1-olefin stereoblock polymer wax, and a process for the preparation thereof

1-Olefin stereoblock polymer waxes having a very narrow molecular weight distribution are obtained by means of a catalyst which comprises a metallocene compound containing cyclopentadienyl radicals substituted by chiral groups, and an aluminoxane, in the presence of small amounts of hydrogen during the polymerization.

The invention relates to 1-olefin stereoblock polymer waxes having a narrow 
molecular weight distribution M.sub.w /M.sub.n, and to a process for the 
preparation thereof. 
Stereoblock polymers are homopolymers in whose molecular chains isotactic 
sequences having an opposed configuration alternate with one another. 
A process is known for the preparation of polypropylene which has a 
block-like structure and in which the isotactic sequences are 2 to 17 
monomer units long (cf. U.S. Pat. No. 4,522,982). The catalyst employed is 
a metallocene of a metal from group 4b, 5b or 6b of the Periodic Table, 
for example titanium, vanadium or hafnium, in particular titanium. This 
metallocene is a mono-, di- or tricyclopentadienyl or substituted 
cyclopentadienyl metal compound. The cocatalyst employed is an 
aluminoxane. 
However, the titanocenes preferably used are not of sufficient 
thermostability in dilute solution to be used in an industrial process. 
Finally, the cocatalysts must be employed in a comparatively high 
concentration in order to achieve an adequate catalyst yield, which has 
the result that the catalyst residues present in the polymer product have 
to be removed in a separate purification step. 
The preparation of high-isotacticity polyolefin waxes (Isotactic Index 
80-85%, melt enthalpy 63 J/g, mixtures of atactic and isotactic polyolefin 
chains) by means of supported catalyst, cocatalyst and stereoregulator at 
temperatures of greater than 95.degree. C. is known (cf, De-A No. 
3,148,229). However, it is necessary to employ large amounts of hydrogen 
as molecular weight regulator since catalyst systems of this type develop 
their greatest activity in the area of high-molecular-weight polyolefin 
plastics. In order to achieve the degrees of polymerization which are 
typical of waxes, propylene: hydrogen partial pressure ratios of &lt;1 are 
required. 
It is known that hydrogenation of propylene to propane occurs to a 
significant extent under such reaction conditions and thus results in 
considerable loss of propylene. The low catalyst activities which are 
achieved under these reaction conditions result in high residual ash 
contents and, in particular, extremely high chlorine contents in the wax 
products, and require complex purification steps for removal. 
Furthermore, an MgCl.sub.2 -supported catalyst is known which results in 
crystalline PP waxes having a narrow molecular weight distribution (JP 
59/206,409). However, this catalyst likewise has the disadvantage of a 
poor response to hydrogen, and very large amounts of hydrogen are 
necessary for molecular weight regulation. This results in a poor 
space-time yield and comparatively low activity. In addition, relatively 
high chlorine contents of, in some cases, greater than 1,000 ppm are found 
in the polymer waxes if the catalyst residues are not removed by specific 
aftertreatment. Here too, the high hydrogen partial pressures result in 
significant hydrogenation of propylene to propane and thus in considerable 
loss of propylene. 
A specific pre-activation method of metallocene using an aluminoxane has 
also been proposed; this results in a considerable increase in the 
activity of the catalyst system and in a significant improvement in the 
grain morphology of the polymer (cf. DE No. 3,726,067). 
In addition, it has been proposed to use a metallocene having several 
centers of chirality for the preparation of 1-olefin stereoblock polymers 
(cf. DE No. 3,640,948). 
It is furthermore known from the literature that the molecular weight of 
polyolefins prepared using metallocene/aluminoxane can be controlled via 
the polymerization temperature. Specifically, a high polymerization 
temperature results in a low molecular weight. Experiments have now shown 
that, in the case of metallocene/aluminoxane catalysts, the temperature 
range available in industry is not sufficient to include and cover the 
important molecular weight range for wax types. 
A further disadvantage in using polyolefins prepared by means of 
metallocene/aluminoxane systems is the fact that the chain ends produced 
on chain termination always contain an unsaturated group. 
