Polydispersity of ethylene-propylene copolymers synthesized on supported ziegler catalysts

1"~4

A.. G. RODIONOV e$ al.

2..V,, I. KLENIN, S. Yu. SHOHEGOLEV and L. O. L EBEDEVA, O p t i k a i spektroskopiya 35: l~Ior 6, L161, 1973 8. H. SCHNELL, K h i m i y a i fizik[ polikarbonatov (Chemistry and Physics of Polyearbonates). I z d . " K h i m i y a " , Moscow, 1967 9. L. B. GAVRILOV, Yu. A. MIZEYEV, D. ¥ a . TOPTYGIN and M. S. AKUTIN, Vys0: kernel, soyed. A23: 598, 1981 (Translated in Polymer Sci. U.S.S.R. 23: 3, 670, 19@1) 10~ I . N. RAZINSKAYA, L. I. VIDYAIKINA, T. L RADBIL' and B. P. S H T A R K M A ~ , Vysokomol. soyed. A14: 968, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 4, 10~74, 1972)

Potyr~r ScienceU.S]S~B,.Vol. 23, No. 7, pp. 1724-1732, 1981 Printed in Poland

0032-3950/81/071724-09507:50/0 © 1982 Pergamon press Ltd.

POLYDISPERSITY OF ETHYLENE-PROPYLENE COPOLYMERS SYNTHESIZED ON SUPPORTED ZIEGLER CATALYSTS* A . G. RODIO~OV, N . M. DOMAREVA, A . A . ]3A1YLIN, YE. L . I)OI~OMAREVA a n d S. S. IVANCttEV " P l a s t p o l i m e r " Scientific and I n d u s t r i a l Association, Okhtinsk

(Received 12 May 1980) A GPC s t u d y has been made of the polydispersity of e t h y l e n e - p r o p y l e n e eopoly,mers synthesized in the presence of typical (TiCla'½A1C13, TIC14) and supported (TIC14 :MgO, TIC14 :A1203, SiO2) Ziegler catalysts a c t i v a t e d b y AI(C2I-[5)a. I t is shown t h a t the character of the polydispersity of ethylene-propylene copolymers is determined p r i m a r i l y b y the n a t u r e of" the t i t a n i u m component of tile catalytic complex, and in p~rticular b y the nature of the support and the composition of the monomer mixt.ure. On the basis of a comparison of distribution curves according to the degree of polymerization of ethylene -propylene copolymers it is proposed t h a t practically all of the t i t a n i u m in active centres of the TiCl~ : MgO catalyst are in the trivalent state, whereas a broad distribution of the valence state of t i t a n i u m in active centres is charaeterisVic of the catalyst TiCl~ : A1208, SiO2. I T IS k n o w n t h a t t h e m e c h a n i c a l p r o p e r t i e s a n d r h e o l o g i c a l c h a r a c t e r i s t i c s o f ethylene-propylene copolymers (EPC) depend largely on their molecular weight distribution (MWD). There are a number of papers [1-6] relating to the influence of the chemical nature of typical Ziegler catalytic systems and to the

* Vysokomol. soyed. A23: No. 7, 1560-1567, 1981.

P o l y d i s p e r s i t y of e t h y l e n e - p r o p y l e n e c o p o l y m e r s

