Emulsion polymerization kinetics of methyl methacrylate in the presence of organic acids and amines and cation-active emulsifier

792

S.D. STAVROVAet al.

2. A. N. NESMEYANOV, A. M. RUBINSHTEIN, G. L. SLONIMSKII, A. A. SLINKIN,

3. 4. 5. 6. 7. 8. 9. 10. 11.

N. S. KOCHETKOVA and R. B. MATERIKOVA, Dokl. Akad. Nauk SSSR 188: 125, 1961 A. A. DULOV, A. A. SLINKIN and A. M. RUBINSHTEIN, Vysokomol. soyed. 5: 1441, 1963 F. W. KNOBLOCH and W. H. RAUSHER, J. Polymer Sci. 54: 651, 1961 Yu. V. KORSHAK, Dissertatsiya, 1964 A. A. BERLIN, B. I. LIOGON'KH and V. P. PARINI, Vysokomol. soyed. 5: 330, 1963 V. A. KARGIN, V. A. KABANOV, V. P. ZUBOV and A. B. ZEZIN, Dokl. Akad. Nauk SSSR 159: 605, 1961 V. A. KABANOV andV. P. ZUBOV, ZhVKhO im, Mendeleyeva 7: 131, 1962 W. F. LITTLE and R. EISENTHAL, J. Amer. Chem. Soc. 82: 1578, 1960 H. HOPFF and H. OHLINGER, Angew. Chem. 61: 183, 1949 F. ULLMANN, Encyklop/klie der teehnischen Chemie, 3 Aufl., Bd. 5 Mfinch.--B., S. 70, 1954

EMULSION POLYMERIZATION KINETICS OF METHYL METHACRYLATE IN THE PRESENCE OF ORGANIC ACIDS AND AMINES AND CATION-ACTIVE EMULSIFIER* S. D. STAVROVA, M. F. MARGARITOVA a n d S. S. MEDVEDEV The M. V. Lomonosov Institute of Fine Cher~ical Technology, Moscow

(Received 1 July 1964) W E SHOWED in t h e p r e v i o u s p a p e r [1] t h a t m e t h y l m e t h a c r y l a t e (MMA) polym e r i z a t i o n in emulsions can be i n i t i a t e d b o t h b y t h e benzoic acid ( B A ) - d i m e t h y l aniline (DMA) s y s t e m a n d b y d i m e t h y l a n i l i n e alone. A d e t a i l e d s t u d y is m a d e in this p a p e r of t h e p o l y m e r i z a t i o n of MMA in emulsions stabilized b y c e t y l p y r i d i n e chloride (CPC), p o l y m e r i z a t i o n being init i a t e d b y t h e B A - D M A s y s t e m a n d b y d i m e t h y l a n i l i n e alone. EXPERIMENTAL Purification of initial substances, methods of investigation and determination of polymer molecular weights have been described previously [1]. All experiments were carried out at a monomer : aqueous phase ratio of 1 : 2 (by volume). RESULTS AND DISCUSSION

Polymerization of methyl methalerylate, initiated by dimethylaniline. I n order to elucidate t h e effect o f emulsifier c o n c e n t r a t i o n on t h e r a t e o f p o l y m e r i z a t i o n of MMA, e x p e r i m e n t s were carried o u t w i t h [DMA] ----0.015 mole/100 ml of a q u e o u s * Vysokomol. soyed. 7: No. 4, 717-724, 1965.

793

Polymerization of MMA

phase and with different CPC concentrations. The results are shown in Fig. 1, a and b, which show t h a t the rate of reaction increases linearly with increase of emulsifier concentration up to approximately 3 ~ and, in the region of 3-6 CPC, remains constant. The molecular weights of the polymers formed remain unchanged in practice over the whole range of emulsifier concentration. The activation energy of MMA polymerization initiated by amine, was calculated from the data of Table 1 and is 14.2 kcal/mole. The molecular weights of the polymers decrease with rise of reaction temperature. From the dependence of the rate of MMA polymerization on DMA concentra-

