Relative monomer reactivities in the copolymerizations at large conversions

¥E. N. ZIL'BERhIAN et al.

2198

REFERENCES 1. A. V. SIDOROVICH, E. V. KUVSHINSKII, M. M. KOTON, N. A. ADROVA et al., Dokl. Akad. Nauk SSSR,,219: 1382, 1974 2. A. T. KALASHNIK and S. P. PAPKOV, Vysokomol. soyed. B18: 455, 1976 (Not translated in Polymer Sci. U.S.S.R.) 3. E. T. LUR'E and V. V. KOVRIGA, Mekhanika Polimerov, No. 4, 587, 1977 4. A. V. MURZINOV, A. V. 0RLOV and A. M. STALEVICH, Plast. Massy, No. 4, 35, 1977 5. A. V. MURZINOV, E. S. TSOBKALO and A. M. STALEVICH, Vysokomol. soyed. BI9.* 524, 1977 (Not translated in Polymer Sci. U.S.S.R.) 6. A. T. KALASHNIK, A. V. VOLOKHINA, A. S. SEMENOVA, L. K. KUZNETSOVA and S. P. PAPKOV, Khim. Volokna, No. 4, 51, 1977 7. G. I. KUDRYAVTSEV, A. A. ASKADSKII and I. F. KHUDOSHEV, Vysokomol. soyed. A2O: 1879, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 8, 2112, 1978) 8. S. P. PAPKOV, Vysokomol. soyed. A19: 3, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 1, 1, 1977) 9. S. P. PAPKOV, Khim. Volokna, No. 1, 3, 1973 10. A. T. KALASHNIK, O. I. ROMANKO, A. S. SUMENOVA, I. N. ANDREYEVA et ed., Vysokomol. soyed. B21: 71, 1979 (Not translated in Polymer Sci. U.S.S.R.) 11. A. T. KALASHNIK, A. V. VOLOKHINA, A. S. SEMENOVA, L. K. KUZNETSOVA a n d S. P. PAPKOV, Khim. Volokna, No. t, 46, 1978

Polymer Science U.S.S.R.

Vol. 22, 1~o. 9, pp. 2198-2204, 1980

Printed in Poland

0032-3950]80/092198-07$07.50/0, ©1981 Pergamon Press Ltd..

RELATIVE MONOMER REACTIVITIES IN THE COPOLYMERIZATIONS AT LARGE CONVERSIONS* YE. N. Zm'BERMAI~, R. A. NAVOLOKI17A a n d O. P. KVVXRZr~A Dzherzhinsk Branch of A. A. Zhdanov ~Polyteetmical Institute, Gor'ki

(Received 24 July 1979) The solution polymerizations of methacrylamide with methacrylic acid or sodium methacrylate, and t h e bulk copolymerization of methyl- with butyl-methacrylate were investigated to large ~/o conversions. The first 2 systems mentioned have been found to have varying relative monomer reactivities, while they remained constant in the last system. The question of the effect of the monomer composition on their reactivities .in high-conversion copolymerizations has been examined. The reactivity ratios have been determined for m e t h y l with butyl-methacrylate (80°C, in bulk); they were rl----0'82~:0-07, and r2=0.91±0"I3 respectively. I x p r a c t i c e one o f t e n h a s t o c a l c u l a t e t h e a v e r a g e a n d t h e " i n s t a n t " c o m p o s i t i o n o f a c o p o l y m e r . T h i s is n o r m a l l y c a r r i e d o u t b y i n t e g r a t i o n u s i n g t h e M a y o - L e w i s e q u a t i o n , e.g. b y u s i n g t h e S k e i s t e q u a t i o n in t h e s h a p e s u g g e s t e d b y M e y e r a n 4 * Vysokomol. soyed. A22: No. 9, 2006-2011, 1980.

Relative monomer reactivities in copolymerizatious

2199

Lowry [1], which is based on the copolymerization constants found for the initial process stages. The relative monomer reactivities are not always constant however [2]; they vary quite considerably when acrylamide is eopolymerized with acrylonitrile, for instance [3], so that it is impossible to calculate the average or "instant" compositions by means of the equations in which a constancy of the process constants over the whole process is assumed. A clarification thus appears to be required of whether the principles established elsewhere [2, 3] also apply to other monomer systems. We planned to find out here the effect of the forming copolymer on the changes of the relative monomer reactivities (RMR) during the free-radical eopolymerizations on three pairs of monomers, i.e. methacrylamide (M~A)-methacrylic acid (M_A_),MA&-sodium methacrylate, and methyl methacrylate (M~A)-butyl methacrylate (BM~k) at high % conversions and also more about the production methods. EXPERIMENTAL

