Organoaluminium compounds as catalysts for anionic polymerization of methacrylates

O r g a n o a l u m m m m compounds as catalysts

1393

culated from previously published data [11] are in good agreement (Table 5). This demonstrates the applicability of the results of the kinetic investigation to determination of the structure of copolymers prepared by non-equilibrium copolycondensation in solution Translated by E O. PHILI~PS REFERENCES

1. L. V. KURITSYN and V. M. KURITSYNA, Zh org khlm. 8 1469, 1972 2. L. V. KURITSYN a n d L. B. SOKOLOV, Vysokomol soyed AI4- 2028, 1972 (Translated in Polymer SOL U.S.S R. 14" 10, 2382, 1972) 3. N. K. VOROB'EV, L. N. SMIRNOVA and Ye A. CHIZHOVA, K h m u y a 1 khlm tekhnol. 14: 965, 1971 4 L. W. A. MEYER and W. M. GEARHART, I n d Engng Chem 43: 1585, 195I 5. V. V. KORSHAK, V. A. VASNEV, S. V. BOGATKOV, A. I. TARASOV and S. V. VINOGRADOVA, Reakts. sposob org soyed 10: 375, 1973 6. S. W. BENSON, J. Amer. Chem Soc 80: 5151. 1958 7. A. FROST a n d R. PIRSON, Kmetms and Mechamsm, New York-London, 1962 8. A. P. KRESH]KOV, N. Sh. ),LDAROVA, A. I. TARASOV, V. A. VASNEV, S. V. VINOGRADOVA, M. V. SLAVGORODSKAYA, T. I. MITAISHVILI and V. V. KORSHAK, Reakts. sposob org. soyed 7: 279, 1970 9. V. V. KORSHAK, S. V. VINOGRADOVA, V. A VASNEV, Ye. V. BRYO'KHOVA and G. K. SEMIN, Izv Akad. Nauk SSSR, ser k h l m , 681, 1970 10 S. V. VINOGRADOVA, V. V. KORSHAK, P. O. OKULEVICH, Yu. I. PERFILOV a n d V. A. VASNEV, Vysokomol soyed BI5: 470, 1973 (Not translated m Polymer Scl.

U.S.S.R.) 11. S. I. KUCItANOV, Vysokomol soyed A16- 1125, 1974 (Translated in Polymer Scl. U.S.S R. 16: 5, 1302, 1974) 12. V. V. KORSHAK, S. V. VINOGRADOVA, P. O. OKULEVICH, Yu. I. PERFILOV, V. A. VASNEV a n d E. I. FED]N, Izv. Akad. Nauk SSSR, ser. k h i m , 1629, 1972

ORGANOALUMINIUM COMPOUNDS AS CATALYSTS FOR ANIONIC POLYMERIZATION OF METHACRYLATES* Y~.. V. MILOVSKAYA,M. N. !VIAKARYCHEV-]V[IKHAILOVand E. P. SKVORTS~VICH I n s t i t u t e of Maeromoleeular Compounds, U S.S.R Academy of Scmnces

(Received 24 January 1974) I t is shown t h a t methyl methacrylate polymerlzes at a high rate m the low temperature region under the influence of dmthyl alurmnmm dlphenylamlde. Imtlatlon is slow, with essential partm~patlon of monomer m formation of the active centres a n d some chain t e r m m a h o n occurs. Complex formation between the monomer * Vysokomol. soyed A17: No 6, 1217-1222, 1975.

1394

YE. V. ~.ILOVSKA.YAet

al.

