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Correlation between the reduction of titanium in ziegler catalysts and catalytic activity in polymerization of ethylene
Catalytic activity in polymerization of ethylene
13. 14.
15. ][6.
2~
A. V. UVAROV, Vysokomol. soyed. A18: 1951, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 9, 2227, 1976) G. V. BENIG, Nenasyshchennye poliefiry, stroyeniye i svoistva (Unsaturated Polyester, Structures and Properties). p. 74, Izd. "Khimlya", 1968 A. M. RYKE and W. PRINS, J. Polymer Sci. 59: 171, 1962 V. Ira. DAVYDOV, A. V. KISELEV and T. V. SILINA, Kolloidn. zh. 36: 945, 1974 A. A. TAGER, Fizlko-khimiya polimerov (Physmo-chemistry of Polymers). p. 501, Izd. "Khimiya", 1968
]Polymer Science U.S S.R. Vol. 22, pp. 205-214. Pergamon Press Ltd. 1980. Printed in Poland
0032-3950/80/0101-0205507J0
CORRELATION BETWEEN THE REDUCTION OF TITANIUM IN ZIEGLER CATALYSTS AND CATALYTIC ACTIVITY IN POLYMERIZATION OF ETHYLENE* _h. A. BAULnV, YE. I. NOVIKOVA, G. YA. MAL'KOVA, V. L. I~[_AKSIMOV, L. I. VYSHI~CSKAYA a n d S. S. IVA~CHV,V Scientific Industrial Association "Plastpolymer", Okha
(Received 20 November 1978) Using results of experimental determination of the valence state of titanium in Ziegler catalysts a study was made of the correlation between the reduction of titanium applied on the surface of carriers ~dth alkyl alumininm and the activity of catalytic systems formed and kinetic mechanisms of polymerization of ethylene in the presence of these systems. I t was shown that securing components of Z,egler catalytic systems that contain titanium on the surface of carriers and selecting a carrier ~)f requisite chemical composition enable the extent to which transition metals are reduced by alkyl aluminium to be lowered considerably and the stability of active complexes of polymerization, increased. ][-IIGHLY effective Ziegler c a t a l y s t s on carriers which, as i n d i c a t e d p r e v i o u s l y [1-3], u n d e r s u i t a b l e conditions of p o l y m e r i z a t i o n e n a b l e 30-350 t i m e s h i g h e r P E yield to be o b t a i n e d in u n i t w e i g h t o f t r a n s i t i o n metals, c o m p a r e d w i t h classical Ziegler c a t a l y s t s , h a v e b e e n used i n c r e a s i n g l y d u r i n g p a s t y e a r s for t h e : p r e p a r a t i o n of polyolefms. I t w a s e s t a b l i s h e d in these stndies t h a t t h e carriers u s e d m a y f u n c t i o n n o t s i m p l y as a n i n e r t s u b s t r a t e (such as for e x a m p l e a l u m i n o silicate w h i c h m e r e l y increases t h e a r e a o f d i s t r i b u t i o n of t h e t i t a n i u m c o m :ponent), b u t h a v e a surface a c t i v a t i n g effect on t h e r e a c t i v i t y o f a c t i v e centrea, e.g. m a g n e s i u m oxide a n d a n h y d r o u s m a g n e s i u m chloride [2, 3]. * Vysokomol. soyed. A22: No. I, 181-188, 1980.
~}6
A . A . BA~LIN et a/.
Processes of formation, functioning and deactivation of active centres o f Ziegler catalytic systems of polymerization of olefins are known to be closely linked with processes of reduction of transition metal compounds by organi~ alumininm compounds (OAC), particularly with a reduction in the valency o f transition metals [4]. This paper examines the reduction of titanium tetrachloride secured on the surface of the inorganic carriers mentioned, OAC, as related to the catalyti~ activity of these catalysts in ethylene polymerization. Methods of preparing catalysts on oxide carriers are described in a separate paper [5]. The catalyst on a carrier, anhydrous magnesium chloride, was prepared b y grinding a giver~ a m o u n t of methoxytitanlumtrichloride with MgCI~ at 40-50 ° m a metal ball mill. All opera° tions concermng the preparation and study of catalysts were carried out in purified argon. The overall content of t i t a n i u m T1 (IV} in catalyst samples was determined p h o t o ° metrically, the optical density of the Ti (IV) complex with diantipyrylmethane being m c a s ured in hydrochlorm acid with a wave length ~ - 4 3 2 nm. Interaction of t i t a n i u m catalysts (0.05-1-0 g sample, according to Ti content in the* catalyst) with OAC was carried out without ethylene in a glass vessel while stirring u n d e r conchtions similar to those of polymerization, in n-heptane (0.05 1.) with given molar ratios~ of components of the catalytm system, temperature and reactmn time. The concentratior, of t i t a n i u m was maintained constant in all expemments ( ~ 1.0 × 10-3 mole/1.1. T i t a n i u m content in oxidation of Ti (III) and Ti (II} was determined b y methods m o dified b y the authors [6]. I n the first experunent b y adding 5 ~ HC1 solution and a saturated[ solution of (1VH,)zSO4 to the ester-heptane suspension of the reaction mixture Ti (II} was~ converted to Ti (III}. Then, b y adding 0.1 ~ solution of ferric a m m o n i u m sulphate Ti (III~ was oxidized to Ti (IV) and the Fe (III) excess titrated with a 0.1 ~ solutmn of Trilon B i n the presence of sulphosalicylic acid as indicator. I n the second expemment b y adding a 0.1 N solution of ferric a m m o n i u m sulphate to the ester-heptane suspension of the reactior~ mi~rture Ti (II) and Ti (III) were oxidized to Ti (IV) a n d the Fe (III} excess titrated th~ aame way as in the first experiment. The content of Tl (II) was calculated from the differ° ence in the amounts of ferrm a m m o n i u m sulphates used for oxidation of t i t a n i u m in the* second and first experiments. Ti (III) content was calculated from the difference of the* double a m o u n t of alums used in the first experiment and the a m o u n t of alum used in the* second experiment. Methods of investigating interaction between t i t a n m m catalysts and OAC b y E P R , determining specific surface 8sp of catalysts, p.urifymg reagents to remove impuritms that, inhibit polymerization and examming polymerization kinetics of ethylene were described[ previously [1].
Table 1 shows the yield of PE prepared using unit weight of titanium irk polymerization with classical (without carriers) and Ziegler catalysts and Figs. 1 - ~ (curve 1) indic/ate the general form of corresponding kinetic curves of polymerization expressing the dependence of the effective rate constant of the gross reaction of polymerization kef~ on the time of polymerization, ket~ Values were calculated as before [1] and reduced to unit weight of the entire solid catalyst; this enabled the difference in the type of variation of the rate of ethylene polymerization to be shown in a single figure for the CHsOTiC18-AI(C~H~)8 catalytiet t~ystem (without a carrier) and for the same catalytic system but on an anhyd°
Catalytic activity in polymerization of ethylene
201
rous MgCls carrier, which is characterized b y an activity 350 times "higher a n d reduced to unit weight of titanium. Experimental results indicate that applying components of Ziegler catalytie systems on carriers enables not only polymer yield to be increased considerably, b u t produces significant differences in kinetic mechanisms of polymerization, compared with processes taking place on conventional Ziegler catalysts. As see~ in Figs. 1 and 2, polymerization of ethylene in the l~resence of typical Ziegler catalytic systems based on tetravalent titanium compounds (TiCl~ and CHsOTiCls) TABLE
l.