'1725

effect of technological parameters in copolymerization processes on the MWD of the resulting EPC. I n an earlier paper we showed that titanium tetrachloride attached to the surface of various mineral supports make it possible both to increase the EPC yield [7] and also, 'by selecting appropriate supports, to modify important parameters of the eopolymer structure such as composition [8], viscosity-average molecular weight 2~v [7] and compositional inhomogeneity (CI) [9]. In view of this, it was in the present instance desired to determine, in addition, relat ions between MWD and the chemical structure of supports for EPC synthesized in the presence of supported catalysts. E P C wcre s y n t h e s i z e d a t 343°K a n d 0.41 M P a p r e s s u r e , u s i n g tile m e t h o d of [7]. Th,' c~tal y s t s were p r o d u c t s of TIC14 i n t e r a c t i o n w i t h MgO a n d A-14 g r a d e a l m n o s i l i c a t e p r e p a r e d as in [10], a n d c h a r a c t e r i z e d b y specific s u r f a c e s (S~,) o f 14.5 a n d 218-0 m2/g r e s p e c t i v e l y a n d Ti c o n t e n t s 0.2 a n d 3.6 wt..°,~ r e s p e c t i v e l y (tile m e t h o d o u t l i n e d in [11] was used t o d e t e r m i n e S~p, a n d t o a n a l y s e c a t a l y s t c o m p o s i t i o n s ) . I n all eases t h e e o e a t a l y s t was AI (C~I~) a. T h e c o p o l y m e r c o m p o s i t i o n w a s d e t e r m i n e d b y i n f r a r e d s p e c t r o s c o p y [7]. T h e poly(tisp e r s i t y of E P C s p e c i m e n s w a s i n v e s t i g a t e d b y t h e G P C m e t h o d ( W a t e r s GPC-201 c h r o m a t o g r a p h ) w i t h a set of c o l u m n s filled w i t h m a e r o p o r o u s glass of t y p e s MPS-1600, M P S - 2 5 0 a n d silica gel w i t h a p o r e d i a m e t e r of 20 A. Tile s o l v e n t w a s o - d i e h l o r o b e n z e n e (DCB) a t 135 ° . C a l i b r a t i o n of t h e c h r o m a t o g r a p h w a s c a r r i e d o u t w i t h respect, to P E , u s i n g a S t a n d a r d S R M - 1 4 7 5 - N B S s p e c i m e n , h i g h d e n s i t y P E ( P E I t D ) f r a c t i o n s w h i c h h a d p r e v i o u s l y been c h a r a c t e r i z e d a c c o r d i n g t o M W b y n l e a n s of v i s e o s i m e t r y a n d l i g h t s e a t t e r i n o , a n d u s i n g low m o l e c u l a r l i n e a r paraffins; i t w a s f o u n d t h a t t h e r e l a t i o n [ , ] = 5 - 2 5 × 1 0 - ~ v °'°~° is s a t i s f i e d for P E I - I D i n D C B a t 408°K. T h e r e l i a b i l i t y of t h e " u n i v e r s a l c a l i b r a t i o n " in t h e f o r m of e l u t e d v o l u m e ['e v s . log (2~/v'[,1]) p l o t s for P E a n d P P w a s v e r i f i e d b y e x a m i n i n g s p e c i m e n s of u n f r a e t i o n a t e d : P P w i t h ~ / ~ = 7 × 104 a n d 4.3 × 10 ~, u s i n g t h e r e l a t i o n i t / ] = 1"0 × 1 0 - 4 M °'~8

f o r P P i n D C B a t 135 ° . F i g u r e l a s h o w s c a l i b r a t i o n c u r v e s of log 3/i V~ for P E I - I D a n d P P p l o t t e d respectivelyin accordance with experimental data and from calculations based on the "universal c a l i b r a t i o n " p r i n c i p l e . W e m u s t e x p r e s s o u r v i e w as t o t h e v a l i d i t y of t h e m e t h o d i n q u e s t i o n for a n a l y s i n g t h e p o l y d i s p e r s i t y of E P C . C e r t a i n l y , c a l i b r a t i o n c u r v e s for e o p o l y m e r s m a y i n g e n e r a l b e s i t u a t e d e i t h e r i n t h e a r e a b e t w e e n c u r v e s for t h e r e s p e c t i v e h o m o p o l y m e r s . or o u t s i d e t h i s area., d e p e n d i n g o n t h e e o p o l y m e r c o m p o s i t i o n , a n d o n specific a s p e c t s o f t h e b e h a v i o u r of i t s c o m p o n e n t s i n s o l u t i o n . W e a s s u m e t h a t for t h e E P C c o n s i s t i n g as i t does of c h e m i c a l r e l a t e d c o m p o n e n t s i n a s o l v e n t t h a t is a " g o o d " o n e for b o t h c o m p o n e n t s , t h e c a l i b r a t i o n c u r v e s will b e l o c a t e d b e t w e e n t h o s e for P E t I D a n d P P . T h i s ass u m p t i o n w a s s u b s t a n t i a t e d i n [12], o n t h e b a s i s of a g r e e m e n t b e t w e e n t h e r e s u l t s of a n a n a l y s i s of t h e p o l y d i s p e r s i t y of E P C f r a c t i o n s b a s e d o n t h e r e s u l t s o f l i g h t s c a t t e r i n g a n d o s m o m e t r y , a n d , o n t h e o t h e r h a n d , b a s e d o n t h e G P C d a t a , a s s u m i n g a d d i t i v i t y in calib r a t i o n for E P C . S i n c e t h e p o s i t i o n of t h e E P C c a l i b r a t i o n c u r v e is a f u n c t i o n of i t s c o m p o s i t i o n , it follows t h a t t o o b t a i n i n f o r m a t i o n o n t h e E P C M W D b a s e d o n G P C a n a l y s i s we h a v e t o b r i n g in d a t a o n t h e c o m p o s i t i o n of E P C m a c r o m o l e e u l e s r e l a t i v e t o t h e i r 2¢IW or t o E P C d i s t r i b u t i o n a c c o r d i n g t o [t/].

