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The mechanism of epoxide oligomer hardening by diamines under advancing reaction front conditions
Polymer Science U.S.S.R. Vol. 19, No. 12, pp. 3 1 4 9 - - 3 1 5 4 . (~) Pergamon Press Ltd. 1978.Printed in Poland
0032-3950/77/1201-3149507.50/0
THE MECHANISM OF EPOXIDE OLIGOMER HARDENING BY DIAMINES UNDER ADVANCING REACTION FRONT CONDITIONS* S. :P. DAVTYAN, KH. A. ARUTYUNYAN, K. G. SHKADINSKII, B. A. ROZENBERG and N. S. YENIKOLOPYAN Chemical Physics I n s t i t u t e Department, U.S.S.R. Academy of Sciences
(Received 31 January 1977) The kinetics of hardening of epoxide polymers b y amines under advancing reaction front conditions have been subjected to a theoretical analysis and the results compared with the experiment. The effects of the initial conditions on the stationary rate of the advancing reaction front, the peak rate and the time required for the establishment of a stationary rate, have been examined.
WE showed in earlier work [1] that the hardening process of epoxide oligomers (EO) by amines can take place under advancing reaction front conditions. I n this study we deal with the reactions of epoxydiane oligomers with aromatic amines which have the kinetics found in earlier work [2, 3]; we also make a theoretical examination of the kinetics of hardening under advancing reaction front (ARF) conditions and investigate the effect of the initial conditions on the stationary rate of the ARF, v, the peak rate (tiT~dr)max, and the time required for the establishment of a stationary rate of ARF, v. We found in earlier work [2, 3] that the setting conditions for epoxydiane oligomers (ED-20, ED-6, and other) by aromatic amines (m-phenylenenediamine} under adiabatic conditions are described by a kinetic scheme which considers the uncatalysed and catalysed reactions of epoxy with the primary and secondary amino groups. AI-{-E ~ A~A-C
Kp
E-bC ~
EC
A I ~ E C k,, A2~2 C A2~EC k., A8~2C, * Vysokomol. soyed. AlP: No. 12, 2726-2730, 1977. 3149
(1~
3150
S. 1). DAVTYANeb al.
in which A 1, A2, and A3--primary, secondary, and tertiary amino groups, E and C--epoxy and hydroxyl groups respectively, and EC--the complex of E and C. The kinetic equation describing the setting according to eqn. (1) can be written as follows: dA1/dt= --k~(T) A1E--lc~'(T ) A~EC (2)
dY /dt + dA,/dt-= A~E [ k2(T) + k ~(T) _~C] One must still add to system (2) the material balance equations A3=AI-~Y~-EC--A o A~=Y--2A3--EC C=E+2Y--E0+Co+2EC
(3)
Y----Eo--E--EC (EC=K~EC) embracing the following initial conditions: t ~ 0; A~----A10; E----E0; and A~= Y = 0. To the reactions proceeding under ARF conditions one must add that for thermal conductivity which, for a unJdimensional model having heat capacity Q; specific heat content C; density p and thermal conductivity t, is independent of temperature, viscosity and composition of the reaction medium (the latter had been dealt with earlier in greater detail [2, 3]); this takes the form. aT
a2T
Cp ~ =i ~
d¥
+Q d--[
(4)
The following are the initialand the limitLng conditions for eqn. (4):
t=O;
T (x)=T o
x=O; x=h ;
T (x=O)=T, dT/dx/x=h=O ,
(5)
in which x is the reaction coordinate in space; To, T,, initial temperature and initiation temperature of the reaction respectively; h, length of the hardening sample. The system of differential eqn. (2)-(5) was solved on a computer. The methods of solving this type of problem are of special interest, but we just mention here thc~ the basis of the algorithm was a 4 point scheme for the thermal conductivity equation and a linearized scheme for the kinetic part of the system. The algorithm used in our calculations considered the solution structure (the heat exchange in the polymerizing part, the essential parameter changes in the relatively narrow polymerization range and the adiabatic regime ( i = 0 ) in the original mixture), and also ensured the automatic fulfilment of all the balances of the system. The calculations made use of the kinetic, thermodynamic and thermophysical
Mechanism of epoxido oligomer hardening by diamines
8151
parameters which had been determined before [1-3]. Two reaction zones can be seen on coordinate x in Fig. 1, the first in the range of small x is characterized b y the nonestablishment of A R F conditions. The peak rate and that of the reaction front advance vary as a function of x. The second zone is that in which the regime establishes itself, i.e. the stationary ARF, in which v as well as (dT/dt)max become stationary. T~°C
