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Analysis of the kinetics and mechanism of polymerization of N,N′-4,4′-diphenylmethane-bis-maleimide and 4,4′-diaminodiphenylmethane
404
V . S . VOLKOV e$ al.
9. T. NISHI and T. T. WANG, Macromoleeules 8: 6, 909, 1975 10. H. G. Z A C ~ N , Angew. Makromolek. Chemie 6D/61: 2, 249, 1977 11. Yu. K. GODOVSKII, L. M. BRAUDE, Yu. D. SHIBANOV, Ye. I. LEVIN, P. M. VA° LETSKII, S. V. VINOGRADOVA and V. V. KORSHAK, Vysokomol. soyed. A21: 1, 127, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 1, 138, 1979) 12. Yu. K. GODOVSKII a n d Yu. D. SHIBANOV, Vysokomol. soyed. 23: 4, 866, 1981 (Trans. lated in Polymer Sei. U.S.S.R. 23: 4, 966, 1981) 13. S . P . PAPKOV, Ravnovesiye faz v sisteme polimer-rastvoritel (Phase Equilibrium in the P o l y m e r - S o l v e n t System), Khimiya, Moscow, 1981 14. Yu. K. GODOVSKII, P. M. VALETSKII, L. M. BRAUDE, Ye. I. LEVIN, Yu. D. SHIRANOV, S. V. VINOGRADOVA and V. V. KORSHAK, Dokl. Akad. l~auk SSSR 244: 5, 1149, 1979
P o l y m e r Science U.S.S.R. Vol. 25, No. 2, lap. 404-412, 1983 Printed in Poland
0032-3950/83 $10.00-b.00 © 1984 Pergamon Press T.td.
ANALYSIS OF THE KINETICS AND MECHANISM OF POLYMERIZATION OF N,N'-4,4'-DIPHENYLMETHANE-bisMALEIMIDE AND 4,4'-DIAMINODIPHENYLMETHANE* V. S. VOLKOV, S. A . DOLMATOV, L . V. YUDI~A, V. S. LEVSHAI~OV, L . I . ~/[ARINYUK a n d L . A . SHOLOKHOVA
(Received 1 September 1981) A s t u d y has been made of the interaction of l~,N'-4,4'-diphenylmethane-bis-maleimide and 4,4'-diaminodiphenylmethane (DAPM) at a molar ratio of 2 : 1, in the melt and in solution in DMF, using methods of I R , potentiometric titration and sol fraction extraction. I t was found t h a t the resulting three-dimensional polymer is polybis-maleimidamine formed in 2 stages. I n the first stage the D A P M amino-group is a d d e d to C----C of the maleimide ring of the bis-maleimide, and oligo-bis-maleimideamine is formed; simultaneously in the first stage an inconsiderable degree of bismaleimide homopolymerization takes place. I n the second stage we have mainly crosslinking of oligo-bis-maleimideamine at the expense of C = C bond opening in the maleimide ring. THERMOSETTING polyimides (TPI) are polymers of a novel t y p e t h a t first became available in 1969. Materials based on T P I are relatively cheap; in addition to their good technological properties, a long service life (up to 103 hr) is obtained for the fabricated articles at 523 K, as well as good mechanical properties. Commercial variants of T P I are prepared mainly from aromatic bis-maleimides and aromatic diamines, particularly I~,I~'-4,4'-diphenylmethanebis-maleimide (DPM) and 4,4'-diaminodiphenylmethane (DAPM). The reaction is conducted in the melt or in solution, using amide solvents. Moreover the formation of polymer takes * Vysokomol. soyed. A25: No. 2, 346-352, 1983.
Polymerization of N,N'-4,4'-diphenylmethane-bis-maleimide
405
place in two stages, the first loading to formation of the fusible and soluble oligo-bis-maleimideamhle (OMA), which is t h e r m a l l y hardened in the second stage, giving the infusible and insoluble poly-bis-maleimideamino (PMA). I t appears from [1-3] t h a t the following reactions p r o b a b l y t a k e place during the interaction of DPM with DAPM. 1. Nucleophilie addition of the amino-group of DAPM to the maleimide double bond 0
\ 7 1
/? 0
o
0
%
-N<
\
- NCI
oZ/
os N~
// 0 2. Maleimide ring opening in DPM
0
+%
~N/~\_]
()
+
()
___
+ -xlt+
OJ
'\.....
3. Maleimide double bond opening 0 ~N C 0
0 ~ N 0
I n view of the d a t a in [2-6] on the interaction of individual p~irs of bis-m~leimides and aromatic diamines, wo would assume t h a t in solutions it is most probable t h a t only the p r i m a r y amino group of the diamine adds to the double bond of bis-maleimide; maleimide ring opening does riot take place in d r y anhydrous solvents, b u t a three-dimensional poly~ner is formed through the opening of free C = C bonds of the maleimide.
Our aim in the present work was to investigate the mechanism and kinetics of polymerization for DPM and DAPM at a molar ratio of 2 : 1 in the m e b and in I ) N F solution. Study of the polymerization kinetics was based on changes in the concentrations of double bonds, primary amino groups and gel fraction during the reaetion, using each of these variables as means of determining the order of the reaction n, the activation energy E and the vMue of the pre-exponent Ko.
406
V . S . V o ~ o v et
al.
