Sulphonated Polyaryletherketones

The present invention relates to certain sulphonated polyaryletherketone polymers.

We have found that polyaryletherketones containing the repeat unit of formula ##STR3## can be sulphonated under conditions such that sulphonation occurs slowly, e.g. using concentrated sulphuric acid (98% w/w) at ambient temperature.

Consequently the degree to which such a polymer can be sulphonated may be controlled under such conditions by selecting the time of sulphonation. Nevertheless, we have found that sulphonation conditions can be employed wherein these polymers sulphonate very rapidly, monosubstitution occurring in substantially all or a majority of the aromatic rings in the sub-units ##STR4## of the polymers. Rapid sulphonation of this type may be effected using concentrated sulphuric acid (98 % w/w) at an elevated temperature (e.g. .gtoreq.50.degree. C., particularly .gtoreq.80.degree. C.) or a more powerful sulphonating agent.

We have also found that sulphonation conditions may be employed where polyaryletherketones containing only the repeat unit of formula ##STR5## are virtually non-susceptible to sulphonation under the same conditions where the polyaryletherketones of repeat unit A are rapidly sulphonated. Consequently polyaryletherketone copolymers containing repeat units A and B may be controllably sulphonated, e.g. using concentrated sulphuric acid (98% w/w/) at an elevated temperature (e.g. .gtoreq.50.degree. C., particularly .gtoreq.80.degree. C.), to give hydrophilic sulphonated copolymers (ranging up to completely water soluble polymers) by varying the proportion of the repeat units B in the copolymer.

According to the present invention there is provided a polyaryletherketone copolymer which is a hydrophilic sulphonated copolymer derived by controllably sulphonating a copolymer having repeat units of formula ##STR6## together with repeat units of formula ##STR7## at least 70% of all the units A being sulphonated after sulphonation and substantially all the units B remaining non-sulphonated after sulphonation. Preferably substantially all (say .gtoreq.95%) the units A are sulphonated after sulphonation.

The sulphonation of the repeat units A is, e.g. very rapid in concentrated sulphuric acid (98% w/w) at an elevated temperature, while the repeat units B remain substantially non-sulphonated. Thus at least 70% of the units A are usually sulphonated within 1 hour, and at least 95% within 24 hours.

The polyaryletherketone copolymer of the invention is preferably one derived by sulphonating a copolymer which has 1 to 99 mole % of units A and, correspondingly, 99 to 1 mole % of units B, and in particular a copolymer which has 5 to 80 mole % of units A and, correspondingly, 95 to 20 mole % of units B.

The control of the sulphonation reaction should be such that the resulting copolymer preferably has a degree of hydrophilicity corresponding to a water absorption capacity at ambient temperature of about 2 weight % water absorption to complete solubility in water.

The hydrophilic copolymers of the invention (which more preferably absorb 2-40 weight % water, particularly 5-30 weight % water, at ambient temperature) are potentially useful as membrane materials, e.g. for ultrafiltration processes, e.g. desalination and removal of micro-organisms, since they are not only hydrophilic in character but retain considerable strength even when containing a significant quantity of water (e.g. up to 20 weight % water).

Ionomers of the above-defined copolymers which are sulphonated with --SO.sub.2 OH groups may be readily prepared e.g. by converting the --SO.sub.2 OH groups to salts such as SO.sub.3 --M.sup.+ (where M= an alkali metal or NR.sub.4, R being an alkyl group); these too have utility as hydrophilic polymers. Accordingly, the sulphonyl groups of the copolymers of the invention preferably have the formula --SO.sub.2 Y where Y is H, an alkali metal, or NR.sub.4 where R is an alkyl group.

Copolymers having the repeat units A and B and inherent viscosity (IV) of at least 0.7 (measured at 25.degree. C. as a 0.1% w/v solution in H.sub.2 SO.sub.4 of density of 1.84 ) may be conveniently prepared by condensation of hydroquinone, 4,4'-dihydroxybenzophenone and 4,4'-difluorobenzophenone and an alkali metal carbonate or bicarbonate in the presence of an aromatic sulphone solvent at 150.degree.-400.degree. C.--as described in our European Patent Publicaton No. 0 001 879.

The present invention is now illustrated by the following examples.

A copolymer containing 50 mole % of repeat units A and 50 mole % of repeat units B (10 g), (IV 1.30), was added to 100 ml concentrated sulphuric acid (98% w/w). The stirred dispersion was heated to 80.degree. C. and the copolymer had completely dissolved after 0.5 hours to yield a cherry-red solution. the solution was maintained at 80.degree. C. for a further 0.5 hours and then poured into demineralised water whereupon a pink lace precipitated. The lace was filtered off, chopped up in a blender, washed repeatedly with demineralised water until the washings were enutral to pH paper and then the pale pink polymer dried overnight in a vacuum oven at 60.degree. C. Analysis by 220 MHz nuclear-magnetic-resonance (nmr) spectroscopy showed that 75-80% of the repeat units A bore one --SO.sub.2 OH group on the sub-units ##STR8## while substantially all the repeat units B were non-sulphonated. The yield of sulphonated copolymer was 8.0 g; its IV was 0.86.

The procedure of Example 1 was repeated except that the copolymer solution was maintained at 80.degree. C. for 19 hours before isolation and work-up. Analysis by 220 MHz nmrspectroscopy showed that 95% of the repeat units A bore one --SO.sub.2 OH group on the sub-units ##STR9## while substantially all the repeat units B were non-sulphonated. The yield of sulphonated copolymer was 9.52; its IV was 0.71.

Films were cast from solutions of the sulphonated copolymer in dimethylformamide from which films were cast. The water absorption of these films after steeping in water for 24 hours at ambient temperature ranged from 10 tp 14 weight %.

It can be predicted that results similar to those of Examples 1 to 2 are obtainable with sulphonated copolymers derived from copolymers containing 5 to 80 mole % of repeat units A and, correspondingly, 20 to 95 mole % of repeat units B.

The procedure of Example 1 was repeated except that the copolymer dispersion was stirred in the concentrated sulphuric acid (98% w/w) for 1 hour at ambient temperature. Dissolution was observed but nmr analysis of the product after isolation and work-up as per Example 1 showed that relatively little sulphonation had occurred (about 10-20% of the repeat units A having been sulphonated).

A homopolymer containing the repeat unit B (50 g) was dissolved in hot (80.degree. C.) concentrated sulphuric acid (98% w/w) and the solution stirred for 24 hours at 80.degree. C. The solution was poured into water and worked up as per Example 1. Analysis (nmr) showed it to be substantially unchanged from the starting material.