The invention relates to a polymer composition comprising a polymer A and a polymer B, with polymer A bein a polyamide and polymer B containing vinylaromatic monomer units, dicarboxylic acid anhydride monomer units and/or imide monomer units.

Such a polymer composition is known from EP-A- 348,000. A drawback of the known polymer composition is that its heat deflection temperature is insufficient for a number of applications.

The Vicat according to ISO 306/B is a measure of the heat deflection temperature. The aim of the invention is to provide a polymer composition that does not have the aforementioned drawback.

Surprisingly, this aim is achieved if polymer B contains at least 1 wt.% spirodilactone monomer units. Further advantages of the polymer composition according to the invention are improved impact resistance, improved ^" thermal stability and improved chemical resistance in comparison with the known polymer composition.

In principle, all polyamides or mixtures thereof are suitable for use as polymer A. The polyamides are for example condensation products of dicarboxylic acids having 4-12 carbon atoms with diamines having 4-14 carbon atoms or of lactams or of mixtures thereof. Examples of common polyamides are polyhexamethylene adipamide (PA 6,6), polyhexamethylene azelamide (PA 6,9), polyhexamethylene sebacamide (PA 6,10), polyhexamethylene lauramide (PA 6,12), polytetramethylene adipamide (PA 4,6), polycaprolactam (PA 6), polylauryllactam (PA 12) and the like. Polycondensates of two or more dicarboxylic acids and/or two or more

diamines, as well as mixtures of two or more polyamides are also suitable for use as polymer A. Preferably, PA 6, PA 6,6 or PA 4,6 is used as polymer A. Polymer B is known per se from WO-90/06956. Examples of vinylaromatic monomers that are suitable for use in polymer B are styrene, α-methylstyrene, para-methyl- styrene and mixtures thereof. Preferably, use is made of styrene. Suitable dicarboxylic acid anhydrides are for example maleic anhydride, chloromaleic anhydride, citraconic acid anhydride, cyclohexylmaleic anhydride, benzylmaleic anhydride, phenyl aleic anhydride, aconitic acid anhydride, propylmaleic anhydride and mixtures hereof. Preferably use is made of maleic anhydride (MA).

Polymer B can be prepared by preparing a polymer C that contains the dicarboxylic acid anhydride and the vinylaromatic monomer in a first step, using one of the known methods, and heating polymer C for a certain amount of time to a temperature of, preferably, 200-300°C in a second step.

During the heating a conversion takes place in the chain of the polymer, in which dicarboxylic acid anhydride- vinylaromatic monomer-dicarboxylic acid anhydride (Formula I) reacts to form spirodilactone (Formula II) according to the reaction equation:

*ι - C - C - C - C - C - C (Formula I)

I I I I 1

C C R ₂ C C ₇ \ /\\ // /\\

0 0 0 0 0 0

^R ι - \ C - C

- C - C C - C - + C0 ₂ t (Formula II)

In these formulae R _x is an aryl group and R ₂ is for example a hydrogen atom or an alkyl group. The polymer must be heated for a sufficiently long time to cause the desired degree of conversion to take place. There is however the risk that after some time, before the desire degree of conversion is reached, secondary thermal decomposition processes in the polymer will start to play a significant part. Partly because of this, the heating is preferably done in the presence of a basic catalyst. Becaus of the use of the catalyst the desired degree of conversion can be reached faster and at a lower temperature. Examples of suitable catalysts are secondary and tertiary amines? preferably, use is made of triethylamine (TEA) or l,4-diazabicyclo[2,2,2]octane (DABCO).

It is also possible to add the basic catalyst to the polyme in the form of a buffer solution. The reaction can for example be carried out by heating the polymer as such, with the reaction taking place while the polymer is in molten condition. It is also possible to carry out the reaction when the- polymer is in solution. Suitable solvents are for example dimethylformamide, tetrahydrofuran, acetone and methyl ethyl ketone or other ketones. The heat deflection temperature increases as the concentration of spirodilactone monomer units in polymer B increases. That is why polymer B preferably contains at least 2 wt.% spirodilactone monomer units. In a further preferred embodiment polymer B contains at least 4 wt.% spirodilactone monomer units.

In general polymer B has a weight average molecular weight of between 30,000 and 200,000 kg/kmol, preferably of betwee 50,000 and 150,000 kg/kmol. If, as described above, polymer B is prepared from polymer then, dependent on i.a. the concentration of dicarboxylic acid anhydride and vinylaromatic monomer units in polymer C and their distribution across the chain of this polymer, after the conversion to the spirodilactone, the polymer B thus obtained will still contain a certain amount of the

dicarboxylic acid monomer units.

