Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-02-25
2001-02-06
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S127000, C526S128000, C526S140000, C526S141000, C526S143000, C526S150000, C526S151000, C526S160000, C526S347200, C502S121000, C502S122000, C502S124000, C502S125000, C502S129000, C502S131000, C502S154000
Reexamination Certificate
active
06184316
ABSTRACT:
The present invention relates to a catalyst and a process for the syndiotactic polymerization of vinylaromatic compounds.
More specifically, the present invention relates to a process for the preparation of highly syndiotactic polymers of compounds having a primary vinyl group bound to an aromatic ring, especially styrene monomers, by polymerizing these latter in the presence of a metallocene catalyst.
As is known, polymers of styrene, and particularly polystyrene, are thermoplastic materials which can be obtained with high molecular weights. Their thermal resistance, adaptability to various hot moulding techniques and excellent insulating properties, make them particularly suitable for the production of extruded, moulded or expanded articles which can be used mainly in the fields of sound and thermal insulation and as dielectric materials. Polystyrene can be obtained by the radicalic, cationic or anionic polymerization of styrene. The polymer which can be obtained radicalically, which is the one prevalently used, is an amorphous material which shows an
1
H-NMR spectrum with wide and poorly defined bands in the chemical shift zone relating to protons of aliphatic —CH< and —CH
2
— groups, coherent with a statistic distribution in the polymeric chain of monomeric units having a different steric configuration (atactic structure). These amorphous styrene polymers, which are transparent and relatively inexpensive, have various applications but are limited to use within a relatively limited temperature range owing to the low glass transition temperature (T
g
) which is slightly less than 100° C. for the polystyrene homopolymer. As is known, in fact, around and above this temperature there is a softening of the polymer with a drastic deterioration in all the mechanical properties.
The normal techniques of anionic and cationic polymerization also lead to the production of a substantially amorphous polymer although, in some cases, the presence of short syndiotactic sequences of the monomeric units have been observed.
It is also known that crystalline polystyrene, prevalently isotactic, can be obtained by the stereospecific polymerization of styrene in the presence of Ziegler-Natta type catalysts, which are normally based on the combination of a halogenated compound of a transition metal with an alkyl derivative of aluminum, possibly with the addition of an electron-donor compound (Lewis base) to favour steric control.
A detailed description of the methods for obtaining isotactic polystyrene can be found, for example, in U.S. Pat. Nos. 3,161,624 and 2,882,263. This material, although potentially of great industrial interest, has never been widely distributed owing to its extremely slow and difficult crystallization, which is unacceptable in normal moulding and forming technologies.
European patent application publication number 210,615 describes a polystyrene having a structure characterized by a high degree of stereoregularity, in which the monomeric units have a regularly alternating configuration, thus producing a polymer with a syndiotactic structure. This material does not have the above disadvantages of atactic or isotactic polystyrene; it is a material which crystallizes rapidly, having a high melting point generally between 250 and 275° C., and can be oriented during transformation processes, producing end-products with excellent thermal resistance and resistance to organic solvents. These properties produce a material of great technological interest, comparable to thermoplastic technopolymers such as polyesters, polyamides, polyimides, etc.
Syndiotactic polystyrene can be prepared according to what is prepared in literature, for example, in accordance with what is described in the above European patent application, as well as in European patent application EP 272,584 and in U.S. Pat. No. 4,978,730. These preparation methods comprise the polymerization of styrene (or other styrene monomers) in bulk or in solution of an inert solvent such as toluene, at temperatures ranging from room temperature to 150° C., in the presence of a catalytic system obtained from the combination of a compound of a transition metal, normally selected from Ti, Zr, Hf, V or Ni, and an organo-oxygenated compound of aluminum, normally consisting of aluminoxane. Among the compounds of transition metals described in the art, halides, alcoholates, acetylacetonates and complexes containing at least one &eegr;
5
-cyclopentadienyl ring coordinated to the metal (metallocenes), are preferably used.
Other catalytic systems suitable for the purpose are those described in published European application 421,659, consisting of compounds of boron containing fluorinated groups.
The tacticity index (syndio) specified in literature in the specific case of polystyrene, expressed as a weight percentage of polymer insoluble in methylethylketone at boiling point, is between 92 and 97% at best.
Another measure commonly used for expressing the (syndio) tacticity index is the percentage of syndiotactic dyads which can be revealed by
13
C-NMR spectroscopy. The latter index may be different from the former, for instance in case of stereoblock polymers.
The mechanical, chemical and thermal properties of syndiotactic polystyrene largely depend on the percentage of stereoregularity of the polymer (syndiotacticity index). Percentages of soluble polymer of more than 2% by weight are generally sufficient to give it unsatisfactory characteristics especially in relation to resistance to organic solvents (mineral oils, oxygenated solvents) and thermal resistance. Syndiotactic polystyrenes with syndiotacticity indexes of more than 99% can normally be obtained only after extraction of the soluble part, this is an onerous process in terms of time and costs, which can preclude the use of this material for applications of high technological value.
The necessity has therefore been felt for further improvements in the field of the syndiotactic polymerization of styrene with traditional processes, aimed at increasing the stereochemical purity of the product as obtained by the polymerization process, but at the same time maintaining satisfactory yields and high molecular weights.
It is also important for the catalysts used for the preparation of syndiotactic polystyrene to be obtained with simple and rapid processes, starting from reagents which are easily available on the market.
On the other hand, it is also desirable to have production processes of syndiotactic polystyrene which enable the polymerization reaction to be carried out in relatively reduced volumes, without the necessity of using large quantities of inert liquids necessary in the traditional solution/suspension processes.
Polymerization in bulk, or with reduced quantities of diluents, could advantageously overcome this problem and it has been experimented, for example, in accordance with European patent application EP-A 584,646. It has the disadvantage however of a very slow reaction kinetics, with unsatisfactory hourly productivities and low conversions of the monomer which make it necessary to separate and recycle the non-reacted part. Furthermore, a relevant amount of atactic polymer is formed during the process, partially due to the parallel radical polymerization, especially at elevated temperature.
It would be then desirable to have catalytic systems capable of effecting bulk polymerization of styrene with a higher productivity and conversion, but at the same time maintaining a satisfactory control of the stereoregularity of the polymer obtained.
It has now been surprisingly found that using a particular catalytic system based on metallocene compounds of titanium, it is possible to polymerize styrene or other vinylaromatic compounds, either in the presence or in the absence of a liquid diluent, with high conversions of the monomer, to obtain stereoregular polymers with a high average molecular weight.
A first object of the present invention therefore relates to a catalyst for the polymerization of vinylaromatic monomers, comprising the product consisting of the following t
Altomare Angelina
Cardi Nicoletta
Ciardelli Francesco
Conti Giuseppe
Masi Francesco
Enichem S.p.A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Teskin Fred
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