The reactants investigated were as follows: pure grade DPM (TU 6-09-06-386-74, m.p. 430-431 K); DAPM (TU 6-14-415-75, m.p. 361.5-362.5 K); pure grade DMF (GOST 20289-74) without a n y further purification. The reaction of OMA formation in DMF was investigated on the basis of change in the bouble bond concentration in the interval 373-423 K up to the moment of the onset of gelation. The reaction of OMA formation in melts was investigated in the interval 423-473 K through change in the concentration of double bonds and primary amino groups. The hardening reaction of OMA was investigated in the interval 423-523 K through change in the concentration of double bonds and gel fl'action. The synthesis of OMA m DMF solution was carried out with continuous stirring in a flask provided with a reflux eolJdenser. The synthesis and hardening of OMA in the melt was performed with melting a n d thorough stirring of a mixture of DPM and DAPM powders with a particle size of 30 l~m in a glass ampoule. The reaction time was taken to be that passing from the moment of complete melting of the mixture of monomers so as to take no account of the diffusion period during melting of the mixture. The reaction was terminated b y freezing the reaction mass irt liquid nitrogen. The mlmber of double bonds was determined by infl~red (UR-10 spectrophotomcter) ill DMF solution and in K B r discs. We took as an analytical band t h a t at 690 cm -~ relating to out-of-plane stretching of C - - H linked to C ~ C . When a,talyzing a solution in DMF we calculated the intensity ratio for the band at 960 cm-1 ar~¢~ for that of the solvent at 660 em --~. When recording the spectrum of a solution we placed some drops of the latter between NaC1 plates. Calibration curves w e ~ used when calculating double bond concentrations. The potentiometric titration method [7] (ptI-121 potentiometer) was used to determine ~mine group concentrations. As a solvent we took a mixture made up of four parts chloroform and one part acetonitrile. A solution of HC104 in methyl ethyl ketone was used as the titrant. To determine the exact normality of the t i t r a n t we carried out the potentiometric titration of recrystallized diphenylguanidine. The equivalence point, viz. the flex point on t.he potentiometric curve was determined, using a second order linear interpolation method. The gel fl'action concentration was determined by Soxhlet extraction of the reaction ma~ss with DMF. The stability of the experimental results was evaluated b y comparing the scatter of results of parallel syntheses and parallel measurements in each of the latter, using the Fischer criterion [8]. I t was found that at all the temperature-time points on the kinetic curves the results of tlm parallel syntheses could be proportionally combined with a 95% confidence probability, i.e. technological errors during experiments have no significant influence on the results obtained. The kinetics of the formation and hardening of OMA prepared by reacting DPM and DAPM (molar ratio 2 : 1) can be seen in Figs. 1 and 2. To describe the experimental data on the polymerization kinetics we used a kinetic equation for an nth order irreversible chemical reaction
dP:K°C~j!(1--p)'exP(d--[ --~E), where p is the degree of completeness of the reaction. T h e a n a m o r p h o s e s o f ghe k i n e t i c c u r v e s p l o t t e d o n c o o r d i n a t e s In ~
-
l n ( 1 - - p ) p r o v e d t o b e l i n e a r a n d h a d a s i n g l e i n f l e x i o n for p o l y m e r i z a t ~ i o n i n t h e m e l t i n v e s t i g a t e d f r o m c h a n g e i n ~he n u m b e r o f d o u b l e b o n d s , u s i n g K B r discs. T h e a m o u n t o f a m i n o - g r o u p s a n d gel f r a c t i o n , w e r e l i n e a r o v e r t h e e n t i r e t e m p e r a t u r e - t i m e i n t e r v a l i n v e s t i g a t e d i n t h e m e l t a n d for ~he s o l u t i o n p o l y -
P r i l n a r y anlino-group concentration C o n c e n t r a t i o n o f gel fraction
Ditto
Double b o n d concentration
o! solution in 20/o DMF
8 0 % solution in DMF Melt
Characteristi('s b e i n g llleasilred
Reaction conditions
122"5~16"3 123"4~11"3
2"0±0"] 2"01:0-2 40"2~5-4
98"7&4'2
75"8~18.8
-
-
7"$~1"5
28"0i4"5 28.7±3-2
20.4i1"3
13.3±5.7
. . . . . . . . . . E, In No kJ/mole
-1" sectiol[ . . . .
2"0±~'11
I R spectroscopy, K B r discs P o t e n t l o m e t r i e t i t r a - i 1"8±0"2 tion Extraction of DMF
Dith~
n
2"0~0"1
......
wI~}i DAPM
137.8~23-4 148"0~23.0
1"2~0"3
l ~ - 0 & 10.4
]l'0:h@2
-2.2±0.2
--
2.8
30.4~5'8
34.8t6"6
46.2
inierv~d-[~l . . . . . . . . . . . . . . . . . . . . . . . E, n In Ko kff/mole
(2 : 1)
i
-
!:0"2
n
l
i
188.n~ 10"4
E, kJ/mole
interval B
i
I 2"0i0"5i165'2i38-1
2"2
i~
i i I I t
f I seeti m
Kinetic parameters of the reaction
}
i
FORMATION DURING INTERACTION OF D P M
I R spectroscopy of the D M F solution
M'ethods of analy~is
KI~C~TIc PARAMETERS OF P M A
32"7~9"8
46"2~2'8
In Ko
Z
©
o
L
408
V . S . VOLKOV e~ al.
m e r i z a t i o n f r o m t h e change in the n u m b e r o f double bonds in D M F solution. T h e discontinuities on t h e curves show t h a t the l a t t e r comprise two portions relating to t w o successive reactions, t h a t of OMA formation, a n d t h e OMA h a r d e n i n g reaction. T h e OMA hardening stage has likewise to be s u b d i v i d e d into two intervals.
