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Polymerization of formaldehyde in the presence of the dimethyl ether of polyoxymethylene glycol
2898
A . G . G B u z s o v e~ a/.
5. A. A. BERLIN, B. I. LIOGON'KII, A. A. GUROV a n d Ye. F. RAZVADOVSEH, Vysokom01. soyed. Ag: 532, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 3, 596, 1967) 6. A. A. GUROV, B. I. LIOGON'KH and A. A. BERLIN, Vysokomol. soyed. Ag: 2259, 1967 (Translated in P o l y m e r Sci. U.S.S.R. 9: 10, 2555, 1967) 7. A. A. BERLIN, B. I. LIOGON'KII and E. ABDULA-ZADE, Vysokomo]. soyed. A9: 1725, 1967 (Translated in P o l y m e r Sci. U.S.S.R. 9: 8, 1943, 1967)
POLYMERIZATION OF FORMALDEHYDE IN THE PRESENCE OF THE DIMETHYL ETHER OF POLYOXYMETHYLENE GLYCOL* A. G. GRuz~ov, L. 1~I. PUSHCHAYEVAand L. M. R o ~ o v Scientific Research I n s t i t u t e of Plastics
(Received 18 November 1967) TKE production of a stable polyformaldehyde b y cationic polymerization is based on t h e elemental act of chain transfer with fracture of macromolecules (CTFM). The CTFM can be basically described as: +
~ O--CH,--O--CH,~-R1--O--R,--O--CH, ~ + -* ~ O - - C H , - - OCH~-- OR2-- OR1 + CH, N O--CHIn-- OCHa-- O R I + R ~ - - O - - C H , ~ , in which R - - C H s or any other hydrocarbon radical, R a - - a radical containing a t least a - - C H I - - C H ~ group. The blocking compound used can be t h e dimethyl ether of polyoxymethylene glycol [2] of general formula CHs-- O - - (CH20), CHs, in which n = 1,2,3... The result of this should be a polyformaldehyde (PFA) having stable m e t h o x y end groups. The paper describes the study of the mechanism of gas-phase formaldehyde ( F A ) p o l y m e r i z a t i o n i n t h e p r e s e n c e o f SnCId, a n d w i t h a d d i t i o n s o f t h e d i m e t h y l ether of trioxymethylene glycol (DETOMG).
EXPERIMENTAL Toluene was purified with oxides of nitrogen, washed w i t h HsSO,, then with water to neutral reaction, aqueous alkali, water, then dried and distilled over metallic sodium. T h e fraction coming over at 110.6°C was collected. DETOMG was purified as described in the U.S. p a t e n t [3]; it was dried over metallic s o d i u m a n d also distilled over it. The fraction with b~p. 155.2°C was collected. SnCl,. The commercial preparation was refluxed and the fraction coming over a t * Vysokomol. soyed. AIO: No. 11, 2495-2499, 1968.
Polymerization of formaldehyde
2899
113.5-113-8°C was collected. The product was frozen and thawed in vacuo, and then distributed as 0.05-0'2 g samples into ampoules. Method. The polymerization was carried out in the a p p a r a t u s illustrated in Fig. 1. The flask 1 was filled with 800 g ~-polyoxymethylene a n d heated on a b a t h (2) to 180°C. The F A forming during this period was purged with an argon stream and the gas, on reaching 180°C, was fed into column 3 p a c k e d with glass rings, a n d from there into coil 4 (25 m long, 8 m m in diameter), which was cooled to --19°C. The purified F A present on the chilled walls then entered the reaction flask 5 which h a d been supplied with toluene, DETOMG, and t h e required a m o u n t of s t a n d a r d SnO14 solution in toluene. The t o t a l volume of the system was 50 ml. The reaction vessel was k e p t at 30°C b y means of an ultra-thermostat. The F A feed was calculated so t h a t the gas bubbled continuously through the bubbler vessel which was filled with toluene, situated at the reactor outlet. I t was stopped on completion of polymerization and a triethanolamine solution in ethanol was a d d e d immediately to neutralize the catalyst. The polymer was separated b y filtration, washed with acetone, boiling water, acetone, ether, a n d then dried at 60°C.
