Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-06-16
1998-08-18
Teskin, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525 53, 525 95, 525194, 525197, 525198, 528501, C08L 5302, C08L 2506
Patent
active
057959382
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to toughened molding materials based on polymers of styrene and other vinyl aromatic compounds, which have a particularly low content of low molecular weight byproducts and residual monomers, and to a process for their preparation based on anionic polymerization. Molding materials having a residual monomer content of less than 50 ppm, in particular less than 10 ppm, and containing not more than 10 ppm of oligomers having molecular weights of less than 1000 are preferably obtained.
In the description below, the term styrene is used even when other vinyl aromatic compounds are suitable; the present invention can of course equally be applied to molding materials comprising derivatives of styrene, such as alpha-methylstyrene, 2-, 3- or 4-methylstyrene, tert-butylstyrene, 1,1-diphenylethylene or mixtures thereof.
High impact polystyrene (HIPS) has been produced industrially to date exclusively by free radical polymerization of styrene in the presence of a dissolved rubber, the rubber itself being the starting point of living styrene chains (grafting; cf. DE-A-40 46 718; U.S. Pat. No. 3,903,202) and thus being compatible with the styrene homopolymers. The processes usually employed in industry are very expensive and are usually carried out in a plurality of reaction apparatuses in succession, for example in a 2-kettle 2-tower cascade or in a 3-tower cascade according to the above documents. Furthermore, the use of horizontal reactors (DE-A-24 44 650) has already been proposed.
All free radical polymerization processes have the disadvantage that the polymerization is incomplete and relatively large amounts of oligomers are formed as byproducts and have to be separated off together with the residual monomers after the polymerization in an expensive purification process, since especially monomeric styrene, owing to its strong odor, cannot remain in the prepared molding material. A residual content of from about 100 to 200 ppm of styrene has to date been accepted as unavoidable.
It is known that styrene can be subjected to anionic polymerization (EP-A-176 611; U.S. Pat. No. 3,035,033; FR-A-2 146 581), it being possible to carry out polymerization to virtually complete conversion. A recent overview of the anionic polymerization of, in particular, styrene is given by Priddy (J. Polym. eng. 10 (1991), 334).
In the known anionic polymerization processes, however, only polymers which are not toughened can be prepared: since no grafting of the rubber present takes place in the anionic polymerization, the rubber cannot enter into any interactions with the surrounding styrene homopolymer (the matrix), and only products having entire inadequate mechanical properties are obtained.
It is an object of the present invention, therefore, to find a process for continuous preparation of toughened molding materials based on polystyrene which comprise, in a matrix of the styrene homopolymer, an elastomeric styrene-butadiene block copolymer, the target proportion of butadiene in the styrene-butadiene block copolymer being from 15 to 80% by weight and in the molding material as a whole being from 2 to 50% by weight.
It is a particular object of the present invention to prepare toughened molding materials based on polystyrene and having only a low content of residual monomers and oligomers and high thermal stability and good mechanical properties, which molding materials are at least equivalent to the corresponding molding materials obtained by free radical polymerization.
The novel process essentially comprises the following: without heat exchange with the environment and, if required, with the addition of a solvent, until complete conversion is achieved, and the living chain ends are terminated in a manner known per se; and butadiene are subjected to isothermal anionic polymerization with the use of a suitable solvent, likewise to complete conversion, to give an elastomeric block copolymer whose living chain ends are terminated with a proton-active substance either immediately or after appropriate coupling
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Fischer Wolfgang
Gausepohl Hermann
Knoll Konrad
Loth Wolfgang
BASF - Aktiengesellschaft
Teskin Fred
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