CNH ,% J
CL CC:c ~% I
I
a
I08 "*3 6 ~
8 4
I
f
I
I
80 8
z/O
6
1"2
3"6 6"0 Time ~,lO-~ ~ec FIG. 1
•
I 3"6
I
I I I 10.8 18"0 T/me t~lO'~S~ec FIG. 2
FI(]. 1. Interaction of DPM and DAPM (2 : 1) in the melt based on change in the number of arn~uo-groups cz~H,(a) and in the number of double bonds Cc_c (b) and in the gel fraction q (e) at 423 (1), 433 (2), 443 (3), 453 (4), 473 (5) and 493 K (6). FIo. 2. Interaction of DPM and DAPM (2 : 1) in DM-F solution at 373 (1), 403 (2), 423 K (3). Solution concentrations 25 (a) and 30~o (b). Calculations o f t h e kinetic p a r a m e t e r s o f t h e reaction were done s e p a r a t e l y for each portion o f t h e c u r v e and for each i n t e r v a l in t h e h a r d e n i n g reaction, using t h e m e t h o d outlined in [5]. The Table gives the values of t h e kinetic parameters. F i g u r e 3 shows the I R spectra of DPM, and for DAPM, t h e oligomer and t h e h a r d e n e d polymer. T h e p o l y m e r s p e c t r u m is similar t o t h a t o f t h e linear t h e r m o plastic P M A p r e p a r e d f r o m t h e same m o n o m e r s in [4]. I t is seen from t h e F i g u r e t h a t n o change occurs during oligomerization a n d p o l y m e r i z a t i o n in t h e abs o r p t i o n bands for t h e carbonyl group at 1729 and 1780 cm -1 or in t h a t for t h e maleimide ring at 1390 cm -1. I n t h e region o f lqH v a l e n c y vibrations t h e r e are b r o a d b a n d s at 3300-3500 cm -1. I t is seen f r o m t h e Figure t h a t quite a large
Polymerization of ~ff,BT'-4,4'-diphenyhnethane-bis-maleimide
40&
number of double bonds of maleimide ring remain in the oligomer (bands at 690, 3100 and 1150 era-l), whereas in the spectrum of the hardened polymer the latter bands either fail to appear at all, or are very weak. The position and intensity of the bands for amino-groups linked to the double bond of the maleimide ring remain practically constant on going from oligomer to polymer. Thus we conclude from the results of the IR-analysis that the structure of the oligomer and the crossiinked polymer is similar to t h a t of PMA, i.e. only one hydroger~ of the primary amino group is linked to the C-~C bond of the maleimide ring, no maleimide ring opening takes place, and hardening of the OMA takes place on account of opening of the remaining bonds in the maleimide ring.
I
i
3.z
I
I..
z,6'
I
I
1.6
l
I
l.z
I
l
I
I
o.s ~,,lo~, crn -~
Fzo. 3. II~ spectra of DPI~{ (a), DAPM (b), OMI (c) and PM~ (d). Sirme DAX)M is quite an efficient inhibitor of free radical reactions [9], one would expect that polymerization of OMA through the double bond will proceed only when depletion of DAPM in the reaction mass is complete. I t is admitted in this case t h a t only the primary amino group of DAt)M is added by a reversible Mikhael reaction [10], and moreover the equilibrium constant will be such t h a t under the conditions adopted the addition m a y be regarded as irreversible, and the cross]inking of OMA will take place solely by a free radical mechanism. I f these assumpVions were entirely fulfilled, one would expect the kinetic parameters for consumption of the primary amino group to agree with those for double bond expenditure up to a degree of completeness of the reaction of 0.5, and the kinetic parameters of gel fraction formation could be expected to agree
410
V.S. VOLKOVetal.
with those for the reaction based on double bond expenditure after a degree of completeness of 0.5. This means, therefore t h a t points of discontinuity will appear on linear anamorphoses of the kinetic curves of change in the double bond concentration. Clearly, the lower the synthesis temperature the greater the probability of the above scheme being relevant. It is seen from the Table that the ideal scheme outlined above is not fully borne out. In the early stage of the reaction the reaction rates for double bond and primary amine group expenditure obey a second order equation, which accords with findhlgs reported in [4, 5]. However, the apparent activation energies differ fundamentally from one another. It is known [ll] that the activation energies for a nucleophilic reaction of amino group addition to the activated double bond are usually low, amounting to 21-25 kJ/mole, while the activation energy of homopolymeriza~ion of bis-maleimides is 117-144 kd/mole [6]. Points of discontinuity on the kinetic curves separating the portion for soluble OMA formation from that relating to crosslinked polymer formation are displaced, as the temperature falls, towards greater completeness of the reaction based on the amino group, and accordingly into the area where the degree of completeness of the reaction through the double bond is equal to 0.5. Thus at 423 K ~he discontinuity on the kinetic curve and the onset of gelation appear at a degree of completeness of ~0.7 as regards the amino group, and ~0-5 as regards the double bond. At 453 K the discontinuity appears at a degree of completeness o f ~0-3 as regards the amino group, and ~0.4 as regards the double bond. It can therefore be said that in the interval 423-473 K the reaction in the melt relating to the first portion of ~he kinetic curve is mainly one of addition o f the primary amine group of DAPM to the double bonds of DPM and OMA, t h o u g h there is also concurrent homopolymerization of D P M through the double bond. As the temperature falls the share of DPM homopolymerization is reduced, and the kinetic pattern approximates to the ideal scheme. In the second kinetic stage we have mainly the formation of crosslinked polymer. However, the same stage also includes addition of the primary amine group of DAPM to double bonds o f D P M and OMA, hindered by theJaigh viscosity of the partially crosslinked melt. This would account for the fact that the apparent activation energy for the reaction based on change in the number of amino groups amounts to 138 kJ/mole. Data analogous to the above were also obtained in [5]. A join~ process of OMA polymerization through the double bond and primary amine addi$ion ~o the double bond leads to a slight distortion of the kinetic pattern observed for the reaction based on change in the number of double bonds and the amount of gel fraction. In particular, in interval A, when the number of aminogroups of DAPM in the reaction mass is fairly large, the order of the reaction with respect to the double bond is twice that based on the gel fraction, and the apparent activation energy of the reaction based on the double bond exceeds that for the reaction based on the gel fraction b y 45 kJ/mole. In the second portion of the kinetic curve of hardening based on the gel fraction (interval B)