i( ~
N
J
FIQ. 1. Schematic illustration of the a p p a r a t u s used to polymerize gaseous formaldehyde. F o r explanation see text. The viscosity was determiued in a vlscometer with a suspended level indicator a t 150°C, using a 0"5~o P F A solution in DMF, also containing 2~/o diphenylaxaine. The molecular weight (m.w.) of t h e polymer was calculated from the formula: [t]]----4. 4 X 104M °'6t [4]. RESULTS
T h e p o l y m e r i z a t i o n o f g a s e o u s F A i n t o l u e n e a t 30°C, w i t h SnC14 a s c a t a l y s t , w i t h o r w i t h o u t D E T O I ~ I G , is c h a r a c t e r i z e d b y a n u m b e r o f f e a t u r e s ( F i g . 2). A l o w i n i t i a t o r c o n c e n t r a t i o n (8 × 10 -e t o 2 × 10 -5 m o l c f l . ) g a v e a r a p i d m . w . d e c r e a s e w i t h i n c r e a s i n g SnC14 c o n t e n t . T h e m . w . - [ S n C l a ] r e s p o n s e c u r v e s with and without added ])ETOMG were practically identical. An increase of [SnC14] b e y o n d t h e e a r l i e r m e n t i o n e d c o n t e n t c a u s e d t h e c u r v e s t o d i v e r g e o n approaching the abscissa. T h e r a t e o f p o l y m e r i z a t i o n w a s c o n s t a n t w i t h t i m e f o r 20 r a i n ( F i g . 3a) a n d w a s p r a c t i c a l l y i n d e p e n d e n t o f i n i t i a t o r c o n c e n t r a t i o n i n t h e r a n g e 8 × 10 -6
2900
A.G. GRuz~ov eta/.
to 5 X 10 -3 mole/1. (Fig. 3b). The latter indicates that the polymerization takes place in the diffusion range as regards the monomer. The m.w. changes should therefore be inversely proportional to the initiator concentration. M.w. • 10-3 5OO #00 300 2OO 100
×~"<'~c~
1 2' / / o)c I
I
1o
20
lo , ote / l.
FIG. 2. Molecular weight of PFA as a function of SnC14 concentration: /--homopolymerization, 2--FA polymerization in the presence of 0.44 mole/1. DETOMG. Consequently, Fig. 4a shows the curves in the coordinates 1/P-[SnCI¢] to have coincident straight sections at 8 × 10 -s to 5 × 10 -~ mole/1. SnC14; this was without additive. Where DETOMG was present, the straight sections were in the range 9 × 10 -e t o 7 × 10 -5 mole/1.
The change to the range of higher initiator concentrations (up to 1 × 10 -4 mole/].) caused a deviation from the initially increased m.w. A further SnCI~ concentration increase again gave linear sections, b u t with different slopes. The characteristics of the m.w.-initial concentration function can be explained b y assuming that an active chain transfer agent is present from the start and is consumed as shown below: A * + X k-~PA * + p . The presence of DETOMG in the system causes it to be consumed in a similar t manner: b'
A* +EI-~A*-}-p in which A* is the active centre, X and E are chain transfer agents (admixture and DETOMG), bp and k~ are rate constants of the chain transfer reaction, and P is the polymer. I f initiation is instantaneous, A * = c 0 (in which co is the initial SnCl 4 concentration) and dX dE
~------kpcoX, ~---kp'Co t
from which we get X = X o . e - k p c~ and E-~E0.e-k' c0t.
Polymerization of formaldehyde
2901
Where the polymerization proceeds in the diffusion range with respect to the monomer .P--
a
q Co-+-(Xo--X) + (Eo--E) '
(1)
x/
h
~5
//7
,
,
fo
20 Time, mio
I.
30
2
i
.
z~
I
I
I
6
8
lO
[SnC{4]"!05,mole/l.
F I e . 3. P F A yield as a function of (a) time: 1--homopolymorization, 2 - - F A polymerization with 0.44 mole/1. DETOMG present; (b) of SnC14 concentration. m
in which P--polymerization coefficient, q--monomer consumption determined from the polymer yield. By inserting into eqn. (1) the values X and E, we get P=
q
co+Xo(1--e~pCot)+Eo(1--e-r~d)
or
1=c0 +X0(1-ekp~) ~-E0(1-e~°' !. P
q
q
(2)
q
At lower initiator concentration, where (1 -- e -kp ¢0t) ~ kpcot 1 __ Co ~ X°kvc°t ~ Eokp'cot
P
q
q
(3)
q
I f kp~ kp, one can neglect the last term of eqn. (3) and write 1
P
Co ~- XokpOot
q
(4)
q
which was actually observed (Fig. 4a) as the coinciding linear section at low [SnC14]. The value of e-kp~0t-->0 at larger initiator concentrations in the absence of DETOMG, and l=c~+Xo. P q q
(5)
2902
A.G. GBvz~ov et ~d.
