Copolymerization of acrylamide with citraconic acid

COPOLYMERIZATION OF ACRYLAMIDE WITH CITRACONIC ACID* V. A. ~g[YAGCHEI~KOV,V. F . KURENKOV, YE. V. KUZNETSOVand S. YA. FRElgKEL' S. lYI. Kirov Chemicotechnological Institute, Kazan High Molecular Weight Compounds Institute, U.S.S.R. Academy of Sciences

(Received 19 July 1968) THE known methods of comparing the relative activity of monomers are based on quantitative determination of the copolymerization constants and are applicable to systems in which the reactivity of the eomonomers does not vary with variations in the substrate composition (7) and the degree of conversion (~) [1]. I n the case of "anomalous" processes (for which the Mayo-Lewis equation [2] is invalid) recourse is had to the introduction of parameters giving fuller information regarding the eopolymer system instead of characterization based on the average composition for fixed values of ~ and 7- This is done by means of integral composition distribution curves (ICCD) for different ~ and 7 values [3]. There are two methods of plotting ICCD: 1) b y analysing fractions of the copolymer sample, ensuring that the method of fractionation adopted and the selected solvent-precipitant systems will result in fractions with sufficiently homogeneous chemical compositions [4, 5]; 2) by t r e a t m e n t of the kinetic curves of comonomer uptake [6].

The information obtained in this investigation was based on the results of polarographic analysis; the experimental procedure and the method of evaluating the data were described in [3, 7]. We would further add that in a citrate-phosphate buffer solution with p H i 2 . 2 E1/2 for citraconie acid E1/2----0.8 V, and for acrylamide El/2-~ 1.3 V. The residual monomer concentrations were found by the polarographic method, and the quantitative analysis of acrylamide and citraconic acid was performed in a single test, since the marked difference in the halfwave potentials of the components ensured good control of separate reduction 7. The copolymerization was conducted in 5% aqueous solutions at 70 ° in a nitrogen atmosphere. Prior to copolymerization the initial monomers were repeatedly recrystallized; acrylamide--m.p. 85 °, citraconic acid, m.p. 91 °. Ammonium persulphate was recrystallized from double-distilled water. The ~ a y o - L e w i s equation is generally written in molar concentrations, though in many cases weight concentrations are more convenient for comparing theoretical with experimental data. I f cA (t) and cB (t) are the volume-weight concentrations in the reaction region for monomers A and B, and dCA----cA(t)-cA(t~dt ) and

dCB-~CB(t)--%(tWdt )

it is obvious that

dCA ~A--d%_~d%

characterizes the weight

content of component A in the copolymer in the period of time from t to t~-dt (aB= 1--aA). I f dt is fairly small we m a y calculate the composition and weight * Vysokomol. soyed. A l l : No. S. 1789-1792, 1969. 2035

2036

V . A. M Y A G C H E N ' K O V et a~.

of the fractions q=dcA~dc B and then there will be no difficulty in converting to ICCD [6] (in weight concentrations); moreover there is less work in treating the experimental data for ICCD curves plotted in weight concentrations compared

5

0 0

o

-5 :

!

I

0

1

I

I

2 T#ne , hp FIG.

I

4

3

A

-10

0 0

oo

o °oo

o~o

o

w

f

10

o0 0

0 0

1

Fro. 2

1

FIo. 1. Curves of monomer uptake in the copolymerization of acrylamide (1) with citraconic acid (2) (1 : 1). F i o . 2. Dependence of fl (A/B-- 1/7) on

fl'/y.

with those plotted in molar concentrations [8]. As an example Fig. 1 shows the curves of comonomer uptake for a fixed substrate composition. It is more convenient to write the Mayo-Lewis equation in weight concentrations, as follows:

B'7

g--

Here A and B are the molecular weights of the comonomers,

)'=~-, and ~=~. -.&

In this way the curve of p (A/B--1/),) vs. ,62/), m a y be used to find r A (£rom the section intercepted on the ordinate axis) and r~ (from the tangent of the angle of the curve). The experimental data (Fig. 2) obtained by treatment of the kinetic curves are similar to those in Fig. 1 for the copolymer system acrylamide-citraconic acid do not fit the curve, and this indicates the "anomalous" nature of the copolymerization. The ICCD based on the kinetic curves arc shown in Fig. 3; some theoretical curves for model systems (rA----3, rB=0; rA=10 , rB-----0) are also given [13]. The parameters of quantitative determination of compositional in_homogeneity were cMc~ated for a number of model systems to confirm the "'anomalous" character of the copolymerization in respect to the system under review. We know from [3] t h a t

i=l

i=l

i=l

where wi is the amount by weight of the fraction made up of ~i~-d~i,

Copolymerization of acrylamide with citraconie acid

2037

The choice of extreme values of r A for the model systems (rA)mln=3 and (rA)ma~= 10 was governed by the need to include all possible experimental values of rA; it is seen from Fig. 2 that ibr the system acrylamide-citraconic acid Xi 1 2 3#5 10 - - - - I - - T 7 t - / - - - 7 -

6

7

/ /Y//

I //

/i/!