.ACTIVITY
OF C O N V E N T I O N A L A N D
APPLIED
ZIEGLER
CATALYTIC
SYSTEMS
II~"
ETHYLEI~J~ P O L Y M E R I Z A T I O N
(Cocatalyst AI(C2Hs)s, pc*v=4arm, 70°, solvent n-heptane (0.1 1.))
Catalyst tic1, ~-TiCls. 0"3A1C1, ~HsOTiCls ric1,/A1,Os, SiOs riCl,/MgO ric1,/MgO ]~iCl,/MgO ~HaOTiCI,/MgClm
, Ti content wt. %
[
25"2 22"7 25"8 3"71 0"80 0"60 0"27 0"23
PE yield A1/Ti, in 100 Ssp, m2/g [Cat], g/1. [OAC],g/1. mole/mole rain, kg/g Ti 44.0 Not determined 218 31.0 33.0 14.5 5.5
0.049 0-128 0.105
0.432 0.516 0"253
14-7:1 7.6:1 3-9:1
0.151 0.103 0-104 0.180 0.202
0-201 0.295 0-204 0.205 0.224
15"1:1 150:1 138:1 178:1 203:1
5"34 6"62 1"8~. 16"~ 192 237 441 632
* ~ o , - - o v e r a l l pressure in the reactor.
and triethylaluminium at a temperature of 70 ° is clearly non-stationary, the r a t e of polymerization decreasing over 20 fold in 2 hr, as compared with the maximun~ value, for a TiC14-(C~H~)3 system. As shown b y Fig. 1, securing this catalytic system on an aluminosilicate carrier enables under adequate conditions, th~ process to be carried out at a fixed rate, the form of the kinetic curve, which has an "acceleration" section being similar to the kinetic curve of polymerization in the presence of a catalytic system based on titanium trichloride. The 15"net]e curve of polymerization is also similar for the CttsOTiC18/MgC12-AI(CsHs) s system, except for the fact that the initial section of this curve is not extrapolated to zero. The dependence of the rate of polymerization on time is more complicated for the TiC14/MgO-A1 (C2Hs)s system, characterized b y two stationary "seetions", the initial one corresponding to maximum catalytic activity. I t is remarkable that if for a non-stationary system of TiCI4-AI(C2Hs) s the rate o f polymerization decreases 20 fold, for applied catalytic systems of TiCldMgO-AI(CsHs) s containing 0.2-1.0~/o wt. Ti, this rate only decreases 2-3 times. For magnesium oxide and ab~minosilicate carriers it m a y be assumed that
~ovalent bonds are formed of Ti(IV) with the surface of carriers, since the TiC14 applied is secured b y protonolysis with the participation of hydroxyl surface groups; according to results of I R spectroscopy, the band intensity of bond stretching vibrations of OH groups at 3670 cm -1 (for aluminosilicate) and 3450 -~m -1 (for magnesium oxide) decreases considerably on applying titanium t e -
5-
S
30
"
: " " : : =2
/ I0
~
2
1 0
~/0 80 Time, rain
FIG. 1
I-
120 .
1
0
#0 8Q T i m e , rain
FIG. 2
120
i
:FIG. 1. Kinetic curves of polymerization of ethylene on various catalysts activated with "~riethylaluminium: 1--TIC14; 2--~-TiC1,.0.3 A1C1,; 3--TiC14/A1,O,, SiO,. Conditions of polymerization for Fzgs. 1-3 are the same as shown in Table 1. :FIG. 2. Effect of an MgCI= carrier on the activity and stability in polymerization of ethyl. ~ene of catalytic systems based on methoxytztanium trichloride: 1--CH,OTiCla-AI(C=Hs)8; 2-- CH=OTzC13/MgC1,-AI(C~H~)3. trachloride on these carriers [7]. For a MgCl~ carrier the problem of securing ~nethoxytitanium trichloride has not been studied, however, there is no doubt a s to the presence on its surface of titanium with a degree of oxidation of + 4. I t ~ a s established b y preliminary experiments that the entire titanium fixed on the surface of all the carriers examined (including MgC]2) is in the tetravalent ~tate before interaction with OAC. This is confirmed b y the absence of the E P R •~ignal for all catalysts untreated with OAC and the absence of using ferric am~nonium sulphate during interaction with catalyst samples before the addition ~f OAC. Table 2 shows experimental results of the quantitative determination of tit a n i u m of various valence states in the catalytic systems examined using a chemical analytic method and the content of trivalent titanium was detected l~y E P R . For a more complete study of the effect of carrier (and its properties) o n the valence state of fixed titanium, the interaction of the titanium containing c o m p o n e n t with OAC was carried out under "milder" conditions than during polymerization--at room temperature and using diethylaluminium chloride ~(DEAC), a reducing agent which is weaker than A/(C=Hs) s.
Catalytic activity in polymerization of ethylene
20t)
Analysing results of Table 2 it is essential to note t h a t the quantitative determination of titanium in different valence states at a certain m o m e n t in time is not a simple experimental problem. Results in the literature concerning tyl~ical Ziegler systems of TiC14-OAC type obtained b y various authors therefore often show considerable variation. According to results obtained by Kern and Hurst, who used a combination of methods of chromatographic and gravimetrie analyses of products formed in the system of TiC14-AI(C~Hs) 3 at 26 ° and a period of interaction of components of 30 rain, the entire titanium is in the bivalent state with a molar ratio of A1/Ti of 3 : 1 [8]. According to results of Kollar eta/., who used a chemico-analytical method, under adequate conditions it is only ~ 10% titanium which is reduced to Ti (II) in this system [9]. Table 2 indicates t h a t our results for the catalytic system examined show a higher degree of agreem e n t with results of the study mentioned [9].
~ 3OO
kerr,L/mole T/.sec 500
!
0
40
8O
IEO
Time, rnin ~FIO. 3. Effect of "ageing" at 70° and a molar ratio of AI/Ti of 75 : 1 on the activity in polymerization of othylene of the catalytic system of TiC1JMgO (0.60% Ti)Al(CsHl)a: 1--without "ageing"; g--1.5; 3--3; 4--5 hr. According to our experiments, in typical Ziegler systems the proportion of titanium reduced, other conditions being the same, depended not only on the molar ratio of AI/Ti, but also on effective concentrations of OAC and TiCl 4 themselves (with identical Al/Ti ratios). In all experiments concerning determination of Ti (III) and Ti (II) we therefore maintained a constant concentration of the initial titanium, while the A1/Ti ratio showed a proportional variation for the pair of titanium compound--applied catalyst, based on this compound. Results of Table 2 enable us to draw the following eonelusions: 1) the degree a n d rate of reduction of titanium using OAC decrease considerably on being secured on the surface of carriers; 2) the degree of reduction of Ti depends on
A . A . BAITLHV 6f ed.
210
the type of caxrier ~sed-for using aluminosilicate.
c a r r i e r s c o n t a i n i n g m a g n e s i m n i t is l o w e r t h a n o n
I n f a c t , a c o m p a r i s o n , f o r e x a m p l e , o f N o s . 4 a n d 17 i n T a b l e 2 i n d i c a t e s t h a t a t 25 ° a n d a m o l a r r a t i o o f A I / T i o f 40 : 1 ( r e d u c i n g a g e n t D E A C ) d u r i n g a p e r i o d o f i n t e r a c t i o n o f c o m p o n e n t s o f 15 r a i n o n e t e n t h o f T i ( I V ) a t o m s o f t h e CH3OTiC13/ TABLE 2. EFFECT OF CARRIER ON THE EFFECTIVENESS OF REDUCTION OF Ti (IV) usiNG OAC, ACCORDING TO I~ESULTS OBTAINED BY .% CHEMICO-ANALYTICALMETHOD AND E P R
IAl/Ti, No.