A. G. RODIONOV et aZ.

1726

The method of obtaining such information is very laborious, and requires elaborate equipment. To avoid these complications chromatograph calibration was carried out on the basis of the degree of polymerization P (see Fig. lb). I t can be seen that, within a range of variation in log P of 1.6-4.8, this calibration m a y be regarded as being sufficiently "universal", since the curves for P E and P P practically coincide. On a previous occasion a similar finding was reported [13] in regard to the ratio of homo- and copolymers based on styrene, =-methylstyrene a n d butadiene. Thus data on the degree of polymerization distribution was obtained in the present instance b y means of GPC analysis of EPC, and in the calculations calibration for P E or for P P was used, depending on the average composition of the copolymer. Calculations of degree of polymerization distribution for EPC were carried out with the aid of a Minsk-32 computer, using a program previously developed in [14].

Io8/'/ @

6

5

q

3

2

14

/8

22

LogP

b

q

3-

22 I

/5

I

I

I

I

19

I

I

1

I

I

E

23

FIG. 1. Calibration curves for the gel chromatograph on coordinates log M-Ve (a) log P - V , (b); / - - P E , 2 - - P P .

Polydispersity of ethylene-propylene eopolymers

1727

T h e T a b l e gives t h e n u m b e r - a v e r a g e /sn, w e i g h t - a v e r a g e /~w a n d z - a v e r a g e /~z d e g r e e s of p o l y m e r i z a t i o n a n d t h e r a t i o b e t w e e n t h e s e v a l u e s for E P C o f differing c o m p o s i t i o n s y n t h e s i z e d on t y p i c a l s u p p o r t e d Ziegler c a t a l y s t s . I t can be seen t h a t t h e q u a n t i t i e s in question l a r g e l y d e p e n d on t h e c h e m i c a l n a t u r e of t h e t i t a n i u m c o m p o n e n t of t h e c a t a l y t i c c o m p l e x , w h i c h is b a s i c a l l y in agreeMOLECITLA.R W E I G H T CHAI~ACTERISTICS P.EL&TIVE TO COMPOSITION OF TYPICAL

~

ON

SUPPORTED

CaHB mole content,,O/o Catalyst

TiCI4 : MgO (I)

TiC'q, : AI,O,, SiOi (II)

TIC1, (III)

TIC%. ~A~C4 (IV)

in reaction in copozone lymer 0 10 33 56 84 97 100 84 92 97 100 43 58 78 93 66 89 97 100

0 1-3 5'5 16"2 44-0 79"0 100 30"0 45"0 72"0 100 15"1 27"0 43"5 75"5 30"3 63"3 86'0 100

ZIEGLER

pn ×

10-"/5 ×

5.70 2.62 1-29 0-92 0-67 0.32 0.27 0"22 0.17 0.12 0.11 0"81 0.32 0.21 0-10 0-52 0.37 0-17 0.12

