Inverse Ugelstad particles

A method of forming monodisperse crosslinked hydrogel polymer particles comprising:

• forming a solution (a) of at least 2% wt of a hydrophilic vinylic monomer in an aqueous solution, the solution also comprising a crosslinker comprising at least two vinyl groups, wherein the crosslinker comprises at least one compound of formula (IIa) or (IIb):
• wherein R6 is selected from —C1—C6 alkyl—, —C1—C6 heteroalkyl—, —C1—C6 cycloalkyl—, —C1—C6 hydroxyalkyl—, —C1—C6 ether—, or polyether comprising 2 to 100 C2—C3 ether units;
• R7 and R8 are each independently selected from —H, —C1—C6 alkyl, —C1—C6 heteroalkyl, —C3—C6 cycloalkyl, —C1—C6 hydroxyalkyl, or —C1-C6 ether;
• R9 is —N(R11)C(O)CH═CH2;
• R10 is selected from —H and —N(R12)C(O)CH═CH2;
• and
• R11 and R12 are each independently selected from —H, —C1—C6 alkyl, —C1—C6 heteroalkyl, —C3—C6 cycloalkyl, —C1—C6 hydroxyalkyl, or —C1—C6 ether;
• optionally wherein one or more of R6, R7, R8, R9, R10, R11 and R12 are independently substituted, where chemically possible, by 1 to 5 substituents which are each independently at each occurrence selected from:
• oxo, ═NRa, ═NORa, halo, nitro, cyano, NRaRa, NRaS(O)2Ra, NRaCONRaRa, NRaCO2Ra, ORa;
• SRa, S(O)Ra, S(O)2ORa, S(O)2Ra, S(O)2NRaRa, CO2Ra C(O)Ra, CONRaRa, C1—C4—alkyl, C2—C4—alkenyl, C2—C4—alkynyl, C1—C4 haloalkyl;
• wherein Ra is independently at each occurrence selected from:
• H, C1—C4 alkyl and C1—C4 alkenyl;
• forming a solution (b) of stabilizer in an organic solvent, wherein the organic solvent is not miscible in water, and wherein at least one of solution (a) and solution (b) comprises a radical initiator;
• mixing solutions (a) and (b) to form a water-in-oil emulsion (c) and adding monodisperse seed particles to the emulsion;
• allowing the monodisperse seed particles to form swollen particles in the emulsion;
• and
• polymerizing the swollen particles to form the monodisperse crosslinked hydrogel polymer particles, wherein when the monodisperse cross-linked hydrogel polymer particles are in aqueous solution, the particles each absorb at least 20% of their weight of the solution.

A method of forming monodisperse crosslinked hydrogel polymer particles comprising:

• forming a solution (a) of at least 2% wt of a hydrophilic vinylic monomer in an aqueous solution, the solution also comprising a crosslinker, wherein the crosslinker is or comprises N,N-((ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl))diacrylamide, polyethyleneglycol diacrylamide (MW≤2000) or 4-Arm PEG-Acrylamide (MW≤2000);
• forming a solution (b) of stabilizer in an organic solvent, wherein the organic solvent is not miscible in water, and wherein at least one of solution (a) and solution (b) comprises a radical initiator;
• mixing solutions (a) and (b) to form a water-in-oil emulsion (c) and adding monodisperse seed particles to the emulsion;
• allowing the monodisperse seed particles to form swollen particles in the emulsion;
• and
• polymerizing the swollen particles to form the monodisperse crosslinked hydrogel polymer particles, wherein when the monodisperse cross-linked hydrogel polymer particles are in aqueous solution, the particles each absorb at least 20% of their weight of the solution.