5 Mechanism and Kinetics of the Curing Process in a Resin System J. MOACANIN, M . CIZMECIOGLU, S. D. HONG, and A . GUPTA Applied Mechanics Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, C A 91109
The starting point in course of development of a network model of a thermoset is the reactivity relationships which control the curing reactions at any stage of conversion. We have investigated the cure kinetics of the title resin using differential scanning calorimetry and FT-IR spectroscopy, in order to obtain a correlation between the total conversion as monitored by differential scanning calorimetry, with the rates of formation and disappearance of specific functionalities, as monitored by FT-IR spectroscopy. Reaction rates measured under isothermal conditions at two temperatures yielded preliminary estimates of the principal reaction rates in this system within the experimental temperature range as well as heats (enthalpies) of reaction for each reaction. Previous investigations of the cure kinetics in this system have either emphasized the changes in physical properties such as loss modulus and viscosity of the medium or chemical properties such as the concentration of epoxide or amine functionalities at various stages of cure.(1-7) In several earlier reports, we attempted to derive an overall mechanistic picture for this system which would recognize constraints due to both changing reactivity as well as increasing viscosity.(8-10) Experimental Materials A commercial grade of tetraglycidyl diaminodiphenyl methane (TGDDM), namely MY720 supplied by Ciba Geigy was used as received. Diaminodiphenyl sulfone (DDS) was recrystallized twice to form off-white needles. N,N'dimethyldiphenyl sulfone (DMDDS) was synthesized as follows: 31.7 g (0.1 mole) of 4,4'-dichlorodiphenyl sulfone; 62 ml of 60% aqueous methyl amine, and 5 g of Cu2Cl2 were heated at 0097-6156/83/0227-0083$06.00/0 © 1983 American Chemical Society
84
CHEMORHEOLOGY O F THERMOSETTING P O L Y M E R S
220°C
f o r 24
p r o d u c t
was
hours then
c h a r c o a l
a n d
i s o l a t e d
from
at
f i l t e r e d
- 1 0 ° C and
y i e l d The
was
and
o f
Ν,Ν'
p r e s s u r e
s o l u t i o n from
t h e e l e m e n t a l %C
T h e
a f t e r
a
p r o d u c t
one
m e l t i n g
a n a l y s i s ,
-61.00,
%H
r e a c t i o n
t r e a t e d
c o o l i n g
e t h a n o l
h a s
The
e t h a n o l ,
c e l i t e .
t h e p r o d u c t
a r e :
bomb.
i n b o i l i n g
t h r o u g h
t h e e t h a n o l
e x p e r i m e n t a l l y , %S
h i g h
r e c r y s t a l l i z e d
52%
r e s u l t s
i n a
d i s s o l v e d
a s
w i t h
was
o v e r n i g h t
more
time.
p o i n t
a t
T h e
173°C.
d e t e r m i n e d
-5.85,
%N
-10.21
and
-11.80.
t e t r a m e t h y l d i p h e n y l
s u l f o n e
(TMDDS)
was
s y n t h e s i z e d
a s
f o l l o w s : In
a
2-1
t h r e e - n e c k e d
thermometer, m o l e )
o f
b i c a r b o n a t e
o f
30-50 When
a
powdered
m a i n t a i n e d m o l e )
and
m i l o f
20°C
a
were
p l a c e d
d i m e t h y l
a n
s u l f a t e
t h e a d d i t i o n
o f
f o r 1
was
r a i s e d
60-65°
v a l u e
t o
u n t i l
The
o f
r a p i d l y
added.
The
f l a s k
added
w h i l e w i t h
a t
25
ml
i n a n
o f
s u l f a t e
10
o f
minutes
c a r b o n
c o l d
i c e b a t h
over
a
t h e r e a c t i o n ml
10
was
s l u r r y
i t
i s h e a t e d
140°C
w i t h
t o
i n s m a l l h e a t i n g
s l u r r y water
p o r t i o n s
b a t h
p r o v i d e s
a n
d i s t i l l s .
d r o p p i n g
added
a n d
t h e
m i n u t e s . i n n e r
water
The
f l a s k
(25 m l )
i s then ml
o f
s e v e r a l
times
ml)
f i n a l l y
2 0
8 N
2
S
ml
o f
15
i s added
h e a t i n g
s l u r r y
b a t h .
o f a t
a d d i t i o n a s
t h e
t h e A s
soon
a s
e t h a n o l a m i n e 160-170°
t h e
h e a t i n g
i s
p e r i o d .
t h e
water.
ml
a n d
above
120-140°
t h r o u g h
a n d
from
e t h a n o l a m i n e ,
i s complete,
i s m a i n t a i n e d
c o o l e d
t h e p r o d u c t
Y i e l d :
15
was was
a
50-minute
a t
f l a s k
removed
2 3 0 - 2 4 0 ° ,
160°C,
120-140°
water.
d r y i n g , a n d
w i t h
r e a c h e d
o f
t o
a t
t h i s
A f t e r
f u n n e l
i s
f o r 20 a t
an
i s c o n t i n u e d
u n t i
i s d i s t i l l e d o f f .