Material. The MAA (pure grade T U 15P-445-68) was recrystallized twice from a mixture of equal volumes of benzene and isopropa~ol containing 99"4~o of the monomer; TmN 110°C: The MA (pure grade, T U 219-70), the MMA (pure grade, T U 8P-156-68), and the BMA (pure grade, ~¢IRTU 6-09-2941-66) were purified by vacuum-distillation a~d were 98.9, 99'9 and 99'8% pure respectively. The sodium metacrylate was produced b y neutralizing the MA with a 40~o ~ a O H solution. The benzoyl peroxide (BP; GOST 1488-69) was recrystallized from acetone a n d was 99.7% pure; the potassium persulphate (PPS; GOST 7172-65) a n d the b u t y l mercaptan (pure grade, l~IRTU-6-09-1537-69) were used wit~hout further purification. Method and analysis. Equimolax amounts of MA (5.03 g) and MAA (4.97 g) were copolymerized in a n aqueous medium containing 10% of the monomer and KiS~Os as 0.15 and 0.30 wt.~o of the sum of monomers. The reactor was a 4-necked flask fitted with a stirrer, reflux condenser, a sampling tube and an inlet for purified nitrogen. The vessel was mainrained at 50°C a n d filled with 85 g double-distilled water, the monomers, and nitrogen bubbled through at the reaction temperature for about 20 min, after which the KIS2Os dissolved in 5 g double-distilled water was added. The moment of the initiator addition was taken as the starting time. The reactor was cooled under r u n n i n g water after the required reaction time and the polymer present as sediment was removed on a Schott filter while the mother liquor was analyzed for the earboxyl groups a n d C = C bond content. Equimolax amounts of the sodium methacrylate and MAA were copolymerized at a 20~o concentration of the monomers in water in the presence of K~S2Os (0.6 wt.~o on monomers content) as described above. The thermostated reactor was filled with 67 g of double-distilled water, 8.91 g MA, 7-54 ml of a 40~o solution ( d = 1.425 g/ml) of NaOH and 8"81 g MAA. The mixture was sampled at predetermined time intervals after the mixture (with the initiator) had reached the reaction temperature (50°C), the samples cooled, and analyzed for C = C bond content. The copolymer was precipitated Out of parallel samples with acetone, was then separated, a n d the mother liquor tested by the Kjeldahl method for its nitrogen content. Equimolar amounts of MMA (28.9 g) and BMA {41.1 g) were copolymerized in bulk at 80°C in the pre~noo of B P (0.06 w~.~o of both monomers) and of the mol.wt, regulator, i.e. 1.03 g of b u t y l mercaptan under an atmosphere of purified nitrogen. The mixture of the monomers was heated to the reaction temperature, the initiator dissolved in 10 ml of the monomer mixture was added, and the viscous r ~ e t i o n mixture sampled at predetermined

YE. N. Z ~ ' ~ E ~ A ~ et al.

2200

time intervals; the samples were placed in a beaker, hydroquinone was added and they were then dissolved in acetone; this was followed by the analysis for the C = C bonds content. Parallel samples were dissolved in acetone and subjected to gas-chromatography. The copolymerizations of these monomers at other molar ratios were carried out by the same method. A "Tsvet- 2" chromatograph with the gas-liquid variant of separation and a flame-ionization detector was employed in the chromatographic analysis. The conditions were the following: a 0.8 mm long glass column of 4 mm diameter was packed with Chromaton-N-AW as sorbent and Reoplex-400 (15% on sorhent) as liquid phase; the evaporator temperature was 160°C, that of the thermostat 70°C. The flow rate of the hydrogen and the carrier gas (nitrogen) was 2 1./hr, that of the air 20 1./hr, ~he MMA and BMA contents in the reaction blends dissolved in acetone (diluted to about 6 w~. %) were determined by absolute calibra. tion. Any copolymer present in the solution did not affect the analytical results. Calculations. The "instant" experimental copolymcr composition was determined from the tangents to the kinetic utilization curves for each monomer [2, 3]. The composition was calculated according to the Skeist method [1] and the % conversion was found for any specific monomers content, after which these values and the % conversions were used to geb the respective "instant" composition from the formula

rj~+/J, "L~Z~

2

'

8 t

rxfz + 2fJ2+ rJ2 in which f~ and -~z--melar fraction of the first monomer in the mixture and in the copolymer.

RESULTS

The M A - M A A solution copolymerization with sedimentation. T h e k i n e t i c curves o f utilization (Fig. 1) show t h e M A t o be m o r e r e a c t i v e t h a n t h e MA/k (rx>r~), b u t t h e plots o f t h e m i x t u r e composition as a f u n c t i o n o f t h e % con-

[HI,

mmole

60~

60~T.

