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The degradation of poly (acid) amide based on pyromellitic dianhydride and bis-4-aminophenyl hydroquinone
T H E D E G R A D A T I O N OF P O L Y ( A C I D ) A M I D E B A S E D ON PYROMELLITIC D I A N H Y D R I D E A N D B I S - 4 - A M I N O P H E N Y L HYDROQUINONE* N. G. BEL'NIKEVICH, N. A. A~I)ROVA, L. •. KORZHAVIN, M. M. KoTo~, Y v . N . PA~OV and S. YA. FRv,gKEL' High Polymers Institute, U.S.S.R. Academy of Sciences (Received 15 November 1971)
The results of viscometric studies of the stability of solutions of poly(aeid)amide (PAN) based on pyromellitie dianhydride and bis-4-aminophenyl hydroquinono have shown the dry polymer to have the greatest stability, while dilute solutions in dimethylformamide or dimethyl sulphoxide were the least stable. PAN decomposes as a result of first the hydrolytic cleavage of the amide bond, and secondly due to spontaneous imidlzation. l g ~ Y of the physical properties of poly(amido)acids (PAN) are said b y a number of authors [1-4] to change when their solutions are stored, and the reason given is hydrolysis initiated b y the water which is introduced into the system b y the components, or is absorbed from the atmosphere, or forms during spontaneous cyclization (imidization). This problem was examined in greatest detail on PAA synthesized from pyromelitic dianhydride and 4,4-diaminodiphenyl ether [1]; the same author also suggested a mechanism for the hydrolytic cleavage of the chains. We thought it advisable to verify the validity of the suggested mechanisms o f decomposition on other PAA, particularly on that produced b y polycondensing pyromellitic dianhydride with bis-4-aminophenyl hydroquinone, P P H [2]. F o r this purpose we made a viscometric study of the stabilities of dilute and concentrated solutions, and also of the polymer which precipitates out during storage. In addition to this we determined the intldnsic viscosity [~/] of the PAA during: fibre drawing and during settling in inert precipitants. The [~]-values were determined at 25°C in an Ostwald viscometer in absolutely dry solvents to which 0.1 ~ LiBr had been added to suppress polyelectrolytie properties [3]. The 15-20% P P H solutions were produced b y heterogeneous polycondensation in dimethyfformamide (DMF) (adding the dry dianhydride to the diamine solution) [2]. These solutions were subjected to ageing on the basis o f the relative viscosity changes [~re~ of the PAA at 25°C. The 1% original P P H solution used for the [7] determination, and the 0-5% solution aged immediately
* Vysokomol. soyed., AI5: No. 8, 1826-1830, 1973. 2057
2058
N. G. BEL'I~IKEVICH et a~.
after ~reparation, were produced from the concentrated solution. One can gather from the comparison of the results in Figs. 1 and 2 (~.5~o error) that the dilute solution was least stable during storage, and the dry polymer the most stable, the reaction increasing, as expected, at higher temperatures. The substitution of dimethyl sulphoxide (DMSO) for the DMF did not produce any significant stability changes, but the use of N-methylpyrrolidone (N-MP) gave a significantly more stable solution. The DMSO and N - M P solutions were prepared from the reprecipitated polymer which was compared in a parallel ageing test with the non-precipitated one in DMF. The polymer was reprecipitated in dry benzene and washed with absolute ether sulphate. As with other PAA, the curves of the decrease in viscosity of P P H consisted of two distinct parts [4], i.e. the initial (showing a rapid decrease in viscosity) and the subsequent, in which the process was strongly inhibited and the viscosity approached a constant value.