-g

~

~/4

// y 4

40

#'me, rain

b

120 M,IO-S 4O

°1~

008

WlA

°

X

I

0

88

2

2O

4

I

8 [sJ,~

FIO. 1. Polymerization of MMA with varying CPC concentrations at 50° [DMA] =0.015 mole/100 ml of the aqueous pha~e, a--CPC content (% of the aqueous phase): 1--0.5; 2--1"0; 3--2.0; 4--3.0, 4-0; 5--5.0, 6-0. g--yield, g of polymer per 100 ml of the aqueous phase; b--dependence of the rate of polymerization (1) of MMA and polymer molecular weight (2) on CPC concentration ([S], ~/o);w--rate, g of polymer per 100 ml of the aqueous phase × rain.

794

S. D. STAVROVA

et al.

TABLE 1. POLYMERIZATIONOF MMA IN THE PRESENCE OF DMA (@015 MOLE/100 ML OF THE AQUEOUS PHASE) AT VARIOUS TEMPERATURES.

(CPC content--2yo of the aqueous phase) Temperature, °C

Rate of polymerization g of polymer/ 100 ml of the aqueous phase, rain

30 40 50 60

0.019 0.0375 0"059 0.152

Intrinsic viscosity,

Molecular weight M× 10-~

10"3 8"6 5"5 5"0

42.76 24.89 18.74 16.52

tion [1] and from the results of this study, the overall rate of emulsion polymerization can be expressed by the equation: WoveralI = ]~[I]0' 5[M] IS ]

( 1)

where Woveranis the overall rate o f MMA polymerization; [I] is the DMA concent r a t i o n in the h y d r o c a r b o n phase; [M] is the m o n o m e r c o n c e n t r a t i o n in the polym e r - m o n o m e r particles (constant value); [S] is the emulsifier concentration, ~o of the aqueous phase. To v e r i f y the mechanism proposed for the initiation of MMA p o l y m e r i z a t i o n w i t h dimethylaniline, where MMA (an ester) is considered as a c o m p o n e n t of t h e 8

•

! 0

/ /

vJ

//.,.-" 40

80

/20

Time, m/n FIG. 2. Polymerization of styrene (ST) in the presence of DMA and ethylbenzoate (EB) at 50% CPC content--2%. I--DMA (0.015 mole/100 ml of the aqueous phase); 2--DMA==EB=0.015 mole/100 ml of the aqueous phase; 3--50~/o of ST+50~/o EB (DMA=0.015 mole[100 ml of the aqueous phase); 4--BA=DMA=0.015 mole/100 ml of the aqueous phase.

795

Polymerization of MMA

initiating system [1], styrene polymerization was initiated with DMA with the addition of the ethyl ester of benzoic acid. (Immediately before the experiment, ethyl benzoate was distilled in a purified nitrogen flow). Styrene does not polymerize in the presence of DMA alone, b u t on adding ethylbenzoate polymerization takes place, when, with increase of ester concentration the rate of styrene polymerization increases (Fig. 2). These data give direct confirmation of the possibility of initiating polymerization b y the ester-DMA system. Polymerization of methyl methacrylate initiated by the B A - D M A system with equimolecular ratio of components. The results of experiments on MMA polymerization over a wide range of equimolecular concentration of BA and DMA are shown in Fig. 3a, b and c. The dependence of the reaction rate on initiator coneentra-. w i

02

H,,IO-5

b

03'

2s

o

///t.

18

I

I

002

// 2

/

1o

~06 A

Iog w

T.2

i o

004

8 i

1

20

Time, rain

i

i

30

i

3.2

I

58

I

70

I

34

log[BA]odDMA]

