Process for the production of vinylaromatic polymers with a high degree of syndiotacticity

Process for the preparation of crystalline vinylaromatic polymers with a high degree of syndiotacticity which comprises polymerizing vinylaromatic monomers in the presence of a catalytic system essentially consisting of: PA1 a) a complex of titanium selected from those having the general formula: EQU (CpR.sub.1 R.sub.2 R.sub.3 R.sub.4 R.sub.5)TiX.sub.3 (I) PA1 wherein the groups R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 represent a hydrogen atom or C.sub.1 -C.sub.10 alkyl groups; PA2 X represents a hydrogen atom, a halogen such as chlorine, a C.sub.1 -C.sub.10 alkyl or oxyalkyl radical or a C.sub.6 -C.sub.12 oxyaryl radical; PA1 b) an alkylaluminoxane; and PA1 c) an organic derivative of tin; characterized in that the alkylaluminoxane is methylaluminoxane (MAO) treated at 20.degree.-80.degree. C. under vacuum for 1-100 hours and the organic derivative of tin is tin tetraphenyl.

The present invention relates to a process for the preparation of 
vinylaromatic polymers with a high degree of syndiotacticity. 
More specifically, the present invention relates to a process for the 
preparation of crystalline polystyrene in which the polymeric chains have 
an essentially syndiotactic configuration and the catalyst suitable for 
the purpose. 
Polystyrene is a thermoplastic polymer obtained by the radicalic 
polymerization of styrene and is used in the production of moulded 
articles, films, electrical materials, materials for packaging, etc. It is 
an atactic, amorphous polymer with excellent insulating properties and 
reasonable thermal resistance. For numerous applications it is preferable 
however to use crystalline materials with a high thermal resistance and 
resistance to solvents, characteristics which atactic polystyrene does not 
have. 
European patent 210.615 describes a polystyrene having a structure 
characterized by an extremely high degree of stereoregularity, in which 
the phenyl substituents are so arranged as to provide a syndiotactic 
polymer. This material does not have the above disadvantages of atactic 
polystyrene as it is crystalline and therefore, once transformed, can be 
subjected to orientation processes, it is almost completely insoluble in 
organic solvents and has a melting point within the range of 
260-280.degree. C., giving it a high thermal resistance, comparable to or 
higher than that of condensation thermoplastic polymers (polyesters, 
polyamides, polyimides, etc.). 
Syndiotactic polystyrene can be prepared according to what is described in 
literature, for example in European patent EP 272.584 or in U.S. Pat. No. 
4,978,730, by polymerization catalyzed by compounds of Ti or Zr, in the 
presence of a cocatalyst represented by methylaluminoxane (a mixture of 
cyclic and linear oligomers containing the repetitive unit --AlCH.sub.3 
O--) or, as described in published European patent application 421.659, 
from derivatives of boron containing fluorinated groups. 
Examples of catalysts for the synthesis of syndiotactic polystyrene 
provided in literature are titanium halides (chloride, bromide, etc.), 
titanium alcoholates (methoxide, ethoxide, propoxide, isopropoxide, 
butoxide, etc.), titanium carboxylates, metallocenes (cyclopentadienyl 
titanium trichloride, cyclopentadienyl titanium dichloride, 
pentamethylcyclopentadienyl titanium trichloride, cyclopentadienyl 
titanium alkoxides, cyclopentadienyl titanium alkyls, 
pentamethylclopentadienyl titanium alkyls, dicyclopentadienyl titanium 
dichloride, dicyclopentadienyl titanium alkoxides, etc.), titanium alkyls 
(titanium tetrabenzyl, titanium tetramethyl, titanium tetraethyl, etc.) 
and the corresponding zirconium compounds. 
The Applicant has now found that it is possible to synthesize crystalline 
vinylaromatic polymers, and in particular crystalline polystyrene, having 
a highly syndiotactic configuration using a new catalytic system which has 
never been described in literature. 