Polymerization of N,N'-4,4'-diphenylmethane-bis-maleimide
411
t h e reaction of OMA h a r d e n i n g a t t h e expense of double b o n d opening takes pla, ee u n d e r conditions d i s t u r b e d ~o a minimal e x t e n t t h e r e a c t i o n o f a m i n o gr,~,ups addition, since t h e amino g r o u p c o n c e n t r a t i o n in t h e reaction mass is practically zero. This is w h y t h e r e is good a g r e e m e n t between kinetic p a r a meters (n, E, In K0) for t h e second portion o f t h e kinetic curve based on t h e double b o n d in i n t e r v a l B a n d the kinetic curve based on t h e gel fraction. W e would t h i n k t h a t t h e kinetics as a whole in t h e melt, as shown in t h e Table, is fairly close to t h e ideal kinetics, particularly in the l o w - t e m p e r a t u r e region, w h e n the c o n t r i b u t i o n of D P M h o m o p o l y m e r i z a t i o n and OMA crosslinking t h r o u g h the double b o n d in t h e first portion of t h e kinetic curve becomes minimal, whiie the degree of conversion o f amino groups a~ the m o m e n t of t h e onset o f gel~tiol~ is maximal. T h e similarity of t h e kinetic p a r a m e t e r s of t h e r e a c t i o n o f OMA f o r m a t i o n in the melt based on change in the n u m b e r o f double b o n d s me~sured in D M F solution a n d in K B r discs means t h a t results o b t a i n e d are unaffected b y t h e m e t h o d of m e a s u r e m e n t , and a p p e a r t o be reliable. On examining the t a b u l a t e d d a t a it is seen t h a t t h e kinetic p a r a m e t e r s for t h e reaction of DP1K-DAPM (2 : 1) i n t e r a c t i o n in D ~ F solution based on t h e do~~ble bond e x p e n d i t u r e are in r e a s o n a b l y good m u t u a l a g r e e m e n t for different concentrations o f t h e reaction mass. A t the same t i m e t h e order o f t h e r e a c t i o n is the same in solution as in the melt, t h o u g h t h e a c t i v a t i o n e n e r g y is h i g h e r in t h e melt t h a n in solution. This means t h a t w h e t h e r in solution or in t h e m e l t t h e reaction takes place b y t h e same mechanism, a n d t h e lower a c t i v a t i o n e n e r g y w h e n tlm reaction is r u n in solution is a t t r i b u t a b l e go t h e cat~lytic a c t i o n t h a t a polar solven~ has [4] on t h e reaction of prima.ry amino group addition t o t h e d,)l~ble hond.
Translated by R. J. A. HENDR~: REFERENCES
1. M. MALLET, hfforms, chim., No. 112, 20i, 209, 1972 2. V. V. SHEREMETEVA, Izv. Akad. Igauk SSSR,, Seriya khim., No. 8, 1474, 1966 3. V. S. IVANOV, Radiatsionna.ya polimerizatsiya {Radiation Polymerization). p. 232, Khimiya, Leningrad, 1967 4. J. CRI.VELLO, J. Polymer Sci. Polymer Chem. Ed. ll: 1185, 1973 5. A. P. SUSLOV, S. A. DOLMATOV, Ye. A. KARGINOVA ~md V. S. LEVSHANOV, Vysokernel, soyed. A22: 6, 1286, 1980 (Translated in Polymer Sci. U.S.S.R. 22: 6, 1412, 1980) ~. D. O. HUMMEL, J. Appl. Polymer Sei. 18: 2015, 1974 7~ A. P. KRESHKOV, L. N. BYKOVA mid I. D. POVZNER, Dokl. Akad. Nauk SSSR 150: 1. 99, 1963 ~. K. KHARTMAN, E. LETSKII and V. SHEFER, Planirovaniye eksperimenta v issle~lowmii tekh~mlogieheskikh protsessov (Plam~ing the Experiments in Investigations ,f Chemical Processes). p. 532, Mir, Moscow, 1977 ~*. I. P. MASLOV, N. A. ZOLOTAREVA, N. A. GLAZUNOVA, A. S. BARANOVA, L. A. DELYUSTO, L. A. PUGACHEVA and G. A. BARYSHINKOVA, KhimichesMe dobavki k i),~limt~ram (Chemical Additions to Polymers). Handbook, p. 51, Khimiya, Moscow, 197;~
412
~'. I. YEGORENKOV a n d A. I. KUZAVKOV
10. G. BECKER, Vvedenie v elektronnuyu teoriyu organicheskikh reaktsii (Introduction to the Electron Theory of Organic Reactions) (Trans. from the Gorman, V. M. I)otapov, Ed.). p. 658, Mir, Moscow, 1977 11. S. I. SUMINOV and A. N. KOST, Uspekhi khimii 38: l l , 1933, 1969
Polymer ScienceU.S.S.R. Vol. 25, i~o. 2, pp. 412-420, 1983 Printed in Poland
0032-3950/83 $10.00÷.00 © 1984PergamonPress Ltd.
STUDY OF THE ADHESION OF POLYETHYLENE TO METALS AT CRYOGENIC TEMPERATURES* N. I. YEOORENKOV and A. I. KUZAVKOV I n s t i t u t e for the Mechanics of Metal-containing Polymer Systems, B.S.S.R. Academy of Sciences
(Received 2 September 1981) A study was made of the influence of temperature (80-295 K) on the adhesion of P E coatings to metals (resistance to separation of the metal foil substrate). I t is shown t h a t a fall in the test temperature a n d a n increase i n the rate of separation leads to a several-fold increase in the resistance to separation and alters the type of failure of adhesive joins. The degree of increase in separation resistance depends on the thickness of the P E coating, and on the nature a n d thickness of the foil substrate. The effectiveness of factors making for better adhesion of P E (oxidation, filling, addition of peroxide compounds, a n d other factors) is impaired when the test temperature is reduced. The paper also e o n t a ~ s data on the adhesion of other polymers, a n d possible explanations of the observed phenomena are discussed.
SEVERAL papers have been published by authors [1-8] investigating the adhesion of PE to metals. Most of these relate to the influence of oxidative processes (and controlling factors) in PE on the adhesive joins. It was found that moderate oxidation of PE makes for better adhesion. In most cases the adhesion investigations were carried out at room temperatures (285-300 K). However, it is known that the adhesion of polymers to metals, characterized by metal--polymer bond strength, e.g. by resistance to separation or peeling is markedly dependent on the polymer relaxation processes, and, accordingly, on the test temperatures [9-11]. It has been pointed out in earlier work [12-14] that in the case of PE-metal adhesive joins resistance to separation and uniform direct pull will vary in line with change in the test temperatures. Our aim in the present instance was to investigate the adhesion of PE coatings to metals at cryogenic temperatures (up to 80 K) in relation to the time * Vysokomol. soyed. A25: No. 2, 353-359, 1983.
