Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1998-01-05
2000-10-31
Mulcahy, Peter D.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524577, C08L 7500
Patent
active
061404098
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to antidrip agents for thermoplastic molding materials which contain polymers which are based on vinylaromatic monomers and have molecular weights (M.sub.w) of at least 800 000 g/mol and a narrow molecular weight distribution. Preferred embodiments are described in the subclaims and the description.
When thermoplastic materials are ignited, they generally soften very rapidly (unless crosslinking reactions occur) since their viscosity decreases markedly owing to the high temperatures. Frequently, therefore, particles of the material separate off from the molding. This process is referred to as dripping or, if the sample is still burning, as the dripping of flaming particles. Dripping material particles can readily ignite other articles and thus propagate a fire. Considerable efforts have therefore been made to develop effective antidrip agents for thermoplastic molding materials.
Although halogen-containing polymers, such as polytetrafluoroethylenes, counteract dripping, they should be avoided for reasons of environmental compatibility. EP-A-550 204 describes high molecular weight polyethylenes as halogen-free antidrip agents for thermoplastic molding materials comprising polyphenylene ethers and high impact polystyrenes (HIPS). However, it has been found that even small amounts of high molecular weight polyethylene adversely affect the mechanical properties of precisely these molding materials. In particular, the damaging energy decreases dramatically. EP-A-305 764 recommends polystyrenes having molecular weights of more than 400 000 g/mol and a broad molecular weight distribution as antidrip agents for blends of polyphenylene ethers and HIPS. On the one hand, these antidrip agents do not sufficiently decrease the tendency of the thermoplastic molding materials to drip and, on the other hand, they increase the melt viscosity at the shear rates relevant to processing by injection molding. Furthermore, the toughness of the molding materials is reduced as the proportion of antidrip agent increases.
That blends of polyphenylene ethers and HIPS may additionally contain polystyrenes is furthermore disclosed, for example, in U.S. Pat. No. 4,128,602, 4,128,603 and 5,008,314 and EP-A-476 366. The molding materials described in U.S. Pat. No. 5,008,314 have improved stress cracking resistances and those of EP-A-476 366 are particularly suitable for blow molding.
It is an object of the present invention to provide novel effective halogen-free antidrip agents for thermoplastic molding materials, in particular for polyphenylene ether/HIPS blends, which have very little effect on the mechanical properties of the blends.
We have found that this object is achieved by the antidrip agents defined at the outset.
The polymers contained in the novel halogen-free antidrip agents and based on vinylaromatic monomers may be both homopolymers and random copolymers or block copolymers, such as alternating block copolymers, star block copolymers or three-block or five-block copolymers. Blends of different polymers are also suitable. Homopolymers are preferably used. The polymers based on vinylaromatic monomers may be either syndiotactic or atactic. In general, however, atactic polymers based on vinylaromatic monomers are used.
Suitable vinylaromatic monomers have, as a rule, 8 to 12 carbon atoms. Styrene or styrenes substituted in the nucleus or in the side chain are particularly suitable. Examples are o-methylstyrene, m-methylstyrene, p-methylstyrene and p-tert-butylstyrene.
Other monomers may also be present, in particular those which are capable of anionic copolymerization with the stated monomers. These include acrylonitrile, methacrylonitrile, 2-vinylpyridine, 4-vinylpyridine and vinylpyrrolidone.
Very particularly preferred novel antidrip agents contain polystyrene homopolymers.
According to the invention, the polymers based on vinylaromatic 35 monomers have weight average molecular weights (M.sub.w) of at least 800 000, for example 900 000, g/mol or more. In general, the molecular weights (M.sub.w)
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Heckmann Walter
Hingmann Roland
Hofmann Jurgen
McKee Graham Edmund
Weber Martin
BASF - Aktiengesellschaft
Mulcahy Peter D.
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