It is known from the literature that organometallic compounds, such as, for 
example, AlR.sub.3 or ZnR.sub.2, are capable of initiating 
chain-termination reactions, even in combination with 
metallocene/aluminoxane systems. However, experiments have shown that the 
catalyst activities usually fall drastically and, in addition, the 
undesired residual ash content in the wax increases greatly due to the 
necessary addition of relatively large amounts of these molecular weight 
regulators. Only AlMe.sub.3 allows the catalyst activity to increase, but 
the action as a molecular weight regulator is unsatisfactory and the 
necessary use of large amounts likewise results in an increase in the 
residual ash content in the polymer. 
The object was to find a process using which polyolefin waxes containing 
saturated chain ends can be prepared in direct synthesis using 
metallocene/aluminoxane catalysts. 
It has been found that the object can be achieved when hydrogen is used as 
the molecular weight regulator. The metallocenes used have a surprisingly 
high sensitivity for hydrogen, which means that waxes can be produced 
using small amounts of hydrogen. 
The invention thus relates to a stereoblock polymer wax comprising units 
derived from a 1-olefin of the formula RCH=CH.sub.2 in which R denotes an 
alkyl radical having 1 to 28 carbon atoms, with alternating isotactic 
sequences of opposed configuration and having a length of 3 or more 
monomer units in the molecular chain, having a molecular weight 
distribution M.sub.w /M.sub.n of from 1.8 to 3.0 and having a viscosity 
number of from 2 to 60 cm.sup.3 /g. 
The invention furthermore relates to a process for the preparation of a 
1-olefin stereoblock polymer wax by polymerization of a 1-olefin of the 
formula R--CH.dbd.CH.sub.2 in which R is an alkyl radical having 1 to 28 
carbon atoms, in one or more steps at a temperature of from -50.degree. to 
200.degree. C., at a pressure of from 0.5 to 120 bar, in solution, in 
suspension or in the gas phase, in the presence of a catalyst comprising a 
transition metal compound and an aluminoxane, which comprises carrying out 
the polymerization in the presence of a catalyst whose transition metal 
compound is a metallocene compound of the formula I 
##STR1## 
in which R.sup.1 and R.sup.2 are identical or different and denote a 
halogen atom, C.sub.1 -C.sub.10 -alkyl, C.sub.6 -C.sub.10 -aryl, C.sub.2 
-C.sub.10 -alkenyl C.sub.7 -C.sub.40 -arylalkyl, C.sub.7 -C.sub.40 
-alkylaryl or C.sub.8 -C.sub.40 -alkenylaryl R.sup.3 and R.sup.4 are 
identical or different and denote a substituted cyclopentadienyl radical, 
where this radical contains one or more centers of chirality and has been 
produced by reacting an alkali metal cyclopentadienide with a chiral 
alcohol, and Me is titanium, zirconium or hafnium, and has been 
pre-activated before the polymerization using an aluminoxane of the 
formula II 
##STR2## 
for the linear type and/or one of the formula III 
##STR3## 
for the cyclic type, where, in the formulae II and III, R.sup.5 denotes 
methyl, ethyl or isobutyl, and n is an integer from 5 to 40, for 5 minutes 
to 60 minutes at a temperature of from -78.degree. to 100.degree. C., and 
the activator is likewise an aluminoxane of the formulae II or III, and 
hydrogen is present in the 1-olefin:H.sub.2 molar ratio of from 3 to 
3,000. 
To prepare the stereoblock polymer wax according to the invention, a 
metallocene of the formula (I) is employed: 
##STR4## 
In this formula, Me is titanium, zirconium or hafnium. R.sup.1 and R.sup.2 
are identical or different and denote a halogen atom, C.sub.1 -C.sub.10 
-alkyl, C.sub.6 -C.sub.10 -aryl, C.sub.2 -C.sub.10 -alkenyl, C.sub.7 
-C.sub.40 -arylalkyl, C.sub.7 -C.sub.40 -alkylaryl or C.sub.8 -C.sub.40 
-alkenylaryl. 