[YJ/fY)o 1"0
0"8
~
oJ
i
[
Z
~
I
I
G 8 Time , da~s
i
i
I0
IZ
FIG. 1-. The intrinsic viscosity changes of PPH during storage at (°C) 1,3--0; 2,4,5-20. 1,2--storage of dry polymer; 3-5--DMF solutions with a polymer concentration of: 3,4--23~; 5--0.5~. The activation energies of the decompositions were assessed from the initial slope of the viscosity curve. The derivate (&l/dr)t= o proportional to the initial r a t e of PAA decomposition (Fig. 3) was selected as the critical characteristic. The ~ l c u l a t e d activation energies were: 12=]=2kcal/mole in DMF, 1 5 ± 2 in DMSO a n d 214-2 kcal/mole in N-MP. These values were in good agreement with those .given in the literature for hydrolytic cleavage of the amide bond, i.e. 18-20 keal/ ]mole [5], and confirmed once more that PAA decomposition primarily occurs as a result of the amide bond hydrolysis. The prior history of the polymer has ,a strong influence on the progress of the decomposition (Fig. 4). A polymer subjected to partial decomposition showed a decrease in viscosity which was only half that of a freshly prepared sample, but the mechanism of the process remained t h e same. (There was only a slight change of the activation energy, i.e. from 12 t o 15 kcal/mole). The [~/]-value dropped suddenly (by a factor of ~ 2) as a result of t h e polymer reprecipitation in absolute benzene, apparently because of the
2059
Degradation of poly(acid)amide
damage to the solvation sheath during precipitation, so that the water could more easily attack the P A A molecule. The same also happened in the fibredrawing process (ethylene glycol with ethanol in the settling tank, water in the TABLE
1. T H E
[17] R E D U C T I O N
[t/]0
Settling tank
1.44
Ethanol with ethylene glycol
OF PPH
i
[t/]*l[t/]0 0.62 0"66
2.0"/ *
DUBIEG
BEPRECIPTITATION
[~]0
BY VARIOUS BEAGENTS
Settling tank
1.90 9..50
Dry benzene
[t/]*/[t/]o Ii I i
0.64 0.'/4
[~]-repreetpitatedpolymerkeptundervacuumfor 3 days. [~],--Intrlnstc viscosityof originalpolymer.
plasticization tank) (Table 1). Comparison of these facts proved again t h a t enough water is introduced into the PAA solution for hydrolysis and t h a t any further water addition will not change its progress.
t/rwl/l"/~l 1"0
"
:~
I
~
0'8
2
I0
JO
'I~,II*P, l'a~ l
n
~
50
~
20
z
.._
=-I
-Z
6"0
I00 Tl'rne , ht~
g
a'g 10
za
do
T/me , hr
FIG. 2. The relative viscosity changes of a 0"5Yo PPH solution in: a--DM_F; b--DMSO; c--N-MP. Temperatures, °C: a: 1--0; 2--20; 3--60; 4--80, b, c: 1--0; 2--20; 3--40; 4--60; 5--80.
1~. G. BEL'NIKEVICH ~ Ul.
2060
The [g] of the P A A was not altered by a second precipitation (Table 2), b u t the resulting polymer was much purer and continued to decompose at the same rate as before (Fig. 3). TABLE 2.
I ExperiI merit I No. / I 2 3
THE [g] CHA_WG~S AZCD H U G G I N S CONSTANTS A F T E R TIO~r OF P P H Freshly prepared polymer
Polymer reprecipitated once twice
Hugghus [~/], dl/g
constant
1'25 1-41 2-03
0.44 0"47 0"37
A S I N G L E AND D O U B L E P R E C I P I T K -
Huggins [t/], dl]g 0"75 0.90 1"40
Huggins
constant
[t/I, dl/g
constant
0"64 0"96 0"56
0"70 0.90 0.36
0"32 0"46 0"30
Longer storage (5 months) was found to result in a partial loss of solubility of PAA. The insoluble part was spectroscopicaUyexamined and the infrared (IR) spectra showed a considerable number of imide rings to be present (about 10%). [g] of the soluble part was 0.3 dl/g (the same as t h a t of a polymer heated once to 100°C). The imidization continued in the diluted solution as shown by the IR-speetra. • /nu
f
10
•
°
z
I
I
I
I
f "8
3"Z
3"6
q'O
7oa/7FIG. 3. The dependence of the rate of decrease in viscosity v ( ~ / h r ) of P P H solutions on the inverse temperature, using as solvents: 1--1~-MP; 2--DMSO; 3--FDMF.
