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Acrylamide polymerization in concentrated aqueous solutions and in two-phase systems
Acrylam:de polymemzatlor~
423
9. 10. 11. 12. 13.
L. H. LADY, J. F. ~ E ~ S E a n d R. E. ADAMS, J. Appl. Polymer Sci. 3: 71, 1960 K. INGOLD, Uspekhi khlmll, U : 1107, 1964 C. W. CAPP a n d E. G. F. HAWKINS, J. Chem. Soc., 106, 1953 H. E. De La MARE, J. Organ. Chem. 25: 2114, 1960 O. G. TARAKANOV, L. N. KONDRATEVA and L. V. NEVSKII, Plast. massy, No 6, 36, 1970 14. O. G. TARAI(ANOV and L. N. KONDRATEVA, Vysokomo] soyed A13: 565, 1971 (Translated in Polymer Sci. U.S.S.R 13: 3, 642. 1971)
ACRYLAMIDE POLYMERIZATION IN CONCENTRATED AQUEOUS SOLUTIONS AND IN TWO-PHASE SYSTEMS* V. F .
GROMOV,A. P. SHEINKER,P. M. KHOMIKOVSKII and A. D. ABKIN L. Ya Karpov Physical Chemistry Research Institute
(Recewed 16 June 1972) A study was made of the polymemzatlon of acrylamlde (AA) m two-phase systems contammg water and m concentrated aqueous solutions m presence of a m m o m a or caustic soda. I t was found that polymers ~ d b y polymemzatlon m these systems, wheh the latter contain n o t less t h a n 0.5 wt.~o caustic soda, or 1.3 wt.~o ammoma, dmsolve, completely in water. The rate of chain transfer through ~,~',p"-nitrdetnpropto~amlde molecules was deternnned. The probable causes of the formation of soluble polyacrylannde m concentrated aqueous systems m the presence of ammorea or caustic soda are analysed. WATER soluble acrylamide (AA) polymers are widely used as floceulants for acceleration of the settling a n d filtration of suspensions, and for a n u m b e r of other important purposes. The polymerization of acrylarmde (AA) m aflueous solutions, with monomer concentrations exceeding 10-15Vo, results, already m the early stages of the process, m crosslmked waterinsoluble polymers [1]. I n mew of tins one finds t h a t if the polymerlzatton is carried out m aqueous solutions with ]ngh concentrations of AA it is impossible to obtain products with a molecular weight exceeding t h a t obtainable b y polymerization m relatively ddute solutions. We assumed that the action of hydrogen lens was responstble for the formation of network polymers of AA m concentrated aqueous systems. I f the latter assumption is vahd, the polymerization of AA m these systems m presence of ammoma or alkalm, L e. under condltlous of marked reduction m the H+ concentrations, should ensure t h a t water soluble products are obtained at advanced stages of the polymemzatlon. Certainly our investigations chd show that even where there was complete conversion of the monomer, water soluble polymers are obtained b y polymenzmg AA m presence of ammoma or caustic alkahs (m amounts of from 1 to 10~o by wt.) m concentrated aqueous * Vysokomol. soyed. A16: No. 2, 365-369, 1974.
424
V . F . GItoMov e$ al.
solutions*, as well as m two-phase systems (a saturated solution of AA in water a n d a crystalline monomer) containing u p to 95yo AA. The resulting polymers have molecular weight of M > 10T;the maxamum average molecular weight of the polymers obtained m 10 ~o aqueous solutions amounts to ~ 3 × 106. Polymers synthesized m aqueous systems with monomer conce~ltratlons exceeding 2 0 ~ are superior m respect to the rate of precipitation of suspeuaions, the rate being from 3-10 times higher t h a n m the case of known compounds of AA [2]. The marked flocculating activity of these polymers is due n o t only to their ingher molecular weight, b u t also to the fact that hydrolysis takes place during the polymerization m a n alkah medium, and along with the amide groups there are also - - C O O H and ---COON-Ha or ---COONa groups in the polymer. This paper describes an investigation of some problems relating to the radiat i o n p o l y m e r i z a t i o n of A A in c o n c e n t r a t e d aqueous 'solutions or in two-phase systems.