c~ mole/l 3 d
11
I
I
I
i
, I
I""
b"
~I ~" I "
8
b ,~'j C/'/'/
6
18
FIo. 1. The dependence of."a--temperature; b--epoxide concentration c; c--content of OH-groups; d--primary; e--secondary; f--teriary amines; on the reaction coordinates. A10=3; 3-2mole/l; reaction time, see: 1--75; 2--150; 3--230; 4--320; 5--440; 6--490. To= 60, and Tg= 200°C here and in the Figs. 2-5. The same number of epoxy groups react in each narrow layer after the establishment of the stationary rate of ARF, as Fig. lb shows; the reaction temperature found at its maximum (Fig. la) will at the same cause the complete conversion of the epoxy groups (Fig. lb). The effect of the initial concentration of A1 on v, v and (tiT/dr)maxis illustrated in Fig. 2a. The dependence of the latter parameters on A10 when small is quite large, b u t t h e y become almost independent of A~0 at 6 mole/1, concentration. The dependence of these parameters on E 0 concentration is similar (Fig. 2b). One can determine the order of the stationary rate of A R F with respect to A~o ~ 0 . 6 5 -nO.8 and E 9 from Fig. 2, i.e. v ~ ~ l o "~o , and this is confirmed b y the experimental depende.uce found in our earlier s t u d y [1]. There is also good agreement of experimental (dots) with the calculated (dashes) v values and the (tiT/dr)max, as Fig. 2a shows. This agreement supports the kinetics outlined in (1) and, as suggested before [2, 3], correctly reflects the main setting kinetics of the epoxydiane oligomers in the presence of aromatic amines in an adiabatic regime, and Chat the determined kinetic and thermo-physieal constants are true values; it also confirms the validity of the earlier made suggestion of Q/Cp and 2/Cp having only a sligh¢ dependence , on temperature and the reaction efficiency.
8152
S. P. D A V T Y A N ~ aZ.
We had shown in a recent study [13] that the differences in the detected hardening rate of epoxydiane oligomers having different molecular weights are due only to differing hydroxyl group contents Co in these oligomers. We therefore wanted to find out the effects of varying the concentration of hydroxyl groups,. and to clarify the influence of the tool. wt. of the original epoxydiane oligomer on v, ~, and (dT/dt)max. "r, see
/d7
b
e ~
la'r/mox
d
_ 4
q
0./4 ~
1qo
- 80
~2
o,z ;
1oo e!
2
-
t~
i
t
I
I
6
[A,] n ,molell. Fz(,. ,
- qo
~/
I
,
I
,
10"n/
I
[e]o, ,.o/e/t.
The parameters 1 - v; 2--(dT/dt)=ax and 3 - as functions of: a E o = 3 mole/1, in a; A10=3 mole/1, in b
Azo; b - E0;
The value of v was found to be almost independent of Co at identical epoxy group concentrations; (dT/dt)max increased with Co, while T only depended on Co hen the additions were small (Fig. 3a). The comparison of the found correlation shown in Fig. 3a makes it possible to estimate the v, r, and (dT/dt)max for oligomers having different molecular weights. For instance, as the C additions do not affect v, a tool. wt. increase of the original oligomer must cause it to decrease (Fig. 2b) in relation to tile decrease of epoxy groups present in these oligomers. The values of Tchange from about 70 to 100 sec for a change in hydroxyl content from 0 to 1 mole/1. Such a content of the latter is present in the oligomers ranging from ED-20 to ED-16, in which the E 0 concentration changes in the 5.8-6 mole/1. range. Such a change of E o causes T to change by 10 see according to Fig. 2b. which means that ~ ought to increase in the case of oligomers having a tool wt. of 600-700 and than drop in proportion with the decrease in E o. The analysis also showed that a tool. wt. increase of the oligomer must cause the decrease in (dT/dt)raa~. The mechanisms are obviously correct not only for the hardening epoxydiane oligomers under ARF conditions in the presence of m-phenylenediamine, but also of other aromatic amines and epoxy resins having similar kinetic, thermodynamic and thermophysical parameters. As to other systems, any substantial differences of ~.hese parameters may mean different kinetics. This question was clarified by analysing the system of equations (2)-(5) by varying the kinetic al~d thermodynamic parameters of some zeactions falling into scheme (1).