The present invention therefore relates to a process for the preparation of 
crystalline vinylaromatic polymers with a high degree of syndiotacticity 
which comprises polymerizing vinylaromatic monomers, either alone or mixed 
with at least one other ethylenically unsaturated copolymerizable monomer, 
in the presence of a catalytic system essentially consisting of: 
a) a titanium complex having general formula: 
EQU (CpR.sub.1 R.sub.2 R.sub.3 R.sub.4 R.sub.5)TiX.sub.3 (I) 
wherein the groups R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5, the 
same or different, represent a hydrogen atom or C.sub.1 -C.sub.10 alkyl 
groups; 
Cp is a cyclopentadienyl group; 
X represents a hydrogen atom, a halogen such as chlorine, a C.sub.1 
-C.sub.10 alkyl or oxyalkyl radical or a C.sub.6 -C.sub.12 oxyaryl 
radical; 
b) an alkylaluminoxane; and 
c) an organic derivative of tin; 
characterized in that the alkylaluminoxane is methylaluminoxane (MAO) 
treated at 20.degree.-80.degree. C. under vacuum for 1-100 hours and the 
organic derivative of tin is tin tetraphenyl. 
With respect to the traditional catalytic systems, essentially based on 
compounds (a) and (b), the catalytic system of the present invention 
proves to be very active. Activities of over 1,000 Kg of polymer per 
grammoatom of titanium, for example of up to 4,000 Kg, as well as a high 
degree of syndiotacticity, can be easily obtained. 
The compounds having general formula (I) are products which are known in 
literature and described in "Progress in Polymer Science" vol. 21, page 
47, 1996. 
Typical examples of complexes of titanium having formula (I) which are 
particularly suitable for the present invention are CpTiCl.sub.3 ; 
CpTi(OCH.sub.3).sub.3 ; CpTi(OC.sub.2 H.sub.5).sub.3 ; CpTi(OC.sub.3 
H.sub.7).sub.3 ; CpTi(Oi-C.sub.3 H.sub.7).sub.3 ; CpTi(OC.sub.4 
H.sub.9).sub.3 ; Cp(CH.sub.3).sub.5 !TiCl.sub.3 ; Cp(CH.sub.3).sub.5 
!TiBr.sub.3 ; Cp(CH.sub.3).sub.5 !TiF.sub.3 ; CpTi(OC.sub.5 
H.sub.6).sub.3 ; Cp(CH.sub.3).sub.5 !Ti(OCH.sub.3).sub.3 ; 
Cp(CH.sub.3).sub.5 !Ti(OC.sub.2 H.sub.5).sub.3 ; Cp(CH.sub.3).sub.5 
!Ti(OC.sub.3 H.sub.7).sub.3 ; Cp(CH.sub.3).sub.5 !Ti(OC.sub.4 
H.sub.9).sub.3 ; Cp(CH.sub.3).sub.5 !Ti(OC.sub.5 H.sub.6).sub.3 ; 
CpTiH.sub.3 ; CpTi(CH.sub.3).sub.3 ; CpTi(C.sub.2 H.sub.5); CpTi(CH.sub.2 
C.sub.5 H.sub.6).sub.3 ; Cp(CH.sub.3).sub.5 !TiH.sub.3 ; 
Cp(CH.sub.3).sub.5 !Ti(CH.sub.3).sub.3 ; Cp(CH.sub.3).sub.5 !Ti (C.sub.2 
H.sub.5).sub.3 ; Cp(CH.sub.3).sub.5 !Ti(CH.sub.2 C.sub.5 H.sub.6).sub.3 ; 
CpTi(OPh).sub.3 ; Cp(CH.sub.3).sub.5 !Ti(OPh ).sub.3. Particularly 
preferred are the complexes in which the cyclopentadienyl group is 
pentamethyl substituted. 
The compounds of titanium having general formula (I) are added to the 
polymerization mixture in such a quantity that the molar ratio 
vinylaromatic monomer/Ti is between 10,000 and 1,000,000, preferably 
between 100,000 and 500,000. 