and the active centre m the propagatmn stage m an essentml condltmn for the occurrence of polymerization. Cataly%m amount of electron donors n~hlblt the process. Factors promoting catalyCm actlwty m organoalummmm compounds are dmcussed. Polymers formed under the influence of organoalummmm catalysts are syndlotactic and have higher thermal decompomtlon temperatures than those obtained with radmal or ordinary amomc (butyl hthmm) catalysts. IT is well k n o w n t h a t as p a r t o f m u l t i - c o m p o n e n t s y s t e m s o r g a n o a l u m i u n i u m c o m p o u n d s c a n i n d u c e radical [1-3] or cationic [4] p o l y m e r i z a t i o n o f u n s a t u r a t e d monomers. There is considerably less i n f o r m a t i o n on their anionic activity. U~like alkali m e t a l or alkaline e a r t h m e t a l alkyls, a l u m i n i u m alkyls do n o t o n t h e i r o w n show a n y t e n d e n c y to bring a b o u t anionic p o l y m e r i z a t i o n . The change t o c o m p o u n d s w i t h a m o r e electronegative element t h a n carbon, especially t o c o m p o u n d s w i t h a n A 1 - - N bond, i.e. t o a l u m i n i u m alkylamides, increases t h e anionic n a t u r e o f t h e b o n d * a n d c o n s e q u e n t l y such derivatives b e c o m e capable o f bringing a b o u t anionic p o l y m e r i z a t i o n o f m e t h y l m e t h a e r y l a t e (MMA) a n d o t h e r m e t h a c r y l a t e m o n o m e r s [7, 8]. A t the same time the i n f o r m a t i o n available does n o t p r o v i d e a basis for d e d u c i n g factors t h a t would affect the r e a c t i v i t y o f o r g a n o a l u m i n i u m c o m p o u n d s as c a t a l y s t s o f anionic p o l y m e r i z a t i o n , especially t h e role o f t h e n a t u r e o f t h e A1-- X bond. F u r t h e r m o r e t h e fine details o f the sep a r a t e stages o f t h e process c a t a l y s e d b y an a l k y l a l u m i n i u m a m i d e h a v e n o t been discussed in t h e h t e r a t u r e [7, 8]. I n p l a n n i n g t h e p r e s e n t i n v e s t i g a t i o n we were interested in t w o problems, n a m e l y a more detailed c h a r a c t e r i z a t i o n o f the p o l y m e r i z a t i o n o f MMA c a t a l y s e d b y d i e t h y l a l u m i n i u m d i p h e n y l a m i d e (an a l u m i n i u m amide) (DEAA), which is k n o w n in t h e literature as a c a t a l y s t [7], a n d t h e possibility o f creating active c a t a l y s t s based on o t h e r o r g a n o a l u m i n i u m c o m p o u n d s After the usual purification the reagents and solvents were thoroughly dried (Call, or metalhc sodmm) and re&stilled An v a o u o T h e crystalhne amides were purified by repeated recrystalhzatlon. The subsequent work was carrmd out m an atmosphere of argon or under vacuum. A solution of commercial A1Et, m toluene was used for preparation of the catalysts. The method of reference [7] was used for preparatmn of Et,A1N(C6Hs)2 and the course of the reaction was followed by measurement of the quantity of gas evolved. The concentration of the DEAA. solution used m thin work was measured volumetmcally. Similar methods of preparatmn, monitoring of the reactmn and analysis of the reactmn rmxture were used m preparatmn of phenyl-fl-naphthylamlde and dmthylalummmm phenoxldc. In contrast to the aromatm ammes, plperldme &d not react with A1Ets at room temperature and it was necessary to raise the temperature of the reactmn mixture to 100-105 ° (momtormg and analysm as m the prewous instances). The starting material for preparatmn of 2-ethyl-2propylbutoxydmthylalummmm was heptan-4-ol. The reactmn was carrmd out at room temperature and then at 30-40 ° [9] Gas evolutmn did not occur m thin mstance and the reaction was followed by volumetmc analysm of the reactmn mixture. * To a rough approxunatmn the extent to whmh a bond is mmc can be caloulated from the electronegatlwtms of its component elements. For AI--C, AI--I~ and LI--C the figures are 22~o, 43~/o and 43~o and 43% respectively [6].

