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Polymerization of ethylene and its copolymerization with vinylcyclohexane using homogenous catalysts based on zirconocene-methylalumoxane systems
PolymerScienceU.S.S.R.Vol. 32,No. 9, pp.X%8-1872,1990 Printed in GreatBritain.
0032-395ODO $10.00+ .OO 0 1991Pergamon Pressplc
POLYMERIZATION OF ETHYLENE AND ITS COPOLYMERIZATION WITH VINYLCYCLOHEXANE USING HOMOGENEOUS CATALYSTS BASED ON ZIRCONOCENEMETHYLALUMOXANE SYSTEMS* L. A. NEKHAEVA,
V. L. KLEINER, B. A. KRENTSEL’, YE. B. UVAROVA,
N. N. KORNEEV
and I. M. KHRAPOVA Topchiyev Institute of PetrochemicalSynthesis, U.S.S.R. Academy of Sciences (Received 31 July 1989)
A kinetic study has been made of the homo- and copolymerization of ethylene with vinylcyclohexane, using catalytic systems based on methylalumoxane
and bb-(terr-butylcyclopentadienyl)zirconium
bb-(trimethylsilylcycyclopentadienyl)zirconium
dichloride. The effective rate constants were determined
the interval from 20-70°C for the homo- and copolymerization energies and the copolymerization
dichloride and in
reactions, and the observed activation
constant were obtained. Some properties of the resultant polymers were
investigated.
HOMOGENEOUScatalytic systems based on zirconocenes
and methylalumoxanes have recently been of interest to investigators. Their interest is due on the one hand to the extremely high reactivity of these systems in ethylene polymerization processes [l, 21 and on the other hand to the fact that such systems may be used as initiators for the stereospecific polymerization of cY-olefins [3] and vinyl aromatic hydrocarbons [4]. It is noteworthy that the systems studied appear extremely promising when used for the synthesis of linear low density polyethylene (LDPE) which is a copolymer of ethylene and a small number of units of linear and branched ar-olefins. Polymerization and copolymerization of ethylene (of polymerization grade) was carried out in a 0.11 steel autoclave, having a stirrer and jacket, in pure air [7], the ethylene pressure being constant. Zirconocene and MAO were introduced into the reactor (in an inert atmosphere) in the form of toluene solutions of known concentration, and were stirred for 20 minutes at 20°C in the absence of monomers. The purified VCH was introduced by means of a syringe prior to the ethylene feed. The reaction was stopped with the aid of a 5% solution of HCl in isopropanol. The polymer was washed with isopropanol and vacuum dried to constant weight at 80°C. The intrinsic viscosity of the polymer solutions was measured in decalin at 105°C in an Ubbelohde viscosimeter. Molecular weights were calculated by the formula [v] = 5.1 x 10-4i@‘.725[8]. Determination of the melting point was based on DSC, using a DSM-2M apparatus; the heating rate was 80Wmin. The density of the polymers was measured by a flotation method in line with State Standard GOST 15139-69. The elongation at break of a sample was determined by means of an FPZ-10 tensile tester and was calculated by the formula E = Al/Zx 100%. The reactivity of the catalytic systems was determined in the course of the reaction on the basis of
‘Vysokomol.
soyed. A32: No. 9,1951-1955,199O.
1868
Polymerization of ethylene using homogeneous catalysts
1869
the value of the effective rate constant for ethylene polymerization kef f = W/Ccat 0 X Ce,
where coat° is the starting concentration of zirconocene, mol Zr; ce is the liquid phase ethylene concentration calculated on the basis of Henry's law Ce = 1.8 x 10 -3 e2460/RTx Pm [9], mol/l; Pm is the partial ethylene pressure, MPa; T is the reaction temperature, K; w is the current rate of ethylene polymerization determined from the drop in its pressure in a graduated buffer container, mol/min. A characteristic feature of the catalytic systems under the conditions examined is the fact that practically a maximum rate of polymerization is attained immediately the ethylene has been fed into the reaction medium (containing the catalytic system without the ethylene), and stationary conditions of polymerization are maintained for several days (Fig. 1). w x 10 4, m o l l m i n
6 J 2 1 2
o--o-o-oi,
30 FIG. 1.
I
1
SO
150
Time,min
Time dependence of the polymerization rate with [I] = 6.2 × 10 6 mol/1, 323 K. AI:Zr = 5 × 103 and the ethylene concentration is 0.38 (1); 0.40 (2); 0.51 (3) and 0.74 mol/I (4).