Mechanism of epoxido oligomer hardening by diamines
3153
Figure 3b shows values v, T and (dT/dt)max as functions of the enthalpy AH of the EC complexing reaction. One can see t h a t AH depends only slightly on v, (dT/dt)max only when its values are small, while T is a linear function. A R F becomes stationary in the system at all sensible values of AH. ~ 8ec lO0
n 1
/
~3
"r,seo
b
dT O.8
0"8 ~3
- I00
o.s
-60
-80 =
O.l/ ,
I
1
i
I
,
_
2 Co, too/ell.
I
3
t
J
5 7 AH , kca/ /rnole
Fio. 3. The effects of: a--C0; b--AH on: l--v; 2--(dT/dt)max, and 3--r. A0=E0=3 mole/1. A v a r i a t i o n in t h e a c t i v a t i o n e n e r g y E 1 of the n o n - c a t a l y t i c reactions, a n d t h e epoxide ring opening showed (Fig. 4) t h a t v a n d (dT/dt)max will increase as E1 becomes larger, while T changes non-.parallel to v a n d (dT/dt)max. Such r changes "C~ 8eC
s
I
/
(•t)m=•
T,*C
0"8
140 4L
q
200
5~
O.Zt i
I0 lq El, kca//mo/e Fro. 4
,
l
I
2O
i
i
l Cc ~ c m
I
qO
Fro. 5
Fl.q. 4. The values: 1 - v; 2--(dT/dt)max ; 3 - r, as functions of Ez. A0= E0 = 3 mole/1. Fro. 5. The temperature profile along coordinate x for A0=E0= 3 mole]l. ; E~ = 6 kcal/mole. Reaction -'.ime, sec: 1--53; 2--120; 3--160; 4--450; 6--500; 6--570; 7--655. are due t o h e a t c o n d u c t a n c e f r o m t h e reaction zone t o t h e a d j a c e n t layers a t small E z a t t h e p a r t i c u l a r t e m p e r a t u r e , wlzile t h e r e a c t i o n develops in t h e m o r e r e m o t e layers simul¢ane~;:~ly e i t h e r in A R F or acdiabati conditions. T h e s y s t e m o f differential eqns. ('2)-(5) was a n a l y s e d a t small Ez values b y t a k i n g into a c c o u n t t h e reaction progress in space u n d e r a d i a b a t i c conditions,
3154
S. P. D A V T Y A N
et
aZ.
using the equation
dT dY Cp ~ = Q d-t'
(6)
where T-~ T o when t ~ 0. The analysis of equation system (2)-(6) is graphically illustrated in Fig. 5. As expected, a part of the reaction medium sets under A R F conditions (the left hand part of the line of dashes), and the rest under adiabatic (the right hand part). The rate of advance of the reaction front is evidently non-stationary under such conditions and there is a disappearance of ARF. At still smaller E 1 values there is a widening of the adiabatic reaction zone and all the setting process can then take place under adiabatic conditions. The initical temperature of the reaction mixture also plays such a part. One concludes from the above results t h a t the establishment of a stationary rate of A R F is essential for the setting processes of EO as in the polymerization [4], and also a ratio of v (ARF rate) to w (reaction rate) in which v ~ w .
Translated by K. A. ALLEY, REFERENCES
1. Kh. A. ARUTYUNYAN, S. P. DAVTYAN and B. A. ROZENBERG, Dokl. Al~ad. l~auk SSSR 223: 657, 1975 2. Kh. A. ARUTYUNYAN, S. P. DAVTYAN, B. A. ROZENBERG and N. S. YF~rIXOLOPYAN,
Vysokomo]. soyed. A16: 2115, 1974 (Translated in Polymer Scl. U.S.S.R. 16: 9, 2452, 1974) 3. Kh. A. ARUTYUNYA~, S. P. DAVTYAN, B. A. ROZENBERG and N. S. YENIKOLOPYAN,
Vysokomol. soyed. AI7: 289, 1975 (Translated in Polymer Sei. U.S.S.R. 17: 2, 333, 1975) 4. G. G. ALEKSANYAN, Kh. A. ARUTYUNYAN, V. L. BODNEVA, S. P. I)AVTYAN et a/.)