Dogradation of poly(aoid)amide
2061
Two processes thus took place in PAA during storage (in the intermediate products of reactions: monomers ~ PAA ~ polyimide), i.e. decomposition and spontaneous imidization. Unusual polycondensation conditions prevailed, i.e. a stepwise polymerization with ring-opening and production of PAA with a larger tool. wt. than during the normal polycondensation. The equilibrium seems to have shifted towards PAA decomposition and the formation of products differing in composition from that of the monomers, so that the actual progress of the reaction was as follows: 2
-~ Polyimide Monomers 1 pAA__2 ~ Monomers. Reaction 2' is easily traced by viscometry (one rupture is sufllcient per moleo cule to reduce the viscosity to half its value). A check of reaction 2 is at present rather difficult because of the low sensitivity of determining very small imidiza-
l-0~A Z
j
7 0"8
jI Zr
0"6
II 10
JO
50
70
Time, hr
Fio. 4. The relative viscosity changes of the: /,/'--freshly prepared polymer precipitate, 2,2'--the same polymer after 50 days, 3,3'--a polymer reprecipitated 50 days after its first precipitation. Temperatures, °C: 1-3-- 20; 1'-- 3'-- 80. tion percentages, including spontaneous imidization. The l a t e r is a very low tool. wt. product when precipitating out of solution (a dimer or trimer), as the rate of formation is an order of magnitude less than that of the decomposition rate. A polyimide of large molecular weight will be obtained either by changing the polycondensation conditions (achieving an equilibrium or a pseudo-equilibrium at larger tool. wt. of PAA), or at ra~es far exceeding those of decomposition (heat treatment at 300°C). The latter is the case i n practice [6] during polyimide fibre production.
2062
Z. I~V,A(}Z~OVA et al.
REFERENCES 1. L. W. FROST and J. KESSL, J. Appl. Polymer Sci. B2: 1039, 1964 2. N. A. ADROVA, M. M. KOTON and A. M. DUBNOVA, Vysokomol. soyed. BI0: 354, 1968 (Not translated in Polymer Sci. U.S.S.R.) 3. M. I. WALLACH, Polymer Preprints 6: 53, 1965 4. S. A. Z A K O S H C ~ O V , Vysokomol. soyed. B l l : 106, 1969 (Not translated in Polymer Sci. U.S.S.R.) 5. P. D. BOLTON and J. K. WILSON, Austral. J. Chem., 1013, 1966 6. L. N. KORZHAVlN, Dissertation, 1971
THE MOLECULAR AND STRUCTURAL PLASTICIZATION OF POLYVINYL FLUORIDE* Z. IBRAOIMOVA, A. A. YUL'unIgAYEV, YU. V. ZELE!~EV a n d KH. U. USMA~ov V. I. Lenin State University, Tashkent and V. I. Lenin Governmental Pedagogical Institute
(Received 22 November 1971) The thermomeehanical and other physical properties of polyvinyl fluoride (PVF) produced by various methods and plasticized with dibutyl phthalate, dioctyl phthalate, butyl stearate or castor oil were studied. The results showed plasticization to depend on the methods of polymer synthesis and on the plasticizer used. The molecular plasticization will be produced by addition of dibutyl-or dioctyl phthalate to PVF, while butyl stearate will produce structural plasticization, and castor oil an intermediate type of plasticization.
THE theories of molecular (intra-packet) and structural (inter-packet) plasticization had been developed by Kargin and co-workers [1-3]. The type of plasticization was found to depend on the type of interaction of the plasticizer molecules with reactive groups of the polymer chain. Where the energy of this interaction was larger than that of molecular interactions in the polymer, the plasticizer molecules will be capable of destroying the supermolecular structural formations and thus produce molecular plasticization. Where this energy is smaller than that of the intermolecular interactions the plasticizer will not destroy the macromolecular structures and will deposit itself between them, giving structural plasticization. The glass temperature (Tg) of the plasticized system will decrease in proportion to the amount of plasticizer in the first case, while it will decrease to start with in the second for small contents, and then remain almost constant. * Vysokomol. soyed. AI5: No. 8, 1831-1838, 1973.