R.sup.3 and R.sup.4 are identical or different and denote a substituted 
cyclopentadienyl radical, where this radical contains one or more centers 
of chirality and has been produced by reacting an alkali metal 
cyclopentadienide with a chiral alcohol. 
R.sup.3 and R.sup.4 may also be connected by a C.sub.1 -C.sub.2 -alkylene 
bridge or an R.sub.2.sup.6 Si bridge. R.sup.6 denotes C.sub.1 -C.sub.10 
-alkyl, C.sub.6 -C.sub.10 -aryl, C.sub.2 -C.sub.10 -alkenyl, C.sub.7 
-C.sub.40 -arylalkyl, C.sub.7 C.sub.40 -alkylaryl or C.sub.8 -C.sub.40 
-alkenylaryl. 
In the formula I, Me is preferably zirconium or hafnium, and R.sup.1 and 
R.sup.2 preferably denote a halogen atom or an alkyl group, preferably 
methyl, in particular a chlorine atom. R.sup.3 and R.sup.4 have been 
produced by reacting an alkali metal cyclopentadienide, preferably sodium 
cyclopentadienide, and, for example, one of the following chiral alcohols: 
thujyl alcohol; neothujyl alcohol; cis- and trans-sabinol; 
2,5-dimethyl-4-vinyl-2,5-hexadien-1-ol; lavandulol; iso-pulegol; 
neoisopulegol; cis- and trans-pulegol; isomenthol, neomenthol; 
neoisomenthol; menthol; cis- and trans-.DELTA..sup.1 (7)-p-menthen-2-ol; 
cis- and trans-.DELTA..sup.1 (7)8-p-menthadien-2-ol; dihydrocarveol; 
neodihydrocarveol; isodihydrocarbeol; neoisodihydrocarveol; carvomenthol; 
neoisocarvomenthol; isocarvomenthol; neocarvomenthol; perilla alcohol; 
phellandrol; butan-2-ol; cycloisolongifolol; isolongifolol; 
2-methylbutanol; octan-2-ol; pentan-2-ol; phenylethanol; 
hydroxycitronellal; hydroxycitronellol; cis- and trans-myrtenol; 
2,6-dimethyloct-3-ene-2,8-diol; 2,6-dimethyloct-1-ene-3,8-diol; 
dihydrocitronellol; citronellol; 2,6-dimethylocta-2,7-dien-4-ol; 
2,6-dimethylocta-1,7-dien-3-ol; .DELTA..sup.1,8 -p-menthadien-9-ol; 
.DELTA..sup.1 -p-menthen-9-ol; cis- and trans-sobrerol; cis-m-menthan-5-l, 
.DELTA..sup.4/10 -caren-5-ol; .DELTA..sup.3 -caren-2-ol; caran-3-ol; 
isocaran-3ol; neocaran-3-ol; neoisocaran-3-ol; .alpha.,.beta.-fenchol; 
borneol; isoborneol; cis- and trans-myrtanol; neoverbanol; neoisoverbanol; 
cis- and trans-chrysanthenol; cis- and trans-verbenol; isoverbanol; cis- 
and transpinocarveol; pinocampheol; neopinocampheol; isopinocampheol; 
neoisopinocampheol and methylnopinol. 
Of these chiral alcohols, the cyclic ones are preferably applied. 
Neomenthol is particularly preferred. The metallocene compound preferably 
used is thus bis(neomenthylcyclopentadienyl)zirconium dichloride, 
bis(neoisomenthyicyclopentadienyl)zirconium dichloride or 
bis(cis-myrtanylcyclopentadienyl)zirconium dichloride, particularly 
preferably bis(neomenthylcyclopentadienyl)-zirconium dichloride. 
These compounds can be prepared, for example, in the following manner: 
##STR5## 
Before use in the polymerization reaction, the metallocene is 
pre-activated using an aluminoxane. This aluminoxane is a compound of the 
formula II 
##STR6## 
for the linear type and/or of the formula III 
##STR7## 
for the cyclic type. In these formulae, R.sup.5 denotes a C.sub.1 -C.sub.6 
-alkyl group, preferably methyl, ethyl or isobutyl, in particular methyl, 
and n denotes an integer from 5 to 40, preferably 15 to 35. 