Vysokomol. soyed. A17: 913, 1975 Translated ir~ Polymer Sci. U.S.S.R. 17: 4, 1052, 1975,
0032-3950/77/1201-3149507.50/0
THE MECHANISM OF EPOXIDE OLIGOMER HARDENING BY DIAMINES UNDER ADVANCING REACTION FRONT CONDITIONS* S. :P. DAVTYAN, KH. A. ARUTYUNYAN, K. G. SHKADINSKII, B. A. ROZENBERG and N. S. YENIKOLOPYAN Chemical Physics I n s t i t u t e Department, U.S.S.R. Academy of Sciences
(Received 31 January 1977) The kinetics of hardening of epoxide polymers b y amines under advancing reaction front conditions have been subjected to a theoretical analysis and the results compared with the experiment. The effects of the initial conditions on the stationary rate of the advancing reaction front, the peak rate and the time required for the establishment of a stationary rate, have been examined.
WE showed in earlier work [1] that the hardening process of epoxide oligomers (EO) by amines can take place under advancing reaction front conditions. I n this study we deal with the reactions of epoxydiane oligomers with aromatic amines which have the kinetics found in earlier work [2, 3]; we also make a theoretical examination of the kinetics of hardening under advancing reaction front (ARF) conditions and investigate the effect of the initial conditions on the stationary rate of the ARF, v, the peak rate (tiT~dr)max, and the time required for the establishment of a stationary rate of ARF, v. We found in earlier work [2, 3] that the setting conditions for epoxydiane oligomers (ED-20, ED-6, and other) by aromatic amines (m-phenylenenediamine} under adiabatic conditions are described by a kinetic scheme which considers the uncatalysed and catalysed reactions of epoxy with the primary and secondary amino groups. AI-{-E ~ A~A-C
Kp
E-bC ~
EC
A I ~ E C k,, A2~2 C A2~EC k., A8~2C, * Vysokomol. soyed. AlP: No. 12, 2726-2730, 1977. 3149
(1~
3150
S. 1). DAVTYANeb al.
in which A 1, A2, and A3--primary, secondary, and tertiary amino groups, E and C--epoxy and hydroxyl groups respectively, and EC--the complex of E and C. The kinetic equation describing the setting according to eqn. (1) can be written as follows: dA1/dt= --k~(T) A1E--lc~'(T ) A~EC (2)
dY /dt + dA,/dt-= A~E [ k2(T) + k ~(T) _~C] One must still add to system (2) the material balance equations A3=AI-~Y~-EC--A o A~=Y--2A3--EC C=E+2Y--E0+Co+2EC
(3)
Y----Eo--E--EC (EC=K~EC) embracing the following initial conditions: t ~ 0; A~----A10; E----E0; and A~= Y = 0. To the reactions proceeding under ARF conditions one must add that for thermal conductivity which, for a unJdimensional model having heat capacity Q; specific heat content C; density p and thermal conductivity t, is independent of temperature, viscosity and composition of the reaction medium (the latter had been dealt with earlier in greater detail [2, 3]); this takes the form. aT
a2T
Cp ~ =i ~
d¥
+Q d--[
(4)
The following are the initialand the limitLng conditions for eqn. (4):
t=O;
T (x)=T o
x=O; x=h ;
T (x=O)=T, dT/dx/x=h=O ,
(5)
in which x is the reaction coordinate in space; To, T,, initial temperature and initiation temperature of the reaction respectively; h, length of the hardening sample. The system of differential eqn. (2)-(5) was solved on a computer. The methods of solving this type of problem are of special interest, but we just mention here thc~ the basis of the algorithm was a 4 point scheme for the thermal conductivity equation and a linearized scheme for the kinetic part of the system. The algorithm used in our calculations considered the solution structure (the heat exchange in the polymerizing part, the essential parameter changes in the relatively narrow polymerization range and the adiabatic regime ( i = 0 ) in the original mixture), and also ensured the automatic fulfilment of all the balances of the system. The calculations made use of the kinetic, thermodynamic and thermophysical
Mechanism of epoxido oligomer hardening by diamines
8151
parameters which had been determined before [1-3]. Two reaction zones can be seen on coordinate x in Fig. 1, the first in the range of small x is characterized b y the nonestablishment of A R F conditions. The peak rate and that of the reaction front advance vary as a function of x. The second zone is that in which the regime establishes itself, i.e. the stationary ARF, in which v as well as (dT/dt)max become stationary. T~°C