//

, ~

1!iiI

i!/

II i!II Jl

iI

i l~l

I Ill

"1 Iiiil ll~

J

/', I / ',/,

10

9 -7" - -

//

l l /i I ~ 0.5

8

-/--,7---

i !

I

/t

i/I

/I

t /

'/,

l

I 20

, 30 c~,%

FIG. 3. Integral curves of composition distribution: plotted from experimental data (solid lines) and calculated by the Skeist method [13] (fractured lines). Compositions ofacrylamide-citraconic acidsubstrate: 1 - - 4 : 1 (~A=0"56, rA=10"0); 2 - - 3 : 2 (¥A =0"39, r A = 1 0 " 0 ) ; 3 - - 4 : 1 (~A=0"56), 4 - - 1 : 1 (~A=0"35, rA=10"0); 5 - - 4 : 1 (~A =0"56, rA=3"0); 6--3 : 2 (~A=0"39); 7--3 : 2 (~A=0"39, rA=3"0); 8--1 : 1 (~A =0"35, rA =3"0); 9-- 1 : 1 (~A =0"35); Xi--integral weight fraction of acid in copolymer; ~--weight content of acid in copolymcr; yA--conversion in respect to acrylamide.

3 < r A < 8 . The fact that fl for the experimental curves was a lot higher than for the theoretical ones again confirms the anomalous nature of the process of copolymerization. Let us consider the reasons for this anomalous behaviour in some detail. Ingeneral "special" (anomalous)systems may formally be described by introducing the spectrum of the copolymerization constants, i.e. rA=r A (7, ~) and r B= r B (7, W). It was shown in our previous study of copolymerization in the system aerylamidemaleic acid [9] that pH = p H (7), and this factor alone may account for the dependk,. kBB ence of the copolymerization constants rA=k~AB and r B= - - on the substrate comkBA position (see Table). Here kAA, /CAB,kBB, and bBA are the rate constants for the reactions of macroradicals having terminal units A, A, B, B with monomer units A, B, B and A respectively. With an acrylamide-citraconic acid system we may assume that rB=0 and that the dependence o f r A = r A (7) will appe~ar when: a) kAA=kAA (7), /CAB=const; b)/¢AB=kAB (7), bAA=eonst; C) bAB=kAB (7), k ~ = k ~ (7) Similar conclusions may be reached when rB¢0, e.g. 0~
2038

V.A.

~¢IYAGCHENKOV et at.

to be incorrect to assume that r B> 0 . 2 for copolymerization in the system acrylamide-citraeonic acid, as is already apparent on analyzing constants for the copolymerization of vinyl monomers with unsaturated dicarboxylic acids [1, 10]). I t was shown in reference [11] that kAA=]CAA (pH), and this means that k ~ = k A A (7). We m a y further assume that kAB------kAB(pH)----ICAB (y) and that the relative reactivity of the acrylamide will depend on the substrate composition, so that it will not be possible to describe the copolymerization within a framework of fixed values of r A and r B. P A R A M E T E R S OF QUANTITATIVE DETERMINATION OF COMPOSITIONAL INHOMOGEI~YEITYF OR EXPERI]HENTAL AND Tn~EORETICAL I C C D CURVES

Degree of Substrate composition conversion in acrylamide : citraconic respect to aerylamide, acid, y ~A 4:1

3:2 1:1

0"56 0"39 0"35

L j': x l O s

0"57 0"65 1"73

fi* X l0 s fa × 10s

0.29 0-40 0"34

0"05 0-07 0"16

* f~ fs are the compositional inhomogeneity parameters based on the theoretical ICCD for the eopolymerization constants r , = 3 ' 0 ; r a = 0 for f~; rA=10"0, rB=0 for f..

Together with the factor referred to above a further reason for change in the relative reactivity of the comonomers may be variation in the effective ionic strength in the copolymerization process [9]. I f n is the degree of polymerization (and out of n units n A refers to monomer units of type A, and n B= n - - h A ) it follows that the copolymerization conditions within the growing macroradical will vary with increase in n. In the case under consideration a rise in n is accompanied b y increase in the number of ionogenic units in the macroradicats, and the effective d e ~ e e of ionization of ionogenic groups within the growing macroradical will be reduced with increase in n, since the number of gegenions within the volume of the macromolecule will be higher than the average with respect to the solution [12]. moreover the degree of ionization of A and B units within the macromolecule wil! be slightly lower than in the case of the unsaturated A and B units. The possible dependence of r A = r A (~) m u s t therefore necessarily require the presence of ionogenic groups in the copolymerizing system (in our case represented b y units of citraconic acid (k1=5.4X10 -a, k2----7.15×10 -~) and also b y the presence of acrylamide units capable of undergoing hydrolysis [14]); besides this the solvent must have sufficient ionizing power [15]. Iu the copolymerization of aerylamide with citraconie acid in aqueous solution the necessary conditions are fulfilled, and the anomalous nature of the copolymerization is evidently due to two causes: 1) rx = r x (7) and 2) r A = r A (~). To obtain direct confirmation of the dependence of r A = r ~ (~) the p H of the solutions