The alkylalumoxane (cocatalyst) essentially consists of mixtures of 
products having a linear or cyclic or caged structure. In the first case 
the structure is represented by the general formula (II): 
##STR1## 
whereas in the second case by the general formula (III): 
##STR2## 
wherein m represents an integer between 1 and 40 and R' a methyl. The 
caged structure is described in Molecular Symposium, Vol. 97, 1995. 
Alkylaluminoxanes are known in literature and described, for example, in 
published European patent applications 272.584 and 421.659 or in U.S. Pat. 
No. 4,978,730. 
The cocatalyst is treated at a temperature of between 20.degree. and 
80.degree. C. under vacuum for at least one hour and can then be added to 
the polymerization mixture as such or in the form of a solution in a 
suitable solvent, for example toluene. 
The cocatalyst is generally used in such quantities that the molar ratio 
aluminum/Ti is between 50 and 5,000. 
Tin tetraphenyl is a commercial product and is used in such a quantity that 
the molar ratio Sn/Ti is between 0.1 and 100, preferably below 20. 
According to the process of the present invention, the catalytic system 
described above can also comprise, optionally, an aluminium alkyl in which 
the alkyl group contains from 1 to 6 carbon atoms, for example aluminium 
trimethyl, aluminium triethyl, aluminium triisobutyl etc. in such a way 
that a part of the MAO can be substituted, corresponding to a percentage 
varying from 0 to 75% in moles. 
The term "vinylaromatic polymers" as used in the present invention and 
claims basically refers to polymers of styrene and derivatives of styrene 
and the relative copolymers containing up to 20% in moles of another 
copolymerizable monomer selected from those having general formula (IV): 
EQU CH.sub.2 .dbd.CH--R" (IV) 
wherein R" represents a hydrogen atom or a C.sub.1 -C.sub.6 alkyl radical 
or a C.sub.4 -C.sub.12 cycloalkyl radical. 
Derivatives of styrene comprise alkyl styrenes, in which the alkyl group 
contains from 1 to 4 carbon atoms, halogenated styrenes, C.sub.1 -C.sub.4 
alkoxy styrenes, carboxy styrenes, vinylnaphthalenes such as alpha- or 
beta-vinyl naphthalene, vinyl tetrahydro naphthalene such as 
1,2,3,4-tetrahydro-6-vinylnaphthalene, etc. Typical examples of 
substituted styrenes are p-methylstyrene, m-methylstyrene, alone or mixed 
with each other, ethylstyrene, butylstyrene, p-ter-butylstyrene, 
dimethylstyrene, chlorostyrene, bromostyrene, fluorostyrene, 
chloromethylstyrene, methoxystyrene, acetoxy methylstyrene, etc. 
The polymerization reaction can be carried out in mass or in solvent. In 
the latter case, the solvent can consist of aliphatic or aromatic 
hydrocarbons or their mixtures and is used in such quantities that the 
ratio by volume solvent/monomers is between 0 and 10. The preferred 
solvent is toluene. 
More specifically, according to the general procedure adopted for this type 
of reaction, the vinylaromatic monomers are subjected before 
polymerization to specific treatment to eliminate catalytic poisons, such 
as phenol stabilizers, water, phenylacetylene, and consisting in 
distillation, passage on columns containing activated molecular sieves or 
activated alumina, etc. The monomers and, optionally, the solvent are 
charged into the reaction equipment together with the possible aluminium 
alkyl and cocatalyst. After a time varying from 5 seconds to 30 minutes, 
the catalytic system comprising the titanium complex having general 
formual (I) and the tin tetraphenyl is added, preferably in the form of a 
solution. The reaction proceeds for times varying from 15 minutes to 10 
hours at temperatures of between 20.degree. and 100.degree. C. At the end, 
the polymer obtained is recovered using the traditional methods.

The following illustrative but non-limiting examples are provided to give a 
better understanding of the present invention and for its embodiment. 
Analysis procedure: 
The percentage of syndiotactic polymer is determined by extracting the 
polymer with acetone or methylethylketone (MEK) at boiling point for 10-20 
hours. 
The degree of stereoregularity is determined by nuclear magnetic resonance 
spectroscopy of carbon 13 as described in U.S. Pat. No. 4,680,353. 