EPC

PREPARED

OX

CATALYSTS

Ir / ~ . × 10 -~], X 1 0 - a

22.86 50.3 15.20 i 47.1 9.00 37.0 6.84 33.5 5.03 27.7 10.7 2.13 7-6 1-56

4.76 2.75 1.45 0.95 12.23 5.07 2.42 0.94 5.97 1-50 0.76

26.7 22.8 10.6 6.0 41-4 35.1 15.3 4.8 39.1

Pw

Pw

4.0 5-8 7-0 7.4 7.5 6.7 5.9 21.6 16.2 12.1 8.6 15.1 15.6 11.4 9.4 11.7 10.1 8.7 6.2

2.2 3.1 4.0 4.9 5-5 5-0 4.9 5.6 8.3 7.2 6.4 3.4 7.0 6.4 5.1 6.5 4.2 3.9 3.3

m e n t w i t h t h e results of a p o l y d i s p e r s i t y i n v e s t i g a t i o n c a r r i e d o u t for P E on s i m i l a r c a t a l y t i c s y s t e m s [15]. F o r i n s t a n c e , TiC14 on a n MgO surface leads to a m a r k e d r e d u c t i o n in t h e p o l y d i s p e r s i t y coefficient ( y = Pw/Pn)of t h e r e s u l t a n t E P C , w h e r e a s w i t h a l u m o s i l i c a t e u s e d as t h e s u p p o r t we h a v e a n increase in y. I t is n o t e w o r t h y t h a t t h e c h e m i c a l n a t u r e of t h e c a t a l y s t c o m e s to light n o t o n l y in t h e w i d t h of d i s t r i b u t i o n a c c o r d i n g to 19, b u t also in t h e c h a r a c t e r of t h e d i s t r i b u t i o n (the a s y m m e t r i c a l n a t u r e of curves of p o l y m e r i z a t i o n degree d i s t r i b u t i o n increases w i t h increasing difference in (/~w//~)-(/~z//~w)). T h i s is c l e a r l y a p p a r e n t on c o m p a r i n g differential curves o f d i s t r i b u t i o n a c c o r d i n g to log P for E C P s y n t h e s i z e d on s y s t e m s I - I V w h e n t h e c o m p o s i t i o n s of m o n o m e r m i x t u r e s in t h e r e a c t i o n zone are i d e n t i c a l (80 mole % p r o p y l e n e ) , as h a s b e e n d o n e in Fig. 2a. I t is seen f r o m t h e F i g u r e that. f u n c t i o n W - l o g P for E C P s p e c i m e n s s y n t h e s i z e d on i n i t i a l s y s t e m I I I is u n i m o d a l in c h a r a c t e r a n d h a s

4~

!

I

1

I

I

I

e.6 I

i I

I

e~

i

I

I

I

I

I

I'

I

O

0

b~

Polydispersity of ethylenc-propylene copolymers

2

q

1729

~.oyP

FIG. 2. Differential curves of distribution according to log P for EPC: a--ECP specimens synthesized with an 80 mole~o content of CsI-Ie in the reaction zone, using catalysts I (1), IV (2), III (3), II (4); b--EPC specimens synthesized with catalyst I with C8I-I6iI1 the react,ion zone=0 (•); l0 (2); 56 (3); 89 (4); 100 mole% (5); c--usirtg catalyst II with Catt 6 84 (1); 92 (2); 97 (3); 100 moleC~ (4). well defined high- and low-molecular "shoulders". A copolymer t h a t is markedly more homogeneous in respect to P is obtained under like copolymerization conditions using hydroxymagnesium catalyst I. Use of alumosilicate catalyst I I results in an EPC containing relatively large fractions of both low- and highmolecular copolymers, which points to a polymodal (or at least bimodal) mode of distribution according to log/~. Indirect information regarding the structure of active centres (AC) of polymerization of supported catalysts is obtainable by analyzing the experimental results alo~lg with a comparison of the data on the molecular structure of EPC formed in the presence of systems I-IV. I t is known [15, 16] t h a t the polydispersity of polyolefines (PC) is normally associated with heterogeneity of AC, and, in particular, with differing valence states of transition model atoms in the centres. On a previous occasion [17] it was found by chemical-analytical analysis t h a t TiC14 fixation on mineral oxide surfaces markedly inhibits processes of Ti reduction, which leads to Ti being attached to catalyst surfaces in valency states of "-k2", " - k 3 " and "+4" with a marked predominance of the trivalent state. Considering t h a t the a m o u n t of transition used in AC does not exceed 40% of the total a m o u n t of supported Ti [18], the problem of the valence state of Ti in AC remains unresolved.