The aluminoxane can be prepared in various ways. 
In one of the processes, finely powdered copper sulfate pentahydrate is 
slurried in toluene, and sufficient trialkylaluminum is added in a glass 
flask under an inert gas at about -20.degree. C. such that about 1 mole of 
CuSO.sub.4.5H.sub.2 O is available for each 4 Al atoms. After slow 
hydrolysis with elimination of alkane, the reaction mixture is left at 
room temperature for 24 to 48 hours, cooling sometimes being necessary so 
that the temperature does not exceed 30.degree. C. The aluminoxane 
dissolved in toluene is subsequently separated from the copper sulfate by 
filtration, and the toluene is removed by distillation in vacuo. It is 
assumed that the low-molecular-weight aluminoxanes condense in this 
preparation process to form higher oligomers with elimination of 
trialkylaluminum. 
In addition, aluminoxanes are obtained when trialkylaluminum, preferably 
trimethylaluminum, dissolved in an inert aliphatic or aromatic solvent, 
preferably heptane or toluene, is reacted at a temperature of -20.degree. 
to 100.degree. C. with aluminum salts containing water of crystallization, 
preferably aluminum sulfate. In this case, the volume ratio between the 
solvent and the alkylaluminum used is 1:1 to 50:1 --preferably 5:1--and 
the reaction time which can be monitored by elimination of the alkane, is 
1 to 200 hours--preferably 10 to 40 hours. 
Of the aluminum salts containing water of crystallization, those are used, 
in particular, which have a high content of water of crystallization. 
Aliminum sulfate hydrate is particularly preferred, above all the 
compounds Al.sub.2 (SO.sub.4).sub.3.18H.sub.2 O and Al.sub.2 
(SO.sub.4).sub.3.16H.sub.2 O having the particularly high water of 
crystallization content of 18 and 16 moles of H.sub.2 O/mole of Al.sub.2 
(SO.sub.4).sub.3 respectively. 
The pre-activation is carried out in solution, with the metallocene 
preferably being dissolved in a solution of the aluminoxane in an inert 
hydrocarbon. Suitable inert hydrocarbons are aliphatic and aromatic 
hydrocarbons. 
Toluene is preferably used. 
The concentration of the aluminoxane in the solution is in the range from 
about 1% by weight to the saturation limit, preferably from 5 to 30% by 
weight, in each case based on the total solution. The metallocene can be 
employed in the same concentration, but is preferably employed in an 
amount of from 10.sup.-4 -1 mole per mole of aluminoxane. The 
pre-activation time is 5 minutes to 60 minutes, preferably 10-20 minutes. 
Significantly longer pre-activation is possible, but normally neither 
increases the activity nor decreases the activity and has no effect, in 
particular, on the molecular weight of the polyolefin wax produced, but 
may be thoroughly appropriate for storage purposes. The preactivation is 
carried out at a temperature of from -78.degree. to 100.degree. C., 
preferably 0.degree. to 70.degree. C. 
The pre-activation can be carried out either with exclusion of light or 
under the action of light since the metallocenes, which are generally 
photosensitive, are stabilized by the aluminoxane. It is nevertheless 
preferred to exclude direct incidence of light, particularly at relatively 
long pre-activation times and in the case of particularly sensitive 
metallocenes. 
The second component of the catalyst to be used according to the invention 
is an aluminoxane of the formula (II) and/or (III). Preferably, the same 
aluminoxane is used for pre-activation and for polymerization. 
The catalyst to be used according to the invention is employed for 
polymerization of 1-olefins of the formula R--CH.dbd.CH.sub.2 in which R 
denotes an alkyl radical having 1 to 28 carbon atoms, preferably 1 to 10 
carbon atoms, in particular one carbon atom, for example propylene, 
1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. Propylene is 
particularly preferred. Furthermore, the catalyst is also employed for 
copolymerization of these olefins with one another and with ethylene, it 
being possible to copolymerize more than 50% by weight of ethylene. 