EXAMPLE 1 
500 ml of a commercial solution of methylaluminoxane at 10% in toluene 
(Witco GmbH) were charged into a jacketed reactor placed in an inert 
atmosphere. The solvent was removed by distillation under vacuum at 5 torr 
and 55.degree. C., after which the application of the vacuum at a 
temperature of 55.degree. C. was maintained for a further 1.5 hours. At 
the end, the white powder obtained was transferred to a container in an 
inert atmosphere and used for the subsequent tests, after dissolution in 
toluene. 
Comparative Example 1 
This example describes the polymerization of styrene without tin 
tetraphenyl. 
20 ml of styrene (0.175 moles) purified by passage on a column of basic 
alumina, 0.42 ml of a 1.66M solution of MAO (treated as described in 
example 1) in toluene (6.97.times.10.sup.-4 moles) and 0.30 ml of an 
0.00383M solution of Cp(CH.sub.3).sub.5 !Ti(OPh).sub.3 in toluene 
(1.15.times.10.sup.-6 moles) were charged in an inert atmosphere into a 
tailed test-tube. 
The reaction was carried out for 2 hours at 90.degree. C. At the end, the 
mixture was suspended in 200 ml of methanol acidified with 0.5 ml of 
concentrated HCl. 
404 mg (2.2%) of polymeric product were obtained, which were not further 
characterized. 
Comparative Example 2 
This example describes the polymerization of styrene without tin 
tetraphenyl. 
20 ml of styrene (0.175 moles) purified by passage on a column of basic 
alumina, 0.62 ml of a 1.66M solution of MAO (treated as described in 
example 1) in toluene (1.03.times.10.sup.-3 moles) and 0.30 ml of an 
0.00383M solution of Cp(CH.sub.3).sub.5 !Ti(OPh).sub.3 in toluene 
(1.15.times.10.sup.-6 moles) were charged in an inert atmosphere into a 
tailed test-tube. 
The reaction was carried out for 2 hours at 90.degree. C. At the end, the 
mixture was suspended in 200 ml of methanol acidified with 0.5 ml of 
concentrated HCl. 
447 mg (2.6%) of polymeric product were obtained, which were not further 
characterized. 
Comparative Example 3 
This example describes the polymerization of styrene with non-treated 
methylaluminoxane. 
20 ml of styrene (0.175 moles) purified by passage on a column of basic 
alumina, 0.33 ml of a 1.57M commercial solution of MAO in toluene 
(5.18.times.10.sup.-4 moles) and 0.54 ml of an 0.00326M solution of 
Cp(CH.sub.3) .sub.5 !Ti(OPh).sub.3 in toluene (1.75.times.10.sup.-6 
moles) were charged in an inert atmosphere into a tailed test-tube. 
The reaction was carried out for 2 hours at 90.degree. C. At the end, the 
mixture was suspended in 200 ml of methanol acidified with 0.5 ml of 
concentrated HCl. 
935 mg of polymeric product were obtained. 876 mg of polymer were extracted 
with methylethylketone at boiling point for 8 hours, producing 133 mg of 
syndiotactic polystyrene (insoluble fraction 15.2%, yield of syndiotactic 
polystyrene: 0.8%). 
Comparative Example 4 
This example describes the polymerization of styrene in the presence of tin 
tetramethyl. 
15 ml of styrene (0.131 moles) purified by passage on a column of basic 
alumina, 0.49 ml of a 1.62M solution of MAO (treated as described in 
example 1) in toluene (7.86.times.10.sup.-4 moles), 0.53 ml of an 0.00992M 
solution of tin tetramethyl in toluene (5.24.times.10.sup.-6 moles) and 
0.47 ml of an 0.00281M solution of Cp(CH.sub.3). .sub.5 !Ti(OPh).sub.3 in 
toluene (1.31.times.10.sup.-6 moles) were charged in an inert atmosphere 
into a tailed test-tube. 
The reaction was carried out for 2 hours at 90.degree. C. At the end, the 
mixture was suspended in 200 ml of methanol acidified with 0.5 ml of 
concentrated HCl. 