Copolymerization of acrylamide with citraconie acid

2039

m a y be m e a s u r e d a t different values of ~/, and this will be t h e s u b j e c t of f u r t h e r investigations. T h e a n o m a l o u s widening of t h e I C C D c u r v e m a y to some e x t e n t be due t o possible c o m p l e x i n g of t h e m o n o m e r units (no special s t u d y of this was m a d e in t h e p r e s e n t investigation), as was o b s e r v e d in the s y s t e m f u m a r i c a c i d - a c r y l i c acid [16, 17], a l t h o u g h this m a y n o t be t h e d e t e r m i n i n g factor, seeing t h a t t h e f o r m a t i o n o f a c o m p l e x m a y a c c o u n t for the m a r k e d a n o m a l y of t h e d e p e n d e n c e a = ~ (7), b u t the b r o a d e n i n g o f t h e I C C D due to possible c o m p l e x i n g should n o t be so p r o n o u n c e d [15]. CONCLUSIONS A s t u d y h a s been m a d e o f t h e c o p o l y m e r i z a t i o n kinetics for t h e s y s t e m a c r y l a m i d e - c i t r a c o n i e acid in 5 % a q u e o u s solutions w i t h different s u b s t r a t e compositions. T h e e x p e r i m e n t a l a n d theoretical (for some m o d e l s y s t e m s ) c o m p o s i t i o n d i s t r i b u t i o n curves h a v e b e e n c o m p a r e d a n d t h e " a n o m a l o u s " n a t u r e of t h e e o p o l y m e r i z a t i o n has been inferred. T h e l a t t e r h a s b e e n a t t r i b u t e d to change in the r e l a t i v i t y r e a c t i v i t y of t h e com o n o m e r s d u r i n g t h e reaction. Translated by R. J. A. YrI~DRY

REFERENCES 1. G. HAM, Copolymerization, New York, London, Sydney, 1964 2. F. R. MAYO and F. M. LEWIS, J. Amer. Chem. Soc. 66: 1594, 1944 3. V. A. MYAGCHENKOV, V. F. KURENKOV and Ye. V. KUZNETSOV, Prom. khimicheskikh reaktivov i osobo chistykh veshehestv (Production of Chemical Reactants and Specially Pure Substances). IREA, No. 12, p. 167, 1967 4. V. A. AGASANDYAN, L. G. KUDRYAVTSEVA, A. D. LITMANOVICH and V. Ya. SHTERN, Vysokomol. soyed. A9: 2634, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 12, 2979, 1967) 5. L. G. KUDRYAVTSEVA and A. D. LITMANOVICH, Vysokomol. soyed. A9: 18, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 1967) 6. V. A. MYAGCHENKOV, V. F. KURENKOV, Ye. V. KUZNETSOV and S. Ya. FRENKEL, Vysokomol. soyed. B9: 251, 1967 (Not translated in Polymer Sci. U.S.S.R.) 7. V . A . MYAGCHENKOV, V. F. KURENKOV, A. V. DUSHCHECHKIN and Ye. V. KUZNETSOV, Zh. analit, khimii 22: 1272, 1967 8 V. A. MYAGCHENKOV, V. F. KURENKOV and E. V. KUZNETSOV, Trudy Kazan. Chemicotech. Instituta 36: 332, 1967 9. V. A. MYAGCHENKOV, V. F. KURENKOV and S. Ya. FRENKEL, Vysokomol. soyed. A10: 1740, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 8, 2013, 1968) 10. F. LEWIS and J. YOUNG, J. Polymer Sei. 54: 411, 1961 11. D. I. CURRIE, F. S. DAINTON and W. S. WATT, Polymer 6: 451, 1965 12. V. P. BARABANOV, Thesis, 1964 13. L. I. SKEIST, J. Amer. Chem. Soc. 68: 1781, 1946 14. FUN SIN-TO and TE SHCHU-KOU, Acta ehimica sinica 24: 228, 1958; Khim. i tekhnologiya polimerov, No. 9, 80, 1959 15. V. A. MYAGCHENKOV and S. Ya. FRENKEL, Uspekhi khimii 37: 2247, 1968 16. A. A. EL'SAID, S. Ya. lYlIRLINA and V. A. KARGIN, Dokl. AN SSSR 177: 380, 1967 17. A. A. EL'SAID, Thesis, 1968