The polymerization is carried out in a known manner in liquid monomers, in 
solution, in suspension or in the gas phase, continuously or batchwise, in 
one or more steps, at a temperature of -50.degree. to 200.degree. C., 
preferably -20 to 120, in particular -20.degree. to 80.degree. C. 
Hydrogen is added as a molecular weight regulator. The hydrogen partial 
pressure in this case is between 0.05 and 50 bar, preferably 0.1 to 25 
bar, in particular 0.5 to 10 bar. 
The 1-olefin:hydrogen molar ratio is thus 3 to 3,000, preferably 6 to 
1,500, in particular 15 to 300. 
The overall pressure in the polymerization system is thus 0.5 to 120 bar. 
Polymerization in the pressure range from 5 to 100 bar, which is 
particularly interesting in industry, is preferred. 
The metallocene compound is used in a concentration, based on the 
transition metal, of from 10.sup.-3 to 10.sup.-7, preferably 10.sup.-4 to 
10.sup.-6, mole of transition metal per dm.sup.3 of solvent or per 
dm.sup.3 of reactor volume. The aluminoxane is used in the concentration 
of from 10.sup.-4 to 10.sup.-1 mole, preferably 10.sup.-3 to 
2.times.10.sup.-2 mole per dm.sup.3 of solvent or per dm.sup.3 of reactor 
volume. In principle, however, higher concentrations are also possible. 
It is advantageous to firstly stir the aluminoxane into the polymerization 
system for a few minutes together with the polymerization liquid phase 
before adding the metallocene. The stirring time is preferably 10 to 30 
minutes. However, shorter stirring times are also possible without 
suffering to any great extent, and a longer stirring time has no notable 
effect on the polymerization result. 
The polymerization is carried out in an inert solvent which is customary 
for the low-pressure Ziegler process, for example in an aliphatic or 
cycloaliphatic hydrocarbon; examples which may be mentioned are butane, 
pentane, hexane, heptane, isooctane, cyclohexane and methylcyclohexane. In 
addition, it is possible to use a petroleum or hydrogenated diesel oil 
fraction which has been carefully freed from oxygen, sulfur compounds and 
moisture. Toluene can also be used. The monomer to be polymerized is 
preferably employed as a solvent or suspending agent. 
The duration of polymerization is as desired since the catalyst system to 
be used according to the invention only exhibits a low time-dependent 
decrease in the polymerization activity. 
In the process according to the invention, the use of hydrogen as a 
molecular weight regulator results in a drastic increase in the catalyst 
activity. At the same time, the molecular weight can be controlled 
precisely in the desired range. The molecular weight distribution M.sub.w 
/M.sub.n here is extremely narrow, with values between 1.8 and 3.0. The 
use according to the invention of hydrogen at the same time results in a 
significant reduction in the residual ash content. Using the process 
according to the invention, a polyolefin wax can be prepared which has a 
stereoblock structure. Isotactically opposed sequences having a length of 
3 or more monomer units alternate in the molecular chains. In general, the 
chain ends are built up from saturated hydrocarbon groups. At room 
temperature, stereoblock polymer waxes exist in the form of waxy solids or 
high-viscosity liquids. The viscosity numbers are in the range from 2 to 
60, preferably 4 to 30, in particular 5 to 20, cm.sup.3 /g. 
The examples below are intended to illustrate the invention. In these 
examples:

EXAMPLE 1 
A dry 16 dm.sup.3 reactor is flushed with nitrogen and filled with 40 
dm.sup.3 (s.t.p.)corresponding to 2.5 bar) of hydrogen and with 10 
dm.sup.3 of liquid propylene. 70 cm.sup.3 of a toluene solution of 
methylaluminoxane (corresponding to 68 mmol of Al, mean degree of 
oligomerization n=30) were added, and the batch was stirred at 30.degree. 
C. for 15 minutes. 
In parallel, 100 mg (0.176 mmol) of 
bis-(-)-neomenthylcyclopentadienylzirconium dichloride were dissolved in 
35 cm.sup.3 of a toluene solution of methylaluminoxane (34 mmol of Al), 
and the mixture was pre-activated by standing for 15 minutes. 
