Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-02-17
2001-10-16
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...
C526S173000, C526S177000, C526S178000, C525S053000, C525S271000, C525S308000, C525S310000, C525S316000
Reexamination Certificate
active
06303721
ABSTRACT:
The present invention relates to a process for the anionic polymerization of dienes or copolymerization of dienes and vinylaromatic monomers in a vinylaromatic monomer or monomer mixture to give homopolydienes or copolymers or mixed homopolydienes and copolymers.
The invention further relates to a diene polymer solution, its use for preparing molding compositions comprising vinylaromatic monomers and also a continuous process for preparing impact-modified, thermoplastic molding compositions.
It is generally known that anionic polymerization proceeds completely, ie. to complete conversion, but also very quickly. The conversion rate can, apart from selection of a very low temperature, only be reduced by selecting a lower concentration of the polymerization initiator, but this forms only few, very long chain molecules. Owing to the considerable evolution of heat and the difficulty of removing the heat from a viscous solution, limiting the reaction temperature is not very effective.
An excessively high reaction temperature has particularly disadvantageous consequences, especially in block copolymerization, because thermal termination interferes with the formation of uniform block copolymers and, if it is intended to follow the polymerization with a coupling reaction, the coupling yield would be unfavorably low.
The temperature therefore has to be controlled by appropriate dilution of the monomers, but this makes the reaction space required unnecessarily large, ie. the anionic polymerization can, despite the high reaction rate with can be achieved, only be operated with a relatively low space-time yield.
Various continuous and batches processes in solution or suspension are known for preparing high-impact polystyrene. In these processes, a rubber, usually polybutadiene, is dissolved in monomeric styrene which has been polymerized to a conversion of about 30% in a preliminary reaction. The formation of polystyrene and the simultaneous decrease in the concentration of monomeric styrene leads to a change in the phase coherence. During this phenomenon known as “phase inversion”, grafting reactions also occur on the polybutadiene and these, together with the intensity of stirring and the viscosity, influence the formation of the disperse soft phase. In the subsequent main polymerization, the polystyrene matrix is built up. Such processes carried out in various types of reactor are described, for example, in A. Echte, Handbuch der technischen Polymerchemie, VCH Verlagsgesellschaft Weinheim 1993, pages 484-489 and U.S. Pat. Nos. 2,727,884 and 3,903,202.
In these processes, the separately prepared rubber has to be comminuted and dissolved in a complicated procedure and the polybutadiene rubber solution in styrene obtained in this way has to be filtered to remove gel particles before the polymerization.
Various attempts have therefore been made to prepare the necessary rubber solution in styrene directly by anionic polymerization of butadiene or butadiene/styrene in nonpolar solvents such as cyclohexane or ethylbenzene and subsequent addition of styrene (GB 1 013 205, EP-A-0 334 715 and U.S. Pat. No. 4,153,647) or by incomplete conversion of butadiene in styrene (EP-A 0 059 231). The block rubber thus prepared either has to be purified by precipitation or else the solvent and other volatile materials, in particular monomeric butadiene, have to be distilled off. In addition, owing to the high solution viscosity, only relatively dilute rubber solutions can be handled, which results in a high solvent consumption, purification costs and energy consumption.
EP-A 0 304 088 describes a process for the selective polymerization of conjugated dienes in a mixture of dienes and vinylaromatic compounds. The catalysts used display virtually no polymerization activity toward the vinylaromatic compound.
U.S. Pat. No. 3,264,374 describes the preparation of polybutadiene in styrene. However, the experiments reported there without any indication of the scale cannot be controlled on an industrially relevant scale because of the abovementioned problems of heat removal. In addition, the viscosities are very high at the relatively low reaction temperatures.
The influence of Lewis acids and Lewis bases on the reaction rate in anionic polymerization has been described in Welch, Journal of the American Chemical Society, Vol 82 (1960), pages 6000-6005. It was found that small amounts of Lewis bases such as ethers and amines accelerate the n-butyllithium-initiated polymerization of styrene, while Lewis acids such as zinc alkyls and aluminum alkyls can reduce the polymerization rate. Hsieh and Wang too, in Macromolecules, Vol 19 (1966), pages 299-304 describe the polymerization-retarding action of dibutylmagnesium by means of complex formation with the alkyllithium initiator or the living polymer chain without influencing the stereochemistry.
U.S. Pat. No. 3,716,495 discloses initiator compositions for the polymerization of conjugated dienes and vinylaromatics, in which a more effective utilization of the alkyllithium as initiator is achieved by addition of a metal alkyl such as diethylzinc and polar compounds such as ethers or amines. Owing to the large amounts of solvent required, relatively low temperatures and long reaction times in the range of a few hours, the space-time yields are correspondingly low.
U.S. Pat. No. 3,826,790 discloses a process for the polymerization of conjugated dienes and, if desired, monovinylaromatic hydrocarbons in solution to give polymers having an increased cis-1,4 content. The initiator employed for this purpose contains an alkyllithium compound and a trihydrocarbylboron compound.
It is an object of the present invention to find a process for the anionic polymerization of dienes and vinylaromatic monomers which, at high monomer concentration, can be operated particularly economically and enables vinylaromatic-monomer solutions of diene polymers which are low in diene monomers to be prepared for further processing to give molding compositions. The process should use predominantly monomeric starting materials and make it possible to achieve high space-time yields. Furthermore, reliable control of the polymerization rate and thus the temperature should be made possible. In addition, the invention should provide a continuous process for preparing impact-modified molding compositions having a low residual monomer content.
We have found that this object is achieved by a process for the anionic polymerization of dienes or copolymerization of dienes and vinylaromatic monomers in a vinylaromatic monomer or monomer mixture to give homopolydienes or copolymers or mixed homopolydienes and copolymers, wherein the polymerization is carried out in the presence of a metal alkyl or aryl of an element having a valence of at least two without addition of Lewis bases.
Furthermore, we have found a diene polymer solution, its use for preparing molding compositions comprising vinylaromatic monomers, in particular high-impact polystyrene, acrylonitrile-butadiene-styrene polymers and methyl methacrylate-butadiene-styrene copolymers and also a process for the continuous preparation of impact-modified, thermoplastic molding compositions which comprise a soft phrase comprising a diene polymer dispersed in a hard vinylaromatic matrix, which comprises
preparing, as described in the introduction, the diene polymer required for the formation of the soft phase in a first reaction zone,
feeding the diene polymer obtained in this way, either directly or after addition of a termination or coupling agent, to a second reaction zone in which, if desired with addition of further vinyl monomers in an amount which is sufficient to achieve phase inversion and, if desired, further initiators and/or solvents, anionic or free-radical polymerization is carried out until phase inversion occurs and
in a third reaction zone, anionic or free-radical polymerization is continued until complete with the amount of vinylaromatic monomer required to form the impact-modified thermoplastic molding composition.
The process can be applied to th
Fischer Wolfgang
Gausepohl Hermann
Lätsch Stefan
Schade Christian
Warzelhan Volker
BASF - Aktiengesellschaft
Keil & Weinkauf
Teskin Fred
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