V . S . VOLKOV e$ al.
9. T. NISHI and T. T. WANG, Macromoleeules 8: 6, 909, 1975 10. H. G. Z A C ~ N , Angew. Makromolek. Chemie 6D/61: 2, 249, 1977 11. Yu. K. GODOVSKII, L. M. BRAUDE, Yu. D. SHIBANOV, Ye. I. LEVIN, P. M. VA° LETSKII, S. V. VINOGRADOVA and V. V. KORSHAK, Vysokomol. soyed. A21: 1, 127, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 1, 138, 1979) 12. Yu. K. GODOVSKII a n d Yu. D. SHIBANOV, Vysokomol. soyed. 23: 4, 866, 1981 (Trans. lated in Polymer Sei. U.S.S.R. 23: 4, 966, 1981) 13. S . P . PAPKOV, Ravnovesiye faz v sisteme polimer-rastvoritel (Phase Equilibrium in the P o l y m e r - S o l v e n t System), Khimiya, Moscow, 1981 14. Yu. K. GODOVSKII, P. M. VALETSKII, L. M. BRAUDE, Ye. I. LEVIN, Yu. D. SHIRANOV, S. V. VINOGRADOVA and V. V. KORSHAK, Dokl. Akad. l~auk SSSR 244: 5, 1149, 1979
P o l y m e r Science U.S.S.R. Vol. 25, No. 2, lap. 404-412, 1983 Printed in Poland
0032-3950/83 $10.00-b.00 © 1984 Pergamon Press T.td.
ANALYSIS OF THE KINETICS AND MECHANISM OF POLYMERIZATION OF N,N'-4,4'-DIPHENYLMETHANE-bisMALEIMIDE AND 4,4'-DIAMINODIPHENYLMETHANE* V. S. VOLKOV, S. A . DOLMATOV, L . V. YUDI~A, V. S. LEVSHAI~OV, L . I . ~/[ARINYUK a n d L . A . SHOLOKHOVA
(Received 1 September 1981) A s t u d y has been made of the interaction of l~,N'-4,4'-diphenylmethane-bis-maleimide and 4,4'-diaminodiphenylmethane (DAPM) at a molar ratio of 2 : 1, in the melt and in solution in DMF, using methods of I R , potentiometric titration and sol fraction extraction. I t was found t h a t the resulting three-dimensional polymer is polybis-maleimidamine formed in 2 stages. I n the first stage the D A P M amino-group is a d d e d to C----C of the maleimide ring of the bis-maleimide, and oligo-bis-maleimideamine is formed; simultaneously in the first stage an inconsiderable degree of bismaleimide homopolymerization takes place. I n the second stage we have mainly crosslinking of oligo-bis-maleimideamine at the expense of C = C bond opening in the maleimide ring. THERMOSETTING polyimides (TPI) are polymers of a novel t y p e t h a t first became available in 1969. Materials based on T P I are relatively cheap; in addition to their good technological properties, a long service life (up to 103 hr) is obtained for the fabricated articles at 523 K, as well as good mechanical properties. Commercial variants of T P I are prepared mainly from aromatic bis-maleimides and aromatic diamines, particularly I~,I~'-4,4'-diphenylmethanebis-maleimide (DPM) and 4,4'-diaminodiphenylmethane (DAPM). The reaction is conducted in the melt or in solution, using amide solvents. Moreover the formation of polymer takes * Vysokomol. soyed. A25: No. 2, 346-352, 1983.
Polymerization of N,N'-4,4'-diphenylmethane-bis-maleimide
405
place in two stages, the first loading to formation of the fusible and soluble oligo-bis-maleimideamhle (OMA), which is t h e r m a l l y hardened in the second stage, giving the infusible and insoluble poly-bis-maleimideamino (PMA). I t appears from [1-3] t h a t the following reactions p r o b a b l y t a k e place during the interaction of DPM with DAPM. 1. Nucleophilie addition of the amino-group of DAPM to the maleimide double bond 0
\ 7 1
/? 0
o
0
%
-N<
\
- NCI
oZ/
os N~
// 0 2. Maleimide ring opening in DPM
0
+%
~N/~\_]
()
+
()
___
+ -xlt+
OJ
'\.....
3. Maleimide double bond opening 0 ~N C 0
0 ~ N 0
I n view of the d a t a in [2-6] on the interaction of individual p~irs of bis-m~leimides and aromatic diamines, wo would assume t h a t in solutions it is most probable t h a t only the p r i m a r y amino group of the diamine adds to the double bond of bis-maleimide; maleimide ring opening does riot take place in d r y anhydrous solvents, b u t a three-dimensional poly~ner is formed through the opening of free C = C bonds of the maleimide.
Our aim in the present work was to investigate the mechanism and kinetics of polymerization for DPM and DAPM at a molar ratio of 2 : 1 in the m e b and in I ) N F solution. Study of the polymerization kinetics was based on changes in the concentrations of double bonds, primary amino groups and gel fraction during the reaetion, using each of these variables as means of determining the order of the reaction n, the activation energy E and the vMue of the pre-exponent Ko.
406
V . S . V o ~ o v et
al.