Catalyst
TIC1,
OAC
T,°C
1 3
15 1
25 25 70
6( 6£
47 74 11
-24 88
DEAC TEA
40:1 4:1
25 70
6C
100 23
77
100 100
DEAC TEA
1:1 3:1 10:1 15:1 1:1 3:1 10:1 15:1 150:1 150: 1[ 150 : 1
25 25 70 70 25 25 70 70 70 70 70
6(] 6(}
9 68
---
9 68
60 60 60 60 60 60 5 50
56 66 3 36 77
29 27 --3
85 93 3 36 80
80
4
84
11
35
-9 13
6 12
1 )0
82 80
35 91 93
40:11
25 70 70
15 ~0 50
10 68 81
--16
10 68 97
7'
6
7
TiCldA120 *, SiO~ (3.71% Ti)
8 9
10 11 12
~9
TiC1,/MgO (0.80%
Ti)
13 14 15 16
17 18 19
DEAC TEA 7'
CH,OTiC18/MgCI, (0"23% Ti)
Ti(III), content~ % of Ti(IV) ace. to EPR
mole/ /mole
DEA£ TEA*
CHsOTiCla
Content of reduced Ti, % of initial Time TI(IV), according to of in- results of chemicotorac- analytical method tion, T1 rain Ti Ti (III) (III) (II) -{-Ti (II)
DEAC TEA
1 1
6(
--
47 98 99
Not deter. mined
5 58 49 60 2 $
• T]gA~AI(C,H.).. ]MgC1 z c a t a l y s t w a s r e d u c e d t o t h e t r i v a l e n t s t a t e , w h e r e a s i n t h e c a s e o f t h e initial methoxytitanium triehloride under the same experimental conditions the e n t i r e T i ( I V ) w a s r e d u c e d t o T i ( I I I ) . W h e n u s i n g TiC14 a n d a s t r o n g e r r e d u c i n g a g e n t , AI(C~Hs)a, p r a c t i c a l l y 9 0 % T i w a s i n t h e b i v a l e n t s t a t e a f t e r 1 h r i n t e r a c t i o n o f c o m p o n e n t s a t 70 ° a n d a n A l / T i r a t i o o f 15 : 1, w h e r e a s i n t h e c a s e o f
Catalytic activity in polymerization of ethylene
211
the same system less t h a n one third of titanium was reduced to Ti (II) under the same conditions on an aluminosilicate carrier, while on using an l~IgO earrier this figure was only 4% titanium (Nos. 3, 9 and 13). Table 2 shows that for applied catalysts the total of Ti(III)-~Ti(II) m a y be less than 100% of the initial Ti (IV). The joint existence in a homogeneous system of Ti (IV) and Ti (II) is unlikely since Ti (IV) is an oxidizing agent for Ti (II) [i0]. Results indicate that fixing transition metal complexes on the surface of carriers reduces the probability of bimoleeular interaction. I t is interesting that results of quantitative E P R determination of Ti (III) on the sulfface of carriers containing magnesium do not agree with results of chemico-analy~ical determination (Table 2). E P R on the surface of carriers, MgC12 and MgO could not, normally, record more than 5-12% Ti (III) of the entire Ti applied even under the "strictest" conditions of reducing Ti (IV), which is lower by one order of magnitude than the amount of Ti (III) determined by a chemico-analytical method. When using an aluminosilicate carrier up to 90% Ti (III) detected by a chemico-analytieal method could be recorded by EPR. Results obtained for titanium-magnesium catalysts, the same way as results of :EPR investigation of TiC13 formed in TiCI4-OAC systems, are evidently explained by two possible causes: 1) a significant part of Ti (III) is in the dimer form, which does not give an E P R signal; 2) the E P R signal is poorly recorded as a consequence of the very rapid spin-lattice relaxation of Ti (III) ions [11]. A comparison of structural parameters of applied catalysts indicates that the specific surface of all catalysts (Table i) is known to be adequate for the accomodation of the entire titanium by the monomolecular layer (calculations were carried out the same way as previously [1]). Bearing in mind the prevailing equivalent pore radius of catalysts or~ aluminosilicate (80-90 A) and magnesium oxide of variable pore structure (125-1500/~) [I] it m a y be concluded t h a t there is no difference in the "accessibility" of titanium held on the surface of these catalysts for OAC molecules, i.e. the chemical properties of the carrier and not structural characteristics have the prevailing influence on the effectiveness of reduction processes of transition metals. These effective pore dimensions which are sufficient for fixing several TiCl~ molecules in a single pore do not give a clear explanation of the possible assumption that a considerable part of Ti (III) atoms on the surface of a titanium aluminosilicate catalyst is present in the form of isolated ions determined by EPR, in contrast with titani~tm-magnesium catalysts, on the smfface of which Ti (III) is in the form of "dimers" which do not give an E P R signal. To solve the problem of possible variable spin-lattice relaxation of Ti (III) ions held on the surface of titanium aluminosilicate and titanium-magnesium catalysts, i.e. the problem of variable symmetry of eoml~lexes formed with Ti (III), E P R spectra have to be recorded at temperatures lower than m 196 ° (the lowest temperature used by the authors). Nevertheless, even at this stage of investigations information was obtained
212
A.A. BArium ~ a/.
b y E P R which points to the "ligand" role of carriers in the processes examined. :For example, in the case of an applied catalyst, CttsOTiC18/]KgC1~ treated with DEAC under conditions No. 18 of Table 2, the E P R spectrum is a single line 136 Oe in width with a g-factor of 1.960, and in the case of a system without a carrier, CH3OTiCI3-AI(C~H6)~CI and the same experimental conditions, the line width of the E P R spectrum is 75 Oe, the g factor being 1.995 (in both cases E P R spectra were recorded at --196°). Spectroscopic characteristics obtained point to heterogeneous ligand environment of paramagnetic Ti (III) atoms in both systems. Chemical fixing of the complex containing titanium on the surface of t h e carrier may, in our opinion, lower the effect of titanium reduction using OAC not only as a result of reducing the proportion of possible bimolecular dis:proportionation of unstable alkyl titanium [121 formed in Ziegler systems, but also as a result of changing electron cha~act3ristics of the transition metal in a complex with the carrier. It is precisely the latter condition, which may explain t h e effect of the chemical structure of the carrier on the efficiency of these proc~les. -~ To complete the analysis of titanium reduction, we found it interesting to study polymerization kinetics of ethylene using OAC previously "aged", treated nnder different conditions, i.e. a catalyst on the same carrier. Figure 3 shows kinetic curves of polymerization on a TiCId/MgO catalyst sealed in an ampoule together with AI(CsHs)a with a molar ratio of Alfri of 75 : 1 and "kept" at 70 ~ for a varying length of time* until breaking this ampoule (at the beginning of polymerization the ampoule containing the new batch of AI(CsHs)8 was also broken in the reactor; the overall molar ratio of A1/Ti was brought to 150 : 1). ]Figure 3 shows that the form of kinetic curves of polymerization using an "aged" catalyst (curves 2-4) differs considerably from that of a catalyst activated with triethylaluminium by conventional methods at the beginning of polymerization (curve 1). Curves 2-4 are characterized by a brief section of increased velocity (not extrapolated to zero)', a section of stationary velocity (the longer the "ageing" time of the catalyst the shorter this section) and a section of reduced rate of l~olymerization. The maximum rate of polymerization using an "aged" catalyst containing titanium from the very beginning of the process with a degree of oxidation of less than four (according to results of Table 2, the average degree of oxidation ~ 3 ) , is ~ 5 times lower than that for a "non-aged" catalyst. This result clearly shows the link between processes of reduction of titanium using OAC and the deactivation of the catalytic system. A reduction in the activity of catalysts subjected to "ageing" by the methods described may, no doubt, be explained not only by the reduction in the valency. of titanium in the active centre, but also the accumulation in the reaction zone of products of interaction, e.g. alkylaluminium halides, in the presence of which * Bearing in mind the time the ampoule is kept in the polymerization reactor, which evaeusted in these experiments at 70°.