The results of viscometric studies of the stability of solutions of poly(aeid)amide (PAN) based on pyromellitie dianhydride and bis-4-aminophenyl hydroquinono have shown the dry polymer to have the greatest stability, while dilute solutions in dimethylformamide or dimethyl sulphoxide were the least stable. PAN decomposes as a result of first the hydrolytic cleavage of the amide bond, and secondly due to spontaneous imidlzation. l g ~ Y of the physical properties of poly(amido)acids (PAN) are said b y a number of authors [1-4] to change when their solutions are stored, and the reason given is hydrolysis initiated b y the water which is introduced into the system b y the components, or is absorbed from the atmosphere, or forms during spontaneous cyclization (imidization). This problem was examined in greatest detail on PAA synthesized from pyromelitic dianhydride and 4,4-diaminodiphenyl ether [1]; the same author also suggested a mechanism for the hydrolytic cleavage of the chains. We thought it advisable to verify the validity of the suggested mechanisms o f decomposition on other PAA, particularly on that produced b y polycondensing pyromellitic dianhydride with bis-4-aminophenyl hydroquinone, P P H [2]. F o r this purpose we made a viscometric study of the stabilities of dilute and concentrated solutions, and also of the polymer which precipitates out during storage. In addition to this we determined the intldnsic viscosity [~/] of the PAA during: fibre drawing and during settling in inert precipitants. The [~]-values were determined at 25°C in an Ostwald viscometer in absolutely dry solvents to which 0.1 ~ LiBr had been added to suppress polyelectrolytie properties [3]. The 15-20% P P H solutions were produced b y heterogeneous polycondensation in dimethyfformamide (DMF) (adding the dry dianhydride to the diamine solution) [2]. These solutions were subjected to ageing on the basis o f the relative viscosity changes [~re~ of the PAA at 25°C. The 1% original P P H solution used for the [7] determination, and the 0-5% solution aged immediately
* Vysokomol. soyed., AI5: No. 8, 1826-1830, 1973. 2057
2058
N. G. BEL'I~IKEVICH et a~.
after ~reparation, were produced from the concentrated solution. One can gather from the comparison of the results in Figs. 1 and 2 (~.5~o error) that the dilute solution was least stable during storage, and the dry polymer the most stable, the reaction increasing, as expected, at higher temperatures. The substitution of dimethyl sulphoxide (DMSO) for the DMF did not produce any significant stability changes, but the use of N-methylpyrrolidone (N-MP) gave a significantly more stable solution. The DMSO and N - M P solutions were prepared from the reprecipitated polymer which was compared in a parallel ageing test with the non-precipitated one in DMF. The polymer was reprecipitated in dry benzene and washed with absolute ether sulphate. As with other PAA, the curves of the decrease in viscosity of P P H consisted of two distinct parts [4], i.e. the initial (showing a rapid decrease in viscosity) and the subsequent, in which the process was strongly inhibited and the viscosity approached a constant value.