1730

A.G.

RODIONOV e~ ed.

On comparing functions W = f ( l o g _P) for EPC prepared under identical conditions of copolymerization on supported catalysts I, I I and the typical catalyst IV, characterized in the present case ( A l : T i = 2 . 0 , ssp=44.0 m2/g) b y an insignificant reduction in the initial trivalent Ti it would appear that the AC in catalyst I contain almost entirely Ti ~+ (according to the results of chemico-analytical investigations the amounts held on the MgO surface were, in the case of A1 : T i = 1 5 : 1, 16% Ti 4+, 80% Ti a+ and 4% Ti2+), whereas there is much less uniformity in the AC of catalyst II (on the A120~, SiO2 surface, with A1 : T i = 1 5 : 1 we have 15% Ti 4+, 56% Ti 3+ and 290/o Ti~+). Since the high molecular weight "shoulder" in the polymerization degree (_P) distribution for the EPC synthesized on catalyst IV is most probably related to the presence of AC containing Ti ~+, we surmise that there will be a considerable number of these centres in catalyst II. It is seen from the tabulated data that an increase in the propylene concentration in the reaction zone leads to a marked reduction in P~, Pw and /~z, which is accounted for primarily b y the very significant (more than 2 orders) reduction in the propagation constant on going from ethylene to propylene [18]. Unfortunately the method we used does not allow a sufficiently accurate analysis of the polydispersity of P E and EPC specimens containing a low propylene concentration, and prepared in the presence of catalysts I I - I V and characterized b y ll4v 2 × l0 s. For the same reason there is a marked distortion of the W-log P plot for P E synthesized on catalyst I, and the value of ~= 4.0 is apparently underestimated. In the present work our aim was also to analyze the mechanism underlying the action of the catalysts of interest, and we deliberately refrained from using standard molecular weight regulators for polyolcfines, e.g. H~, since it is known [15] that the latter m a y also affect MWD. Nevertheless on the basis of the information obtained we conclude that in the case of catalysts I I - I V ~ is reduced as the propylene concentration in the reaction zone is increased. The data for catalyst I differ somewhat compared with I I - I V ; in the case of I there is a maximum in the relationship between polydispersity of the EPC and increase in the propylene concentration. Admittedly, there is a small (not more than 25%) difference in ~ for EPC of differing compositions, b u t this will not support any definite conclusion as to its character, particularly as the fact that the polymerization distribution curves for the copolymers are identical (Fig. 2b) points rather to an absence of any relationship between ~ and the composition of the monomer mixture. From the point of view of the copolymerization mechanism these findings point to an absence of change in the chemical nature of AC of catalyst I on going from ethylene to propylene, and mean that there is complete accessibility of centres for the comonomers, which tallies with the results reported in [18], showing that with the group of monomers ethylene, propylene, butene-1 and hexene-1 there is no relationship between the number of AC of supported catalysts and the chemical nature of t h e monomers.