Catalytic activity in polymerization of ethylene
213
t h e rate of polymerization is much lower using the titanium-magnesium catalysts
examined t h a n in the presence of trialkyl OAC [13]. Specific properties of interaction of these products with the active catalytic centre m a y explain the experimental fact t h a t rates of polymerization on a catalyst previously "aged", for example, for 1.5 hr do not reach rates of polymerization achieved in 1.5-2 h r ol~ a catalyst activated with triethylaluminium at the very beginning of tho process (Fig. 3). I t was shown in previous studies [2, 3] t h a t the concentration of active centres on the surface of the catalysts described using carriers of magnesium oxide a n d aluminosilicate, corresponding to a stationary rate of polymerization at 70 °, is ~20~/o of the entire amount of titanium contained. A comparison of this valuse with results concerning the valency state of Ti in, these catalysts u n d e r conditions corresponding to conditions of stationary polymerization of e~hylen~ in their presence (l~os. 9 and 14 in Table 2 and in Figs. 1 and 3 (curve 1)) inclic~tes that there is no direct correlation between the amount of titanium reduced a n d the concentration of active centres (for a catalyst on iVIgO there is 35 wt. o/~ Ti (III), and a catalyst on aluminosilicate, 66 wt. ~ Ti (III) and 27 wt. ~/o Ti (II} of the initial Ti(IV)). On the other hand, results examined in this paper indicating t h a t the degree of reduction of titanium held on magnesium oxide is lower t h a n on alurninosilicate, are in satisfactory agreement with results of studying MWI) of P E synthesized on these catalysts. We have shown [14] t h a t PE obtained under identical conditions of polymerization on a titanium-magnesium catalyst is characterized by a coefficient of polydispersion of 3, while on a titanium aluminosilicate catalyst, b y a coefficient of po]ydispersion of 10 [14]. This points to increased homogeneity of active centres on the surface of a magnesium.containing carrier. Experimental results therefore indicate t h a t securing the titanium containing component of Ziegler catalytic systems on the surface of carriers and selecting a carrier of the appropriate chemical structure enable the degree o f reduction of the transition metal b y alkyl aluminium to be lowered considerably a n d the stability of active complexes of polymerization, increased. Translated by E. SEM/~RF~ REFERENCES 1. A. A. BAULIN, A. S. SEMENOVA, L. G. STEF.A.NOVICH, N. M. CttIR~OV and A. V. STAFEYEV, Vysokomol. soyed. A16: 2688, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 12, 3130, 1974) 2. A. A. B&ULIN, V. N. SOKOLOV, A. S. SEMENOVA, N. M. CHIRKOV and L. F. SHALAYEVA, Vysokomol. soyed. A17: 46, 1975 (Translated in Polymer Sci. U.S.S.R. 17:
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YE. YA. DAVYDOV et al.
4. N. M. CHIRKOV, P. Ye. MATKOVSKII and F. S. D'YACHKOVSKII, Pohmerizatsiya n a kompleksnykh metalloorganicheskikh katalizatorakh (Polymerization on Compotato Organo-metallic Catalysts). Izd. Khimlya, 1976 5. A. A. BAULIN, S. S. IVANCHEV, L. D. UZHINOYA, N. A. PLATE, I. N. ANDREYEVA and L. A. MASHKOVA, Auth. Cert. 614115, 1977; Byull. lzobr. No. 25, 103, 1978 6. Ye. G. TABAKOVA and Z. V. SOLOV'YEVA, Zavodsk. lab. 22: 1417, 1956 7. A. A. BAULIN, S. S. IVANCHEV, V. L. MAKSIMOV, S. Ya. K H A I K I N and Ye. I. NOVIKOVA, Materialy Vsesoyuznogo soveshchaniya "Smtez i kataliticheskiye svoistva kompleksov perekhodnykh metallov, zakreplennykh n a poverkhnosti nositelm" (Proceedings of the All-Union Conference "Synthesis and Catalytic Properties of Transition Metal Complexes held on the Surface of Carriers"). Novosibirsk, 1977 8. R. S. KERN and H. G. HURST, J. Polymer Sei. 44: 272, 1960 9. L. KOLLAR, A. SIMON and J. OSVATH, J. Polymer Sci. 6, A - l : 919, 1968 10. G. SHARLO, Metody analiticheskoi khimii (Methods in Analytical Chemistry). vol. 1, Khimiya, 1969 -11. Ye. N. ADEMA, N. J. M. BARTELINK and J. SMIDT, Rec. tray. chim. 81: 73, 1962 12. Ye. Ye. VERMEL', N. G. MAK,~IMOV, V. M. MAST1KHIN, S. G. ARTAMONOVA, V. F. ANUFRIYENKO and V. A. Z ~ g H A R O V , Kinetika i kataliz 16: 1015, 1975 13. A. G. RODIONOV, A. A. BAULIN, A. L. GOL'DENBERG, Yu. M. ZAV'YALOV, L N. ANDREYEVA and S. S. IVANCHEV, Plast. massy, No. 4, 11, 1979 14. A. A. RAULIN, L. F. SHALAYEVA and S. S. IVANCHEV, Dokl. A N SSSR 231: 413, 1976
:Polymer Science U S.S.R. Vol. 22, pp. 214-222. O Pergamon Press Ltd. 1980. Printed in Poland
0032-3950/80/0101--0214507.5010
FREE RADICAL CONVERSIONS OF TWO COMPONENT POLYURETHANES BY THE ACTION OF LIGHT * Y E . YA. DAVYDOV, YE. V. DAVYDOVA, M. I . KARYAKI~A, V. V. LUK'YAI~OV, G. B. PARIISKII a n d D. YA. TOPTYGII~ I n s t i t u t e of Chemical Physics, U.S.S.R. A c a d e m y of Sciences State Scientific Research and Design I n s t i t u t e for the P a i n t and Varnish I n d u s t r y
(Received 21 November 1978) Various physico-chemical methods were used to investigate photo-oxidation a n d photolysis (initiated b y ferric chloride additives) of erosslinked polyurethanes based on h y d r o x y l containing branched oligoesters of different chemical structures. The t y p e of macroradical was established and a kinetic s t u d y made of d a r k and photochommal degradation.
* VyE~okomol. soyed. A22: ~ o . 1, 189-195, 1980.
13. 14.
15. ][6.