:FIG. 3. Polymerization of MMA in the presence of BAd-DMA at 50°: a--CPC content 2%. [BA]=[DMA], mole/100 ml of the aqueous phase: 1--0.0025; 2--0.005; 3--0.015; 4--0.02; 5--0.025; 6--0.03; 7--0.04; 8--0-05; g--see :Fig. la. b--dependence of the rate of polymerization (1) of MMA and polymer molecular weight (2) on the concentration of [BA]=[DMA]; w--see Fig. lb; A--[BA]~[DMAI, tool/100 ml of the aqueous phase; c--determination of the order of the reaction with respect to the initiator. tion passes through a maximum with [ B A ] = [ D M A ] = 0 . 0 2 5 mole/100 ml of aqueous phase; at high acid and amine concentrations (greater than 0.025 mole/ 100 ml aqueous phase) unstable, laminating latexes are formed. The molecular weights of the polymers decrease with increase of initiator concentration. It was found that in the [BA] = [DMA] zone between 0.0025 and 0.025 mole/ 100 ml aqueous phase, the order of the reaction with respect to the initiator is

796

8. D. STAVROVAet al.

0"5 (Fig. 3c), i.e. the rate of MMA polymerization is respresented b y the equation: w = b [ B A ] °'s or w = b [ D M A ] °'5, (2) which is also valid for bulk polymerization of MMA using the B A - D M A system

[2]. To elucidate the dependence of the rate of MMA polymerization on emulsifier concentration, experiments were carried out where the CPC content varied from 0.25 to 5 ~ . The results are shown in Fig. 4a and b. Here the same relation can be observed as in case of MMA polymerization in the presence of DMA alone (Fig. lb and 4b). The polymer molecular weights remain constant over the "whole range of emulsifier concentrations.

4

•

•

2

w

o

O'3

b

I

M,IO-.~

2 0"2

×

2

20 ×

12

07

0

I

I

1

20

40

80

0

Time, rain

1

4

fs],~

fi

FIG. 4. Polymerization of MMA with varying CPC concentrations at 50°. [BA]~--[I)MA]= ~0-015 mole/100 ml of the aqueous phase, a--CPC content (% of the aqueous phase): 1--0.25; 2--0-5; 3--1.0; 4--2.0; 5--3.0, 4.0, 5.0; g--see Fig. la: b--dependence of the rate of polymerization (1) of MMA and polymer molecular weight (2) on CPC concentration ([S], %). The activation energy of MMA polymerization, in the presence of the B A I)MA system, calculated from data shown in Table 2, was found to be 13.0 kcal/ mole. From the above data the overall rate of MMA polymerization on the presence of B A ~ D M A can be expressed b y equation (3), which is similar te equation (1):

Wo,e,~ = k [i]o.5 [1~] [s] ;

(3)

these equations satisfy the case of emulsion polymerization using oil-soluble iniViators [3].

P o l y m e r i z a t i o n o f MMA

797

From equations (1) and (3) constants (k) for the overall rate of MMA polymerization in the presence of DMA and the B A - D M A system, were calculated. Using values of/c and the activation energy, E the pre-exponential term, A was determined from the Arrhenius equation. Table 3 presents the values of k, A and E for MMA polymerization in the presence of BA and DMA in emulsion and in bulk. TABLE 2. POLYMERIZATION OF M M A IN THE PRESENCE OF [BA] =[DM] =0.015 MOLE/100 ML OF THE AQUEOUSPHASE AT VARIOUSTEMPERATURES (CPC c o n t e n t - - 2 9 / o o f t h e a q u e o u s phase)

Temperature, °C

R a t e o f polylnorization, g of polymer/ 100 m l o f t h e a q u e ous p h a s e , m i n

Intrinsic viscosity [7]

Molecular weight, M × 10 -5

30 40 50 60

0.060 0.125 0-235 0.400

12.7 9"4 6.0 5.8

56.23 38-02 20.99 20.09

Table 3 indicates that the increase of MMA polymerization rate in the presence of the BA-DMA system, on changing from bulk to emulsion, is due only to the increase of A, since the activation energy remains unchanged in practice. (A in emulsions is higher by approximately 3 orders than in bulk). TABLE 3. CONSTANTS OF THE ARRKENIUS EQUATION FOR THEPOLYMERIZATION OF MMA IN THE PRESENCE OF D M A AND B A + D M A In bulk [BA] = [DMA] = 0.3 mole/1, of the organic phase E, kcal/mole

It, mlXl2/gl/2.min A , mll/S/gl/l.min

(in

13.2 0.000607 4.2 × 105

I n e m u l s i o n s [CPC] = 2~/o [BA] = [DMA] = 0.3 mole]l, o f t h e organic p h a s e

[DMA] = 0-3 mole/1. o f t h e organic p h a s e

13.0 1.14 6.27 × l 0 s

14.2 0.296 9.95 × l 0 s

~Vote.To compare values k and A in bulk and in emulsion, the calculations were based on an equal effective volume bulk this volume of the m o n o m e r is 2 ml; in emulsion, the soap volume is 2 ml).