The reactants investigated were as follows: pure grade DPM (TU 6-09-06-386-74, m.p. 430-431 K); DAPM (TU 6-14-415-75, m.p. 361.5-362.5 K); pure grade DMF (GOST 20289-74) without a n y further purification. The reaction of OMA formation in DMF was investigated on the basis of change in the bouble bond concentration in the interval 373-423 K up to the moment of the onset of gelation. The reaction of OMA formation in melts was investigated in the interval 423-473 K through change in the concentration of double bonds and primary amino groups. The hardening reaction of OMA was investigated in the interval 423-523 K through change in the concentration of double bonds and gel fl'action. The synthesis of OMA m DMF solution was carried out with continuous stirring in a flask provided with a reflux eolJdenser. The synthesis and hardening of OMA in the melt was performed with melting a n d thorough stirring of a mixture of DPM and DAPM powders with a particle size of 30 l~m in a glass ampoule. The reaction time was taken to be that passing from the moment of complete melting of the mixture of monomers so as to take no account of the diffusion period during melting of the mixture. The reaction was terminated b y freezing the reaction mass irt liquid nitrogen. The mlmber of double bonds was determined by infl~red (UR-10 spectrophotomcter) ill DMF solution and in K B r discs. We took as an analytical band t h a t at 690 cm -~ relating to out-of-plane stretching of C - - H linked to C ~ C . When a,talyzing a solution in DMF we calculated the intensity ratio for the band at 960 cm-1 ar~¢~ for that of the solvent at 660 em --~. When recording the spectrum of a solution we placed some drops of the latter between NaC1 plates. Calibration curves w e ~ used when calculating double bond concentrations. The potentiometric titration method [7] (ptI-121 potentiometer) was used to determine ~mine group concentrations. As a solvent we took a mixture made up of four parts chloroform and one part acetonitrile. A solution of HC104 in methyl ethyl ketone was used as the titrant. To determine the exact normality of the t i t r a n t we carried out the potentiometric titration of recrystallized diphenylguanidine. The equivalence point, viz. the flex point on t.he potentiometric curve was determined, using a second order linear interpolation method. The gel fl'action concentration was determined by Soxhlet extraction of the reaction ma~ss with DMF. The stability of the experimental results was evaluated b y comparing the scatter of results of parallel syntheses and parallel measurements in each of the latter, using the Fischer criterion [8]. I t was found that at all the temperature-time points on the kinetic curves the results of tlm parallel syntheses could be proportionally combined with a 95% confidence probability, i.e. technological errors during experiments have no significant influence on the results obtained. The kinetics of the formation and hardening of OMA prepared by reacting DPM and DAPM (molar ratio 2 : 1) can be seen in Figs. 1 and 2. To describe the experimental data on the polymerization kinetics we used a kinetic equation for an nth order irreversible chemical reaction
dP:K°C~j!(1--p)'exP(d--[ --~E), where p is the degree of completeness of the reaction. T h e a n a m o r p h o s e s o f ghe k i n e t i c c u r v e s p l o t t e d o n c o o r d i n a t e s In ~
-
l n ( 1 - - p ) p r o v e d t o b e l i n e a r a n d h a d a s i n g l e i n f l e x i o n for p o l y m e r i z a t ~ i o n i n t h e m e l t i n v e s t i g a t e d f r o m c h a n g e i n ~he n u m b e r o f d o u b l e b o n d s , u s i n g K B r discs. T h e a m o u n t o f a m i n o - g r o u p s a n d gel f r a c t i o n , w e r e l i n e a r o v e r t h e e n t i r e t e m p e r a t u r e - t i m e i n t e r v a l i n v e s t i g a t e d i n t h e m e l t a n d for ~he s o l u t i o n p o l y -
P r i l n a r y anlino-group concentration C o n c e n t r a t i o n o f gel fraction
Ditto
Double b o n d concentration
o! solution in 20/o DMF
8 0 % solution in DMF Melt
Characteristi('s b e i n g llleasilred
Reaction conditions
122"5~16"3 123"4~11"3
2"0±0"] 2"01:0-2 40"2~5-4
98"7&4'2
75"8~18.8
-
-
7"$~1"5
28"0i4"5 28.7±3-2
20.4i1"3
13.3±5.7
. . . . . . . . . . E, In No kJ/mole
-1" sectiol[ . . . .
2"0±~'11
I R spectroscopy, K B r discs P o t e n t l o m e t r i e t i t r a - i 1"8±0"2 tion Extraction of DMF
Dith~
n
2"0~0"1
......
wI~}i DAPM
137.8~23-4 148"0~23.0
1"2~0"3
l ~ - 0 & 10.4
]l'0:h@2
-2.2±0.2
--
2.8
30.4~5'8
34.8t6"6
46.2
inierv~d-[~l . . . . . . . . . . . . . . . . . . . . . . . E, n In Ko kff/mole
(2 : 1)
i
-
!:0"2
n
l
i
188.n~ 10"4
E, kJ/mole
interval B
i
I 2"0i0"5i165'2i38-1
2"2
i~
i i I I t
f I seeti m
Kinetic parameters of the reaction
}
i
FORMATION DURING INTERACTION OF D P M
I R spectroscopy of the D M F solution
M'ethods of analy~is
KI~C~TIc PARAMETERS OF P M A
32"7~9"8
46"2~2'8
In Ko
Z
©
o
L
408
V . S . VOLKOV e~ al.
m e r i z a t i o n f r o m t h e change in the n u m b e r o f double bonds in D M F solution. T h e discontinuities on t h e curves show t h a t the l a t t e r comprise two portions relating to t w o successive reactions, t h a t of OMA formation, a n d t h e OMA h a r d e n i n g reaction. T h e OMA hardening stage has likewise to be s u b d i v i d e d into two intervals.