Organoalummmm compounds as catalysts

1395

Polymerization was carrmd out in a sealed tube or smgle bulb d d a t o m e t e r with a side e n l a r g e m e n t for holdmg the catalyst. The toluene and monomer were addltlonaUy purified b y contact with the organometalhc compound and were redlstllled rote the reactmn b u l b from a measuring vessel on a dmtributmn manifold. The catalyst solutmn was poured m from a Schlenk flask. Polymerization was stopped b y decomposing the reactmn m i x t u r e with d d u t e hydrochlorm acid and the polymer was separated by preclpltatmn m petroleum ether The number average molecular w e i g h t / ~ / , was determined b y the method of reverse ebulhoscopy m a Hitachi apparatus. The l~Ph~ end groups m the polymer were d e t e r m m e d b y ultravmlet spectroscopy m a Speccord UV VIS spectrometer. A specially prepared torttory amine C2H6--N--Ph~ [10] was used for determining the c x t m c t m n coefficmnt E. The carefully purfficd model compound (fraetmn boiling at 99-101°/1 tmr) had 2ma~= 301 n m a n d E = 1 1 , 2 0 0 1./mole/cm (m chloroform) The polymer gave 2ma~=296 n m and HNPH2 gave 2max=285 m n and E = 16,800 1/mole/cm (chloroform). The number average molecular weight b y end group analysis (2~Npg2), assuming one gloup per p e l y m e r chain, was calculated from the formula "~NPh,

[p°lymer]M

[NPh~] where M is the molecular weight of the monomer, fflv was calculated from the formula [t/I=0 48)< 10-4"21~ ° s (the wscoslty was determined m chloroform at 25 °) [11] The 1~1~I1~ spectra were recorded m o-chlorobenzene at 182 ° m a Varmn-60 spectrometer.

Methyl methacrylate polymerizes at a high rate under the influence of DEAA in the low temperature region The maximal rate occurs at --50 ° and the polymer produced is syndiotactic (Table 1) A quantitative yield is obtained only when the catalyst concentration is comparatively high CATALYSED BY D E A A

TABLE 1. 17)OLYMERIZATIOI~ OF ~

([M]=2 mole/1. [ C ] = 5 × 10 -2 m o l e / l , toluene) T~ °C

0 --30 --50 --78

Time,

Ymld,

hr

%

1,0 0-5 0-5 30

62 80 100 43

M , × 10 -s 11 12 30 37

Stereoregulamty, % syndlo heterolSO -

77 79 77

23 21 23

0 0 0

T h e m o l e c u l a r w e i g h t i n c r e a s e s w i t h t i m e b u t t h e i n c r e a s e is n o t p r o p o r t i o n al to the degree of conversion. The efficiency of initiation F also increases with t i m e ( T a b l e 2). T h e t i m e r e l a t i o n s h i p s f o u n d c o u l d b e a t t r i b u t e d e i t h e r t o a h i g h degree of chain transfer to monomer or to slow initiation. Table 2 presents the r e s u l t s o f m e a s u r e m e n t o f /~/n b y a n a l y s i s f o r N P h 2 e n d g r o u p s a n d t h e s e - a r e c o m p a r e d w i t h -~/n f o u n d e b u l l i o s c o p i c a l l y . T h e c o n s t a n c y o f t h e r a t i o ~ / ~ p h , / M n gives grounds for attributing the effect to the second of the above causes.* * The d e v l a h o n of t h e ratio J~/mph2//~rn fl'om u m t y can evidently be a t t r i b u t e d only to &florence between the e x t m c h o n coefflcmnts of the model compound a n d the actual polymer.

1396

YE. V. ~.II,OVSKAYA et al.

F r o m t h e results o b t a i n e d it is seen t h a t t h e degree of utilization o f t h e init i a t o r b e c o m e s quite high, m u c h higher t h a n is a t t a i n e d w i t h m a n y o t h e r a n i o n i c c a t a l y s t s [12]. I n c r e a s e in t h e c o n c e n t r a t i o n o f m o n o m e r brings a b o u t a n increase in molecu l a r weight, b u t t h e r e l a t i o n s h i p is n o t linear (Table 3). F r o m t h e increase in F TABLE 2. DEPENDENCE OF MOLECULAR WEIGHT AND EFFICIENCY Olq TIME AI~D CONVERSION ([M]=2 mole/l; [C]=2.5× 10 -~ mole/1.; --50°; toluene) Time, mm 3.75 7"5 15 30 90 180