EXPERIMENTAL The AA used for the investigation (produced b y Gee Lawson Chemmals Ltd.) was twine sublimed m vacuum at 80 °. The procedure adopted m the polymemzatlon expermaents has already been described [3] m respect to the aqueous solutions. W i t h the two-phase systems the polymemzatlon experiments were carried out m ampoules t h a t were charged as follows. To a weighed portion of AA m an ampoule was added the reqmred a m o u n t or water or of a n aqueous solution of caustic soda, and the reaction mixture was evacuated . for 3 hr (10 -s torr) at -- 196% Ammonia was fed in from the gas phase, using a manometer to control the a m o u n t being introduced. After a n ampoule had been sealed off from the v a c u u m apparatus the contents of the ampoule were melted at 60 °, while agitating mgorously, after winch the contents were crystallized at the temperature reqmred for the experiment. The ampoules tmderwent gamma-Lrradlatlon with a Co 6e source [4]. The polymers were separated from the reaction mixture b y extraction of the unreacted monomer w]th a mixture of ethyl alcohol and water ( 9 0 : 1 0 b y vol.), followed b y extraction with ethyl alcohol m the presence of phenol. After the extraction had been completed, the polymers were vacuum-drmd to constant weight at room temperature. The phase state of the A_k-water system was investigated b y means of thermography. The crystallization temperatures were determined for mixtures of different composition. fl,~',p"-Nltrdetriprepionamlde (N-PA) was prepared by reacting 535 pts (by wt.) of a 45~/o aqueous solution of AA with 500 pts of a 28~o aqueous solution of ammonia at room temperature for 24-36 hr [5]. After some of the water had evapora(ed, white crystals separated out from solution. The NPA used in the experiments was twice recrystalhzed from a mixture of water and methanol; m. p. 186 °. The results of elemental analysis were in good agreement with the formula N(CH2CHICONHs)s. The molecular weight of the polyacrylamlde (PAA) were calculated from the intrinsic wscbmty, using the following equations [3, 6]: [~]=6 80× 10 -4 AT/°w';[t/]=3.73× 10 -6/~.66;
DISCUSSION OF RESULTS
Polymerization in the two-phase aqueous syatems. I t is s e e n f r o m F i g . l t h a t A A w i t h w a t e r forms a s y s t e m w i t h a simple eutectic, t h e c o m p o s i t i o n of which c o r r e s p o n d s t o 12 mole~/o (35 wt.~/o) o f A A . T h e e u t e c t i c t e m p e r a t u r e w a s - - 1 0 °. * The solublhty of AA m water is ~ 6 0 % (by wt.) at 20 ° .
425
Acrylamlde polymerization
Small additions of water to the crystalline AA greatly increase the polymer yield under conditions of gamma-irradiation of the monomer at 20 ° . For example the PAA yield is increased by more than one order by adding 2 wt. ~/o of water to the monomer (given a dose rate of 2.3 rad/sec, the yield was increased in 10 min from 0.013 to 0.55% by adding water). A higher yield of PAA in the presence of small amounts of water was also reported in [7]
7O o
50 3O /0 -/0 0
I
I
I
i
*
I
I
I
0 2 0 4 06" 0 8 t-t~0, mole frucL/o~s FIG. 1
I
/'O
0
0"2 0-4 06' 06' / 0 H20 , m ele froctions FIG. 2
FIG. 1. Phase diagram for the system AA-water FIG. 2. Polymer yaeld W vs. HaO content m the lmtxal rmxture during AA polymemzation in water. Polymerization time, 10 mm; 20°; dose rate 2,7 rad/sec; a m m o m a content m the system 2 mole Yo For explanatxon of the curves see the text.
It is seen from Fig. 2 that curve 1, which describes polymer yield in relation to the content of H~O in the system, passes through a maximum at an ASk content of 25-28 mole %, which practically corresponds to ~ saturated solution of AA m water at 20 °. Using the phase diagram (Fig. 1) one can readily show t h a t where there are two-phases, i. e. when the content of AA in a mixture exceeds 28 mole %, the rise in the PAA yield to a maximum is the result of an increase in the amount of liquid phase in which, for the most part, the polymerization reaction takes place. Under these conditions the polymer yield, as a ratio of one mole of liquid phase, remains practical]y constant, irrespective of the content of AA in the initial mixture (Fig. 2, curve 2). Of major significance is the fact t h a t this yield is equal to the polymer yield when the AA is polymerized in a saturated solution of monomer in water in the absence of crystalline phase. Passing now from two-phase to single-phase solutions, i e. where the amount of AA in an initial mixture is below 28 mole ~/o, the polymer yield rises with increase in the AA content in the system (Fig. 2). The observed rise in the polymer yield is due to the gel effect, since the polymerization of AA in dilute aqueous solutions is first-order in relation to monomer concentration. The magnitude of
426
V . F . GRo~ov e$ a/.