CNH ,% J
CL CC:c ~% I
I
a
I08 "*3 6 ~
8 4
I
f
I
I
80 8
z/O
6
1"2
3"6 6"0 Time ~,lO-~ ~ec FIG. 1
•
I 3"6
I
I I I 10.8 18"0 T/me t~lO'~S~ec FIG. 2
FI(]. 1. Interaction of DPM and DAPM (2 : 1) in the melt based on change in the number of arn~uo-groups cz~H,(a) and in the number of double bonds Cc_c (b) and in the gel fraction q (e) at 423 (1), 433 (2), 443 (3), 453 (4), 473 (5) and 493 K (6). FIo. 2. Interaction of DPM and DAPM (2 : 1) in DM-F solution at 373 (1), 403 (2), 423 K (3). Solution concentrations 25 (a) and 30~o (b). Calculations o f t h e kinetic p a r a m e t e r s o f t h e reaction were done s e p a r a t e l y for each portion o f t h e c u r v e and for each i n t e r v a l in t h e h a r d e n i n g reaction, using t h e m e t h o d outlined in [5]. The Table gives the values of t h e kinetic parameters. F i g u r e 3 shows the I R spectra of DPM, and for DAPM, t h e oligomer and t h e h a r d e n e d polymer. T h e p o l y m e r s p e c t r u m is similar t o t h a t o f t h e linear t h e r m o plastic P M A p r e p a r e d f r o m t h e same m o n o m e r s in [4]. I t is seen from t h e F i g u r e t h a t n o change occurs during oligomerization a n d p o l y m e r i z a t i o n in t h e abs o r p t i o n bands for t h e carbonyl group at 1729 and 1780 cm -1 or in t h a t for t h e maleimide ring at 1390 cm -1. I n t h e region o f lqH v a l e n c y vibrations t h e r e are b r o a d b a n d s at 3300-3500 cm -1. I t is seen f r o m t h e Figure t h a t quite a large
Polymerization of ~ff,BT'-4,4'-diphenyhnethane-bis-maleimide
40&
number of double bonds of maleimide ring remain in the oligomer (bands at 690, 3100 and 1150 era-l), whereas in the spectrum of the hardened polymer the latter bands either fail to appear at all, or are very weak. The position and intensity of the bands for amino-groups linked to the double bond of the maleimide ring remain practically constant on going from oligomer to polymer. Thus we conclude from the results of the IR-analysis that the structure of the oligomer and the crossiinked polymer is similar to t h a t of PMA, i.e. only one hydroger~ of the primary amino group is linked to the C-~C bond of the maleimide ring, no maleimide ring opening takes place, and hardening of the OMA takes place on account of opening of the remaining bonds in the maleimide ring.
I
i
3.z
I
I..
z,6'
I
I
1.6
l
I
l.z
I
l
I
I
o.s ~,,lo~, crn -~
Fzo. 3. II~ spectra of DPI~{ (a), DAPM (b), OMI (c) and PM~ (d). Sirme DAX)M is quite an efficient inhibitor of free radical reactions [9], one would expect that polymerization of OMA through the double bond will proceed only when depletion of DAPM in the reaction mass is complete. I t is admitted in this case t h a t only the primary amino group of DAt)M is added by a reversible Mikhael reaction [10], and moreover the equilibrium constant will be such t h a t under the conditions adopted the addition m a y be regarded as irreversible, and the cross]inking of OMA will take place solely by a free radical mechanism. I f these assumpVions were entirely fulfilled, one would expect the kinetic parameters for consumption of the primary amino group to agree with those for double bond expenditure up to a degree of completeness of the reaction of 0.5, and the kinetic parameters of gel fraction formation could be expected to agree
410
V.S. VOLKOVetal.
with those for the reaction based on double bond expenditure after a degree of completeness of 0.5. This means, therefore t h a t points of discontinuity will appear on linear anamorphoses of the kinetic curves of change in the double bond concentration. Clearly, the lower the synthesis temperature the greater the probability of the above scheme being relevant. It is seen from the Table that the ideal scheme outlined above is not fully borne out. In the early stage of the reaction the reaction rates for double bond and primary amine group expenditure obey a second order equation, which accords with findhlgs reported in [4, 5]. However, the apparent activation energies differ fundamentally from one another. It is known [ll] that the activation energies for a nucleophilic reaction of amino group addition to the activated double bond are usually low, amounting to 21-25 kJ/mole, while the activation energy of homopolymeriza~ion of bis-maleimides is 117-144 kd/mole [6]. Points of discontinuity on the kinetic curves separating the portion for soluble OMA formation from that relating to crosslinked polymer formation are displaced, as the temperature falls, towards greater completeness of the reaction based on the amino group, and accordingly into the area where the degree of completeness of the reaction through the double bond is equal to 0.5. Thus at 423 K ~he discontinuity on the kinetic curve and the onset of gelation appear at a degree of completeness of ~0.7 as regards the amino group, and ~0-5 as regards the double bond. At 453 K the discontinuity appears at a degree of completeness o f ~0-3 as regards the amino group, and ~0.4 as regards the double bond. It can therefore be said that in the interval 423-473 K the reaction in the melt relating to the first portion of ~he kinetic curve is mainly one of addition o f the primary amine group of DAPM to the double bonds of DPM and OMA, t h o u g h there is also concurrent homopolymerization of D P M through the double bond. As the temperature falls the share of DPM homopolymerization is reduced, and the kinetic pattern approximates to the ideal scheme. In the second kinetic stage we have mainly the formation of crosslinked polymer. However, the same stage also includes addition of the primary amine group of DAPM to double bonds o f D P M and OMA, hindered by theJaigh viscosity of the partially crosslinked melt. This would account for the fact that the apparent activation energy for the reaction based on change in the number of amino groups amounts to 138 kJ/mole. Data analogous to the above were also obtained in [5]. A join~ process of OMA polymerization through the double bond and primary amine addi$ion ~o the double bond leads to a slight distortion of the kinetic pattern observed for the reaction based on change in the number of double bonds and the amount of gel fraction. In particular, in interval A, when the number of aminogroups of DAPM in the reaction mass is fairly large, the order of the reaction with respect to the double bond is twice that based on the gel fraction, and the apparent activation energy of the reaction based on the double bond exceeds that for the reaction based on the gel fraction b y 45 kJ/mole. In the second portion of the kinetic curve of hardening based on the gel fraction (interval B)
Polymerization of N,N'-4,4'-diphenylmethane-bis-maleimide
411
t h e reaction of OMA h a r d e n i n g a t t h e expense of double b o n d opening takes pla, ee u n d e r conditions d i s t u r b e d ~o a minimal e x t e n t t h e r e a c t i o n o f a m i n o gr,~,ups addition, since t h e amino g r o u p c o n c e n t r a t i o n in t h e reaction mass is practically zero. This is w h y t h e r e is good a g r e e m e n t between kinetic p a r a meters (n, E, In K0) for t h e second portion o f t h e kinetic curve based on t h e double b o n d in i n t e r v a l B a n d the kinetic curve based on t h e gel fraction. W e would t h i n k t h a t t h e kinetics as a whole in t h e melt, as shown in t h e Table, is fairly close to t h e ideal kinetics, particularly in the l o w - t e m p e r a t u r e region, w h e n the c o n t r i b u t i o n of D P M h o m o p o l y m e r i z a t i o n and OMA crosslinking t h r o u g h the double b o n d in t h e first portion of t h e kinetic curve becomes minimal, whiie the degree of conversion o f amino groups a~ the m o m e n t of t h e onset o f gel~tiol~ is maximal. T h e similarity of t h e kinetic p a r a m e t e r s of t h e r e a c t i o n o f OMA f o r m a t i o n in the melt based on change in the n u m b e r o f double b o n d s me~sured in D M F solution a n d in K B r discs means t h a t results o b t a i n e d are unaffected b y t h e m e t h o d of m e a s u r e m e n t , and a p p e a r t o be reliable. On examining the t a b u l a t e d d a t a it is seen t h a t t h e kinetic p a r a m e t e r s for t h e reaction of DP1K-DAPM (2 : 1) i n t e r a c t i o n in D ~ F solution based on t h e do~~ble bond e x p e n d i t u r e are in r e a s o n a b l y good m u t u a l a g r e e m e n t for different concentrations o f t h e reaction mass. A t the same t i m e t h e order o f t h e r e a c t i o n is the same in solution as in the melt, t h o u g h t h e a c t i v a t i o n e n e r g y is h i g h e r in t h e melt t h a n in solution. This means t h a t w h e t h e r in solution or in t h e m e l t t h e reaction takes place b y t h e same mechanism, a n d t h e lower a c t i v a t i o n e n e r g y w h e n tlm reaction is r u n in solution is a t t r i b u t a b l e go t h e cat~lytic a c t i o n t h a t a polar solven~ has [4] on t h e reaction of prima.ry amino group addition t o t h e d,)l~ble hond.