Conversion, °/o

~r n

F, ~o

2//Nph,

15 28 47 67 73 76

5400 6800 7350 8700 9170 9650

24 34 51 62 64 64

8950 11,500 12,400 15,100 16,000 18,500

Ml~ph,/-;~/I i

1.7

1.7 1"7 18 1"7 19

w i t h increase in m o n o m e r c o n c e n t r a t i o n a n d t h e f a c t t h a t t h e r a t i o ~ll~Fh,/Nn r e m a i n s c o n s t a n t it m a y be considered t h a t this i n d i c a t e s p a r t i c i p a t i o n o f t h e m o n o m e r in f o r m a t i o n of a c t i v e centres CM*, i e. a r e a c t i o n of t h e t y p e C~-M~(CM)..

initiation

t a k e s place. TABLE 3. DEPENX)EI~CE OF MOLECULARWEIGHT A2ffD EFFICIElffCY ON" MONOMER CONCENTRATION ([C]=2 5× 10 .2 mole/1 ; 15 ram; --50°; toluene) [M], mole/1

Convermon, %

_~/.

F

-~/Nrh,

~I~rh~/Nl"

0"25 0"5 10 20 30

56 56 50 47 48

2600 3580 4500 7350 7130

22 31 44 51 75

5900 7100 7700 12,400 14,700

22 2.0 19 17 21

Chain t e r m i n a t i o n t a k e s place d u r i n g t h e entire course o f p o l y m e r i z a t i o n ~ r e t a r d a t i o n o f t h e process occurs w h e n t h e m o n o m e r h a s f a r f r o m c o m p l e t e l y d i s a p p e a r e d a n d t h e r e is no i n d u c t i o n period. T h e l a t t e r w o u l d be e x p e c t e d i f i n i t i a t i o n is slow. M e a n w h i l e s o m e o f t h e chains c o n t i n u e t o g r o w as is seen f r o m t h e results p r e s e n t e d a b o v e . T h e e x p e r i m e n t a l evidence a t p r e s e n t a v a i l a b l e does p e r m i t t h e c h e m i s t r y o f t h e c h a i n t e r m i n a t i o n r e a c t i o n t o be r e p r e s e n ~ d . I t c a n b e s t a t e d o n l y t h a t it is a r e a c t i o n o f t h e first o r d e r w i t h r e s p e c t to a c t i v e

O r g a n o a l u m m m m compounds as catalysts

1397

centres (graphs) and C = O groups corresponding to a cyclic ketoester* were not detected in the deactivated polymer (by irffr~red spectroscopy). The effect of electron donors (EDs) on the polymerization was very specific Strong electron donors such as hexametapol, T H F and DMF stopped the process completely when added in the initiation stage in catalytm quantities. This fact supports the opinion stated above that monomer is involved in formation of the active centres Polymerization occurred only in the presence of EteO, the complex-forming tendency of which is comparable with that of MMA, b u t even m this instance polymerization was suppressed to a considerable extent t The experimental conditions were. [M]=2"mole/1, [C]=2 5X10 -2 mole/1, [C]/[ED]~--I/5, solvent toluene, --50 ° After an hour the yield was 43% and without the ED it was 72~o M,fO-J i0~ o o

/o

9 ,

5/ 1

Z

o

1

i 3

o o

j 5

It/o, 102, r, ole/L Dependence of _7~rn (1) and _~rNph2 (2) on catalyst concentration at [M-J=2 raolefl, --50 °, 15 rain, solvent--toluene

When strong EDs were added during the course of polymerization it came to a complete halt I t obviously follows from this that complex-formation of the monomer with the active centre is a necessary condition for polymerization at each propagation step as well as at the initiation stage. Complex formation increases the anionic nature of the monomer [15] and it m a y be assumed t h a t it is the complexod monomer that is inserted in the growing chain. Additional support for this view is provided by the fact that practically all methacrylio monomers, i e. monomers susceptible to successive insertion of complcxed molecules, can be polymerized under the influence of an aluminium amide. Thus in addition to the results in reference [8] we have polymorized 2-ethylhexyl methacrylate (EHM) in a 100% yield in 1 hr ([M]=2 mole/1, [ C ] = s x 1 0 - ~ mole/1, --50 °, toluene). In turn the known fact that acrylonitrile does not polymerize can be explained b y the fact that the rigid configuration of the monomer excludes the possibility of successive insertion of complexed monomer. * Chain terralnatlon b y formation of six merabered, cyclic groupings with subsequent (or siraultaneous) formation of a ketoester has been found in polyraermatlon of M:MA under the m~uenee of organorn~gneslum derivatives [13]. t Although the available mformatzon on the complex forralng tendencies of R=O and ~ relate to 0so-Bu)~Al, it m a y be assumed t h a t transferring it to the class of amlde derivatives will not alter the picture quahtat~vely.