[YJ/fY)o 1"0
0"8
~
oJ
i
[
Z
~
I
I
G 8 Time , da~s
i
i
I0
IZ
FIG. 1-. The intrinsic viscosity changes of PPH during storage at (°C) 1,3--0; 2,4,5-20. 1,2--storage of dry polymer; 3-5--DMF solutions with a polymer concentration of: 3,4--23~; 5--0.5~. The activation energies of the decompositions were assessed from the initial slope of the viscosity curve. The derivate (&l/dr)t= o proportional to the initial r a t e of PAA decomposition (Fig. 3) was selected as the critical characteristic. The ~ l c u l a t e d activation energies were: 12=]=2kcal/mole in DMF, 1 5 ± 2 in DMSO a n d 214-2 kcal/mole in N-MP. These values were in good agreement with those .given in the literature for hydrolytic cleavage of the amide bond, i.e. 18-20 keal/ ]mole [5], and confirmed once more that PAA decomposition primarily occurs as a result of the amide bond hydrolysis. The prior history of the polymer has ,a strong influence on the progress of the decomposition (Fig. 4). A polymer subjected to partial decomposition showed a decrease in viscosity which was only half that of a freshly prepared sample, but the mechanism of the process remained t h e same. (There was only a slight change of the activation energy, i.e. from 12 t o 15 kcal/mole). The [~/]-value dropped suddenly (by a factor of ~ 2) as a result of t h e polymer reprecipitation in absolute benzene, apparently because of the
2059
Degradation of poly(acid)amide
damage to the solvation sheath during precipitation, so that the water could more easily attack the P A A molecule. The same also happened in the fibredrawing process (ethylene glycol with ethanol in the settling tank, water in the TABLE
1. T H E
[17] R E D U C T I O N
[t/]0
Settling tank
1.44
Ethanol with ethylene glycol
OF PPH
i
[t/]*l[t/]0 0.62 0"66
2.0"/ *
DUBIEG
BEPRECIPTITATION
[~]0
BY VARIOUS BEAGENTS
Settling tank
1.90 9..50
Dry benzene
[t/]*/[t/]o Ii I i
0.64 0.'/4
[~]-repreetpitatedpolymerkeptundervacuumfor 3 days. [~],--Intrlnstc viscosityof originalpolymer.
plasticization tank) (Table 1). Comparison of these facts proved again t h a t enough water is introduced into the PAA solution for hydrolysis and t h a t any further water addition will not change its progress.
t/rwl/l"/~l 1"0
"
:~
I
~
0'8
2
I0
JO
'I~,II*P, l'a~ l
n
~
50
~
20
z
.._
=-I
-Z
6"0
I00 Tl'rne , ht~
g
a'g 10
za
do
T/me , hr
FIG. 2. The relative viscosity changes of a 0"5Yo PPH solution in: a--DM_F; b--DMSO; c--N-MP. Temperatures, °C: a: 1--0; 2--20; 3--60; 4--80, b, c: 1--0; 2--20; 3--40; 4--60; 5--80.
1~. G. BEL'NIKEVICH ~ Ul.
2060
The [g] of the P A A was not altered by a second precipitation (Table 2), b u t the resulting polymer was much purer and continued to decompose at the same rate as before (Fig. 3). TABLE 2.
I ExperiI merit I No. / I 2 3
THE [g] CHA_WG~S AZCD H U G G I N S CONSTANTS A F T E R TIO~r OF P P H Freshly prepared polymer
Polymer reprecipitated once twice
Hugghus [~/], dl/g
constant
1'25 1-41 2-03
0.44 0"47 0"37
A S I N G L E AND D O U B L E P R E C I P I T K -
Huggins [t/], dl]g 0"75 0.90 1"40
Huggins
constant
[t/I, dl/g
constant
0"64 0"96 0"56
0"70 0.90 0.36
0"32 0"46 0"30
Longer storage (5 months) was found to result in a partial loss of solubility of PAA. The insoluble part was spectroscopicaUyexamined and the infrared (IR) spectra showed a considerable number of imide rings to be present (about 10%). [g] of the soluble part was 0.3 dl/g (the same as t h a t of a polymer heated once to 100°C). The imidization continued in the diluted solution as shown by the IR-speetra. • /nu
f
10
•
°
z
I
I
I
I
f "8
3"Z
3"6
q'O
7oa/7FIG. 3. The dependence of the rate of decrease in viscosity v ( ~ / h r ) of P P H solutions on the inverse temperature, using as solvents: 1--1~-MP; 2--DMSO; 3--FDMF.
