Process for preparing hydrogels as spherical beads of large size

Claim 1

An improved process for preparing essentially uniform spherical beads of up to 5 mm diameter of a crosslinked, water-insoluble hydrogel by suspension polymerization of (A) 95 to 30% by weight of the hydrogel of a water-soluble monoolefinic monomer or mixture of said water-soluble monomers, and from 0 to 70% by weight based on the total monomer of a water-insoluble monoolefinic monomer or mixture of said water-insoluble monomers, with the proviso that the final hydrogel does not contain over 60% by weight of said water-insoluble monomer components, with (B) 5 to 70% by weight of the hydrogel of a polyolefinic crosslinking macromer of the formula ##STR9## wherein a is 1 or 2, R 1 is a polycondensate chain having a molecular weight from about 200 to about 8,000 which contains hydrocarbon residues connected via ether, ester, amide or urea linkages or is a polysiloxane of molecular weight between 400 and 8,000; R 2 is hydrogen, methyl or --CH 2 COOR 4 ; R 4 is hydrogen or alkyl of 1 to 10 carbon atoms; R 3 is hydrogen or --COOR 4 with the proviso that at least one of R 2 and R 3 is hydrogen; X is an oxygen atom, --COO-- or --CONR 5 ; R 5 is hydrogen or alkyl of 1 to 5 carbon atoms; Y is a direct bond or the radical R 6 --Z 1 --CONH-- R 7 NHCO--Z 2 --; R 6 is linked to X and represents branched or linear alkylene of 1 to 7 carbon atoms; Z 1 is an oxygen atom or --NR 5 --; Z 2 is Z 1 or a sulfur atom; and R 7 is the diradical of an aliphatic, alicyclic or aromatic diisocyanate with the proviso that in case X is oxygen, Y is different from a direct bond and R 2 and R 3 are hydrogen, with a polymerization initiator in a concentrated aqueous inorganic salt solution wherein the improvement comprises carrying out the suspension polymerization with monoolefinic monomers containing at least 5% by weight of the total monomers of a hydroxy substituted hydrophilic vinyl monomer; employing as the crosslinking agent a polyolefinic macromer having a molecular weight from about 400 to about 8,000 and utilizing from 0.01 to 5% by weight, based on the hydrogel, of a suspending agent selected from the water-insoluble, gelatinous, strongly water-bonding, inorganic metal hydroxides and metal hydroxy salts in the absence of excess alkali or free hydroxyl ions.