This c a s e is r e p r e s e n t e d b y t h e second linear p a r t on t h e curve (Fig. 4a), the i n t e r c e p t of which on the abscissa equals X0/q, f r o m which [ X 0 ] = 3 " 7 × 10 -a mole/1.; kp can be assessed f r o m eqn. (4) as being 7.3 1..mole -1 sec -1. W h e r e D E T O M G is p r e s e n t (for k~>>b~), 1
Co-~X o ~ Eo~Cot
q
q
(6)
V O0
,:,,ooV/ ...I
I
~o
2o
I.
I
3o ~o 108, mole/l.
[SnC[4]"
I
I
l
5o
o.25
0.5o
['DETOMG]
I
o.7~ l.oo , mole/L
]FIQ. 4. I / ~ as a function of (a) SnOl~ concentration; 1, 2 as in Fig. 3; (b) of DETOMG concentration at various concentrations of SnOl a (mole#.): 1--3 X ]0 -e, 2 - - 2 . 5 X I 0 -e,
3--5X 10-*, 4 - - 2 . 5 X 10-a, 5--5X 10-e.
5
/
#
100
2
I
!
I
I"
l~l.
l
,
23#
5 [SnCh], 10~,mole/L
I
O'25
0"50
I
I
~275
1-00
[ a ] , moZe/L
FIG. 5
FIG. 6
FIG. 5. Gradient of the curves as a function of SnCI~ concentration. FIG. 6. 1/P as a function of CHsO(CHsO)nCHn concentration [A] with varying n: 1--1, 2 - - 3 , 3--6.
Polymerization of formaldehyde
2903
this is represented by the second linear part of curve 2 (Fig. 4a). Figure 4b shows the results of experimental FA polymerizations in the presence of DETOMG and with SnC14 concentrations as meeting the requirements of eqn. (6). As could be expected, the gradients of the 1/P--[E0] response lines were proportional to c0(see Fig. 5). From this we find k~ to be 3 x 10 -a 1.'mole-lsec -1. The values of [X0], kp and k~ were determined accurately up to M~/M,, which, on the basis of other works [5-7], is taken to be 2. The chain transfer agent indicated as X is most likely to be water contained in the solvent. The direct determination of water in toluene using the Fischer reagent gave its content as 0.002-0.004%, which agrees well with the calculated values. I t should be noted t h a t k~ is independent of the number of CH20 units present in DETOMG (Fig. 6) and in the extreme case, if transfer varies from 1 to 6. CONCLUSIONS
(1) The polymerization of formaldehyde in toluene as solvent was examined with SnC14 as catalyst in the presence or absence of trioxymethylene glycol dimethyl ether (DETOMG). (2) The process was found to take place in t h e monomer diffusion range and in the kinetic range with respect to admixtures and additives. The rate constants of the chain transfer reaction through DETOMG and water were found to be 3 × × 10 -3 and 7.3 1.-mole-lsec -1. respectively, and were accurate up to M J M n.
Translated by K. A. ALLEN REFERENCES
1. N. S. YENIKOLOPYAN, J. Polymer Sci. 58: 1301, 1962 2. French Pat. 1461969, 1963 3. U.S. Pat. 2449469; Chem. Abs. 43: 1052, 1949 4. I. M. BEL'GOVSKII, N. S. YENIKOLOPYAN and L. S. SAKHONENKO, Vysokomol. soyed. 4: 1197, 1962 (Translated in Polymer Sei. U.S.S.R. 4: 2, 367, 1963) 5. H. L. WAGNER and K. F. WISSBRUN, Makromol. Chemle 81: 14, 1965 6. V. V. IVANOV, A. A. SHAGINYAN and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSR 161: 154, 1965 7. V. V. IVANOV, A. A. SHAGINYAN, V. P. VOLKOV and N. S. YENIKOLOPYAN, Vysokotool. soyed. 7: 1830, 1965 (Translated in Polymer Sci. U,S.S.R. 7: 10, 2015, 1965)
A . G . G B u z s o v e~ a/.