It was found that the nature of the alkyl alumoxane is a factor decisively influencing the catalyst reactivity. For instance, the reactivity of the system based on ethylalumoxane (the degree of oligomerization being n = 2) and zirconocene Cp2ZrCI2 in the polymerization of ethylene is at the level of 30 kg PE/mol Zr × h. The reactivity of the systems based on MAO with n = 10--30 exceeds 1000 kg/mol Zr × h under similar conditions, and on increasing the molar ratio of AhZr from 1000 to 7000 the rate of ethylene polymerization is increased by a factor of - 6 . It was proposed in [10] that in the case of catalysts containing a large excess of alumoxane (metalorganic compound 10-5-10 -6 mol/l, alumoxane 10 -3 mol/l) the latter may be regarded as being a sort of "carrier" that stabilizes the transition metal compound in an active form. The need to maintain such a large excess of MAO relative to the metallocene, exceeding the degree of oligomerization of MAO by at least two orders, is attributed to M A O being in a state of associative-dissociative equilibrium that rules out acid-base complex-formation and/or the formation of electron-deficient bridge bonds. The kinetics of ethylene polymerization were investigated in some detail, using a catalytic system based on MAO and compound I. It was found that, as in the case of ordinary Ziegler-Natta catalysts, the polymerization of ethylene is a first-order reaction with respect to ethylene and Zr (Fig. 2), and the observed activation energy for the reaction was 18 + 1.5 kJ/mol (Figs 3 and 4). The system based on compound II is characterized by a higher catalytic reactivity compared with compound I. Apparently this is due to a change in the electron density on cyclopentadienyl rings. The presence of a weak electron-donor trimethylsilyl group in compound II leads to some increase in kp. In the case of compound I we have the reverse effect [12]. The data in Table 1 show the extent to which the viscosity-average molecular mass of the polymers are influenced by the conditions of their preparation. PS 32"9-K
1870
L.A.
NEKHAEVA et al.
-/og w
2,5-
1,7
t 0.3 I z~,6
0,7 I ~,2
FIG. 2.
I 0.5 I 5.0
-/og[C2H4] -Iog[Zr]
Changes in the catalyst reactivity versus [Zr] and [C2H4] with a constant AI concentration (1) [I] --- 6.2 x 10 6 moi/l, AI:Zr = 5 x 103, 323 K; (2) Co = 0.61 mol/l, 303 K. In k e f f
¢.6
w x 10 4 mol/min 6 8----
oZ
5
0.000
; ~. : :
~' J
7
5
Z o
o~
~'.2
J
I 2O
120
Time, m/n
2,e
~,~
FIG. 3
~,J
(IO~/T)F ~
FIG. 4
FIG. 3.
Rate of ethylene polymerization in the presence of MAO + I (I) and MAO + II (II) versus time at 20 (1), 30 (2), 40 (3), 50 (4), 60 (5) and 70°C (6). Fzc3.4. Plot for calculating the energy of activation of ethylene polymerization on homogeneous catalytic systems of types MAO + I (1) and MAO + II (2) with coat = 6.2 x 10-6 mol]l, AI:Zr = 5 x 103.
TABLE 1.