Translated by R. J. A. HENDR~: REFERENCES
1. M. MALLET, hfforms, chim., No. 112, 20i, 209, 1972 2. V. V. SHEREMETEVA, Izv. Akad. Igauk SSSR,, Seriya khim., No. 8, 1474, 1966 3. V. S. IVANOV, Radiatsionna.ya polimerizatsiya {Radiation Polymerization). p. 232, Khimiya, Leningrad, 1967 4. J. CRI.VELLO, J. Polymer Sci. Polymer Chem. Ed. ll: 1185, 1973 5. A. P. SUSLOV, S. A. DOLMATOV, Ye. A. KARGINOVA ~md V. S. LEVSHANOV, Vysokernel, soyed. A22: 6, 1286, 1980 (Translated in Polymer Sci. U.S.S.R. 22: 6, 1412, 1980) ~. D. O. HUMMEL, J. Appl. Polymer Sei. 18: 2015, 1974 7~ A. P. KRESHKOV, L. N. BYKOVA mid I. D. POVZNER, Dokl. Akad. Nauk SSSR 150: 1. 99, 1963 ~. K. KHARTMAN, E. LETSKII and V. SHEFER, Planirovaniye eksperimenta v issle~lowmii tekh~mlogieheskikh protsessov (Plam~ing the Experiments in Investigations ,f Chemical Processes). p. 532, Mir, Moscow, 1977 ~*. I. P. MASLOV, N. A. ZOLOTAREVA, N. A. GLAZUNOVA, A. S. BARANOVA, L. A. DELYUSTO, L. A. PUGACHEVA and G. A. BARYSHINKOVA, KhimichesMe dobavki k i),~limt~ram (Chemical Additions to Polymers). Handbook, p. 51, Khimiya, Moscow, 197;~
412
~'. I. YEGORENKOV a n d A. I. KUZAVKOV
10. G. BECKER, Vvedenie v elektronnuyu teoriyu organicheskikh reaktsii (Introduction to the Electron Theory of Organic Reactions) (Trans. from the Gorman, V. M. I)otapov, Ed.). p. 658, Mir, Moscow, 1977 11. S. I. SUMINOV and A. N. KOST, Uspekhi khimii 38: l l , 1933, 1969
Polymer ScienceU.S.S.R. Vol. 25, i~o. 2, pp. 412-420, 1983 Printed in Poland
0032-3950/83 $10.00÷.00 © 1984PergamonPress Ltd.
STUDY OF THE ADHESION OF POLYETHYLENE TO METALS AT CRYOGENIC TEMPERATURES* N. I. YEOORENKOV and A. I. KUZAVKOV I n s t i t u t e for the Mechanics of Metal-containing Polymer Systems, B.S.S.R. Academy of Sciences
(Received 2 September 1981) A study was made of the influence of temperature (80-295 K) on the adhesion of P E coatings to metals (resistance to separation of the metal foil substrate). I t is shown t h a t a fall in the test temperature a n d a n increase i n the rate of separation leads to a several-fold increase in the resistance to separation and alters the type of failure of adhesive joins. The degree of increase in separation resistance depends on the thickness of the P E coating, and on the nature a n d thickness of the foil substrate. The effectiveness of factors making for better adhesion of P E (oxidation, filling, addition of peroxide compounds, a n d other factors) is impaired when the test temperature is reduced. The paper also e o n t a ~ s data on the adhesion of other polymers, a n d possible explanations of the observed phenomena are discussed.
SEVERAL papers have been published by authors [1-8] investigating the adhesion of PE to metals. Most of these relate to the influence of oxidative processes (and controlling factors) in PE on the adhesive joins. It was found that moderate oxidation of PE makes for better adhesion. In most cases the adhesion investigations were carried out at room temperatures (285-300 K). However, it is known that the adhesion of polymers to metals, characterized by metal--polymer bond strength, e.g. by resistance to separation or peeling is markedly dependent on the polymer relaxation processes, and, accordingly, on the test temperatures [9-11]. It has been pointed out in earlier work [12-14] that in the case of PE-metal adhesive joins resistance to separation and uniform direct pull will vary in line with change in the test temperatures. Our aim in the present instance was to investigate the adhesion of PE coatings to metals at cryogenic temperatures (up to 80 K) in relation to the time * Vysokomol. soyed. A25: No. 2, 353-359, 1983.