding the BDSDA. By varying the amount of endcapping from 0 to 4%, molecular weight is decreased from 13,900 to 8660. At a processing temperature of 250 C, there is a linear relationship between molecular weight and viscosity, with the viscosity decreasing by two orders of magnitude as the molecular weight decreased from 13,900 to 8660

Burks, H. D.

Stclair, T. L.

English

NASA Technical Reports Server

United States Patent [191 
St. Clair et al. 
[11] Patent Number: 4,552,931 
[45] Date of Patent: Nov. 12, 1989 * 
[54] PROCESS OF END-CAPPING A POLYIMIDE 
SYSTEM 
[75] Inventors: Terry L. St. Clair, Poquoson; Harold 
D. Burks, Newport News, both of 
Va. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
The portion of the term of this patent 
subsequent to Apr. 24,2001 has been 
disclaimed. 
[73] Assignee: The United States of America as 
[ * 3 Notice: 
[21] Appl. No.: 649,328 
[22] Filed: Sep. 11,1984 
[51] Ink Cl.4 .............................................. C08G 73/10 
[52] U.S. Cl. .................................... 525/432; 525/436; 
528/179; 528/182; 528/185; 528/352; 528/353 
[58] Field of Search ............... 528/185, 352, 353, 179, 
528/182; 525/432,436 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,179,630 4/1965 Endrey .................................. 260/78 
3,179,632 4/1965 Hendrix ................................ 260/78 
3,234,181 8/1966 Oliver ................................... 260/47 
3,943,107 3/1976 Seltzer et al. ......................... 260/65 
3,998,786 12/1976 D'Aleiio ............................... 260/47 
4,417,044 11/1983 Parekh ................................ 528/185 
4,429,102 1/1984 Evans et al. ........................ 528/185 
4,443,591 4/1984 Schmidt et al. ..................... 528/185 
4,444,979 4/1984 St. Clair et al. ..................... 528/185 
Primary Examiner-Lester L. Lee 
Attorney, Agent, or Firm-Howard J. Osborn; Wallace 
J. Nelson; John It. Manning 
[571 ABSTRACT 
A process of endcapping a polyimide system with an 
endcapping agent in order to achieve a controlled de- 
crease in molecular weight and melt viscosity along 
with predictable fracture resistance of the molded prod- 
ucts is disclosed. The uncapped system is formed by 
combining an equimolar ratio of 4,4'-bis(3,4dicarboxy- 
phenoxy) diphenylsulfide dianhydride (BDSDA) and 
1,3-bis(aminophenoxy)benzene (APB) dissolved in 
bis(2-methoxyethy1)ether. The endcapped system is 
formed by dissolving APB in bis-(2-methoxyethyl)e- 
ther, adding the endcapping agent, and then adding the 
BDSDA. By varying the amount of endcapping from 0 
to 4%, molecular weight is decreased from 13,900 to 
8660. At a processing temperature of 250" C., there is a 
linear relationship between molecular weight and vis- 
cosity, with the viscosity decreasing by two orders of 
magnitude as the molecular weight decreased from 
13,900 to 8660. A greater drop in viscosity is noted at 
higher temperatures. Apparent viscosity as a function of 
molecular weight at 250" C. and at 280" C. is depicted in 
FIG. 2. Reducing the molecular weight also results in a 
linear decrease in the fracture resistance from 4100 
J/m2 to 296 J/m2, as shown in FIG. 1. 
7 Claims, 2 Drawing Figures 
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tion of molecular weight @fn) at 250" C. and 280" C. for 
BRIEF SUMMARY OF THE INVENTION ORIGIN OF THE INVENTION 
According to the present invention, the foregoing 
ees of the U.S. Government and may be used by or for and other objects are attained by endcapping a novel 
the Government for governmental purposes without linear pO1yphenylene ether sulfide-imide 
the payment of any royalties thereon or therefor. (BDSDA/APB) with phthalic anhydride as the endcap- 
10 ping agent. As the amount of endcapping is varied from 
BACKGROUND OF THE INVENTION 0 to 4%, molecular weight decreased from 13,900 to 
8660. There was also a decrease in apparent viscosity. 
At 250" C., the Viscosity decreased linearly from about 
106 Pa-sec to less than 104 Pa-sec. At higher tempera- 
orders of magnitude at 280" C. (See FIG. 2). Increasing 
a linear decrease in fracture resistance from 4100 J/mf 
to 296 J/m2 (see 
DETAILED DESCRIPTION OF THE 
INVENTION 
PROCESS OF END-CAPPING A POLYIMIDE 
SYSTEM the BDSDA/APB system. 
m e  invention described herein was made by 
polyimides are a class of polymers have proved 
through 
and injection molding. Linear 
are 
useful in aeronautical and space 
aromatic polyimides, although not processable via con- l5 tures there was a greater decrease in viscosity-three 
exceptionally thermally stable, have a high glass transi- to 4% also resulted in 
ventional thermoplastic or hotmmelt 
tion temperature, and are resistant to attack by 
organic solvents. Linear aromatic polyphenylene oxides 