5. A. A. BERLIN, B. I. LIOGON'KII, A. A. GUROV a n d Ye. F. RAZVADOVSEH, Vysokom01. soyed. Ag: 532, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 3, 596, 1967) 6. A. A. GUROV, B. I. LIOGON'KH and A. A. BERLIN, Vysokomol. soyed. Ag: 2259, 1967 (Translated in P o l y m e r Sci. U.S.S.R. 9: 10, 2555, 1967) 7. A. A. BERLIN, B. I. LIOGON'KII and E. ABDULA-ZADE, Vysokomo]. soyed. A9: 1725, 1967 (Translated in P o l y m e r Sci. U.S.S.R. 9: 8, 1943, 1967)
POLYMERIZATION OF FORMALDEHYDE IN THE PRESENCE OF THE DIMETHYL ETHER OF POLYOXYMETHYLENE GLYCOL* A. G. GRuz~ov, L. 1~I. PUSHCHAYEVAand L. M. R o ~ o v Scientific Research I n s t i t u t e of Plastics
(Received 18 November 1967) TKE production of a stable polyformaldehyde b y cationic polymerization is based on t h e elemental act of chain transfer with fracture of macromolecules (CTFM). The CTFM can be basically described as: +
~ O--CH,--O--CH,~-R1--O--R,--O--CH, ~ + -* ~ O - - C H , - - OCH~-- OR2-- OR1 + CH, N O--CHIn-- OCHa-- O R I + R ~ - - O - - C H , ~ , in which R - - C H s or any other hydrocarbon radical, R a - - a radical containing a t least a - - C H I - - C H ~ group. The blocking compound used can be t h e dimethyl ether of polyoxymethylene glycol [2] of general formula CHs-- O - - (CH20), CHs, in which n = 1,2,3... The result of this should be a polyformaldehyde (PFA) having stable m e t h o x y end groups. The paper describes the study of the mechanism of gas-phase formaldehyde ( F A ) p o l y m e r i z a t i o n i n t h e p r e s e n c e o f SnCId, a n d w i t h a d d i t i o n s o f t h e d i m e t h y l ether of trioxymethylene glycol (DETOMG).
EXPERIMENTAL Toluene was purified with oxides of nitrogen, washed w i t h HsSO,, then with water to neutral reaction, aqueous alkali, water, then dried and distilled over metallic sodium. T h e fraction coming over at 110.6°C was collected. DETOMG was purified as described in the U.S. p a t e n t [3]; it was dried over metallic s o d i u m a n d also distilled over it. The fraction with b~p. 155.2°C was collected. SnCl,. The commercial preparation was refluxed and the fraction coming over a t * Vysokomol. soyed. AIO: No. 11, 2495-2499, 1968.
Polymerization of formaldehyde
2899
113.5-113-8°C was collected. The product was frozen and thawed in vacuo, and then distributed as 0.05-0'2 g samples into ampoules. Method. The polymerization was carried out in the a p p a r a t u s illustrated in Fig. 1. The flask 1 was filled with 800 g ~-polyoxymethylene a n d heated on a b a t h (2) to 180°C. The F A forming during this period was purged with an argon stream and the gas, on reaching 180°C, was fed into column 3 p a c k e d with glass rings, a n d from there into coil 4 (25 m long, 8 m m in diameter), which was cooled to --19°C. The purified F A present on the chilled walls then entered the reaction flask 5 which h a d been supplied with toluene, DETOMG, and t h e required a m o u n t of s t a n d a r d SnO14 solution in toluene. The t o t a l volume of the system was 50 ml. The reaction vessel was k e p t at 30°C b y means of an ultra-thermostat. The F A feed was calculated so t h a t the gas bubbled continuously through the bubbler vessel which was filled with toluene, situated at the reactor outlet. I t was stopped on completion of polymerization and a triethanolamine solution in ethanol was a d d e d immediately to neutralize the catalyst. The polymer was separated b y filtration, washed with acetone, boiling water, acetone, ether, a n d then dried at 60°C.