1398

YE. V. ~ILOVSKAYA ~ al.

For solution of the problem of what factors promote anionic activity in aluminium compounds a number of derivatives containing oxygen and nitrogen were synthesized Et (Pr)2 ~C /

Ph 1

EhAI--N~ III

j

O

O

EhAI / A\'IEh, \/ O

EhA1/ \ AIEh, \/ O

r

I

Ph

Ph EhAI~N / \

C

I

Et

/\

IV

~- naphthyl

(Prh

II Compounds I - I I I proved to be inactive in polymerization. I n the case of t h e oxygen-containing compounds this can obviously be attributed to the low Lewis acidity of such compounds and to the considerable strength of the A1--O bond, which makes complex formation and insertion of monomer energetically unfavourable. TABLE 4. POLYMERIZATION WITH DIETHYLA.LUMINIUMPHENYL-~-NAPVfTHYI~kMINE AS CATALYST I

EM3 [ Eq Monomer

MMA

EHM

Time,

mole/l. 25 25 20 2.0

T , °C

+1 Yield, M~×

hr

%

× 10 -3

58 91 42 92

22 47 74

2.5

-- 20

1

5.0

-- 50

1

5.0

- - 78

13

5-0

-- 50

1

Stereoregulanty,% I

syn-dlo, hetero-

70 75 75

25 20 25

1SO-

5

5 0

Thermal decompo sltmn temperature, °C 230 270 250 240

The relationship between the basicity of the original amine and the catalytic activity of the derived a h m i n i u m amide (AA) is quite clearly demonstrated b y the example of the nitrogen containing compounds. Thus in the case of piperidine the AA is obtained with difficulty and it does not possess catalytic activity. This can be attributed to the J-effect of the substituent, resulting in reduction in the polarity of the A1--N bond. In addition to the known catalysts prepared from a fatty-aromatic (methylaniline) [7] and aromatic amine (diphenylamine) [7] an active catalyst was obtained from phenyl-fl-naphthylamine. I t is seen from Tables 1 and 4 t h a t PMMA prepared under the influence of aluminium amides is highly syndiotactic. The thermogravimetric characteristics of the polymers proved to be very interesting. I t was found t h a t the PMMA has a higher thermal decomposition temperature (on the average by 40-60 °)