2~
A. V. UVAROV, Vysokomol. soyed. A18: 1951, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 9, 2227, 1976) G. V. BENIG, Nenasyshchennye poliefiry, stroyeniye i svoistva (Unsaturated Polyester, Structures and Properties). p. 74, Izd. "Khimlya", 1968 A. M. RYKE and W. PRINS, J. Polymer Sci. 59: 171, 1962 V. Ira. DAVYDOV, A. V. KISELEV and T. V. SILINA, Kolloidn. zh. 36: 945, 1974 A. A. TAGER, Fizlko-khimiya polimerov (Physmo-chemistry of Polymers). p. 501, Izd. "Khimiya", 1968
]Polymer Science U.S S.R. Vol. 22, pp. 205-214. Pergamon Press Ltd. 1980. Printed in Poland
0032-3950/80/0101-0205507J0
CORRELATION BETWEEN THE REDUCTION OF TITANIUM IN ZIEGLER CATALYSTS AND CATALYTIC ACTIVITY IN POLYMERIZATION OF ETHYLENE* _h. A. BAULnV, YE. I. NOVIKOVA, G. YA. MAL'KOVA, V. L. I~[_AKSIMOV, L. I. VYSHI~CSKAYA a n d S. S. IVA~CHV,V Scientific Industrial Association "Plastpolymer", Okha
(Received 20 November 1978) Using results of experimental determination of the valence state of titanium in Ziegler catalysts a study was made of the correlation between the reduction of titanium applied on the surface of carriers ~dth alkyl alumininm and the activity of catalytic systems formed and kinetic mechanisms of polymerization of ethylene in the presence of these systems. I t was shown that securing components of Z,egler catalytic systems that contain titanium on the surface of carriers and selecting a carrier ~)f requisite chemical composition enable the extent to which transition metals are reduced by alkyl aluminium to be lowered considerably and the stability of active complexes of polymerization, increased. ][-IIGHLY effective Ziegler c a t a l y s t s on carriers which, as i n d i c a t e d p r e v i o u s l y [1-3], u n d e r s u i t a b l e conditions of p o l y m e r i z a t i o n e n a b l e 30-350 t i m e s h i g h e r P E yield to be o b t a i n e d in u n i t w e i g h t o f t r a n s i t i o n metals, c o m p a r e d w i t h classical Ziegler c a t a l y s t s , h a v e b e e n used i n c r e a s i n g l y d u r i n g p a s t y e a r s for t h e : p r e p a r a t i o n of polyolefms. I t w a s e s t a b l i s h e d in these stndies t h a t t h e carriers u s e d m a y f u n c t i o n n o t s i m p l y as a n i n e r t s u b s t r a t e (such as for e x a m p l e a l u m i n o silicate w h i c h m e r e l y increases t h e a r e a o f d i s t r i b u t i o n of t h e t i t a n i u m c o m :ponent), b u t h a v e a surface a c t i v a t i n g effect on t h e r e a c t i v i t y o f a c t i v e centrea, e.g. m a g n e s i u m oxide a n d a n h y d r o u s m a g n e s i u m chloride [2, 3]. * Vysokomol. soyed. A22: No. I, 181-188, 1980.
~}6
A . A . BA~LIN et a/.
Processes of formation, functioning and deactivation of active centres o f Ziegler catalytic systems of polymerization of olefins are known to be closely linked with processes of reduction of transition metal compounds by organi~ alumininm compounds (OAC), particularly with a reduction in the valency o f transition metals [4]. This paper examines the reduction of titanium tetrachloride secured on the surface of the inorganic carriers mentioned, OAC, as related to the catalyti~ activity of these catalysts in ethylene polymerization. Methods of preparing catalysts on oxide carriers are described in a separate paper [5]. The catalyst on a carrier, anhydrous magnesium chloride, was prepared b y grinding a giver~ a m o u n t of methoxytitanlumtrichloride with MgCI~ at 40-50 ° m a metal ball mill. All opera° tions concermng the preparation and study of catalysts were carried out in purified argon. The overall content of t i t a n i u m T1 (IV} in catalyst samples was determined p h o t o ° metrically, the optical density of the Ti (IV) complex with diantipyrylmethane being m c a s ured in hydrochlorm acid with a wave length ~ - 4 3 2 nm. Interaction of t i t a n i u m catalysts (0.05-1-0 g sample, according to Ti content in the* catalyst) with OAC was carried out without ethylene in a glass vessel while stirring u n d e r conchtions similar to those of polymerization, in n-heptane (0.05 1.) with given molar ratios~ of components of the catalytm system, temperature and reactmn time. The concentratior, of t i t a n i u m was maintained constant in all expemments ( ~ 1.0 × 10-3 mole/1.1. T i t a n i u m content in oxidation of Ti (III) and Ti (II} was determined b y methods m o dified b y the authors [6]. I n the first experunent b y adding 5 ~ HC1 solution and a saturated[ solution of (1VH,)zSO4 to the ester-heptane suspension of the reaction mixture Ti (II} was~ converted to Ti (III}. Then, b y adding 0.1 ~ solution of ferric a m m o n i u m sulphate Ti (III~ was oxidized to Ti (IV) and the Fe (III) excess titrated with a 0.1 ~ solutmn of Trilon B i n the presence of sulphosalicylic acid as indicator. I n the second expemment b y adding a 0.1 N solution of ferric a m m o n i u m sulphate to the ester-heptane suspension of the reactior~ mi~rture Ti (II) and Ti (III) were oxidized to Ti (IV) a n d the Fe (III} excess titrated th~ aame way as in the first experiment. The content of Tl (II) was calculated from the differ° ence in the amounts of ferrm a m m o n i u m sulphates used for oxidation of t i t a n i u m in the* second and first experiments. Ti (III) content was calculated from the difference of the* double a m o u n t of alums used in the first experiment and the a m o u n t of alum used in the* second experiment. Methods of investigating interaction between t i t a n m m catalysts and OAC b y E P R , determining specific surface 8sp of catalysts, p.urifymg reagents to remove impuritms that, inhibit polymerization and examming polymerization kinetics of ethylene were described[ previously [1].
Table 1 shows the yield of PE prepared using unit weight of titanium irk polymerization with classical (without carriers) and Ziegler catalysts and Figs. 1 - ~ (curve 1) indic/ate the general form of corresponding kinetic curves of polymerization expressing the dependence of the effective rate constant of the gross reaction of polymerization kef~ on the time of polymerization, ket~ Values were calculated as before [1] and reduced to unit weight of the entire solid catalyst; this enabled the difference in the type of variation of the rate of ethylene polymerization to be shown in a single figure for the CHsOTiC18-AI(C~H~)8 catalytiet t~ystem (without a carrier) and for the same catalytic system but on an anhyd°
Catalytic activity in polymerization of ethylene
201
rous MgCls carrier, which is characterized b y an activity 350 times "higher a n d reduced to unit weight of titanium. Experimental results indicate that applying components of Ziegler catalytie systems on carriers enables not only polymer yield to be increased considerably, b u t produces significant differences in kinetic mechanisms of polymerization, compared with processes taking place on conventional Ziegler catalysts. As see~ in Figs. 1 and 2, polymerization of ethylene in the l~resence of typical Ziegler catalytic systems based on tetravalent titanium compounds (TiCl~ and CHsOTiCls) TABLE
l.