N

2

\ 0

4

a

2

6

q

6'

Tirne ~hp

~IO. 1. The kinetic,consumption curves of: 1--MA, 2--MAA, during their copolymerization at 800(3 in a 10% aqueous solution. KISIOs, % w/w: a--0.15, b--0-30 (on total monomers).

v e r s i o n (Fig. 2a) do n o t coincide w i t h those g o t b y i n t e g r a t i n g t h e c o m p o s i t i o n b y m e t h o d [1]. F i g u r e 2a shows t h e m i x t u r e to b e c o m e enriched w i t h M A A a s c o n v e r s i o n progresses a n d t h a t it a d d s on to t h e M A to a lesser e x t e n t t h a n e x p e c t e d o n t h e basis o f t h e c o p o l y m e r i z a t i o n c o n s t a n t s f o u n d for lower % conversions [4]. T h e " i n s t a n t " e x p e r i m e n t a l c o p o l y m e r composition as a f u n c t i o n o f t h e % con-

R e l a t i v e monomer reactivitiee in copolymerizations

2201:

version (Fig. 2a) consequently deviates from the calculated curve (Fig. 2a), which indicates a relative reactivity change of the monomers after the process. start. An a t t e m p t to estimate the process constants in the presence of the copolymer b y the Fineman-Ross method, using the "instant" composition, was un-

~

f,,5

l'O-

rl

0"6

Z

t

0"2i

I

1 11

I ",,~ [

0.2

0"6

I

0.2

1"0

I

0.6

I

,l, ,

1.0

t-[M] / rM]o

Fia. 2. 1, ]'--the monomer mixture composition, 2, 2"--the "instant" composition of the: MA-(a) sodium methacrylate, (b) MA-MAA copolymer as functions of the conversion, (1, 2--calcula~l, 1', 2'--experimental). satisfactory because the p o i n t s did not fall on a straight line as for the earlier studied acrylamide-acrylonitrile system [3]~ This means that the R]KR altered throughout the process duration as a function of the monomers-copolymer ratio. The values rx and r~ come closer together during the process because of the production of a copolymer enriched with the more reactive monomer units at the s t a r t ,

mmole 3OO 206 100 2

q

Time ~hr

8

Fro. 3. The kinetic utilization curves of: /--sodium methacrylate, 2--MAA, during thbir copolymerization at 50°C in a 20% aqueous solution. i.e. with MA. B y allowing for the association of the carboxyl with the amide groups [5] b y means of hydrogen bonds which are stronger than those between two amide or two carboxyl groups, there will b~ a larger effective amide concentration present in the reaction zone near the growing macroradicals, and the result will be an apparent reactivity increase of the amide during the copolymerization.

:2202

YE. No ZI.L'BER-MAIq ¢~ a~o

Sodium methacrylate-MAA solution co~olymerization. This system is characterized by solution of the forming copolymer in the reaction medium, and consequently a viscosity increase, which contrasts with the previous binary system in which the product precipitated out. We studied the process kinetics in an aqueous solution containing equimolar quantities of the reagents. The kinetic utilization curves (Fig. 3) show the more reactive ~ to be more rapidly utilized, so that enrichment with the sodium methacrylate (Fig. 2b) is greater ~han expecte d on the basis of the found "instant" copolymer composition as a function of the ~o conversion (Fig. 2b); it therefore strongly deviates from that calculated on t h e basis of constants determined from the initial rates. The experimental points are again remote from the Fineman-Ross line which means that the RMR alter with copolymerization to large ~o conversions. From the results (Fig. 2b) the relative reactivity of the MAA increases while that of the sodium methacrylate drops. The consequence is a copolymer with low structural regularity. The changes of the relative constants in the copolymerization of the discussed system could be connected with a change in the solvation of the monomers by the polymer molecules and a viscosity increase of the medium. One cannot .exclude either a stronger electrostatic repellance of the poly-anion radical from the methacrylate anion which will reduce the rate constant kl~ of the homopolymerization, and thus also constant r~. The study of the sodium methacrylate homopolymerization (Fig. 4) showed a larger % conversion to be accompanied by a gradual decrease of the process rate (while the viscosity increased simultaneously). A typical effect of a process acceleration is "gelling", but this is not evident here because of it being masked by .a decrease of the chain propagation rate constants during the polymerization. M M A - B M A block copolymerization. These two monomers belong to a homologous series and are non-ionic. As they have similar chemical properties one can expect their reactivities to remain constant to high conversion. There are no

2

6 Time, br FIG. 4

10

3|

oN Fro. 5

:FIG. 4. The kinetic homopolymerization ourves of: 1 - - a n 11%, 2 - - a 7o//0 aqueous solution a t 50°C of sodium methacrylate in the presence of 2.25 × 10 -8 mole/l. K=Si0e. FIG. 5. Determination of the copolymerization constants of MMA with BMA at 4-10% f~(1--2F~) { f . ~'(1--_F~).; conversion y-~" ( l - - f z) F I ; x = -- ~1 - - f J FI

