Process for preparation of swellable and degradable microspheres

A process for making a swellable and degradable microsphere preparation comprising the steps of:

• a) forming a first solution having a pH of at least 3 or about 3 comprising:
• (i) water;
• (ii) at least one water miscible monomer selected from the group consisting of acrylic acid, methacrylic acid, salts of acrylic acid and methacrylic acid, acrylamide, methacrylamide, N-substituted acrylamides, N-substituted methacrylamides, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate, provided that:
• (A) if said monomer is acrylamide, methacrylamide, N-substituted acrylamides, 2-hydroxyethyl acrylate, or 2-hydroxyethyl methacrylate, said monomer is used in combination with at least one other monomer selected from subgroup 1 consisting of:
• acrylic acid, methacrylic acid, and salts of acrylic acid and methacrylic acid;
• (iii) a water soluble protecting colloid;
• (iv) an emulsifier;
• and
• (v) a water soluble azo initiator having a low activation temperature;
• b) forming a second solution comprising at least one substantially chlorinated hydrocarbon of less than 6 carbon units,
• provided that the chlorinated hydrocarbon is not a halogenated aromatic hydrocarbon, and an organic soluble protecting colloid;
• c) forming a first suspension with agitation comprising the first and second solutions at a temperature below the activation temperature of the azo initiator of (a);
• d) increasing the temperature of the first suspension to a temperature at which the water soluble azo initiator is activated;
• e) agitating the first suspension until it forms a second suspension comprising a gelatinous precipitate suspended in an organic liquid phase, wherein microspheres are formed;
• f) allowing the second suspension to cool to a temperature that is at about 30° C. or below 30° C. while agitating the second suspension;
• g) washing the second suspension at least once with a dehydrating solvent wherein water is removed from the microspheres, producing a microsphere slurry comprising washed microspheres;
• h) recovering the washed microspheres from the microsphere slurry;
• and
• i) heating the washed microspheres to a temperature above 25° C. for a time sufficient to substantially dry the washed microspheres to form the swellable and degradable microsphere preparation;
• wherein the process is carried out in absence of a crosslinking agent.