The solution was then introduced into the reactor. The polymerization 
system was heated to a temperature of 50.degree. C. and then kept at this 
temperature for 2 hours. 2.45 kg of polypropylene wax were obtained. The 
activity of the metallocene was thus 7.0 kg of PP wax/mmol of Zr .times.h 
or 12.3 kg of PP wax/g of metallocene .times.h. 
VN=5.9 cm.sup.3 /g; M.sub.w =2520, M.sub.n =1200, M.sub.w /M.sub.n =2.1; 
II=62%, n.sub.iso =3.0; no unsaturated chain ends. 
EXAMPLE 2 
The procedure was analogous to Example 1, but 16 dm.sup.3 (s.t.p.) 
(corresponding to 1 bar) of hydrogen were used in place of the 40 dm.sup.3 
(s.t.p.) (corresponding to 2.5 bar) of hydrogen. 2.20 kg of polypropylene 
wax were obtained. The activity of the metallocene was thus 6.3 kg of PP 
wax/mmol of Zr.times.h or 11.0 kg of PP wax/g of metallocene .times.h. 
VN =9.8 cm.sup.3 /g, M.sub.w =3260, M.sub.n =1600, M.sub.w /M.sub.n =2.0; 
II=60%, n.sub.iso =3.1; no unsaturated chain ends. 
EXAMPLE 3 
The procedure was analogous to Example 1, but 4 dm.sup.3 (s.t.p.) 
(corresponding to 0.25 bar) of hydrogen were used in place of the 40 
dm.sup.3 (s.t p ) (corresponding to 2.5 bar) of hydrogen. 1.98 kg of 
polypropylene wax were obtained. The activity of the metallocene was thus 
5.7 kg of PP wax/mmol of Zr.times.h or 9.9 kg of PP wax/g of metallocene 
.times.h. 
VN=12.4 cm.sup.3 /g, M.sub.w =4760, M.sub.n =2150, M.sub.w /M.sub.n =2.2; 
II=69%, n.sub.iso =3.5; no unsaturated chain ends. 
EXAMPLE 4 
The procedure was analogous to Example 1, but the metallocene employed was 
bis-(neoisomenthylcyclopentadienyl)zirconium dichloride (100 mg, 0.176 
mmol). 2.33 kg of polypropylene wax were obtained. The activity of the 
metallocene was thus 6.7 kg of PP wax/mmol of Zr.times.h or 11.6 kg of PP 
wax/g of metallocene .times.h. 
VN=6.2 cm.sup.3 /g; M.sub.w =2420, M.sub.n =1160, M.sub.w /M.sub.n =2; 
II=67%, n.sub.iso =4.0; no unsaturated chain ends. 
EXAMPLE 5 
The procedure was analogous to Example 1, but the metallocene employed was 
bis-(cis-myrtanylcyclopentadienyl)-zirconium dichloride (200 mg, 0.354 
mmol). 1.79 kg of polypropylene wax were obtained. The activity of the 
metallocene was thus 2.5 kg of PP wax/mmol of Zr.times.h or 4.5 kg of PP 
wax/g of metallocene .times.h. 
VN=4.7 cm.sup.3 /g; M.sub.w =1530, M.sub.n =875, M.sub.w /M.sub.n =1.8; 
II=58%, n.sub.iso =3.0; no unsaturated chain ends. 
Comparative experiment A 
The procedure was analogous to Example 1, but 50 mmol of diethylzinc in 50 
cm.sup.3 of toluene were metered in in place of the hydrogen. 
Polypropylene was only formed in traces. The isolated solid was 
predominantly decomposition products of aluminoxane and of diethylzinc. 
Comparative experiment B 
The procedure was analogous to Example 1, but no hydrogen was used. 1.10 kg 
of polypropylene were obtained. The activity of the metallocene was thus 
3.1 kg of PP/mmol of Zr.times.h or 5.5 kg of PP/g of metallocene .times.h. 
VN=26.2 cm.sup.3 /g; M.sub.w =19,600, M.sub.n =8500, M.sub.w /M.sub.n =2.3; 
II=58%, n.sub.iso =3.0; one unsaturated chain end per polypropylene chain 
(determined by .sup.13 C NMR).