EFFECT OF METHOD OF PREPARATION OF THE POLYMERS ON THEIR MOLECULAR MASS Ccat,
(Ai:Zr = 7 x 103)
Ccat,
T, °C
mol/1
r/, dl/g
h4n × 10 -4
T, °C
mol/1
,/, dl/g
hT/~x 10 -4
60 50 30
7.3 x 10 -s 7.2 x 10 -5 7.2 x 10 -5
1.0 1.1 1.25
3.45 3.9 4.5
30 30
1.75 x 10 -5 4.15 x 10 -6
1.8 6.0
7.3 35.0
It is n o w k n o w n [13] t h a t h o m o g e n e o u s s y s t e m s b a s e d o n m e t a l l o c e n e s a n d M A O
are efficient
c a t a l y s t s o f t h e c o p o l y m e r i z a t i o n o f e t h y l e n e w i t h s o m e t~-olefins. W e first s t u d i e d t h e c o p o l y m e r i z a tion of ethylene with VCH on a catalytic system containing MAO
a n d c o m p o u n d I o r II. T h e
i n t r o d u c t i o n o f V C H l e a d s to a c h a n g e in t h e c a t a l y s t n e g a t i v i t y ; t h e n a t u r e o f this c h a n g e is
Polymerization of ethylene using homogeneous catalysts
1871
illustrated in Fig. 5. The reaction rate goes through a weakly defined maximum at CvcH ~ 0.8 mol/l, which accords with information published in references [14--17] on the copolymerization of ethylene with a-olefins. It was noted in [18] that the rate of ethylene polymerization is higher in the presence of 4-methyl-l-pentene with catalytic systems of the following three types: MgClz-TiClaethylbenzoate-(/so-Bu)3A1; MgCl2-TiCl4-diisobutylphthalate-(iso-Bu)3A1, and 6-TIC12-0.33 AICl2-(iso-Bu)3Ar; the effect in question is ascribed to an increase in the number of active centres. However, the observed rise in the reaction rate for the system zirconocene-MAO in the copolymerization of ethylene with a-olefins cannot be attributed to an increase in the number of active centres, since under the conditions stated above the number of active centres reaches practially 100% already in the homopolymerization of ethylene. Apparently the presence of VCH in the reaction system results in the formation of active centres of higher reactivity. A further increase in the concentration of VCH, which has such very low reactivity compared with ethylene, may reduce the rate of ethylene polymerization processes. Using the plot of the copolymer composition determined as previously in [6] versus the composition of the initial mixture of monomers (Fig. 6), it was found in accordance with the equation [l 9, 20]
(Cm)(Cml rl \ Ce /m
that the copolymerization constant r 1 = 62.5 + 2.5. A,. x 10 J, kg PE/mol Zr x h
(Cvc./c.L x 102 5
8~ J J
I
I
a
O, 6
I I, #
I
I
Cvc., mol/I
I
J (Cvc,/c~),,, Fie. 6
Fid. 5 Fl{;. 5.
~
I
Plots of the c a t a l y s t r e a c t i v i t y A,,, v e r s u s V C H c o n c e n t r a t i o n : (1) [ ( C s H a C ( C H 3 ) 3 ) Z r C I 2 ] = 10 _5
mol/l. T = 30°C; (2) [ ( C s H 4 C ( C H 3 ) 3 ) 2 Z r C I 2 ] = 10 -6 mol/l, T = 50°C; (3) [(CsHaSi(CH3)3)2ZrCI2] = 10 -5 mol/l, T = 30°C. FIG. 6.
D e p e n d e n c e of the c o p o l y m e r c o m p o s i t i o n o n that of the m o n o m e r m i x t u r e w i t h [I] = 7 × 10 -5 mol/l, A I : Z r = 1.7 x 103, 50°C.
The amount of VCH introduced into the copolymer may be as high as 5 mol%. The introduction of just 1 mol% of VCH reduces the density of the polymer from 0.98 to 0.96 g/cm3, and the melting point falls from 127 to 122°C, while at the same time the breaking elongation is increased from 700 to 1000%. Thus it is evident that vinylcyclohexane incorporated in chain leads to significant changes in the properties of the polymers. We are now investigating the use of the studied catalysts in the case of ethylene copolymerization with a number of other monomers.