i( ~
N
J
FIQ. 1. Schematic illustration of the a p p a r a t u s used to polymerize gaseous formaldehyde. F o r explanation see text. The viscosity was determiued in a vlscometer with a suspended level indicator a t 150°C, using a 0"5~o P F A solution in DMF, also containing 2~/o diphenylaxaine. The molecular weight (m.w.) of t h e polymer was calculated from the formula: [t]]----4. 4 X 104M °'6t [4]. RESULTS
T h e p o l y m e r i z a t i o n o f g a s e o u s F A i n t o l u e n e a t 30°C, w i t h SnC14 a s c a t a l y s t , w i t h o r w i t h o u t D E T O I ~ I G , is c h a r a c t e r i z e d b y a n u m b e r o f f e a t u r e s ( F i g . 2). A l o w i n i t i a t o r c o n c e n t r a t i o n (8 × 10 -e t o 2 × 10 -5 m o l c f l . ) g a v e a r a p i d m . w . d e c r e a s e w i t h i n c r e a s i n g SnC14 c o n t e n t . T h e m . w . - [ S n C l a ] r e s p o n s e c u r v e s with and without added ])ETOMG were practically identical. An increase of [SnC14] b e y o n d t h e e a r l i e r m e n t i o n e d c o n t e n t c a u s e d t h e c u r v e s t o d i v e r g e o n approaching the abscissa. T h e r a t e o f p o l y m e r i z a t i o n w a s c o n s t a n t w i t h t i m e f o r 20 r a i n ( F i g . 3a) a n d w a s p r a c t i c a l l y i n d e p e n d e n t o f i n i t i a t o r c o n c e n t r a t i o n i n t h e r a n g e 8 × 10 -6
2900
A.G. GRuz~ov eta/.
to 5 X 10 -3 mole/1. (Fig. 3b). The latter indicates that the polymerization takes place in the diffusion range as regards the monomer. The m.w. changes should therefore be inversely proportional to the initiator concentration. M.w. • 10-3 5OO #00 300 2OO 100
×~"<'~c~
1 2' / / o)c I
I
1o
20
lo , ote / l.
FIG. 2. Molecular weight of PFA as a function of SnC14 concentration: /--homopolymerization, 2--FA polymerization in the presence of 0.44 mole/1. DETOMG. Consequently, Fig. 4a shows the curves in the coordinates 1/P-[SnCI¢] to have coincident straight sections at 8 × 10 -s to 5 × 10 -~ mole/1. SnC14; this was without additive. Where DETOMG was present, the straight sections were in the range 9 × 10 -e t o 7 × 10 -5 mole/1.
The change to the range of higher initiator concentrations (up to 1 × 10 -4 mole/].) caused a deviation from the initially increased m.w. A further SnCI~ concentration increase again gave linear sections, b u t with different slopes. The characteristics of the m.w.-initial concentration function can be explained b y assuming that an active chain transfer agent is present from the start and is consumed as shown below: A * + X k-~PA * + p . The presence of DETOMG in the system causes it to be consumed in a similar t manner: b'
A* +EI-~A*-}-p in which A* is the active centre, X and E are chain transfer agents (admixture and DETOMG), bp and k~ are rate constants of the chain transfer reaction, and P is the polymer. I f initiation is instantaneous, A * = c 0 (in which co is the initial SnCl 4 concentration) and dX dE
~------kpcoX, ~---kp'Co t
from which we get X = X o . e - k p c~ and E-~E0.e-k' c0t.
Polymerization of formaldehyde
2901
Where the polymerization proceeds in the diffusion range with respect to the monomer .P--
a
q Co-+-(Xo--X) + (Eo--E) '
(1)
x/
h
~5
//7
,
,
fo
20 Time, mio
I.
30
2
i
.
z~
I
I
I
6
8
lO
[SnC{4]"!05,mole/l.
F I e . 3. P F A yield as a function of (a) time: 1--homopolymorization, 2 - - F A polymerization with 0.44 mole/1. DETOMG present; (b) of SnC14 concentration. m
in which P--polymerization coefficient, q--monomer consumption determined from the polymer yield. By inserting into eqn. (1) the values X and E, we get P=
q
co+Xo(1--e~pCot)+Eo(1--e-r~d)
or
1=c0 +X0(1-ekp~) ~-E0(1-e~°' !. P
q
q
(2)
q
At lower initiator concentration, where (1 -- e -kp ¢0t) ~ kpcot 1 __ Co ~ X°kvc°t ~ Eokp'cot
P
q
q
(3)
q
I f kp~ kp, one can neglect the last term of eqn. (3) and write 1
P
Co ~- XokpOot
q
(4)
q
which was actually observed (Fig. 4a) as the coinciding linear section at low [SnC14]. The value of e-kp~0t-->0 at larger initiator concentrations in the absence of DETOMG, and l=c~+Xo. P q q
(5)
2902
A.G. GBvz~ov et ~d.