the gel effect depends on the amount of monomer in solution. The average rate of the process is therefore increased as the AA concentration rises. The radiation polymerization of AA in aqueous two-phase solutions was investigated with monomer contents ranging from 70 to 95 wt ~ in the presence of ammonia or caustic soda (0.2 to 10 wt.~o on the AA). Under these conditions the rate of the polymerization reaction increases with time The polymer yield in a given time is determined mainly b y the amount of water in the system, and is virtually independent of the amount of ammonia or caustic soda. EFFECT
OF A M O U N T OF TIME T H E R E A C T I O N M I X T U R E IS R E T A I N E D
P R I O R TO T H E IRRADIATIOI~Y O N T H E M O L E C U L A R W E I G H T O F T H E RESULTING- POLYMI~RS
(Retentmn time temperature, 20°; d o ~ rate 5 r a d / ~ e ; ratm of components of the reactmn n u x t u r e of AA : a m m o m a : water
~-70/: 1 : 30 (by wt.); polymerizatmn time, 45 ram) Rotentmn time, hr Polymer yield, ~o
4"7 8"6 17"7
98 99 99 98
[ti] In a 1N aqueous solution of KCI, dl/g 16.0 10"5 6.7 7.0
The molecular weights of the polymers are reduced when the amount of ammonia or caustic soda in the reaction mixture is increased. This is apparently due to a chain transfer reaction, to which further reference will be made below. The intrinsic viscosity of the polymers prepared with a 70 : 30 weight ratio of AA to water in the presence of 2~/o of ammonia amounts to something of the order of 15--16 dl]g, while in the presence of 0.5% of caustic soda the intrinsic viscosity is 13-14 dl/g. The addition of from 0.2 to 0.3% of caustic to the reaction system containing ammonia leads to a marked reduction in the molecular weight of the polymer. For instance, the intrinsic viscosity of polymers obtained at 20 ° in presence of 0.2-0.3~/o of caustic soda and 2% of ammonia is reduced to 5-3.5 dl/g. A similar effect is observed when the reaction mixture is retained, prior to polymerization, in the presence of ammonia (see Table) and similarly when the reaction temperature is raised from 20 to 30 ° . The results of conductometric titration show that the polymers prepared in the aqueous two-phase systems contain units of acrylic acid (up to 8~/o) and of acrylic acid salts (2-3%). Polymerizatio~ in 8olutions. A study was also made of the radiation polymerization of AA in aqueous solutions with the monomer concentrations ranging from 10 to 55 wt.%, and with ammonia concentrations of 1.3-10 w t . ~ , varying the
Aerylarmd~ polymerizatmn
427
conversion; thereafter the rate is reduced. The average molecular weight of polymers obtained in the case of a high degree of conversion are increased as t he monomer concentration rises (Mw increases from 5 × 106 to 2 × l0 T on increasing the AA concentration from l0 to 50%). An increase in the content of ammonia in solution from 1.3 to 10% has virtually no effect on the polymerization rate, but the average molecular weight of the polymers is t h e r e b y considerably reduced*, i. e ammonia acts in t h e same way as a chain transfer agent. The effect in question could possibly be the result of the product of ammonia-AA interaction participating in the polymerization process. I t is k n o w l t h a t at room temperature AA reacts readily with ammonia to form N P A [5]. The effect of this product on the polymerization of AA in aqueous solutions was accordingly investigated /
/01
[M]
,
I JO
I
I
I
I 250
/50
uo , lO ~
[M] [~PA] FIO. 3 Calculatmn of the rate of chain transfer through NPA molecules during the polymemzatmn of AA m water at 20% The polymerization was conducted in dilute aqueous solutions with m o n o m e r concentrations ranging from 0.14 to 0.57 mole/1. (1-4 w t . %) and with N~PA concentrations of 0.013-0.053 mole/1, under the action of UV irradiation in t h e presence of a photosensitizer (dinitrfle of azoisobutyric acid). The reaction rate remains constant at the start of the process, and is a linear function of monomer concentration and proportional to the square root of irradiation intensity. The initial rate of polymerization remains practically constant as the a m o u n t o f N P A in solution rises. However, a rise in the N P A concentrations leads t o a marked reduction in the molecular weight of the PAA This shows t h a t chain transfer takes place t hr ough N P A molecules t. The rate of this reaction was calculated b y using the equation.
1
]Q v0
ktr [I~PA]
(1)
* When the amount of ammoma m solution is below 1 2-1'3yo, the polymers, m the case of complete conversion, are completely insoluble m water. t The authors thank N. P. Paskhm for pointing out the possible role of NPA m the chain transfer reaction during AA polymenzatmn m the presence of ammoma.
428
V.F. GRO~OVet al.