Organoalummmm compounds as catalysts

1399

than samples obtained by the radical method (including the A1R3-peroxide system) and amonically (LiBu m polar and non-polar media) To this can be added the fact that the very nature of the thermal degradation process differs from that of polymers produced both by radical and anionic methods.* The PEHM also has a higher thermal decomposition temperature than a sample produced by the free radical method (Table 4). There must obviously be several reason for the above effects. Primarily they can be attributed to the effect of the phenyl and naphthyl end groups, which can be regarded as special kinds of free radical traps or as agents promotir~g non-radical decomposition of the peroxides formed (the polymerization was carried out in air) [19] Support for this suggestion is given by the known fact that PMMA prepared with lithium diphenylamide as catalyst also has a high decomposition temperature [18] Another reason lies in the nature of the aluminium catalysts themselves. It is well known that polymerization, catalysed by butyllithium produces polymers with a branched structure, as a result of participation of the organolithium compound in secondary reactions [20] Organoaluminium compounds do not tend to take part in such reactions, as is shown by the known fact that the molecular weight of the polymer does not increase when the reaction mixture is kept for a long time after completion of polymerization. Translated by E O. PHILLIPS REFERENCES 1 Ye. B. MILOVSKAYA, L. V. ZAMOISKAYA and Ye. L. KOPP, Uspekhl khlmu 38: 928, 1969 2 L V. ZAMOISKAYA, S. I. VINOGRADOVA and Ye. B. MILOVSKAYA, Vysokomol. soyed A13" 1484, 1971 (Translated m Polymer Scl U S S.R 13: 7, 1670, 1971) 3 Ye. L KOPP, O. S. MIKHAILYCHEVA and Ye. B. MILOVSKAYA, Vysokomol. soyed. AI4: 2653, 1972 (Translated m Polymer Scl U.S S R 14: 12, 3087, 1972) 4 T. SAEGUSA, T. TSURUTA (Ed.), Structure and Mechanism m Vinyl Polymermatmn, p 283, l~ew York, 1969 5. M. IKEDA, T. HIRANO a n d T. TSURUTA, Makromolek Chem 150: 127, 1971 6. L. PAULING, Prlroda khrrmcheskol svyazl (The l~ature of the Chemical Bond) p 65, Goskhlmizdat, 1947 (Russian translatmn) 7. S. MURAHASHI, K. YUKI and K. HATADA, Chem. High Polymers, J a p a n 24: 198, 309, 1967 8 H. YUKI, K HATADA and T. NIINOMI, Polymer J 1: 36, 1970 9 E. JEFFERY and T. MOLE, Australian J Chern 23: 715, 1970 10 C. GUARD, Bull Soc. Chlm. 23: 3, 1875 11 J. BISSCHOPS a n d V. DESREUX, J. Polymer Sci 10: 437, 1953 12 B. L. YERUSALIMSKII, Iormaya pohmerlzatslya polyarnykh monomerov (Iome Polymerization of Polar Monomers) p 180, Izd "Nauka", 1970 13 W. GOODE, F. OWENS and W. MYERS, J Polymer ScL 47: 75, 1960 14 S. I. VINOGRADOVA, V. M. DENISOV and A I. KOL'TSOV, Zh. obshch k_him 42: 1031, 1972 * The method used m this investigation and the results are given m detail m reference [18].

1400

D. T. KOKOREV e~ al.

15. Yu. E. EIZNER, B. L. YERUSAL1MSKII and Ye. B. MILOVSKAYA, Polymer J. 5: 1, 1973

16. K. ZIEGLER, H. ZEISS (Ed.), Organometalhe Chermstry, p. 194, London, 1960 17. J. HAY, P. HOOPER and Y. ROBB, J. Organomet. Chem. 28: 193, I971 18. Yu. N. SAZANOV, E. P. SKVORTSEVICHand Ye. B. MILOVSKAYA,J. Thermal Anal. 6: 53, 1974 19. K. INGOLD, Chem Rev. 61: 583, 1961 20. J. TRECOVAL and P. KRATOCHVIL, J Polymer SCL A-I, 10: 1391, 1972

EMULSION

POLYMERIZATION

PRELIMINARY

OF STYRENE

ULTRASONIC

AFTER

TREATMENT*

D. T. KOKOREV, V. N. MONAKHOV, V. K. PAYLOVA, V. I. FEDYANII~ and S. K. KHITERKHEYEV Moscow Chemmal Engineering Institute (Reveived 4 Maroh 1974)

Emulsion polymerization m systems previously subjected to an ultrasonm field of mtenmty 400 kW/m2 is dmeussed It is shown that a higher ymld of polymer is obtained and the polymerization time :s reduced EMULSION polymerization is accelerated considerably by ultrasonic vibration [1-6]. I t has been shown t h a t the rate of formation of polystyrene is doubled by ultrasonic t r e a t m e n t at frequencies of both 15 kHz and 500 kHz. At the same time the authors of references [1-4] state t h a t acceleration of polymerization occurs only at ultrasonic field intensities [3, 4] (with uniform distribution of the acoustic energy density throughout the system) above some critical value, probably equal to the cavitation threshold [7]. At the contemporary level of development of ultrasonic technology the production of such intensities through the entire volume of the multi-tonnage reactors used in industry is not possible. I t is also not feasible on energetic grounds to combine a large number of ultrasonic generators in parallel [6]. Of considerable interest in this respect is the statement by Goncharov and others [4] t h a t a brief ultrasonic t r e a t m e n t during the induction period is to some extent equivalent to ultrasonic treatment during the entire polymerization process. In view of the fact t h a t polymerization occurs at the interracial boundary, the area of which is dependent on the particle size of the emulsion [8], it m a y be assumed t h a t one of the main causes of acceleration of the process is * Vysokomol soyed. A17: No. 6, 1223-1225, 1975.