The causes of variation of the entropy factor on changing over to emulsions m a y be very different. The m o s t significant are the following: 1) development of spatial conditions which favour monomer initiation and, perhaps, polymer chain growth as a consequence of the orientation of detergent molecules on the surface of polymer particles; 2) reduction of the entropy level of this initial state as a result of complex-formation and solvation. It is very difficult to relate the variations of the entropy factor on changing over from bu]k to emulsions to one or the

S. ~). STAVROVAtt al.

798

other group of causes mentioned. From the experimental information obtained in this study it can be assumed that the increase of the pre-exponential factor is due to both causes. It should also be mentioned that the orienting effect of ordered systems on the surface of polymer particles is not only reflected in the reactions of initiation but also in the forms of introducing the monomer into the growing polymer chain in the steps of reaction chain growth. An example of a similar effect is the substantial macrostructural variation of polyisoprene in emulsion polymerization in the presence of the BA-DMA system, compared with the conventional radical initiator, K~$208 (Table 4). TABLE 4. POLYISOPRENE STRUCTURE Initiator BA-}- D M A

KsS~Os

cis- 1,4

trans- 1,4

1,2

3,4

42 39

43 45 84

8 9 5

7 7 5

5

Polymerization of methyl methacrylate in the presence of the B A - D M A system varying the concentration of one of the components. The results of experiments where MMA was polymerized with constant DMA concentration and varying amounts of BA are shown in Fig. 5a and b. The dependence of the polymerization rate on BA concentration passes through a maximum. With [BA] =0.03 mole/100 ml of aqueous phase and above separation of latex is observed. Comparing these data with experimental results at high BA and DMA concentrations (Fig. 3), it can be concluded that separation of latex is due to the presence of a large amount of BA which disturbs the condition of the emulsion and lowers the polymerization rate. Polymer molecular weights remain unchanged in practice over the whole range of acid concentrations, somewhat decreasing in the range from 0.0025 to 0-02 mole/100 ml of the aqueous phase (Fig. 5b). In the case of MMA polymerization with [BA] =0.015 mole/100 ml of the aqueous phase a continuous increase is observed in the reaction rate and a reduction in polymer molecular weights with increased DMA concentration (Fig. 6a and b). (A similar rate increase was observed on increasing the DMA content of the system and with bulk polymerization of MMA in the presence of BA~-DMA

[2]). Let us denote DMA and BA concentrations by [A] and [B]. Then, in experiments with equimolar ratios of components, [A] ----[B] ------lAB]. If in the initial mixture [A] >[B], in addition to polymerization of MMA taking place under the effect of the BA-DMA system, polymerization of MMA takes place in the presence of DMA alone. Then, the overall rate of MMA polymerization can be expressed by the equation:

Polymerization of MMA

799

=,,.

0

10

20

30

~me , rain

w

b M,lO -5

0,2

28

24

0"I

20 O'Ol

0"03

7"05 A

FIo. 5. Polymerization of.MMAin the presence of BA+ DMA at 50% a--[CPC] = 2~o. [I)MA] ----0.015 mole/100 ml of the aqueous phase; [BA], mole/100 ml of the aqueous phase: 1--0.0025; 2--0.005; 3--0.01; 4--0.015; 5--0.02; 6--0.025; 7--0.03; 8--0.04; 9--0.05; g--see Fig. la; b--dependence of the rate of polymeri~tion (1) of MMA and polymer molecular weight (2) on BA concentration, w--see Fig. lb; A--[BA], mole/100 ml of the aqueous phase.