(where Pn is the number average degree of polymerization, and kt, kp, ktr , the rate constants for chain termination, propagation a n d transfer, respectively, v0, polymerization rate; [M] and [NPA], concentrations of the monomer and N P A respectively and the rate constants obtained in this w a y are: kp/kt~----3.8 and ktr/kp---- 1.5 × 10 -3 (Fig. 3). The value of kp/k t was also found (using the method of intermittent exposure to light) and the values of kp and k t obtained for the AA polymerization in the presence of NPA, are in good agreement with the values obtained for the polymerization of AA in aqueous solution [8]. The experimental results show that the N P A formed through the interaction of AA and ammonia is a very effective chain transfer agent in the polymerization of AA in water. The reactivity of the radical formed as a result of the chain transfer reaction is close to that of the AA radical. It was also shown that the addition of N P A to a concentrated solution of AA in water leads to the formation of soluble polymer at advanced degrees of conversion. For instance, in a 47% solution of AA in water containing 8% of N P A (0.35 mole/l.)a soluble polymer of relatively low molecular weight (Mw--~0.75× × 106) was obtained on complete conversion. The molecular weight of the polymer synthesized under similar conditions in the presence of the equivalent amount of ammonia was 7 × 10s. Without the addition of ammonia or N P A completely insoluble PAA is obtained with the same concentration of monomer. I t was also found that the polymerization of AA in concentrated solutions in an aprotonic solvent (DMSO) leads to the formation of water soluble polymers with molecular weights of up to 9 × 10~ (with a monomer concentration of 40%). Thus it appears that the polymerization of AA in concentrated aqueous solutions, and also m two-phase systems in the presence of ammonia or caustic soda, leads to the formation of water soluble high molecular polymers. Moreover, it was found that m an acid medium crosslinked insoluble are formed even when the polymerization is conducted in dilute solutmns. It is therefore reasonable to assume that hydrogen ions must be responsible for a crosslinking reaction that is accompanied b y the evolution of ammonia and leads to the formation of imide structures. This assumption is also favoured b y the fact that the polymers prepared in concentrated solutions in DMS0, which are of high molecular weight, d]ssolve completely in water In addition, a factor of major importance in regard to the formation of soluble polymers of AA is the presence, in the system, of the product of interaction of ammonia with AA, namely NPA. On the one hand this compound is decidedly active in chain transfer reactions, while on the other hand it is a strong protonacceptor. The decisive role of N P A in the formation of soluble PAA is clear from the fact that soluble polymers are obtainable in the presence of N P A through polymerization in concentrated systems, even m the absence of alkali additions It should be noted that N P A m a y likewise be formed in the presence of caustic soda, as ammonia is formed as a result of AA hydrolysis taking place in an alkaline medium, and the ammonia is then capable of participating in a
Stabdlzatmn of polymers by phosphorous actd esters
429
r e a c t i o n w i t h AA. I t is reasonable to assume t h a t the f a c t o r responsible for t h e m u c h lower molecular weight o f t h e p o l y m e r s p r e p a r e d in presence of a m m o n i a a n d o f small caustic soda additions could well be an increase in t h e rate of N P A formation.
Translated by R J. A. ~-.ENDRY REFERENCES
1. A. CHAPIR0, Radiation Chemmtry of Polymerm Systems, p 326, New York-London, 1962 2. A. D. ABKIN, A. P. SHEINKER, P. M. KHOMIKOVSKII, M. K. YAKOVLEVA, V. F. GROMOV, 8. P. TREMBACHEVA, I. A. YAKUBOVICH, P. I. PARADIYA, N. P. PASKHIN, M. P. VILYANSKII and V. G. NEgHOROSHEV, U.S S R Pat. 235997, 1966; Byul]. izob. No. 6; 1969, French Pat. 1466769 1966, 1492037, 1967; Ital Pat. 753476, 1967; 756445, 1967; U. K. Pat. 1106573, 1968 3. V. F. ,GROMOV, A. V. MATVEYEVA, P. M. ]g~HOMIKOVSKIIand A. D. ABKIN, Vysokomol. soyed. Ag: 1444, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 7, 1616, 1967) 4. A, Kh. BREGER, V. A. BELYNSKII, V. L. KARPOV, 8. D. PROKUDIN and V. B. OSIPOV, Trudy Vsesovyuznoi konf. po primenemyu radioaktivnykh i stabil'nykh isotopov i lzluchenii v narodnom khozyaistve i nauke, (Trans. All-Union Conf. on Use of Radio-Active and Stable Isotopes and Emanations m the Sovmt Economy and in Research). p. 182, Izd. AN SSSR, 1958 5. U. S. Pat. 2663733, 1953 6. F. 8. DAINTON and M. TORDOFF, Trans. Faraday Soc. 53: 499, 1957 7. A. J. RESTAINO, R. B. MESROBIAN, H. MORAW]gTZ, D. 8. BJtLLkNTINA, D. J. DI~I~E~I and D. J. M]gTZ, J. Amer. Chem. Soc. 78: 2939, 1956 8. V. F. GROMOV, P. M. KHOMIKOVSIII and A. D. ABKIN, Vysokomol. soyed. AI2: 767, 1970 (Not translated in Polymer Sci. U S.S R )
ON THE STABILIZATION OF POLYMERS BY PHOSPHOROUS ACID ESTERS* A. G. AKHMADUT.Lr~A, N. A. MUKME~EVA, P. A. KIRPICHNIKOV, N. S. KOLYUBA•rNA a n d D. G. POBEDIMSgn S. M. Klrov Kazan Chemmotechnologlcal Institute
(Received 19 June 1972) Accelerated ageing was the l~nethod used for investigation of the antloxldatlve properties (the exmtenee of crltmal concentrations and the dmplaecment of the latter m the presence of a decomposer of hydroperoxldes) of phosplntes of the cyehc * Vysokomo]. soyed. A16: No 2, 370-375, 1974.