1872
L . A . NEKHAEVA et al.
The authors thank L. I. Vyshinskaya and her coworkers for kindly providing the zirconocene specimens used in this investigation.
Translated by R. J. A. HENDRY
REFERENCES 1. H. SINN and W. KAMINSKY, Advances Organomet. Chem. 18: 99, 1980. 2. W. KAMINSKY, K. KULPER and S. NIEDOVA, Makromolek. Chem. Macromolec. Symp. 3: 377, 1986. 3. W. KAMINSKY, K. KULPE, BRINTZINGER and F. R. W. P. WILD, Angew. Chemie 97: No. 6, 507, 1985. 4. N. ISItIItARA, T. SEIMIYO, M. KUKAMOTO and M. UOI, Macromolecules 19: No. 9, 507, 1988. 5. !~. A. KRENTSEL', V. I. KLEINER and L. L. STOTSKAYA, Vysshie Poliolefiny (The Higher Polyolefins). Moscow, 1984. 6. V. L. KHODZHAEVA, Ye. L. POLOTSKAYA, V. I. KLEINER, V. G. ZAIKIN and B. A. KRENTSEL', Vysokomol. soyed. A30: No. 6, 1306, 1988 (translated in Polymer Sci. U.S.S.R. 30: 6, 1370, 1988). 7. A. WEISSBERGER and E. PROSKAUER, Organicheskie rastvoriteli (Organic Solvents). Moscow, 287, 1958. 8. L. H. TUNG, J. Polymer Sci. 20: No. 96,495, 1956. 9. P. M. NEDOREZOBA, V. I. TSVETKOVA and N. M. CH1RKOV, Vysokomol. soyed. 16: No. 4, 762, 1974 (translated in Polymer Sci. U.S.S.R. 16: 4, 879, 1974). 10. K. I. ZAMAREV and G. I. ZHIDOMIROV, Internat. Symp. on "Svyaz' mezhdu gomogenym i geterogenym katalizom" (Relationship between Homogeneous and Heterogeneous Catalysis). Vol. 1. Novosibirsk, p. 29, 1986. 11. J. C. W. CHIEN and A. RAZAVI, J. Polymer Sci. Polymer Chem. Ed. 26: No. 9, 2369, 1988. 12. K. I. VYSHINSKAYA, N. I. SPIRIDONOVA, V.I. KLEINER, L.A. NEKHAEVA, N.N. KORNEEV, I.M. KHRANOVA, B.N. BOBROV and B.A. KRENTSEL', Tez. Doklad. IV Vsesoyuz. konf. po metalloorgan, khimii (Abstracts of Reports of the IV All-Union Conf. on Metallorganic Chem.). Kazan, 27, 1988. 13. W. KAMINSKY and M. SCHLOBOLM, Makromolek. Chem. Macromolec. Symp. 4: 103, 1988. 14. W. KAMINSKY, Catalytic Polymerization of Olefins. Tokyo, p. 293, 1986. 15. S. LIN, J. WANG, Q. CHANG, Z. LU and Y. LU, Catalytic Polymerization of Olefins. Tokyo, p. 91, 1986. 16. N. KASHIWA and G. YOSHITAKE, Makromolek. Chem. 185: No. 6, 1133, 1984. 17. L. T. FINOGENOVA, V. A. ZAKHAROV, A. A. BUNIYAT-ZADE, G . D . BYKATOV and T. Ye. PLAKSUNOV, Vysokomol. soyed. 22: No. 2, 404, 1980 (translated in Polymer Sci. U.S.S.R. 22: 2, 448, 1980). 18. P . J . TAIT, C. W. DOWNS and A. A. AKINBANU, Regional Technical Conference, Akron, 1986. 19. T. E. NOWLIN, Y. V. KISSIN and K. P. WAGNER, J. Polymer Sci. Polymer Chem. Ed. 26: No. 3,755, 1988. 20. L. G. ECHEVSKAYA, V. A. ZAKHAROV and G. D. BUKATOV, React. Kinet. Catal. Letters 34: No. 1, 99, 1987.