100
washed
40-
t h e a d d i t i o n
temperature
Water
a
a n d o f The
temperature
i s r i n s e d h a s
temperature
the
over
i n n e r
A f t e r
f u n n e l
temperature
s t i r r i n g .
i s m a i n t a i n e d
was
a
ml
a t
e t h a n o l a m i n e
u s i n g
30
added
o f
r e a r r a n g e d f l a s k ,
added
c o n d e n s e r ,
kept
c e a s e d .
and
c r y s t a l l i n e
t h e a p p a r a t u s
was
s t i r r i n g
temperature
water,
r e c e i v i n g
H
was
t h e
a n d
was
1 6
( 0 . 0 5
sodium
m i l ( 0 . 3 4
s t i r r i n g
d i o x i d e
f l a s k
C
32
Then
t h e r e a c t i o n
w i t h
o f
i s c o m p l e t e ,
20-25°C.
d u r i n g
r e s u l t a n t
and
d i s t i l l i n g
d i m e t h y l hour
To
the
12.5 g
temperature
i c e b a t h
was
t h e e v o l u t i o n
a d d i t i o n
c o o l e d
When
s t i r r e r ,
50-minute.
c o n t i n u e d
the
w i t h
water.
u s i n g
was
the
f i t t e d f u n n e l
^ A ' - d i a m i n o - d i p h e n y l s u l f o n e ,
i n 25 a t
f l a s k
d r o p p i n g
g 0
%S
-10.53;
%S
-10.69
2 »
a n d
The w i t h
t h e r e a c t i o n
p r o d u c t water
m.p.
Theory: Found:
and
%C %C
from
249-251°C -63.12;
-63.02;
d i l u t e d i s
i n vacuum.
from
A f t e r
h o t m e t h a n o l
( 5 0
o - d i c h l o r o b e n z e n e . E l e m e n t a l
%H %H
m i x t u r e f i l t r a t i o n
d r i e d
i s r e p r e c i p i t a t e d
r e c r y s t a l l i z e d
( 5 4 % ) ,
a f t e r
-6.62;
-6.64;
%N
a n a l y s i s %N
-9.20;
-9.20;
f o r
5. MOACANiN E T A L . D i f f e r e n t i a l DDS
S c a n n i n g
( c o n t a i n i n g
under
h i g h
177°C
(350°F)
was
p l a t e
on
p l a t e
was
i n t e r v a l s
a t
such
as
the
they
a r e
10°C
per
m i n u t e s
as
w e l l
DSC
R e s u l t s
T i , (
0
C ) l
T
p
w h i c h
as
I
t o t a l
T
f
(3
1/2
t h e r m a l and
e v o l v e d
Samples
, ( ° C ) 3
a t
a o f
h r s . )
p a r a m e t e r s a t
w h i c h
per
C u r e d
u n i t
a t
A H , ( J / g ) 4
A H , ( C a l / g )
TIME
280
505
120.6
10
min.
160
266.0
280
280
67.0
20
min.
160
265.0
280
194
46.3
30
min.
160
264.5
280
125
30.0
45
min.
160
263.5
280
100
24.0
160
265.0
280
69
16.5
180
263.0
280
63
15.0
hour
1 1 / 2
h o u r s
2
h o u r s
190
260.0
280
53
12.7
2
1/2
200
260.0
276
52
12.4
3
h o u r s
200
261.0
276
40
9.5
3
1/2
210
258.0
276
35
8.4
h o u r s
h o u r s
Tj[ «
Onset
t e m p e r a t u r e e x o t h e r m ;
the
sample.
d e c r e a s e
o f
4.
a c h i e v e d
d e s c r i b e d c u r i n g
mass
177°C
267
never
and
mode,
160
1.
the
t i m e s
dynamic
b e g i n
and
oven
i n s i d e
t e n
i n
the
h e a t
MY720/DDS
, ( ° C ) 2
a t
85
120°C
t e m p e r a t u r e
m i n u t e s
g i v e s
a t
The
p l a c e d
The
exotherms
the
f o r
gas.
c a l o r i m e t r y
T a b l e
a t
210
MY720
i s o t h e r m a l l y
N2
w i t h d r a w n to
of
p r e p a r e d
c u r e d o f
p l a c e d .