423
9. 10. 11. 12. 13.
L. H. LADY, J. F. ~ E ~ S E a n d R. E. ADAMS, J. Appl. Polymer Sci. 3: 71, 1960 K. INGOLD, Uspekhi khlmll, U : 1107, 1964 C. W. CAPP a n d E. G. F. HAWKINS, J. Chem. Soc., 106, 1953 H. E. De La MARE, J. Organ. Chem. 25: 2114, 1960 O. G. TARAKANOV, L. N. KONDRATEVA and L. V. NEVSKII, Plast. massy, No 6, 36, 1970 14. O. G. TARAI(ANOV and L. N. KONDRATEVA, Vysokomo] soyed A13: 565, 1971 (Translated in Polymer Sci. U.S.S.R 13: 3, 642. 1971)
ACRYLAMIDE POLYMERIZATION IN CONCENTRATED AQUEOUS SOLUTIONS AND IN TWO-PHASE SYSTEMS* V. F .
GROMOV,A. P. SHEINKER,P. M. KHOMIKOVSKII and A. D. ABKIN L. Ya Karpov Physical Chemistry Research Institute
(Recewed 16 June 1972) A study was made of the polymemzatlon of acrylamlde (AA) m two-phase systems contammg water and m concentrated aqueous solutions m presence of a m m o m a or caustic soda. I t was found that polymers ~ d b y polymemzatlon m these systems, wheh the latter contain n o t less t h a n 0.5 wt.~o caustic soda, or 1.3 wt.~o ammoma, dmsolve, completely in water. The rate of chain transfer through ~,~',p"-nitrdetnpropto~amlde molecules was deternnned. The probable causes of the formation of soluble polyacrylannde m concentrated aqueous systems m the presence of ammorea or caustic soda are analysed. WATER soluble acrylamide (AA) polymers are widely used as floceulants for acceleration of the settling a n d filtration of suspensions, and for a n u m b e r of other important purposes. The polymerization of acrylarmde (AA) m aflueous solutions, with monomer concentrations exceeding 10-15Vo, results, already m the early stages of the process, m crosslmked waterinsoluble polymers [1]. I n mew of tins one finds t h a t if the polymerlzatton is carried out m aqueous solutions with ]ngh concentrations of AA it is impossible to obtain products with a molecular weight exceeding t h a t obtainable b y polymerization m relatively ddute solutions. We assumed that the action of hydrogen lens was responstble for the formation of network polymers of AA m concentrated aqueous systems. I f the latter assumption is vahd, the polymerization of AA m these systems m presence of ammoma or alkalm, L e. under condltlous of marked reduction m the H+ concentrations, should ensure t h a t water soluble products are obtained at advanced stages of the polymemzatlon. Certainly our investigations chd show that even where there was complete conversion of the monomer, water soluble polymers are obtained b y polymenzmg AA m presence of ammoma or caustic alkahs (m amounts of from 1 to 10~o by wt.) m concentrated aqueous * Vysokomol. soyed. A16: No. 2, 365-369, 1974.
424
V . F . GItoMov e$ al.
solutions*, as well as m two-phase systems (a saturated solution of AA in water a n d a crystalline monomer) containing u p to 95yo AA. The resulting polymers have molecular weight of M > 10T;the maxamum average molecular weight of the polymers obtained m 10 ~o aqueous solutions amounts to ~ 3 × 106. Polymers synthesized m aqueous systems with monomer conce~ltratlons exceeding 2 0 ~ are superior m respect to the rate of precipitation of suspeuaions, the rate being from 3-10 times higher t h a n m the case of known compounds of AA [2]. The marked flocculating activity of these polymers is due n o t only to their ingher molecular weight, b u t also to the fact that hydrolysis takes place during the polymerization m a n alkah medium, and along with the amide groups there are also - - C O O H and ---COON-Ha or ---COONa groups in the polymer. This paper describes an investigation of some problems relating to the radiat i o n p o l y m e r i z a t i o n of A A in c o n c e n t r a t e d aqueous 'solutions or in two-phase systems.