0032-395ODO $10.00+ .OO 0 1991Pergamon Pressplc
POLYMERIZATION OF ETHYLENE AND ITS COPOLYMERIZATION WITH VINYLCYCLOHEXANE USING HOMOGENEOUS CATALYSTS BASED ON ZIRCONOCENEMETHYLALUMOXANE SYSTEMS* L. A. NEKHAEVA,
V. L. KLEINER, B. A. KRENTSEL’, YE. B. UVAROVA,
N. N. KORNEEV
and I. M. KHRAPOVA Topchiyev Institute of PetrochemicalSynthesis, U.S.S.R. Academy of Sciences (Received 31 July 1989)
A kinetic study has been made of the homo- and copolymerization of ethylene with vinylcyclohexane, using catalytic systems based on methylalumoxane
and bb-(terr-butylcyclopentadienyl)zirconium
bb-(trimethylsilylcycyclopentadienyl)zirconium
dichloride. The effective rate constants were determined
the interval from 20-70°C for the homo- and copolymerization energies and the copolymerization
dichloride and in
reactions, and the observed activation
constant were obtained. Some properties of the resultant polymers were
investigated.
HOMOGENEOUScatalytic systems based on zirconocenes
and methylalumoxanes have recently been of interest to investigators. Their interest is due on the one hand to the extremely high reactivity of these systems in ethylene polymerization processes [l, 21 and on the other hand to the fact that such systems may be used as initiators for the stereospecific polymerization of cY-olefins [3] and vinyl aromatic hydrocarbons [4]. It is noteworthy that the systems studied appear extremely promising when used for the synthesis of linear low density polyethylene (LDPE) which is a copolymer of ethylene and a small number of units of linear and branched ar-olefins. Polymerization and copolymerization of ethylene (of polymerization grade) was carried out in a 0.11 steel autoclave, having a stirrer and jacket, in pure air [7], the ethylene pressure being constant. Zirconocene and MAO were introduced into the reactor (in an inert atmosphere) in the form of toluene solutions of known concentration, and were stirred for 20 minutes at 20°C in the absence of monomers. The purified VCH was introduced by means of a syringe prior to the ethylene feed. The reaction was stopped with the aid of a 5% solution of HCl in isopropanol. The polymer was washed with isopropanol and vacuum dried to constant weight at 80°C. The intrinsic viscosity of the polymer solutions was measured in decalin at 105°C in an Ubbelohde viscosimeter. Molecular weights were calculated by the formula [v] = 5.1 x 10-4i@‘.725[8]. Determination of the melting point was based on DSC, using a DSM-2M apparatus; the heating rate was 80Wmin. The density of the polymers was measured by a flotation method in line with State Standard GOST 15139-69. The elongation at break of a sample was determined by means of an FPZ-10 tensile tester and was calculated by the formula E = Al/Zx 100%. The reactivity of the catalytic systems was determined in the course of the reaction on the basis of
‘Vysokomol.
soyed. A32: No. 9,1951-1955,199O.
1868
Polymerization of ethylene using homogeneous catalysts
1869
the value of the effective rate constant for ethylene polymerization kef f = W/Ccat 0 X Ce,
where coat° is the starting concentration of zirconocene, mol Zr; ce is the liquid phase ethylene concentration calculated on the basis of Henry's law Ce = 1.8 x 10 -3 e2460/RTx Pm [9], mol/l; Pm is the partial ethylene pressure, MPa; T is the reaction temperature, K; w is the current rate of ethylene polymerization determined from the drop in its pressure in a graduated buffer container, mol/min. A characteristic feature of the catalytic systems under the conditions examined is the fact that practically a maximum rate of polymerization is attained immediately the ethylene has been fed into the reaction medium (containing the catalytic system without the ethylene), and stationary conditions of polymerization are maintained for several days (Fig. 1). w x 10 4, m o l l m i n
6 J 2 1 2
o--o-o-oi,
30 FIG. 1.
I
1
SO
150
Time,min
Time dependence of the polymerization rate with [I] = 6.2 × 10 6 mol/1, 323 K. AI:Zr = 5 × 103 and the ethylene concentration is 0.38 (1); 0.40 (2); 0.51 (3) and 0.74 mol/I (4).