Relative monomor reaetivlties in copolymerizations

2203

qunatitative d a t a to be found in the literature for their copolymerization; we therefore made an experimental determination of the eopolymerization constants based on the results for a process with 4-10% conversions using various molar ratios of these monomers. The constants obtained from these results are shown [M], mmo[e/E 5-

3 I i

i

l

2

i

q

]

I

G Time, hP

2

4

G

Fio. 6. The kinotic utilization curves of: 1--MMA, 2--BMA during their bulk eopolymerization at 80°C using molar ratios of: a--50 : 50, b--30 : 70. in Fig~ 5 in the linear form of the copolymer composition equation [6] and calculabion by the method of least squares gave r1=0.99=[=0.06 and r2=l.03q-0.11 (for a 0.99 correlation coefficient); these were close to those calculated b y the AlfreyPrice method [7] (r1=0"80, r2=0.84). The RMR are thus the same.

r,

el

,° t I

0"2

O'G " I'0

L

0"2

I

I

O.G

~

I

I'0

1-[M] / [M]o Fro. 7. a - - T h e monomer mixture composition, b--"instant" composition of tho MMA (M~)-BMA (M2) copolymer as functions of the conversion. (M1)0 : (M2)0 molar ratios: 1--50 : 50, 2--30 : 70. : ~ I A and BM2k were copolymerized to a large % converssion at 50:50 and 30: 70 molar ratios. The kinetic curves are reproduced in Fig. 6 which shows both the monomers to be utilized to the same extent. The composition of the monomers mixture (Fig. 7a) remained almost the same during the process and the copolymer had a uniform composition (Fig. 7b). The experimental results got for a large % conversion fell on the Fineman-Ross line. The simultaneous processing by the

2204

Y~.. I~T. Z r r ; B E ~

e$ al.

method of least squares of the results got for initial (Fig. 5) and large % conversions gave the constants r1=0.82~0.07 and r 2 = 0 . 9 1 ! 0 . 1 3 a t a 0.92 correlation factor; this means t h a t the constants remain unchanged (within the experimental error limits) to high conversions. Examination of the above findings for several systems showed the rate constants of the elementary reactions to alter irregularly in some cases, so t h a t r, and r~ changed during the process. One can conclude on t h e basis of the results published by Abramova and co-workers [3] t h a t systems made up of monomers not forming specific associates with each other and with the copolymer, and also monomers from the same homologous series will most probably have RMR which remain constant to high conversion. There obviously will be slight changes at the start, but kn and k~, as well as k~2 and k~l will decrease approximately to the same degree as the process progresses to large % conversion; the constants r 1 and r2 will therefore retain their original values.Where a system consists of monomers with largely differing chemical properties or polarities (especially the systems made up of an ionic monomer and a non-ionic), the probability of a change of these constants will be considerable because the rate constants of the chain propagation change in general very unlike each other. At the same time one can not exclude the possibility t h a t the constants k n , /c12 or k2~, k~l in individual systems (or groups of systems) made up of monomers of differing chemistry will change in sueh a manner t h a t r 1 and r~ will remain practically constant to almost complete conversion of the monomers. The copolymer composition produced at a large % conversion from monomer systems of the first type can be quite reliably estimated b y calculations based on an integration of the composition equation in which a constancy of the ratios is assumed for the duration of the process. This method will give results differing from the experimental where the system is made up of monomers of the second type as it neglects changes of the copolymerization constants during the reaction. Translated by K. A. ALLEN

REFERENCES

1. V. E. MEYER and G. G. LOWRY, J. Polymer Sei, A8: 2843, 1965 2. V. A. MYAGCHENKOV,Dissertation, Kazan, 1974 3. L. I. ABRAMOVA, E. N. ZIL'BERMAN and L. S. CHUGUN0VA, Vysokomol. soyed. B2h 813, 1979 (Not translated in Polymer Sci. U.S.S.R.) 4. T. G. BASOVA, E. N. ZIL'BERMAN, G. N. SHVAREVA and V. N. CHERNYKH, Vysokomol, soyed. B17: 379, 1975 (Not translated in Polymer Sci. U.S.S.R.) 5. E. V. KUZNETSOV, L. A. BUDARINA, L. A. EMIKH and R. A. KHAIRULLINA, Zhur. Obsh. Khim. 39: 2635, 1969 • 6. M. FINEMAN and S. D. ROSS, J. Polymer Sci. 5: 259, 1950 7. T. ALFREY. Jr. and C. C. PRICE, J. Polymer Sci. 2: 101, 1947