EXPERIMENTAL The AA used for the investigation (produced b y Gee Lawson Chemmals Ltd.) was twine sublimed m vacuum at 80 °. The procedure adopted m the polymemzatlon expermaents has already been described [3] m respect to the aqueous solutions. W i t h the two-phase systems the polymemzatlon experiments were carried out m ampoules t h a t were charged as follows. To a weighed portion of AA m an ampoule was added the reqmred a m o u n t or water or of a n aqueous solution of caustic soda, and the reaction mixture was evacuated . for 3 hr (10 -s torr) at -- 196% Ammonia was fed in from the gas phase, using a manometer to control the a m o u n t being introduced. After a n ampoule had been sealed off from the v a c u u m apparatus the contents of the ampoule were melted at 60 °, while agitating mgorously, after winch the contents were crystallized at the temperature reqmred for the experiment. The ampoules tmderwent gamma-Lrradlatlon with a Co 6e source [4]. The polymers were separated from the reaction mixture b y extraction of the unreacted monomer w]th a mixture of ethyl alcohol and water ( 9 0 : 1 0 b y vol.), followed b y extraction with ethyl alcohol m the presence of phenol. After the extraction had been completed, the polymers were vacuum-drmd to constant weight at room temperature. The phase state of the A_k-water system was investigated b y means of thermography. The crystallization temperatures were determined for mixtures of different composition. fl,~',p"-Nltrdetriprepionamlde (N-PA) was prepared by reacting 535 pts (by wt.) of a 45~/o aqueous solution of AA with 500 pts of a 28~o aqueous solution of ammonia at room temperature for 24-36 hr [5]. After some of the water had evapora(ed, white crystals separated out from solution. The NPA used in the experiments was twice recrystalhzed from a mixture of water and methanol; m. p. 186 °. The results of elemental analysis were in good agreement with the formula N(CH2CHICONHs)s. The molecular weight of the polyacrylamlde (PAA) were calculated from the intrinsic wscbmty, using the following equations [3, 6]: [~]=6 80× 10 -4 AT/°w';[t/]=3.73× 10 -6/~.66;
DISCUSSION OF RESULTS
Polymerization in the two-phase aqueous syatems. I t is s e e n f r o m F i g . l t h a t A A w i t h w a t e r forms a s y s t e m w i t h a simple eutectic, t h e c o m p o s i t i o n of which c o r r e s p o n d s t o 12 mole~/o (35 wt.~/o) o f A A . T h e e u t e c t i c t e m p e r a t u r e w a s - - 1 0 °. * The solublhty of AA m water is ~ 6 0 % (by wt.) at 20 ° .
425
Acrylamlde polymerization
Small additions of water to the crystalline AA greatly increase the polymer yield under conditions of gamma-irradiation of the monomer at 20 ° . For example the PAA yield is increased by more than one order by adding 2 wt. ~/o of water to the monomer (given a dose rate of 2.3 rad/sec, the yield was increased in 10 min from 0.013 to 0.55% by adding water). A higher yield of PAA in the presence of small amounts of water was also reported in [7]
7O o
50 3O /0 -/0 0
I
I
I
i
*
I
I
I
0 2 0 4 06" 0 8 t-t~0, mole frucL/o~s FIG. 1
I
/'O
0
0"2 0-4 06' 06' / 0 H20 , m ele froctions FIG. 2
FIG. 1. Phase diagram for the system AA-water FIG. 2. Polymer yaeld W vs. HaO content m the lmtxal rmxture during AA polymemzation in water. Polymerization time, 10 mm; 20°; dose rate 2,7 rad/sec; a m m o m a content m the system 2 mole Yo For explanatxon of the curves see the text.
It is seen from Fig. 2 that curve 1, which describes polymer yield in relation to the content of H~O in the system, passes through a maximum at an ASk content of 25-28 mole %, which practically corresponds to ~ saturated solution of AA m water at 20 °. Using the phase diagram (Fig. 1) one can readily show t h a t where there are two-phases, i. e. when the content of AA in a mixture exceeds 28 mole %, the rise in the PAA yield to a maximum is the result of an increase in the amount of liquid phase in which, for the most part, the polymerization reaction takes place. Under these conditions the polymer yield, as a ratio of one mole of liquid phase, remains practical]y constant, irrespective of the content of AA in the initial mixture (Fig. 2, curve 2). Of major significance is the fact t h a t this yield is equal to the polymer yield when the AA is polymerized in a saturated solution of monomer in water in the absence of crystalline phase. Passing now from two-phase to single-phase solutions, i e. where the amount of AA in an initial mixture is below 28 mole ~/o, the polymer yield rises with increase in the AA content in the system (Fig. 2). The observed rise in the polymer yield is due to the gel effect, since the polymerization of AA in dilute aqueous solutions is first-order in relation to monomer concentration. The magnitude of
426
V . F . GRo~ov e$ a/.