It was found that the nature of the alkyl alumoxane is a factor decisively influencing the catalyst reactivity. For instance, the reactivity of the system based on ethylalumoxane (the degree of oligomerization being n = 2) and zirconocene Cp2ZrCI2 in the polymerization of ethylene is at the level of 30 kg PE/mol Zr × h. The reactivity of the systems based on MAO with n = 10--30 exceeds 1000 kg/mol Zr × h under similar conditions, and on increasing the molar ratio of AhZr from 1000 to 7000 the rate of ethylene polymerization is increased by a factor of - 6 . It was proposed in [10] that in the case of catalysts containing a large excess of alumoxane (metalorganic compound 10-5-10 -6 mol/l, alumoxane 10 -3 mol/l) the latter may be regarded as being a sort of "carrier" that stabilizes the transition metal compound in an active form. The need to maintain such a large excess of MAO relative to the metallocene, exceeding the degree of oligomerization of MAO by at least two orders, is attributed to M A O being in a state of associative-dissociative equilibrium that rules out acid-base complex-formation and/or the formation of electron-deficient bridge bonds. The kinetics of ethylene polymerization were investigated in some detail, using a catalytic system based on MAO and compound I. It was found that, as in the case of ordinary Ziegler-Natta catalysts, the polymerization of ethylene is a first-order reaction with respect to ethylene and Zr (Fig. 2), and the observed activation energy for the reaction was 18 + 1.5 kJ/mol (Figs 3 and 4). The system based on compound II is characterized by a higher catalytic reactivity compared with compound I. Apparently this is due to a change in the electron density on cyclopentadienyl rings. The presence of a weak electron-donor trimethylsilyl group in compound II leads to some increase in kp. In the case of compound I we have the reverse effect [12]. The data in Table 1 show the extent to which the viscosity-average molecular mass of the polymers are influenced by the conditions of their preparation. PS 32"9-K
1870
L.A.
NEKHAEVA et al.
-/og w
2,5-
1,7
t 0.3 I z~,6
0,7 I ~,2
FIG. 2.
I 0.5 I 5.0
-/og[C2H4] -Iog[Zr]
Changes in the catalyst reactivity versus [Zr] and [C2H4] with a constant AI concentration (1) [I] --- 6.2 x 10 6 moi/l, AI:Zr = 5 x 103, 323 K; (2) Co = 0.61 mol/l, 303 K. In k e f f
¢.6
w x 10 4 mol/min 6 8----
oZ
5
0.000
; ~. : :
~' J
7
5
Z o
o~
~'.2
J
I 2O
120
Time, m/n
2,e
~,~
FIG. 3
~,J
(IO~/T)F ~
FIG. 4
FIG. 3.
Rate of ethylene polymerization in the presence of MAO + I (I) and MAO + II (II) versus time at 20 (1), 30 (2), 40 (3), 50 (4), 60 (5) and 70°C (6). Fzc3.4. Plot for calculating the energy of activation of ethylene polymerization on homogeneous catalytic systems of types MAO + I (1) and MAO + II (2) with coat = 6.2 x 10-6 mol]l, AI:Zr = 5 x 103.
TABLE 1.