c~ mole/l 3 d
11
I
I
I
i
, I
I""
b"
~I ~" I "
8
b ,~'j C/'/'/
6
18
FIo. 1. The dependence of."a--temperature; b--epoxide concentration c; c--content of OH-groups; d--primary; e--secondary; f--teriary amines; on the reaction coordinates. A10=3; 3-2mole/l; reaction time, see: 1--75; 2--150; 3--230; 4--320; 5--440; 6--490. To= 60, and Tg= 200°C here and in the Figs. 2-5. The same number of epoxy groups react in each narrow layer after the establishment of the stationary rate of ARF, as Fig. lb shows; the reaction temperature found at its maximum (Fig. la) will at the same cause the complete conversion of the epoxy groups (Fig. lb). The effect of the initial concentration of A1 on v, v and (tiT/dr)maxis illustrated in Fig. 2a. The dependence of the latter parameters on A10 when small is quite large, b u t t h e y become almost independent of A~0 at 6 mole/1, concentration. The dependence of these parameters on E 0 concentration is similar (Fig. 2b). One can determine the order of the stationary rate of A R F with respect to A~o ~ 0 . 6 5 -nO.8 and E 9 from Fig. 2, i.e. v ~ ~ l o "~o , and this is confirmed b y the experimental depende.uce found in our earlier s t u d y [1]. There is also good agreement of experimental (dots) with the calculated (dashes) v values and the (tiT/dr)max, as Fig. 2a shows. This agreement supports the kinetics outlined in (1) and, as suggested before [2, 3], correctly reflects the main setting kinetics of the epoxydiane oligomers in the presence of aromatic amines in an adiabatic regime, and Chat the determined kinetic and thermo-physieal constants are true values; it also confirms the validity of the earlier made suggestion of Q/Cp and 2/Cp having only a sligh¢ dependence , on temperature and the reaction efficiency.
8152
S. P. D A V T Y A N ~ aZ.
We had shown in a recent study [13] that the differences in the detected hardening rate of epoxydiane oligomers having different molecular weights are due only to differing hydroxyl group contents Co in these oligomers. We therefore wanted to find out the effects of varying the concentration of hydroxyl groups,. and to clarify the influence of the tool. wt. of the original epoxydiane oligomer on v, ~, and (dT/dt)max. "r, see
/d7
b
e ~
la'r/mox
d
_ 4
q
0./4 ~
1qo
- 80
~2
o,z ;
1oo e!
2
-
t~
i
t
I
I
6
[A,] n ,molell. Fz(,. ,
- qo
~/
I
,
I
,
10"n/
I
[e]o, ,.o/e/t.
The parameters 1 - v; 2--(dT/dt)=ax and 3 - as functions of: a E o = 3 mole/1, in a; A10=3 mole/1, in b
Azo; b - E0;
The value of v was found to be almost independent of Co at identical epoxy group concentrations; (dT/dt)max increased with Co, while T only depended on Co hen the additions were small (Fig. 3a). The comparison of the found correlation shown in Fig. 3a makes it possible to estimate the v, r, and (dT/dt)max for oligomers having different molecular weights. For instance, as the C additions do not affect v, a tool. wt. increase of the original oligomer must cause it to decrease (Fig. 2b) in relation to tile decrease of epoxy groups present in these oligomers. The values of Tchange from about 70 to 100 sec for a change in hydroxyl content from 0 to 1 mole/1. Such a content of the latter is present in the oligomers ranging from ED-20 to ED-16, in which the E 0 concentration changes in the 5.8-6 mole/1. range. Such a change of E o causes T to change by 10 see according to Fig. 2b. which means that ~ ought to increase in the case of oligomers having a tool wt. of 600-700 and than drop in proportion with the decrease in E o. The analysis also showed that a tool. wt. increase of the oligomer must cause the decrease in (dT/dt)raa~. The mechanisms are obviously correct not only for the hardening epoxydiane oligomers under ARF conditions in the presence of m-phenylenediamine, but also of other aromatic amines and epoxy resins having similar kinetic, thermodynamic and thermophysical parameters. As to other systems, any substantial differences of ~.hese parameters may mean different kinetics. This question was clarified by analysing the system of equations (2)-(5) by varying the kinetic al~d thermodynamic parameters of some zeactions falling into scheme (1).