the gel effect depends on the amount of monomer in solution. The average rate of the process is therefore increased as the AA concentration rises. The radiation polymerization of AA in aqueous two-phase solutions was investigated with monomer contents ranging from 70 to 95 wt ~ in the presence of ammonia or caustic soda (0.2 to 10 wt.~o on the AA). Under these conditions the rate of the polymerization reaction increases with time The polymer yield in a given time is determined mainly b y the amount of water in the system, and is virtually independent of the amount of ammonia or caustic soda. EFFECT
OF A M O U N T OF TIME T H E R E A C T I O N M I X T U R E IS R E T A I N E D
P R I O R TO T H E IRRADIATIOI~Y O N T H E M O L E C U L A R W E I G H T O F T H E RESULTING- POLYMI~RS
(Retentmn time temperature, 20°; d o ~ rate 5 r a d / ~ e ; ratm of components of the reactmn n u x t u r e of AA : a m m o m a : water
~-70/: 1 : 30 (by wt.); polymerizatmn time, 45 ram) Rotentmn time, hr Polymer yield, ~o
4"7 8"6 17"7
98 99 99 98
[ti] In a 1N aqueous solution of KCI, dl/g 16.0 10"5 6.7 7.0
The molecular weights of the polymers are reduced when the amount of ammonia or caustic soda in the reaction mixture is increased. This is apparently due to a chain transfer reaction, to which further reference will be made below. The intrinsic viscosity of the polymers prepared with a 70 : 30 weight ratio of AA to water in the presence of 2~/o of ammonia amounts to something of the order of 15--16 dl]g, while in the presence of 0.5% of caustic soda the intrinsic viscosity is 13-14 dl/g. The addition of from 0.2 to 0.3% of caustic to the reaction system containing ammonia leads to a marked reduction in the molecular weight of the polymer. For instance, the intrinsic viscosity of polymers obtained at 20 ° in presence of 0.2-0.3~/o of caustic soda and 2% of ammonia is reduced to 5-3.5 dl/g. A similar effect is observed when the reaction mixture is retained, prior to polymerization, in the presence of ammonia (see Table) and similarly when the reaction temperature is raised from 20 to 30 ° . The results of conductometric titration show that the polymers prepared in the aqueous two-phase systems contain units of acrylic acid (up to 8~/o) and of acrylic acid salts (2-3%). Polymerizatio~ in 8olutions. A study was also made of the radiation polymerization of AA in aqueous solutions with the monomer concentrations ranging from 10 to 55 wt.%, and with ammonia concentrations of 1.3-10 w t . ~ , varying the
Aerylarmd~ polymerizatmn
427
conversion; thereafter the rate is reduced. The average molecular weight of polymers obtained in the case of a high degree of conversion are increased as t he monomer concentration rises (Mw increases from 5 × 106 to 2 × l0 T on increasing the AA concentration from l0 to 50%). An increase in the content of ammonia in solution from 1.3 to 10% has virtually no effect on the polymerization rate, but the average molecular weight of the polymers is t h e r e b y considerably reduced*, i. e ammonia acts in t h e same way as a chain transfer agent. The effect in question could possibly be the result of the product of ammonia-AA interaction participating in the polymerization process. I t is k n o w l t h a t at room temperature AA reacts readily with ammonia to form N P A [5]. The effect of this product on the polymerization of AA in aqueous solutions was accordingly investigated /
/01
[M]
,
I JO
I
I
I
I 250
/50
uo , lO ~
[M] [~PA] FIO. 3 Calculatmn of the rate of chain transfer through NPA molecules during the polymemzatmn of AA m water at 20% The polymerization was conducted in dilute aqueous solutions with m o n o m e r concentrations ranging from 0.14 to 0.57 mole/1. (1-4 w t . %) and with N~PA concentrations of 0.013-0.053 mole/1, under the action of UV irradiation in t h e presence of a photosensitizer (dinitrfle of azoisobutyric acid). The reaction rate remains constant at the start of the process, and is a linear function of monomer concentration and proportional to the square root of irradiation intensity. The initial rate of polymerization remains practically constant as the a m o u n t o f N P A in solution rises. However, a rise in the N P A concentrations leads t o a marked reduction in the molecular weight of the PAA This shows t h a t chain transfer takes place t hr ough N P A molecules t. The rate of this reaction was calculated b y using the equation.
1
]Q v0
ktr [I~PA]
(1)
* When the amount of ammoma m solution is below 1 2-1'3yo, the polymers, m the case of complete conversion, are completely insoluble m water. t The authors thank N. P. Paskhm for pointing out the possible role of NPA m the chain transfer reaction during AA polymenzatmn m the presence of ammoma.
428
V.F. GRO~OVet al.
