Process for preparing rubber-modified moulding compounds

Details Process for preparing rubber-modified moulding compounds Process for preparing rubber-modified moulding compounds

1999-06-08

2001-04-03

Nutter, Nathan M. (Department: 1711)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S240000, C525S242000, C525S299000

Reexamination Certificate

active

06211297

ABSTRACT:

This application claims benefit of priority from PCT/EP 97/06550, filed Nov. 28, 1997.
BACKGROUND OF THE INVENTION
The present invention relates to a process for the preparation of rubber-modified molding compositions. The invention also relates to the rubber-modified molding compositions obtainable by the novel process and to their use for the production of fibers, films and shaped articles. The invention also relates to polymer blends comprising these rubber-modified molding compositions.
PRIOR ART
Processes for the production of rubber-modified molding compositions are sufficiently well known. In DE-A 24 27 960, for example, molding compositions made from ABS (polybutadiene rubber particles, grafted with polystyrene-acrylonitrile in a polystyrene-acrylonitrile matrix) and a process for their preparation are described.
For the preparation of acrylonitrile-styrene-acrylate (ASA) molding compositions, the starting material is generally an acrylate rubber, onto which copolymers based on styrene and acrylonitrile are grafted by polymerization with a mixture of these monomers. The preparation of ASA molding compositions can be carried out, for example, in emulsion or in solution.
The preparation of ASA molding compositions in emulsion is described, for example, in DE 32 06 136, 31 49 046, 31 49 358, 32 27 555, 31 29 378, 31 29 472, 29 40 804, 28 26 925 and 19 11 882. The rubber is prepared here from n-butyl acrylate and small amounts of two monomers containing double bonds, in emulsion. A disadvantage of this process is that relatively large amounts of water are produced in the emulsion polymerization and in the precipitation of the polymer dispersion, and these must be removed and disposed of as waste water which requires treatment. Furthermore, the molding compositions prepared by the process have an impact strength and tear resistance which is not adequate for all applications. In addition, the surface gloss of the shaped articles produced from these molding compositions cannot be varied over a wide range.
EP 0 095 919 and DE 11 82 811 describe a process for preparation of ASA molding compositions in solution.
According to EP 0 095 919, there is no grafting of the comonomers onto the rubber, ie. no effective coupling at the interface. According to DE 11 82 811, the rubber made from n-butyl acrylate with from 0.5 to 10% by weight of a comonomer is prepared with two double bonds capable of free-radical polymerization. The polymerization of the styrene-acrylonitrile (SAN) monomer mixture is initiated at a rubber conversion of from 10 to 80%. This has the result that the grafted proportion of the rubber does not have the same make-up as the polymer matrix, and this leads to poorer mechanical properties of the molding compositions. In addition, the polymerization of rubber units into the graft shell, ie. the graft branches, gives a poorer heat resistance of the products.
In the earlier German Patent Application DE-A-44 40 672.6, rubber-modified ASA molding compositions with improved impact strength, tear resistance and elongation at break are obtained by the additional use, in the free-radical build-up of the graft core, of a monomer having two or more double bonds, creating grafting points for the growing chains of the shell and matrix and reducing the low-molecular-weight proportion of the rubber.
A disadvantage of the known free-radical processes in the construction of polymers or copolymers is that generally at least some steps have to be carried out in aqueous systems; especially on an industrial scale, this requires complicated and costly treatment of the contaminated water. It is also disadvantageous if during the course of the process the reaction medium has to be changed in a complicated manner, as in the preparation according to the abovementioned earlier application DE-A-44 40 676.2, where free-radical polymerization of n-butyl acrylate in cyclohexane is carried out in the first step and then, after removal of the solvent, the polymerization is continued in an aqueous medium, in order to obtain the desired rubber-modified molding composition.
Using the known free-radical methods under the usual process conditions, it is also impossible, or possible only to a very limited extent, to obtain rubber particles with high molecular weight in the presence of monomers which have a tertiary hydrogen atom. Operation at low temperatures with the aim of inhibiting the chain transfer reaction leads to long reaction times which are commercially unacceptable.
The conventional free-radical emulsion processes also mostly require the addition of emulsifiers, such as alkyl metal salts of alkyl- or alkylarylsulfonic acids or sulfosuccinates, in order to ensure a stable emulsion. It is frequently impossible completely to remove the emulsifiers, and also the precipitation reagents, such as calcium chloride or magnesium sulfate, required for the isolation of the rubber-modified polymer from the thermoplastic molding composition. This can result in firstly a worsening of the rheological and mechanical properties and secondly, through the phenomenon of exudation and the formation of specks, can permanently impair the surface quality and the pigmentability of the fibers, films and shaped articles which are produced.
It would therefore be desirable to be able to prepare rubber-modified molding compositions without the necessity for a change of solvent, or even for a conventional solvent at all.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for the preparation of rubber-modified molding compositions which in its entirety, virtually in its entirety or in at least one significant step, does not require water and/or, if desired, also does not require relatively large proportions of conventional solvents and which furthermore allows the formation of high-molecular-weight rubber particles even when monomer components which carry a tertiary hydrogen atom are present.
DETAILED DESCRIPTION OF THE INVENTION
We have found that this object is achieved by means of a process for the preparation of rubber-modified molding compositions in which, in a first step a
1
), a mixture (A) comprising acrylate derivatives or methacrylate derivatives or acrylate derivatives and methacrylate derivatives and a solvent, if desired comprising olefinically unsaturated compounds which are not an acrylate derivative or a methacrylate derivative are subjected to an anionic polymerization or, in a step a
2
), acrylate derivatives or methacrylate derivatives or acrylate derivatives and methacrylate derivatives are sequentially anionically polymerized in the presence of a solvent which, if desired, comprises olefinically unsaturated compounds to give block copolymers, and in which, in a further step b), the reaction mixture obtained in the first reaction step a
1
) or a
2
) or in the reaction steps a
1
) and a
2
) is subjected to a free-radical-initiated polymerization, if desired after the addition of further unsaturated compounds.
The invention also provides rubber-modified molding compositions obtainable by the novel process and the use of the molding compositions for the production of fibers, films and shaped articles. The invention additionally provides polymer blends comprising these rubber-modified molding compositions.
The following monomeric building blocks are preferably used as acrylate derivatives or methacrylate derivatives:
i) compounds of the formula (I)
 where
R
a
is hydrogen or methyl,
R
b
is alkyl having from 1 to 32 carbon atoms,
ii) compounds of the formula (II)
 where
R
c
is hydrogen or methyl,
R
d
,R
e
are hydrogen, alkyl or aryl,
R
f
is C
1
-C
20
-alkyl or C
1
-C
20
-aralkyl containing at least one tertiary hydrogen atom or at least one benzylic hydrogen atom,
iii) compounds having one or more double bonds in the ester unit,
iv) di- or polyesters or -ethers of di- or polyhydric alcohols,
v) acrylamides or methacrylamides, nitrogen-functional acrylates and methacrylates, aromatic and araliphatic (meth)acrylates and (meth)acrylates substituted with functio

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