Mechanism of epoxido oligomer hardening by diamines
3153
Figure 3b shows values v, T and (dT/dt)max as functions of the enthalpy AH of the EC complexing reaction. One can see t h a t AH depends only slightly on v, (dT/dt)max only when its values are small, while T is a linear function. A R F becomes stationary in the system at all sensible values of AH. ~ 8ec lO0
n 1
/
~3
"r,seo
b
dT O.8
0"8 ~3
- I00
o.s
-60
-80 =
O.l/ ,
I
1
i
I
,
_
2 Co, too/ell.
I
3
t
J
5 7 AH , kca/ /rnole
Fio. 3. The effects of: a--C0; b--AH on: l--v; 2--(dT/dt)max, and 3--r. A0=E0=3 mole/1. A v a r i a t i o n in t h e a c t i v a t i o n e n e r g y E 1 of the n o n - c a t a l y t i c reactions, a n d t h e epoxide ring opening showed (Fig. 4) t h a t v a n d (dT/dt)max will increase as E1 becomes larger, while T changes non-.parallel to v a n d (dT/dt)max. Such r changes "C~ 8eC
s
I
/
(•t)m=•
T,*C
0"8
140 4L
q
200
5~
O.Zt i
I0 lq El, kca//mo/e Fro. 4
,
l
I
2O
i
i
l Cc ~ c m
I
qO
Fro. 5
Fl.q. 4. The values: 1 - v; 2--(dT/dt)max ; 3 - r, as functions of Ez. A0= E0 = 3 mole/1. Fro. 5. The temperature profile along coordinate x for A0=E0= 3 mole]l. ; E~ = 6 kcal/mole. Reaction -'.ime, sec: 1--53; 2--120; 3--160; 4--450; 6--500; 6--570; 7--655. are due t o h e a t c o n d u c t a n c e f r o m t h e reaction zone t o t h e a d j a c e n t layers a t small E z a t t h e p a r t i c u l a r t e m p e r a t u r e , wlzile t h e r e a c t i o n develops in t h e m o r e r e m o t e layers simul¢ane~;:~ly e i t h e r in A R F or acdiabati conditions. T h e s y s t e m o f differential eqns. ('2)-(5) was a n a l y s e d a t small Ez values b y t a k i n g into a c c o u n t t h e reaction progress in space u n d e r a d i a b a t i c conditions,
3154
S. P. D A V T Y A N
et
aZ.
using the equation
dT dY Cp ~ = Q d-t'
(6)
where T-~ T o when t ~ 0. The analysis of equation system (2)-(6) is graphically illustrated in Fig. 5. As expected, a part of the reaction medium sets under A R F conditions (the left hand part of the line of dashes), and the rest under adiabatic (the right hand part). The rate of advance of the reaction front is evidently non-stationary under such conditions and there is a disappearance of ARF. At still smaller E 1 values there is a widening of the adiabatic reaction zone and all the setting process can then take place under adiabatic conditions. The initical temperature of the reaction mixture also plays such a part. One concludes from the above results t h a t the establishment of a stationary rate of A R F is essential for the setting processes of EO as in the polymerization [4], and also a ratio of v (ARF rate) to w (reaction rate) in which v ~ w .
Translated by K. A. ALLEY, REFERENCES
1. Kh. A. ARUTYUNYAN, S. P. DAVTYAN and B. A. ROZENBERG, Dokl. Al~ad. l~auk SSSR 223: 657, 1975 2. Kh. A. ARUTYUNYAN, S. P. DAVTYAN, B. A. ROZENBERG and N. S. YF~rIXOLOPYAN,
Vysokomo]. soyed. A16: 2115, 1974 (Translated in Polymer Scl. U.S.S.R. 16: 9, 2452, 1974) 3. Kh. A. ARUTYUNYA~, S. P. DAVTYAN, B. A. ROZENBERG and N. S. YENIKOLOPYAN,
Vysokomol. soyed. AI7: 289, 1975 (Translated in Polymer Sei. U.S.S.R. 17: 2, 333, 1975) 4. G. G. ALEKSANYAN, Kh. A. ARUTYUNYAN, V. L. BODNEVA, S. P. I)AVTYAN et a/.)
Vysokomol. soyed. A17: 913, 1975 Translated ir~ Polymer Sci. U.S.S.R. 17: 4, 1052, 1975,