Woveral|: kx([-A- ] -- [B])1/~_.{_ ~2 [B11/2,

(4)

where wovevanis the overall rate of the reaction; k 1 is the polymerization rate constant in the presence of DMA; ~2 is the reaction rate constant in the presence of the BA-DMA system;. [@] and [B] are the amine and acid concenfrations respectively. As can be seen in Table 5, equation (4) satisfactorily agrees with experimental data.

800

S.D. STAVR0VA~ ~. # 6

5 ,4/s

I

I

/0

I

2o

3O

Time, rain w

M,IO-5

O3

-34

0-2'

0.1 18

0

I

I

I

001

0"02

0.03

I

0.04 A

FIG. 6. Polymerization of MMA in the presence of BA~DMA at 50°. a--[CPC] 2~o. [BA] = 0"015 too!ell00 ml of the aqueous phase; [DMA], mole/100 m] of the aqueous phase; 1--0.005; 2--0.01; 3--0.015; 4--0.02; 5--0.025~ 6--0.03; 7--0.04; g--see Fig. la; b--dependence of the rate of polymerization (1) of MMA and polymer molecular weight (2) on DMA concentration, w--see Fig. lb; A--[DMA] mole/100 ml of the aqueous phase. =

CONCLUSIONS (1) The effect of initiator concentration (BA-DMA system and DMA alone), the concentration of a cation-active emulsifier, CPC and of temperature on t he rate of MMA polymerization and mean molecular weights of polymers, has been investigated. (2) The dependence of the rate of MMA polymerization on/ ni t i at or and emulsifier concentration satisfies the case, of emulsion polymerization using ]ow-so]ub-

801

Polymerization of MMA TABL~ 5. OVER.Z, ~T~. OF ~ A POLY~RIZaTIO~ I~ THE FRZSE~CE OF TIr~ BA-DMA SYSTEM,CALCULATEDFROM EQUATION(4) (CPC content 2Yo, k1-~0"51) ks~1"922, [B]~0.015 mole/100 ml of the aqueous phase, 0.3 mole/1, of the organic phase [A], mole/100 ml of the aqueous phase

~t~1

0.015 0.020 0.025 0.030 0.040

0 0.036 0.051 0.0615 0.0806

W|

0.235 0.235 0.235 0.235 0.235

Wcalo"

'Wexp.

0.235 0.271 0.285 0.296 0-315

0.240 0.265 0.285 0.305 0.405

ility initiators. The molecular weights o f p o l y m e r s r e m a i n u n c h a n g e d over the whole range o f CPC concentrations. (3) A c t i v a t i o n energies o f MMA p o l y m e r i z a t i o n initiated w i t h DMA alone a n d w i t h t h e B A - D M A s y s t e m a n d t h e p r e ~ x p o n e n t i a l t e r m s of the Arrhenius equation h a v e been d e t e r m i n e d . I t is shown t h a t on changing over f r o m b u l k to emulsion, t h e p r e - e x p o n e n t i a l t e r m s increase b y 3-4 orders. This is due to the orientation effect of the emulsifier molecules on t h e surface o f p o l y m e r particles a n d r e d u c t i o n o f t h e e n t r o p y level of t h e initial s t a t e as a result o f complex-formation a n d solvation. TranalaZed by E. SEMERE REFERENCES

1. 8. D. YEVSTRATOVA, M. F. MARGARITOVA and S. S. MEDVEDEV, Vysokomol. soyed. 5: 1574, 1963 2. M. F. MARGARITOVA and S. D. YEVSTRATOVA, Vysokomol. soyed. 3: 391, 1961 3. S. S. MEDVEDEV, P. M. Ki~OMIKOVSKII, A. P. 8HEINKER, E. V. ZABOLOTSKAYA and G. D. BEREZHNOI, Problemy fizicheskoi khlmii, issue 1, Moscow, Goskhimizdat, 1958; G. D. BEREZHNOI, P. M. KHOMIKOVSKII and S. S. MEDVEDEV, Vysokomol. soyed. 2: 141, 1960