The crosslinked polymer poly(α-methylene-γ-butyrolactone-acrylic acid-pentaerythritol allyl ether) was prepared by emulsion polymerization of α-methylene-γ-butyrolactone and acrylic acid with the crosslinking monomer pentaerythritol allyl ether. To a four neck round bottom glass flask, equipped with a mechanical stirrer and a thermocouple with a nitrogen inlet at the side of the inlet-tube and two dropping funnels was added the initial charge of 44.03 g of water and 0.51 g of a 20% solution of sodium dodecyl sulfate surfactant. Into the monomer dropping funnel a mixture of 20.8 g of α-methylene-γ-butyrolactone, 1.1 g of acrylic acid and 0.16 g of pentaerythritol allyl ether were added. Into the second dropping funnel the aqueous mixture consisting of 83.43 g water, 1.32 g 20% sodium dodecylsulfate, 0.14 g sodium persulfate and 0.17 g 20% sodium hydroxide solution were added. The initial charge was heated to 75° C. dropwise addition of the monomer was started. Dropwise addition of the aqueous mixture started 5 minutes later. The monomer feed ended 120 minutes after the start of monomer addition, and the aqueous stream ended 5 minutes after the monomer stream ended. After a cook-down time of one hour, the reaction mixture was cooled to room temperature.