(where Pn is the number average degree of polymerization, and kt, kp, ktr , the rate constants for chain termination, propagation a n d transfer, respectively, v0, polymerization rate; [M] and [NPA], concentrations of the monomer and N P A respectively and the rate constants obtained in this w a y are: kp/kt~----3.8 and ktr/kp---- 1.5 × 10 -3 (Fig. 3). The value of kp/k t was also found (using the method of intermittent exposure to light) and the values of kp and k t obtained for the AA polymerization in the presence of NPA, are in good agreement with the values obtained for the polymerization of AA in aqueous solution [8]. The experimental results show that the N P A formed through the interaction of AA and ammonia is a very effective chain transfer agent in the polymerization of AA in water. The reactivity of the radical formed as a result of the chain transfer reaction is close to that of the AA radical. It was also shown that the addition of N P A to a concentrated solution of AA in water leads to the formation of soluble polymer at advanced degrees of conversion. For instance, in a 47% solution of AA in water containing 8% of N P A (0.35 mole/l.)a soluble polymer of relatively low molecular weight (Mw--~0.75× × 106) was obtained on complete conversion. The molecular weight of the polymer synthesized under similar conditions in the presence of the equivalent amount of ammonia was 7 × 10s. Without the addition of ammonia or N P A completely insoluble PAA is obtained with the same concentration of monomer. I t was also found that the polymerization of AA in concentrated solutions in an aprotonic solvent (DMSO) leads to the formation of water soluble polymers with molecular weights of up to 9 × 10~ (with a monomer concentration of 40%). Thus it appears that the polymerization of AA in concentrated aqueous solutions, and also m two-phase systems in the presence of ammonia or caustic soda, leads to the formation of water soluble high molecular polymers. Moreover, it was found that m an acid medium crosslinked insoluble are formed even when the polymerization is conducted in dilute solutmns. It is therefore reasonable to assume that hydrogen ions must be responsible for a crosslinking reaction that is accompanied b y the evolution of ammonia and leads to the formation of imide structures. This assumption is also favoured b y the fact that the polymers prepared in concentrated solutions in DMS0, which are of high molecular weight, d]ssolve completely in water In addition, a factor of major importance in regard to the formation of soluble polymers of AA is the presence, in the system, of the product of interaction of ammonia with AA, namely NPA. On the one hand this compound is decidedly active in chain transfer reactions, while on the other hand it is a strong protonacceptor. The decisive role of N P A in the formation of soluble PAA is clear from the fact that soluble polymers are obtainable in the presence of N P A through polymerization in concentrated systems, even m the absence of alkali additions It should be noted that N P A m a y likewise be formed in the presence of caustic soda, as ammonia is formed as a result of AA hydrolysis taking place in an alkaline medium, and the ammonia is then capable of participating in a
Stabdlzatmn of polymers by phosphorous actd esters
429
r e a c t i o n w i t h AA. I t is reasonable to assume t h a t the f a c t o r responsible for t h e m u c h lower molecular weight o f t h e p o l y m e r s p r e p a r e d in presence of a m m o n i a a n d o f small caustic soda additions could well be an increase in t h e rate of N P A formation.
Translated by R J. A. ~-.ENDRY REFERENCES
1. A. CHAPIR0, Radiation Chemmtry of Polymerm Systems, p 326, New York-London, 1962 2. A. D. ABKIN, A. P. SHEINKER, P. M. KHOMIKOVSKII, M. K. YAKOVLEVA, V. F. GROMOV, 8. P. TREMBACHEVA, I. A. YAKUBOVICH, P. I. PARADIYA, N. P. PASKHIN, M. P. VILYANSKII and V. G. NEgHOROSHEV, U.S S R Pat. 235997, 1966; Byul]. izob. No. 6; 1969, French Pat. 1466769 1966, 1492037, 1967; Ital Pat. 753476, 1967; 756445, 1967; U. K. Pat. 1106573, 1968 3. V. F. ,GROMOV, A. V. MATVEYEVA, P. M. ]g~HOMIKOVSKIIand A. D. ABKIN, Vysokomol. soyed. Ag: 1444, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 7, 1616, 1967) 4. A, Kh. BREGER, V. A. BELYNSKII, V. L. KARPOV, 8. D. PROKUDIN and V. B. OSIPOV, Trudy Vsesovyuznoi konf. po primenemyu radioaktivnykh i stabil'nykh isotopov i lzluchenii v narodnom khozyaistve i nauke, (Trans. All-Union Conf. on Use of Radio-Active and Stable Isotopes and Emanations m the Sovmt Economy and in Research). p. 182, Izd. AN SSSR, 1958 5. U. S. Pat. 2663733, 1953 6. F. 8. DAINTON and M. TORDOFF, Trans. Faraday Soc. 53: 499, 1957 7. A. J. RESTAINO, R. B. MESROBIAN, H. MORAW]gTZ, D. 8. BJtLLkNTINA, D. J. DI~I~E~I and D. J. M]gTZ, J. Amer. Chem. Soc. 78: 2939, 1956 8. V. F. GROMOV, P. M. KHOMIKOVSIII and A. D. ABKIN, Vysokomol. soyed. AI2: 767, 1970 (Not translated in Polymer Sci. U S.S R )
ON THE STABILIZATION OF POLYMERS BY PHOSPHOROUS ACID ESTERS* A. G. AKHMADUT.Lr~A, N. A. MUKME~EVA, P. A. KIRPICHNIKOV, N. S. KOLYUBA•rNA a n d D. G. POBEDIMSgn S. M. Klrov Kazan Chemmotechnologlcal Institute
(Received 19 June 1972) Accelerated ageing was the l~nethod used for investigation of the antloxldatlve properties (the exmtenee of crltmal concentrations and the dmplaecment of the latter m the presence of a decomposer of hydroperoxldes) of phosplntes of the cyehc * Vysokomo]. soyed. A16: No 2, 370-375, 1974.