.ACTIVITY
OF C O N V E N T I O N A L A N D
APPLIED
ZIEGLER
CATALYTIC
SYSTEMS
II~"
ETHYLEI~J~ P O L Y M E R I Z A T I O N
(Cocatalyst AI(C2Hs)s, pc*v=4arm, 70°, solvent n-heptane (0.1 1.))
Catalyst tic1, ~-TiCls. 0"3A1C1, ~HsOTiCls ric1,/A1,Os, SiOs riCl,/MgO ric1,/MgO ]~iCl,/MgO ~HaOTiCI,/MgClm
, Ti content wt. %
[
25"2 22"7 25"8 3"71 0"80 0"60 0"27 0"23
PE yield A1/Ti, in 100 Ssp, m2/g [Cat], g/1. [OAC],g/1. mole/mole rain, kg/g Ti 44.0 Not determined 218 31.0 33.0 14.5 5.5
0.049 0-128 0.105
0.432 0.516 0"253
14-7:1 7.6:1 3-9:1
0.151 0.103 0-104 0.180 0.202
0-201 0.295 0-204 0.205 0.224
15"1:1 150:1 138:1 178:1 203:1
5"34 6"62 1"8~. 16"~ 192 237 441 632
* ~ o , - - o v e r a l l pressure in the reactor.
and triethylaluminium at a temperature of 70 ° is clearly non-stationary, the r a t e of polymerization decreasing over 20 fold in 2 hr, as compared with the maximun~ value, for a TiC14-(C~H~)3 system. As shown b y Fig. 1, securing this catalytic system on an aluminosilicate carrier enables under adequate conditions, th~ process to be carried out at a fixed rate, the form of the kinetic curve, which has an "acceleration" section being similar to the kinetic curve of polymerization in the presence of a catalytic system based on titanium trichloride. The 15"net]e curve of polymerization is also similar for the CttsOTiC18/MgC12-AI(CsHs) s system, except for the fact that the initial section of this curve is not extrapolated to zero. The dependence of the rate of polymerization on time is more complicated for the TiC14/MgO-A1 (C2Hs)s system, characterized b y two stationary "seetions", the initial one corresponding to maximum catalytic activity. I t is remarkable that if for a non-stationary system of TiCI4-AI(C2Hs) s the rate o f polymerization decreases 20 fold, for applied catalytic systems of TiCldMgO-AI(CsHs) s containing 0.2-1.0~/o wt. Ti, this rate only decreases 2-3 times. For magnesium oxide and ab~minosilicate carriers it m a y be assumed that
~ovalent bonds are formed of Ti(IV) with the surface of carriers, since the TiC14 applied is secured b y protonolysis with the participation of hydroxyl surface groups; according to results of I R spectroscopy, the band intensity of bond stretching vibrations of OH groups at 3670 cm -1 (for aluminosilicate) and 3450 -~m -1 (for magnesium oxide) decreases considerably on applying titanium t e -
5-
S
30
"
: " " : : =2
/ I0
~
2
1 0
~/0 80 Time, rain
FIG. 1
I-
120 .
1
0
#0 8Q T i m e , rain
FIG. 2
120
i
:FIG. 1. Kinetic curves of polymerization of ethylene on various catalysts activated with "~riethylaluminium: 1--TIC14; 2--~-TiC1,.0.3 A1C1,; 3--TiC14/A1,O,, SiO,. Conditions of polymerization for Fzgs. 1-3 are the same as shown in Table 1. :FIG. 2. Effect of an MgCI= carrier on the activity and stability in polymerization of ethyl. ~ene of catalytic systems based on methoxytztanium trichloride: 1--CH,OTiCla-AI(C=Hs)8; 2-- CH=OTzC13/MgC1,-AI(C~H~)3. trachloride on these carriers [7]. For a MgCl~ carrier the problem of securing ~nethoxytitanium trichloride has not been studied, however, there is no doubt a s to the presence on its surface of titanium with a degree of oxidation of + 4. I t ~ a s established b y preliminary experiments that the entire titanium fixed on the surface of all the carriers examined (including MgC]2) is in the tetravalent ~tate before interaction with OAC. This is confirmed b y the absence of the E P R •~ignal for all catalysts untreated with OAC and the absence of using ferric am~nonium sulphate during interaction with catalyst samples before the addition ~f OAC. Table 2 shows experimental results of the quantitative determination of tit a n i u m of various valence states in the catalytic systems examined using a chemical analytic method and the content of trivalent titanium was detected l~y E P R . For a more complete study of the effect of carrier (and its properties) o n the valence state of fixed titanium, the interaction of the titanium containing c o m p o n e n t with OAC was carried out under "milder" conditions than during polymerization--at room temperature and using diethylaluminium chloride ~(DEAC), a reducing agent which is weaker than A/(C=Hs) s.
Catalytic activity in polymerization of ethylene
20t)
Analysing results of Table 2 it is essential to note t h a t the quantitative determination of titanium in different valence states at a certain m o m e n t in time is not a simple experimental problem. Results in the literature concerning tyl~ical Ziegler systems of TiC14-OAC type obtained b y various authors therefore often show considerable variation. According to results obtained by Kern and Hurst, who used a combination of methods of chromatographic and gravimetrie analyses of products formed in the system of TiC14-AI(C~Hs) 3 at 26 ° and a period of interaction of components of 30 rain, the entire titanium is in the bivalent state with a molar ratio of A1/Ti of 3 : 1 [8]. According to results of Kollar eta/., who used a chemico-analytical method, under adequate conditions it is only ~ 10% titanium which is reduced to Ti (II) in this system [9]. Table 2 indicates t h a t our results for the catalytic system examined show a higher degree of agreem e n t with results of the study mentioned [9].
~ 3OO
kerr,L/mole T/.sec 500
!
0
40
8O
IEO
Time, rnin ~FIO. 3. Effect of "ageing" at 70° and a molar ratio of AI/Ti of 75 : 1 on the activity in polymerization of othylene of the catalytic system of TiC1JMgO (0.60% Ti)Al(CsHl)a: 1--without "ageing"; g--1.5; 3--3; 4--5 hr. According to our experiments, in typical Ziegler systems the proportion of titanium reduced, other conditions being the same, depended not only on the molar ratio of AI/Ti, but also on effective concentrations of OAC and TiCl 4 themselves (with identical Al/Ti ratios). In all experiments concerning determination of Ti (III) and Ti (II) we therefore maintained a constant concentration of the initial titanium, while the A1/Ti ratio showed a proportional variation for the pair of titanium compound--applied catalyst, based on this compound. Results of Table 2 enable us to draw the following eonelusions: 1) the degree a n d rate of reduction of titanium using OAC decrease considerably on being secured on the surface of carriers; 2) the degree of reduction of Ti depends on
A . A . BAITLHV 6f ed.
210
the type of caxrier ~sed-for using aluminosilicate.
c a r r i e r s c o n t a i n i n g m a g n e s i m n i t is l o w e r t h a n o n
I n f a c t , a c o m p a r i s o n , f o r e x a m p l e , o f N o s . 4 a n d 17 i n T a b l e 2 i n d i c a t e s t h a t a t 25 ° a n d a m o l a r r a t i o o f A I / T i o f 40 : 1 ( r e d u c i n g a g e n t D E A C ) d u r i n g a p e r i o d o f i n t e r a c t i o n o f c o m p o n e n t s o f 15 r a i n o n e t e n t h o f T i ( I V ) a t o m s o f t h e CH3OTiC13/ TABLE 2. EFFECT OF CARRIER ON THE EFFECTIVENESS OF REDUCTION OF Ti (IV) usiNG OAC, ACCORDING TO I~ESULTS OBTAINED BY .% CHEMICO-ANALYTICALMETHOD AND E P R
IAl/Ti, No.
