Hydrophilic vinylidene fluoride resin composition and method for production thereof

A process for producing a particulate hydrophilic vinylidene fluoride resin composition, comprising:

• polymerizing vinylidene fluoride by way of suspension polymerization in the presence of a polymerization initiator having a 10-hour-half-life temperature T10 of 30-90° C. at a temperature of T10−20° C., to T10+30° C. to produce porous vinylidene fluoride polymer particles having an average particle size of 70-300 μm,
• heat-treating the porous vinylidene fluoride polymer particles at a heat-treating, temperature of 70-100° C. for 1-4 hours, to reduce an amount of the polymerization initiator remaining in the porous vinylidene fluoride polymer particles alter the suspension polymerization,
• then impregnating pores of the porous vinylidene fluoride polymer particles with a monomer having a hydrophilic group and an unsaturated double bond, and
• polymerizing the monomer at a temperature of 20-80° C. in the presence of the reduced amount of the polymerization initiator remaining in the porous vinylidene fluoride polymer particles and in the absence of an additional polymerization initiator to provide a polymer of the monomer having a weight-average molecular weight of 3×105 to 9.13×105 contained in the pores of the porous vinylidene fluoride polymer particle,
• wherein the hydrophilic vinylidene fluoride resin composition exhibits a contact angle of at most 60 degrees before and after immersion in water at 85° C. for 100 hours and a weight loss of at most 10% of the hydrophilic polymer after extraction with water at 85° C. for 100 hours.