EFFECT OF METHOD OF PREPARATION OF THE POLYMERS ON THEIR MOLECULAR MASS Ccat,
(Ai:Zr = 7 x 103)
Ccat,
T, °C
mol/1
r/, dl/g
h4n × 10 -4
T, °C
mol/1
,/, dl/g
hT/~x 10 -4
60 50 30
7.3 x 10 -s 7.2 x 10 -5 7.2 x 10 -5
1.0 1.1 1.25
3.45 3.9 4.5
30 30
1.75 x 10 -5 4.15 x 10 -6
1.8 6.0
7.3 35.0
It is n o w k n o w n [13] t h a t h o m o g e n e o u s s y s t e m s b a s e d o n m e t a l l o c e n e s a n d M A O
are efficient
c a t a l y s t s o f t h e c o p o l y m e r i z a t i o n o f e t h y l e n e w i t h s o m e t~-olefins. W e first s t u d i e d t h e c o p o l y m e r i z a tion of ethylene with VCH on a catalytic system containing MAO
a n d c o m p o u n d I o r II. T h e
i n t r o d u c t i o n o f V C H l e a d s to a c h a n g e in t h e c a t a l y s t n e g a t i v i t y ; t h e n a t u r e o f this c h a n g e is
Polymerization of ethylene using homogeneous catalysts
1871
illustrated in Fig. 5. The reaction rate goes through a weakly defined maximum at CvcH ~ 0.8 mol/l, which accords with information published in references [14--17] on the copolymerization of ethylene with a-olefins. It was noted in [18] that the rate of ethylene polymerization is higher in the presence of 4-methyl-l-pentene with catalytic systems of the following three types: MgClz-TiClaethylbenzoate-(/so-Bu)3A1; MgCl2-TiCl4-diisobutylphthalate-(iso-Bu)3A1, and 6-TIC12-0.33 AICl2-(iso-Bu)3Ar; the effect in question is ascribed to an increase in the number of active centres. However, the observed rise in the reaction rate for the system zirconocene-MAO in the copolymerization of ethylene with a-olefins cannot be attributed to an increase in the number of active centres, since under the conditions stated above the number of active centres reaches practially 100% already in the homopolymerization of ethylene. Apparently the presence of VCH in the reaction system results in the formation of active centres of higher reactivity. A further increase in the concentration of VCH, which has such very low reactivity compared with ethylene, may reduce the rate of ethylene polymerization processes. Using the plot of the copolymer composition determined as previously in [6] versus the composition of the initial mixture of monomers (Fig. 6), it was found in accordance with the equation [l 9, 20]
(Cm)(Cml rl \ Ce /m
that the copolymerization constant r 1 = 62.5 + 2.5. A,. x 10 J, kg PE/mol Zr x h
(Cvc./c.L x 102 5
8~ J J
I
I
a
O, 6
I I, #
I
I
Cvc., mol/I
I
J (Cvc,/c~),,, Fie. 6
Fid. 5 Fl{;. 5.
~
I
Plots of the c a t a l y s t r e a c t i v i t y A,,, v e r s u s V C H c o n c e n t r a t i o n : (1) [ ( C s H a C ( C H 3 ) 3 ) Z r C I 2 ] = 10 _5
mol/l. T = 30°C; (2) [ ( C s H 4 C ( C H 3 ) 3 ) 2 Z r C I 2 ] = 10 -6 mol/l, T = 50°C; (3) [(CsHaSi(CH3)3)2ZrCI2] = 10 -5 mol/l, T = 30°C. FIG. 6.
D e p e n d e n c e of the c o p o l y m e r c o m p o s i t i o n o n that of the m o n o m e r m i x t u r e w i t h [I] = 7 × 10 -5 mol/l, A I : Z r = 1.7 x 103, 50°C.
The amount of VCH introduced into the copolymer may be as high as 5 mol%. The introduction of just 1 mol% of VCH reduces the density of the polymer from 0.98 to 0.96 g/cm3, and the melting point falls from 127 to 122°C, while at the same time the breaking elongation is increased from 700 to 1000%. Thus it is evident that vinylcyclohexane incorporated in chain leads to significant changes in the properties of the polymers. We are now investigating the use of the studied catalysts in the case of ethylene copolymerization with a number of other monomers.
1872
L . A . NEKHAEVA et al.
The authors thank L. I. Vyshinskaya and her coworkers for kindly providing the zirconocene specimens used in this investigation.
Translated by R. J. A. HENDRY
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