Mixtures of liquid-crystal polymers and polyarylene sulfoxides,

Details Mixtures of liquid-crystal polymers and polyarylene sulfoxides, Mixtures of liquid-crystal polymers and polyarylene sulfoxides,

1997-05-02

1999-09-07

Foelak, Morton

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

521 81, 521138, 521182, C08J 904

Patent

active

059488301

DESCRIPTION:

BRIEF SUMMARY
The invention relates to mixtures based on liquid-crystalline polymers (LCPs) and polyarylene sulfoxides which, as blends, have improved properties on conversion into molding compositions. An example of an improved property is improved weld strength.
Foamed polymers are well known. They are used, in particular, where low weight or a high strength/weight ratio is required.
Foamed LCPs can be used as heavy-duty functional components, for example in aircraft and automobile production and in chemical apparatus production or as chemicals- or heat-resistant insulating materials.
In general, however, foaming impairs the mechanical properties of the polymer molding compositions to such an extent that they are no longer suitable for many areas of application. In addition to the inherent advantageous properties of foamed polymers, foamed LCPs are generally required where there is a need for the specific LCP properties, such as high tensile strength, high heat resistance, high chemicals resistance and high toughness, in particular notched impact strength. These foams should also have low anisotropy or orientation.
U.S. Pat. No. 4,429,060 describes high-performance foams made from liquid-crystalline, fully aromatic polyesters containing at least 10 mol % of 6-hydroxy-2-naphthoic acid units. These foams have a good strength/weight ratio, high heat resistance and excellent chemicals resistance. They have lower anisotropy than unfoamed LCPs. These foams can be produced by conventional methods, such as extrusion or injection molding. Foaming requires a blowing agent. Suitable blowing agents mentioned are 5-phenyltetrazole and trihydrazinetriazine.
U.S. Pat. No. 4,429,061 describes heat-treated LCP foams which have high rigidity and strength. The core of the LCP foams has highly oriented cell walls, whose properties are improved by heat treatment. These foamed LCPs have a low degree of anisotropy compared with unfoamed LCPs.
According to U.S. Pat. No. 5,210,107, however, the mechanical properties which can be achieved by means of the abovementioned foams are, owing to the coarse cell structure, inadequate to allow commercial exploitation.
LCP foams of the prior art can be produced either by means of chemical blowing agents or by addition of gases to the melt. The disadvantage of blowing agents is frequently about their health risks and their low melting point, which is frequently below the melting point of the LCPs. In addition, homogeneous mixing both with blowing agents and gases can only be achieved with great difficulty, which results in impaired mechanical property values.
It was an object of the present invention to develop molding compositions based on reactive polymer blends which, as such, have improved weld strength compared with the starting LCPs. A further object of the present invention was to develop a process for the preparation of foams comprising LCPs which are not produced by adding conventional blowing agents or adding gases to the melt of the LCPs to be foamed, but which nevertheless enable considerable expansion.
This object is achieved by a polymer mixture of the generic type mentioned at the outset, which comprises particular from 10 to 95% by weight, of at least one thermotropic-liquid-crystalline polyester and/or polyesteramide and particular from 5 to 90% by weight, of at least one sulfoxide group-containing polymer,
Surprisingly, it has been found that a mixture of thermotropic-liquid-crystalline polymers with polymers containing sulfoxide groups in the polymer chain readily form a foam. On exposure to heat, the thermally unstable sulfoxide decomposes, the sulfoxide groups being reduced to the sulfide. This is accompanied by the release of gases which act as blowing agents. It has also been found that the two mixture components can form a homogeneous molding composition, which can advantageously also be employed as such. Compared with the LCPs as such, the mixture has reduced anisotropy and improved weld strength.
The term "liquid-crystalline polymer" is taken to mean any thermotropic liquid-crys

REFERENCES:
patent: 4710522 (1987-12-01), Huggard

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