466 mg (3.4%) of polymeric product were obtained, which were not further 
characterized. 
EXAMPLE 2 
20 ml of styrene (0.175 moles) purified by passage on a column of basic 
alumina, 0.65 ml of a 1.62M solution of MAO (treated as described in 
example 1) in toluene (6.97.times.10.sup.-4 moles), 4 mg of tin 
tetraphenyl (9.3.times.10.sup.-6 moles) and 0.62 ml of an 0.00281M 
solution of Cp(CH.sub.3).sub.5 !Ti(OPh).sub.3 in toluene 
(1.75.times.10.sup.-6 moles) were charged in an inert atmosphere into a 
tailed test-tube. 
The reaction was carried out for 2 hours at 90.degree. C. At the end, the 
mixture was suspended in 200 ml of methanol acidified with 0.5 ml of 
concentrated HCl. 
9.853 g of polymeric product were obtained. 2.675 g of polymer were 
extracted with methylethylketone at boiling point for 8 hours, producing 
2.359 g of syndiotactic polystyrene (insoluble fraction 88.2%, yield of 
syndiotactic polystyrene: 47.8%). 
EXAMPLE 3 
20 ml of styrene (0.175 moles) purified by passage on a column of basic 
alumina, 0.43 ml of a 1.62M solution of MAO (treated as described in 
example 1) in toluene (6.97.times.10.sup.-4 moles), 0.58 ml of an 0.01M 
solution of tin tetraphenyl in toluene (5.83.times.10.sup.-6 moles) and 
0.42 ml of an 0.00281M solution of Cp(CH.sub.3).sub.5 !Ti(OPh).sub.3 in 
toluene (1.75.times.10.sup.-6 moles) were charged in an inert atmosphere 
into a tailed test-tube. 
The reaction was carried out for 2 hours at 90.degree. C. At the end, the 
mixture was suspended in 200 ml of methanol acidified with 0.5 ml of 
concentrated HCl. 
7.203 g of polymeric product were obtained. 2.459 g of polymer were 
extracted with methylethylketone at boiling point for 8 hours, producing 
2.261 g of syndiotactic polystyrene (insoluble fraction 91.9%, yield of 
syndiotactic polystyrene: 36.4%). 
EXAMPLE 4 
20 ml of styrene (0.175 moles) purified by passage on a column of basic 
alumina, 0.65 ml of a 1.62M solution of MAO (treated as described in 
example 1) in toluene (1.05.times.10.sup.-3 moles), 0.44 ml of an 0.01M 
solution of tin tetraphenyl in toluene (4.4.times.10.sup.-6 moles) and 
0.31 ml of an 0.00281M solution of Cp(CH.sub.3).sub.5 !Ti(OPh).sub.3 in 
toluene (8.75.times.10.sup.-7 moles) were charged in an inert atmosphere 
into a tailed test-tube. 
The reaction was carried out for 2 hours at 90.degree. C. At the end, the 
mixture was suspended in 200 ml of methanol acidified with 0.5 ml of 
concentrated HCl. 
7.064 g of polymeric product were obtained. 4.127 g of polymer were 
extracted with methylethylketone at boiling point for 8 hours, producing 
3.823 g of syndiotactic polystyrene (insoluble fraction 92.6%, yield of 
syndiotactic polystyrene: 36%). 
Table 1 indicates the activities of the catalysts used in the previous 
examples. 
TABLE 1 
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Molar ratios Activity Syndiotacticity 
Example Styrene/Al/Ti/Sn 
(Kg/moles Ti) 
(%) 
______________________________________ 
2 100,000:600:1:5 
4960 &gt;99.5 
3 150,000:600:1:5 
5660 &gt;99.5 
4 200,000:1200:1:5 
7480 &gt;99.5 
comp. 1 150,000:600:1:0 
&lt;350 -- 
comp. 2 150,000:900:1:0 
&lt;390 -- 
comp. 3 100,000:300:1:0 
80 &gt;99.5 
comp. 4 100,000:600:1:4 
&lt;360 -- 
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