Dogradation of poly(aoid)amide
2061
Two processes thus took place in PAA during storage (in the intermediate products of reactions: monomers ~ PAA ~ polyimide), i.e. decomposition and spontaneous imidization. Unusual polycondensation conditions prevailed, i.e. a stepwise polymerization with ring-opening and production of PAA with a larger tool. wt. than during the normal polycondensation. The equilibrium seems to have shifted towards PAA decomposition and the formation of products differing in composition from that of the monomers, so that the actual progress of the reaction was as follows: 2
-~ Polyimide Monomers 1 pAA__2 ~ Monomers. Reaction 2' is easily traced by viscometry (one rupture is sufllcient per moleo cule to reduce the viscosity to half its value). A check of reaction 2 is at present rather difficult because of the low sensitivity of determining very small imidiza-
l-0~A Z
j
7 0"8
jI Zr
0"6
II 10
JO
50
70
Time, hr
Fio. 4. The relative viscosity changes of the: /,/'--freshly prepared polymer precipitate, 2,2'--the same polymer after 50 days, 3,3'--a polymer reprecipitated 50 days after its first precipitation. Temperatures, °C: 1-3-- 20; 1'-- 3'-- 80. tion percentages, including spontaneous imidization. The l a t e r is a very low tool. wt. product when precipitating out of solution (a dimer or trimer), as the rate of formation is an order of magnitude less than that of the decomposition rate. A polyimide of large molecular weight will be obtained either by changing the polycondensation conditions (achieving an equilibrium or a pseudo-equilibrium at larger tool. wt. of PAA), or at ra~es far exceeding those of decomposition (heat treatment at 300°C). The latter is the case i n practice [6] during polyimide fibre production.
2062
Z. I~V,A(}Z~OVA et al.
REFERENCES 1. L. W. FROST and J. KESSL, J. Appl. Polymer Sci. B2: 1039, 1964 2. N. A. ADROVA, M. M. KOTON and A. M. DUBNOVA, Vysokomol. soyed. BI0: 354, 1968 (Not translated in Polymer Sci. U.S.S.R.) 3. M. I. WALLACH, Polymer Preprints 6: 53, 1965 4. S. A. Z A K O S H C ~ O V , Vysokomol. soyed. B l l : 106, 1969 (Not translated in Polymer Sci. U.S.S.R.) 5. P. D. BOLTON and J. K. WILSON, Austral. J. Chem., 1013, 1966 6. L. N. KORZHAVlN, Dissertation, 1971
THE MOLECULAR AND STRUCTURAL PLASTICIZATION OF POLYVINYL FLUORIDE* Z. IBRAOIMOVA, A. A. YUL'unIgAYEV, YU. V. ZELE!~EV a n d KH. U. USMA~ov V. I. Lenin State University, Tashkent and V. I. Lenin Governmental Pedagogical Institute
(Received 22 November 1971) The thermomeehanical and other physical properties of polyvinyl fluoride (PVF) produced by various methods and plasticized with dibutyl phthalate, dioctyl phthalate, butyl stearate or castor oil were studied. The results showed plasticization to depend on the methods of polymer synthesis and on the plasticizer used. The molecular plasticization will be produced by addition of dibutyl-or dioctyl phthalate to PVF, while butyl stearate will produce structural plasticization, and castor oil an intermediate type of plasticization.
THE theories of molecular (intra-packet) and structural (inter-packet) plasticization had been developed by Kargin and co-workers [1-3]. The type of plasticization was found to depend on the type of interaction of the plasticizer molecules with reactive groups of the polymer chain. Where the energy of this interaction was larger than that of molecular interactions in the polymer, the plasticizer molecules will be capable of destroying the supermolecular structural formations and thus produce molecular plasticization. Where this energy is smaller than that of the intermolecular interactions the plasticizer will not destroy the macromolecular structures and will deposit itself between them, giving structural plasticization. The glass temperature (Tg) of the plasticized system will decrease in proportion to the amount of plasticizer in the first case, while it will decrease to start with in the second for small contents, and then remain almost constant. * Vysokomol. soyed. AI5: No. 8, 1831-1838, 1973.