and sulfides, on the other hand, are more easily pro- 
cessed than polyimides, exhibit lower glass transition 
temperatures, have good thermal stability although not 
the amount Of endcapping from 
'1. 
20 
equal to polyimida, and do not have the solvent re& BDSDA/APB* was formed 
h c e  of polyimides. In the present invention a novel by c o m b k g  an equimolar ratio of 4,4'-bis(3,4-dicar- 
polymer has been synthesized that combines the favor- 25 boxyphenoxy)diphenylsulfide dianhydride (BDSDA) 
able properties of both polyimides and polyphenylene and 1y3bis-(aminophenoxY)benzene (APB) dissolved in 
An uncapped 
and me new system can now be pro- 
cessed using conventional thermoplastic techniques. In 
order to maximize use properties and processability, 
molecular weight was varied by varying the amount of 30 
endcapping with a monoanhydride. The effect of end- 
parent viscosity, the latter decreasing by two orders or 
magnitude at a processing temperature of 250" C. and 
of 280" C. 
Accordingly, an object of the present invention is to 
provide a process for making a polyimide that is pro- 
cessable via conventional thermoplastic or hot-melt 
Another object of the present invention is to provide 
a process for endcapping a polyimide system with a 
monoanhydride. 
Another object of the present invention is to provide 
bis(2-methoxyethy1)ether at a 15% solids level. The 
structure Of BDSDA/APB9 the uncapped 
polyimide* is shown 
capping is to decrease both molecular weight and ap- 0 
three orders of magnitude at a processing temperature 35 II 
0 
techniques. 40 
a process for controlling molecular weight and appar- 45 The endcapped system is formed by 
ent viscosity of a polyimide at different temperatures. 
APB dis- 
solved k bis(2-methoxyethyl)ether with an endcapping 
A further object of the invention is to maximize flow 
characteristics for a molecular weight material with the 
agent, e.& phthalic anhydride. The structure of the 
endcapped polymer is as 
V 
60 
desired fracture resistance by establishing the relation- 
ship between the amount of endcapping, molecular 
weight, and fracture resistance. 
BRIEF DESCRIPTION OF DRAWINGS 65 
FIG. 1 is a graph of the fracture energy (GI,) as a where n=5-100. 
function of the molecular weight (an) for the The endcapping agent can be any monoanhydride of 
BDSDA/APB system of the present invention; and the general type 
3 
0 
II 
A 
4,552,93 1 
4 
EXAMPLE I11 
Preparation of Molding Power 
The polymer solution was poured into a mechanical 
blender containing distilled water causing the polya- 
mide-acid to precipitate. The rotating blender blades 
chopped this material into a fluffy consistency. Suction 
filtration isolated the solid polymer which was then air 
dried overnight. The dried polymer was spread in a 
lo baking dish, placed in a forced-air oven and heated to 
loo" C. The polymer was held at this temperature for 
one hour to drive off any residual water and solvent. 
The oven temperature was then increased to 200' C. 
15 and held there for one hour to convert the amide-acid to 
\C' 
II 
0 
where R is any alkyl moiety, or 
0 
II 
\ /  
II 
C 
Ar' '0 imide. 
EXAMPLE IV 
Preparation of Molding 
The imidized powder was placed in a matched-metal 
molding die which had previously been preheated to 
sure of 1.38-2.07 MPa (200-300 psi). After maintaining 
the above temperature and pressure for one-half hour, 
molding was removed. When prepared in discs up to 
brown and transparent. 
C 
0 
where Ar is any aryl moiety, 
or a monofunctional amine of the general type R-N~ 
any aryl moiety. 
the weight decreased from 13'900 to 86609 
ent viscosity was linearly decreased from about 106 
Pa-sec to less than 104 Pa-sec. There were larger de- 
creases in apparent viscosity at higher temperatures as 30 
shown in FIG. 2. While increasing the amount of end- 
20 
where R is any alkyl moiety, or Ar-NHZ where Ar is 160' c. Consolidation Wa.5 effected by applying a pres- 
By the amount Of endcapping from to 4%9 25 the mold was cooled to appro-ately 100" C. and the 
while at a processing temperature Of 250' "9 the aPPar- 0.635 cm in thickness, the resultant molding was light 
EXAMPLE V 
Rheology 
from ' to 4%, fracture resistance linearly A capillary rheometer (Instron Model 321 1) was used 
to determine melt flow properties at both 250' C. and decreased, from 4100 J/m2 to 296 J/m2 (See l). 
SPECIFIC EXAMPLES 
EXAMPLE I 
Preparation of the Uncapped Polymer 
280' C. Because the capillary had a sufficiently large 
35 length-to-diameter ratio of 33, there was no need to 
correct for wall drag. Thus, no end corrections were 
required. 
EXAMPLE VI 
Mechanical Testing 
The uncapped polymer was formed by dissolving 
1.OOO mole of 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl- 40 