This c a s e is r e p r e s e n t e d b y t h e second linear p a r t on t h e curve (Fig. 4a), the i n t e r c e p t of which on the abscissa equals X0/q, f r o m which [ X 0 ] = 3 " 7 × 10 -a mole/1.; kp can be assessed f r o m eqn. (4) as being 7.3 1..mole -1 sec -1. W h e r e D E T O M G is p r e s e n t (for k~>>b~), 1
Co-~X o ~ Eo~Cot
q
q
(6)
V O0
,:,,ooV/ ...I
I
~o
2o
I.
I
3o ~o 108, mole/l.
[SnC[4]"
I
I
l
5o
o.25
0.5o
['DETOMG]
I
o.7~ l.oo , mole/L
]FIQ. 4. I / ~ as a function of (a) SnOl~ concentration; 1, 2 as in Fig. 3; (b) of DETOMG concentration at various concentrations of SnOl a (mole#.): 1--3 X ]0 -e, 2 - - 2 . 5 X I 0 -e,
3--5X 10-*, 4 - - 2 . 5 X 10-a, 5--5X 10-e.
5
/
#
100
2
I
!
I
I"
l~l.
l
,
23#
5 [SnCh], 10~,mole/L
I
O'25
0"50
I
I
~275
1-00
[ a ] , moZe/L
FIG. 5
FIG. 6
FIG. 5. Gradient of the curves as a function of SnCI~ concentration. FIG. 6. 1/P as a function of CHsO(CHsO)nCHn concentration [A] with varying n: 1--1, 2 - - 3 , 3--6.
Polymerization of formaldehyde
2903
this is represented by the second linear part of curve 2 (Fig. 4a). Figure 4b shows the results of experimental FA polymerizations in the presence of DETOMG and with SnC14 concentrations as meeting the requirements of eqn. (6). As could be expected, the gradients of the 1/P--[E0] response lines were proportional to c0(see Fig. 5). From this we find k~ to be 3 x 10 -a 1.'mole-lsec -1. The values of [X0], kp and k~ were determined accurately up to M~/M,, which, on the basis of other works [5-7], is taken to be 2. The chain transfer agent indicated as X is most likely to be water contained in the solvent. The direct determination of water in toluene using the Fischer reagent gave its content as 0.002-0.004%, which agrees well with the calculated values. I t should be noted t h a t k~ is independent of the number of CH20 units present in DETOMG (Fig. 6) and in the extreme case, if transfer varies from 1 to 6. CONCLUSIONS
(1) The polymerization of formaldehyde in toluene as solvent was examined with SnC14 as catalyst in the presence or absence of trioxymethylene glycol dimethyl ether (DETOMG). (2) The process was found to take place in t h e monomer diffusion range and in the kinetic range with respect to admixtures and additives. The rate constants of the chain transfer reaction through DETOMG and water were found to be 3 × × 10 -3 and 7.3 1.-mole-lsec -1. respectively, and were accurate up to M J M n.
Translated by K. A. ALLEN REFERENCES
1. N. S. YENIKOLOPYAN, J. Polymer Sci. 58: 1301, 1962 2. French Pat. 1461969, 1963 3. U.S. Pat. 2449469; Chem. Abs. 43: 1052, 1949 4. I. M. BEL'GOVSKII, N. S. YENIKOLOPYAN and L. S. SAKHONENKO, Vysokomol. soyed. 4: 1197, 1962 (Translated in Polymer Sei. U.S.S.R. 4: 2, 367, 1963) 5. H. L. WAGNER and K. F. WISSBRUN, Makromol. Chemle 81: 14, 1965 6. V. V. IVANOV, A. A. SHAGINYAN and N. S. YENIKOLOPYAN, Dokl. Akad. Nauk SSSR 161: 154, 1965 7. V. V. IVANOV, A. A. SHAGINYAN, V. P. VOLKOV and N. S. YENIKOLOPYAN, Vysokotool. soyed. 7: 1830, 1965 (Translated in Polymer Sci. U,S.S.R. 7: 10, 2015, 1965)