were
m i n u t e .
was
m i x t u r e
t h e r m o c o u p l e
s c a n n i n g
t e m p e r a t u r e s
I.
a
were
Samples 10
DDS)
p r e s s u r e
by
samples
from
A
was
m i x t u r e
p o s i t i v e
d i f f e r e n t i a l
(DSC) o f
(CONTROL)
1
the
T h i s
a
± 2 ° C
maximum,
TABLE
p e r c e n t
c o n t r o l l e d
r a n g i n g by
scanned
of
Ν2·
w h i c h
177°
C a l o r i m e t r y
w e i g h t
under
t e m p e r a t u r e
CURE
22
p u r i t y
m e t a l
a n a l y z e d
Mechanism and Kinetics of Curing Process
i n
Δ Η
i s
•
T h e s e a t
T o t a l
a r e a
a r e a
The o f
r e l a t i v e
shown
of 3.
e x o t h e r m ; T f
i n
p l o t
the t o
F i g u r e
a
«
F i n a l
under
measurements
177°C.
t h e
samples
time
t e m p e r a t u r e e x o t h e r m s ;
the
i n d i c a t e o f
T
c o n t r o l
»
p
Peak
T e m p e r a t u r e
o f
exotherm.
t h a t
c o n v e r s i o n
exotherm
1.
2.
c o m p l e t e as
r e c o r d e d sample
v s .
c u r e
measured
on
the
the
i s
by
above
i s o t h e r m a l
86
CHEMORHEOLOGY O F THERMOSETTING
M i x t u r e s T a b l e
I I ·
thermograms shows DDS
o f MY720,
They were
t y p i c a l
o r
I I .
DDS
r e c o r d e d
T a b l e
DSC
Sample
R e s u l t s
g i v e s
Rate
28
2 5 .
2 2 . 8
21
7
14
14
7
21
DSC
d a t a .
28
I t i s a p p a r e n t i s a p p r o x i m a t e l y
s e c o n d a r y
amine,
a f t e r
m o l e c u l a r
w e i g h t
o f DMDDS
I s o t h e r m a l same as out
b a t c h
f o r cure a t
a t
110°C.
p a r t i a l l y
c u r e
o f MY720
c u r e d
was
r e l a t i v e a l s o
e x c e p t
samples,
a s
a
p
,
t h e
a n d
Temp.
J / g
264
597
20
285
643
40
310
644
10
270
556
20
290
567
699
10
276
558
20
292
589
10
281
575
20
300
564
10
286
549
20
304
563
262
479
5
276
465
10
291
575
20
310
510
40
328
400
e v o l v e d
p e r u n i t
f o r t h e p r i m a r y i s made
DMDDS
Δ Η
°C
254
amine
f o r t h e
mass a n d t h e
h i g h e r
t o DDS. o u t a t
t h e same
that
I I Ig i v e s
T
from
DDS
2 e i t h e r
5
c a r r i e d
a n d
Peak
i n
F i g u r e
10
t h e heat
c o r r e c t i o n
a n d DDS
177°C, T a b l e
a
t h a t
w i t h
2.5
t h e same
shown
a n d DSC
c o n t a i n i n g
d e r i v e d
°C/min
—
100
r e a c t i o n
Scan
( g )
a s
r a t e s .
p a r a m e t e r s
DMDDS
100
100
s c a n n i n g
f o rm i x t u r e s
o f MY720
( g )
100
p r e p a r e d
temperature
o f M i x t u r e s
DDS
100
were
t h e same
r e c o r d e d
( g )
100
a t
a t v a r i o u s
I I a l s o
MY720
No.
a n d DMDDS
a l l mixed
thermograms
DMDDS.
TABLE
were
POLYMERS
1 5 3 ° ±2°C
equipment
t h e i n i t i a l
t h e DSC f u n c t i o n
r e s u l t s o f
cure
u s i n g
a n d
m i x i n g
was
o b t a i n e d time.
t h e
p r o c e d u r e c a r r i e d o n
5.
MOACANiN E T A L .
Mechanism and Kinetics of Curing Process
87
TIME OF CURE (HR) F i g u r e
1.
P l o t
o f
c o n v e r s i o n
i s o t h e r m a l l y DSC
v s .
c u r e d
a n a l y s i s ;
a t
s c a n
c u r i n g 177
r a t e
1
1
1
1
40
80
120
160
β
1
0
C,
time as
samples f r o m
dynamic
10°C/min.
"267,2° C
200
f o r
d e t e r m i n e d
240
280
1
320
1
Γ
360
400
440
TEMPERATURE