Potydispersity of ethylene-propylene eopolymers

1731

On the other hand, the narrowing of polydispersity observed for the EPC prepared on catalysts I I - I V accompanying an increase in the propylene concentration in the reaction zone is, in all probability, due to a reduction in the number of AC t h a t are accessible for propylene molecules. Certainly, in contradistinction to the typical catalyst IV, for which J u n g and Schnecko [19] found that the steady-state concentration of AC is reduced in the series of monomers ethylene, propylene and butene-1, this effect for catalyst II, like catalyst I, has not been observed [18]. We accordingly surmise t h a t the accessibility of AC of an alumosilicate catalyst is reduced, as polymer accumulates in catalyst pores, owing to diffusion hindrances. The probability of AC being accessible in this situation is much greater for ethylene molecules t h a n for propylene, which could account for the marked selectivity of the latter catalyst towards ethylene, and could also explain the formation of eopolymers with a microblock structure when this catalyst is used (the product of the copolymerization constants considerably exceeds unity [8]). Is is clear from the polymerization distribution curves for ECP specimens of differing compositions and for PP, prepared on catalyst I I (Fig. 2c) t h a t in the case of these polymers the polydispersity change takes place mainly at the expense of a reduction in the amount of the high molecular fraction. We therefore conclude, in the light of the experimental results, t h a t the chemical nature of the support in supported ZiegIer catalysts determines so important a parameter of molecular structure of EPC as is represented b y the MWD. The authors wish to thank I. A. Voloshin for kindly providing the P P specimens t h a t were used to calibrate the gel chromatograph. Translated by R. J. A. ]-~ENDRY REFERENCES 1. A. L. GOL'DENBERG, N. N. SEVEROVA, K. I. KOSMATYKI-I, L N. ANDREYEVA, A. M. LOBANOV and B. V. YEROFEYEV, Izv. Akad. Nauk BSSR, Seriya khimieh. nauk. No. 1, 29, 1973 2. Yu. G. KAMENEV, V. P. MIRONYUK, V. A. GRECHANOVSKII and I. A. LIVSHITS, Kauchuk i rezina, No. 6, 13, 1973 3. N . N . SEVEROVA, Ye. I. NALIVAII(O, Ye. V. VESELOVSKAYA, A. L. PECHENKIN and I. N. ANDREYEVA, Kompleksnye metalloorganicheskiye katalizatory polimcrizatsii olefinov (Complex Metalorganic Catalysts for Polymerization of Olefines). No. 6, 139, 1977 4. V. A. KLYUSHNIKOV, N. N. SEVEROVA, K. I. KOSMATYKH, N. M. DOMAREVA, N. A. DOMNICHEVA, L N. ANDREYEVA, A. I. BARKOVA, Z. V. ARI(HIPOVA and L. F. SHALAYEVA, Plast. massy, 7, No. 1, 1969 5. M. TODER, E. ALEXIU and P. BADER, Mater. plast. B15: No. 3, 116, 1978 6. Yu. G. KAMENEV, I. A. LIVSHITS, V. I. STEPANOVA, V. A. GRECHANOVSKII and R. V. KALMYKOVA, Vysokomol. soyed. A16: 2141, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 9, 2483, 1974) 7. A. G. RODIONOV, A. A. BAULIN, A. L. GOL'DENBERG, Yu. M. ZAVYALOV, I. N. ANDREYEVA and S. S. IVANCHEV, Plast. massy, 1~o. 4, 11, 1979

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V . V . KOI~SHAK et al.

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Polymer Science U.S.S.R. Vol. 23, 1~o. 7, pp. 1732-1741, 1981 Printed in Poland

0032-3950/81/071732-10507.50/0 © 1982 Pergamon Press Ltd.

INFLUENCE OF UNIT TYPE INHOMOGENEITY OF THE THERMAL STABILITY OF POLYIMIDES* V. V. KORSHAK, S.-S. A .

PAVLOVA, P.

N . GRIBKOVA,

I. V. VLASOVA, YA. S. VYGODSK1T a n d S. V. VI~OGRADOVA A. N. N e s m e y a n o v I n s t it u t e of Hetero-organic Compounds, U.S.S.R. Academy of ScienCes

(Reoeived 14 M a y 1980) A study has been made of the thermal, hydrolytic and oxidative stability of compounds simulating both the main structure of polyimides, and possible versions of anomalous structures. The investigation was conducted in the temperature range 300-550 ° . I n the case of the model compounds examined the t h er m al stability is highest under all the factors investigated for N-phenylphthalimide, and lowest for N-phenylphthalisoimide. * Vysokomol. soyed. A23 No. 7, 1568-1575, 1981.