Catalyst
TIC1,
OAC
T,°C
1 3
15 1
25 25 70
6( 6£
47 74 11
-24 88
DEAC TEA
40:1 4:1
25 70
6C
100 23
77
100 100
DEAC TEA
1:1 3:1 10:1 15:1 1:1 3:1 10:1 15:1 150:1 150: 1[ 150 : 1
25 25 70 70 25 25 70 70 70 70 70
6(] 6(}
9 68
---
9 68
60 60 60 60 60 60 5 50
56 66 3 36 77
29 27 --3
85 93 3 36 80
80
4
84
11
35
-9 13
6 12
1 )0
82 80
35 91 93
40:11
25 70 70
15 ~0 50
10 68 81
--16
10 68 97
7'
6
7
TiCldA120 *, SiO~ (3.71% Ti)
8 9
10 11 12
~9
TiC1,/MgO (0.80%
Ti)
13 14 15 16
17 18 19
DEAC TEA 7'
CH,OTiC18/MgCI, (0"23% Ti)
Ti(III), content~ % of Ti(IV) ace. to EPR
mole/ /mole
DEA£ TEA*
CHsOTiCla
Content of reduced Ti, % of initial Time TI(IV), according to of in- results of chemicotorac- analytical method tion, T1 rain Ti Ti (III) (III) (II) -{-Ti (II)
DEAC TEA
1 1
6(
--
47 98 99
Not deter. mined
5 58 49 60 2 $
• T]gA~AI(C,H.).. ]MgC1 z c a t a l y s t w a s r e d u c e d t o t h e t r i v a l e n t s t a t e , w h e r e a s i n t h e c a s e o f t h e initial methoxytitanium triehloride under the same experimental conditions the e n t i r e T i ( I V ) w a s r e d u c e d t o T i ( I I I ) . W h e n u s i n g TiC14 a n d a s t r o n g e r r e d u c i n g a g e n t , AI(C~Hs)a, p r a c t i c a l l y 9 0 % T i w a s i n t h e b i v a l e n t s t a t e a f t e r 1 h r i n t e r a c t i o n o f c o m p o n e n t s a t 70 ° a n d a n A l / T i r a t i o o f 15 : 1, w h e r e a s i n t h e c a s e o f
Catalytic activity in polymerization of ethylene
211
the same system less t h a n one third of titanium was reduced to Ti (II) under the same conditions on an aluminosilicate carrier, while on using an l~IgO earrier this figure was only 4% titanium (Nos. 3, 9 and 13). Table 2 shows that for applied catalysts the total of Ti(III)-~Ti(II) m a y be less than 100% of the initial Ti (IV). The joint existence in a homogeneous system of Ti (IV) and Ti (II) is unlikely since Ti (IV) is an oxidizing agent for Ti (II) [i0]. Results indicate that fixing transition metal complexes on the surface of carriers reduces the probability of bimoleeular interaction. I t is interesting that results of quantitative E P R determination of Ti (III) on the sulfface of carriers containing magnesium do not agree with results of chemico-analy~ical determination (Table 2). E P R on the surface of carriers, MgC12 and MgO could not, normally, record more than 5-12% Ti (III) of the entire Ti applied even under the "strictest" conditions of reducing Ti (IV), which is lower by one order of magnitude than the amount of Ti (III) determined by a chemico-analytical method. When using an aluminosilicate carrier up to 90% Ti (III) detected by a chemico-analytieal method could be recorded by EPR. Results obtained for titanium-magnesium catalysts, the same way as results of :EPR investigation of TiC13 formed in TiCI4-OAC systems, are evidently explained by two possible causes: 1) a significant part of Ti (III) is in the dimer form, which does not give an E P R signal; 2) the E P R signal is poorly recorded as a consequence of the very rapid spin-lattice relaxation of Ti (III) ions [11]. A comparison of structural parameters of applied catalysts indicates that the specific surface of all catalysts (Table i) is known to be adequate for the accomodation of the entire titanium by the monomolecular layer (calculations were carried out the same way as previously [1]). Bearing in mind the prevailing equivalent pore radius of catalysts or~ aluminosilicate (80-90 A) and magnesium oxide of variable pore structure (125-1500/~) [I] it m a y be concluded t h a t there is no difference in the "accessibility" of titanium held on the surface of these catalysts for OAC molecules, i.e. the chemical properties of the carrier and not structural characteristics have the prevailing influence on the effectiveness of reduction processes of transition metals. These effective pore dimensions which are sufficient for fixing several TiCl~ molecules in a single pore do not give a clear explanation of the possible assumption that a considerable part of Ti (III) atoms on the surface of a titanium aluminosilicate catalyst is present in the form of isolated ions determined by EPR, in contrast with titani~tm-magnesium catalysts, on the smfface of which Ti (III) is in the form of "dimers" which do not give an E P R signal. To solve the problem of possible variable spin-lattice relaxation of Ti (III) ions held on the surface of titanium aluminosilicate and titanium-magnesium catalysts, i.e. the problem of variable symmetry of eoml~lexes formed with Ti (III), E P R spectra have to be recorded at temperatures lower than m 196 ° (the lowest temperature used by the authors). Nevertheless, even at this stage of investigations information was obtained
212
A.A. BArium ~ a/.
b y E P R which points to the "ligand" role of carriers in the processes examined. :For example, in the case of an applied catalyst, CttsOTiC18/]KgC1~ treated with DEAC under conditions No. 18 of Table 2, the E P R spectrum is a single line 136 Oe in width with a g-factor of 1.960, and in the case of a system without a carrier, CH3OTiCI3-AI(C~H6)~CI and the same experimental conditions, the line width of the E P R spectrum is 75 Oe, the g factor being 1.995 (in both cases E P R spectra were recorded at --196°). Spectroscopic characteristics obtained point to heterogeneous ligand environment of paramagnetic Ti (III) atoms in both systems. Chemical fixing of the complex containing titanium on the surface of t h e carrier may, in our opinion, lower the effect of titanium reduction using OAC not only as a result of reducing the proportion of possible bimolecular dis:proportionation of unstable alkyl titanium [121 formed in Ziegler systems, but also as a result of changing electron cha~act3ristics of the transition metal in a complex with the carrier. It is precisely the latter condition, which may explain t h e effect of the chemical structure of the carrier on the efficiency of these proc~les. -~ To complete the analysis of titanium reduction, we found it interesting to study polymerization kinetics of ethylene using OAC previously "aged", treated nnder different conditions, i.e. a catalyst on the same carrier. Figure 3 shows kinetic curves of polymerization on a TiCId/MgO catalyst sealed in an ampoule together with AI(CsHs)a with a molar ratio of Alfri of 75 : 1 and "kept" at 70 ~ for a varying length of time* until breaking this ampoule (at the beginning of polymerization the ampoule containing the new batch of AI(CsHs)8 was also broken in the reactor; the overall molar ratio of A1/Ti was brought to 150 : 1). ]Figure 3 shows that the form of kinetic curves of polymerization using an "aged" catalyst (curves 2-4) differs considerably from that of a catalyst activated with triethylaluminium by conventional methods at the beginning of polymerization (curve 1). Curves 2-4 are characterized by a brief section of increased velocity (not extrapolated to zero)', a section of stationary velocity (the longer the "ageing" time of the catalyst the shorter this section) and a section of reduced rate of l~olymerization. The maximum rate of polymerization using an "aged" catalyst containing titanium from the very beginning of the process with a degree of oxidation of less than four (according to results of Table 2, the average degree of oxidation ~ 3 ) , is ~ 5 times lower than that for a "non-aged" catalyst. This result clearly shows the link between processes of reduction of titanium using OAC and the deactivation of the catalytic system. A reduction in the activity of catalysts subjected to "ageing" by the methods described may, no doubt, be explained not only by the reduction in the valency. of titanium in the active centre, but also the accumulation in the reaction zone of products of interaction, e.g. alkylaluminium halides, in the presence of which * Bearing in mind the time the ampoule is kept in the polymerization reactor, which evaeusted in these experiments at 70°.