sulfide dianhydride (BDSDA) and LOO0 mole of 1,3- 
bis(aminophenoxy)benzene (APB) in bis(2-methoxye- 
thy1)ether M o w n  as diglyme) at a 15% solids level in a 
flask equipped with ma@etic stirringo The 
n e  fracture energy values (Gd, the Opening mode 
rates, were determined for each strain energy 
system. Each sample was machined from a disc 5.715 
run at a crosshead speed of 0.127 cm/min according to 
ASTM Standard E 399-78A. The results are depicted in 
FIG. 1. 
was 45 cm diameter, 0.127 cm thick, precracked stirred for one hour to build molecular weight. 
EXAMPLE I1 
PreDaration of the EndcaDDed Svstem 
.A 
EXAMPLE VI1 
Molecular Weight 
The number average molecular weight (Mn) was 
determined at room temperature for the polyamide-acid 
dissolved in tetrahydrofuran using a Knauer Membrane 
EXAMPLE VI11 
Apparent Viscosity 
The apparent viscosity was calculated by dividing the 
flow stress by the strain rate, both of which are mea- 
sured using a capillary rheometer. The strain rate was 
not corrected to obtain the wall rate. Therefore, the 
viscosity is an apparent rather than a true viscosity. 
It is thus Seen that the foregoing Examples are illus- 
trative of a novel approach of endcapping a polyimide 
system to control molecular weight, melt viscosity and 
The endeapped system was prepared by dissolving 50 
APB in bis(2-methoxyethy1)ether. Adding phthalic an- 
hydride (PA) and stirring the system for 15 minutes. 
BDSDA was added and the system was stirred for one 
hour to allow molecular weight to build. The ratios of 
reactants used for the different endcapped systems are 55 Osmometer. 
shown in Table I. 
TABLE I 
Endcapping System APB, moles BDSDA, moles PA, moles 
60 
1% 1.000 0.995 0.010 
2% Loo0 0.990 0.020 
4% 1 .oo0 0.980 0.040 
Note that since BDSDA is difunctional, a decrease of 65 
one percent of BDSDA must be offset with a concomi- 
tant increase of two percent in PA which is monofunc- 
tional. fracture resistance. 
4,552,93 1 
5 6 
ll 
Although the invention has been described relative to 
a specific polyimide system (BDSDA/APB) and a spe- 
cific end-capping agent (phthalic anhydride), other 
suitable polymer systems exist, and are considered 
The specific Examples described herein are to merely 
illustrate the invention and are not to be deemed as II 
exhaustive. Thus, various modifications and variations 0 
of the present invention will be apparent to those skilled 
in the art without departing from the spirit and scope of 10 where Ar is any aryl moiety, 
the appended claims. a monofunctional amine of the general type 
Letters Patent of the United States is: 
0 
C 
within the scope of the invention. 5 A/ \o 
\C/ 
What is claimed as new and desired to be secured by R--NH;! 
where R is any alkyl moiety, and Ar-NH2 
where Ar is any aryl moiety. 
2. The process of claim 1 wherein the specific end- 
capping agent is phthalic anhydride. 
3. The process of claim 1 wherein the endcapped 
system is formed by dissolving 1,3-bis-(aminophenoxy)- 
benzene (APB) in bis(2-methoxyethyl)ether, adding the 
adding 4,4'bis-(3,4 dicarboxyphenoxy)diphenylsulfide 
(BDSDA) and stirring for one hour to yield a resultant 
endcapped system having the formula of: 
1. A process of endcapping a polyimide system 
having the uncapped chemical structure of 15 
0 
20 endcapping agent, stirring for 15 minutes, and then 
II S 
0 0 
where n=5-100. 
4. The process of claim 1 wherein the molecular 
35 weight is lowered from 13,900 to ,8660, with a concomi- 
tant decrease in melt viscosity, by endcapping the sys- mowox+ tem 1 4 % .  with varying amounts of phthalic anhydride from 
5. The process of claim 4 wherein there is a linear 
40 relationship between molecular weight and apparent 
viscosity with the 13,900 system having a viscosity of 
about lo6 Pa-sec and the 8660 system with a viscosity of 
less than 104 Pa-SeC at a processing temperature Of 250" 
c- 
6. The process of claim 5 wherein there is a greater 
drop in viscosity at temperatures above 250" C.; at 280" 
C., the loss is more than three orders of magnitude. 
7. The process of claim 4 wherein an increase in end- 
capping from 1 4 % ,  while decreasing molecular weight 
50 from 13,900 to 8660, also results in a linear decrease in 
fracture resistance from 4100 J/m2 to 296 J/m2 thus 
permitting maximization of flow characteristics for a 
molecular weight material with the desired fracture 
resistance. 
where n=5-100 
comprising reacting an endcapping agent with the 
uncapped polyimide system for a controlled period 
of time and wherein the endcapping agent is se- 
lected from the group consisting of: 45 
0 
II 
/\O 
\c/ 
II 
0 
* * + * e  where R is any alkyl moiety, 55 
65 


Process of end-capping a polyimide system

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