It is of course also possible to only partially carry out the conversion to the spirodilactone. Preferably, polymer B contains 5-35 wt.% spirodilactone monomer units and 5-45 wt.% dicarboxylic acid anhydride monomer units.

Examples of imide monomer units that are suitable for use in polymer B are N-phenylmaleimide, maleimide, citraconimide, itaconimide, aconitimide, N-methylmaleimide. Good results are obtained when first polymer B is obtained from polymer C as described above and then in a further step remaining maleic acid anhydride monomer units are converted into imide monomer units by reacting with the corresponding amine. Preferably 0.1-2 wt.% maleic acid anhydride monomer units are left in polymer B after this conversion in order to provide good miscibility with the polyamide.

Preferably the polymer composition according to the invention contains an elastomer as an impact modifier. In general, an elastomer with a glass transition temperature below -10°C, preferably below -40°C, is used for this purpose. Examples of suitable elastomers are: polybutadiene, EPDM, hydroxylated EPDM, polybutylacrylate and silicone rubber.

Preferably, the elastomer is grafted with a polymer that is miscible with polymer A or polymer B, or reactive groups are attached to the elastomer that can chemically combine with polymer A and/or polymer B. Elastomers containing groups that are reactive with respect to the polyamide (polymer A) are described in EP-A-348,000. Elastomers that are grafted with polymers that are miscible with polymer B are described in for example US-4,528,326. Very suitable for use in the polymer composition according to the invention is polybutadiene rubber grafted with styrene-acrylonitrile copolymer (ABS)

Preferably, the polymer A : polymer B mixing ratio in the polymer composition according to the invention is between 1:6 and 3:1, more preferably, the mixing ratio is between

1 : 3 and 2 : 1.

The polymer composition according to the invention may further contain the usual additives, such as fibres, fillers, softeners and stabilizers. A very suitable polymer composition according to the invention contains 10 - 40 parts by weight glass fibres, relative to 100 parts by weight polymer A and polymer B. The polymer composition according to the invention can be used in for example housings and parts of electromechanical and electronic equipment, automotive parts, etc.

The invention will be further elucidated with reference to the examples, without being limited thereto.

Example I, II, Comparative Experiments A, B

Different polymer B samples were prepared by extruding styrene/maleic anhydride copolymers (polymer C) with maleic anhydride monomer units (MA) contents of 28 and 32 wt.% and an average molecular weight of 110,000 kg/kmol via a co-rotating W&P (R) twin-screw extruder of type ZSK 40 supplied by Werner and Pfleiderer, Germany. The throughput was 20 kg/hour. The melting temperature was 250°C. TEA was continuously injected into the extruder and mixed with the molten polymer.

By varying the amount of TEA thus added to the polymer, samples 1-4 of polymer B were obtained with different spirodilactone contents. The MA content of the samples and of the starting polymers C was determined with the aid of a Perkin Elmer (R) IR apparatus, type 1760 FT-IR. This was then used to calculate the spirodilactone monomer units contents of the samples, using the reaction equation given above in the text of this application.

The glass transition temperature (T _g ) was determined with the aid of a Perkin Elmer (R) DSC apparatus, type DSC 7. The sample size was 10-15 mg. The heating rate was 10°C/minute.

The results are shown in Table 1.

Mixtures were prepared of the reference polymers ref. 1 and ref. 2 (Table 2) and polymer B samples 1-4 with Ultramid (R)

B3, a PA 6, supplied by BASF, Germany, by mixing a granulate of a sample with granulate of the nylon 6 in a mixing ratio of 50/50 by weight and then extruding the mixture via the aforementioned twin-screw extruder.

The Vicat measured according to ISO 306/B in °C is a measure of the heat deflection temperature. The composition of the mixtures and the results are given in Table 3.

TABLE 3

mixture Vicat

°C

A (PA 6/ref. 2) 151 I (PA 6/sample 1) 160

B (PA 6/ref. 1) 144

II (PA 6/sample 2) 162

The mixtures according to the invention have a higher heat deflection temperature than the known mixtures.

Example III, Comparative Experiment C

In the manner described in example 1 mixtures were prepared of the reference polymer ref. 3 and polymer B sample 3 of example I with PA 6 (ϋltramid (R) E3, supplied by BASF, Germany) and ABS (Ronfalin (R) TZ 220, supplied by DSM, the Netherlands). See Table 4 for the composition.

TABLE 4

mixture ref. 3 sample 3 PA 6 ABS wt.% wt.% wt.% wt.%

C 10 45 45 III 10 45 45

The impact resistance (Izod) of the samples was measured according to ISO 180. The results are given in Table 5.

TABLE 5

mixture Izod kJ/m ²

C 32 III 44

The mixture according to the invention (mixture III) has a higher impact resistance than the known mixture (mixture C)