Catalytic activity in polymerization of ethylene
213
t h e rate of polymerization is much lower using the titanium-magnesium catalysts
examined t h a n in the presence of trialkyl OAC [13]. Specific properties of interaction of these products with the active catalytic centre m a y explain the experimental fact t h a t rates of polymerization on a catalyst previously "aged", for example, for 1.5 hr do not reach rates of polymerization achieved in 1.5-2 h r ol~ a catalyst activated with triethylaluminium at the very beginning of tho process (Fig. 3). I t was shown in previous studies [2, 3] t h a t the concentration of active centres on the surface of the catalysts described using carriers of magnesium oxide a n d aluminosilicate, corresponding to a stationary rate of polymerization at 70 °, is ~20~/o of the entire amount of titanium contained. A comparison of this valuse with results concerning the valency state of Ti in, these catalysts u n d e r conditions corresponding to conditions of stationary polymerization of e~hylen~ in their presence (l~os. 9 and 14 in Table 2 and in Figs. 1 and 3 (curve 1)) inclic~tes that there is no direct correlation between the amount of titanium reduced a n d the concentration of active centres (for a catalyst on iVIgO there is 35 wt. o/~ Ti (III), and a catalyst on aluminosilicate, 66 wt. ~ Ti (III) and 27 wt. ~/o Ti (II} of the initial Ti(IV)). On the other hand, results examined in this paper indicating t h a t the degree of reduction of titanium held on magnesium oxide is lower t h a n on alurninosilicate, are in satisfactory agreement with results of studying MWI) of P E synthesized on these catalysts. We have shown [14] t h a t PE obtained under identical conditions of polymerization on a titanium-magnesium catalyst is characterized by a coefficient of polydispersion of 3, while on a titanium aluminosilicate catalyst, b y a coefficient of po]ydispersion of 10 [14]. This points to increased homogeneity of active centres on the surface of a magnesium.containing carrier. Experimental results therefore indicate t h a t securing the titanium containing component of Ziegler catalytic systems on the surface of carriers and selecting a carrier of the appropriate chemical structure enable the degree o f reduction of the transition metal b y alkyl aluminium to be lowered considerably a n d the stability of active complexes of polymerization, increased. Translated by E. SEM/~RF~ REFERENCES 1. A. A. BAULIN, A. S. SEMENOVA, L. G. STEF.A.NOVICH, N. M. CttIR~OV and A. V. STAFEYEV, Vysokomol. soyed. A16: 2688, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 12, 3130, 1974) 2. A. A. B&ULIN, V. N. SOKOLOV, A. S. SEMENOVA, N. M. CHIRKOV and L. F. SHALAYEVA, Vysokomol. soyed. A17: 46, 1975 (Translated in Polymer Sci. U.S.S.R. 17:
1, 51, 1975) 3. S. S. IVANCHEV, A. A. BAULIN and A. G. RODIONOV, Tezisy kratkikh soobshehonii Mezhdunarodnogo simpoziuma po makromolekulyarnoi khimii (Summaries of Brief Reports at the International Symposium on Macromolecular Chemistry). vol. 2, ~Tauka~ 1978
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YE. YA. DAVYDOV et al.
4. N. M. CHIRKOV, P. Ye. MATKOVSKII and F. S. D'YACHKOVSKII, Pohmerizatsiya n a kompleksnykh metalloorganicheskikh katalizatorakh (Polymerization on Compotato Organo-metallic Catalysts). Izd. Khimlya, 1976 5. A. A. BAULIN, S. S. IVANCHEV, L. D. UZHINOYA, N. A. PLATE, I. N. ANDREYEVA and L. A. MASHKOVA, Auth. Cert. 614115, 1977; Byull. lzobr. No. 25, 103, 1978 6. Ye. G. TABAKOVA and Z. V. SOLOV'YEVA, Zavodsk. lab. 22: 1417, 1956 7. A. A. BAULIN, S. S. IVANCHEV, V. L. MAKSIMOV, S. Ya. K H A I K I N and Ye. I. NOVIKOVA, Materialy Vsesoyuznogo soveshchaniya "Smtez i kataliticheskiye svoistva kompleksov perekhodnykh metallov, zakreplennykh n a poverkhnosti nositelm" (Proceedings of the All-Union Conference "Synthesis and Catalytic Properties of Transition Metal Complexes held on the Surface of Carriers"). Novosibirsk, 1977 8. R. S. KERN and H. G. HURST, J. Polymer Sei. 44: 272, 1960 9. L. KOLLAR, A. SIMON and J. OSVATH, J. Polymer Sci. 6, A - l : 919, 1968 10. G. SHARLO, Metody analiticheskoi khimii (Methods in Analytical Chemistry). vol. 1, Khimiya, 1969 -11. Ye. N. ADEMA, N. J. M. BARTELINK and J. SMIDT, Rec. tray. chim. 81: 73, 1962 12. Ye. Ye. VERMEL', N. G. MAK,~IMOV, V. M. MAST1KHIN, S. G. ARTAMONOVA, V. F. ANUFRIYENKO and V. A. Z ~ g H A R O V , Kinetika i kataliz 16: 1015, 1975 13. A. G. RODIONOV, A. A. BAULIN, A. L. GOL'DENBERG, Yu. M. ZAV'YALOV, L N. ANDREYEVA and S. S. IVANCHEV, Plast. massy, No. 4, 11, 1979 14. A. A. RAULIN, L. F. SHALAYEVA and S. S. IVANCHEV, Dokl. A N SSSR 231: 413, 1976
:Polymer Science U S.S.R. Vol. 22, pp. 214-222. O Pergamon Press Ltd. 1980. Printed in Poland
0032-3950/80/0101--0214507.5010
FREE RADICAL CONVERSIONS OF TWO COMPONENT POLYURETHANES BY THE ACTION OF LIGHT * Y E . YA. DAVYDOV, YE. V. DAVYDOVA, M. I . KARYAKI~A, V. V. LUK'YAI~OV, G. B. PARIISKII a n d D. YA. TOPTYGII~ I n s t i t u t e of Chemical Physics, U.S.S.R. A c a d e m y of Sciences State Scientific Research and Design I n s t i t u t e for the P a i n t and Varnish I n d u s t r y
(Received 21 November 1978) Various physico-chemical methods were used to investigate photo-oxidation a n d photolysis (initiated b y ferric chloride additives) of erosslinked polyurethanes based on h y d r o x y l containing branched oligoesters of different chemical structures. The t y p e of macroradical was established and a kinetic s t u d y made of d a r k and photochommal degradation.
* VyE~okomol. soyed. A22: ~ o . 1, 189-195, 1980.