10 g of this hydrophilic urethane acrylate and 0 2 g of ammonium peroxodisulphate were dissolved in 40 g of water and separately another 10 g of the hydrophilic urethane acrylate and 1 g of ascorbic acid were dissolved in 40 g of water to which 10 u03bcl of a 3 percent solution of iron ii chloride had been added then the two portions were combined by brief stirring and a hydrogel was obtained after 5 min an initial charge of 200 g of hdi and 1 g of benzoyl chloride had 400 g of a polyether having an ethylene oxide content of 63 and a propylene oxide content of 37 started on tmp 3 functional added to it dropwise at 80 u00b0 c within 2 h and was subsequently stirred for 1 h then the excess hdi was distilled off by thin film distillation at 130 u00b0 c and 0 1 torr to leave 420 g of a prepolymer having an nco content of 2 75 153 g of this prepolymer 0 1 g of bkf and 0 1 g of dbtl were admixed with 21 4 g of 3 acryloyloxy 2 hydroxypropyl ester methacrylate glycerol monoacrylate monomethacrylate at 60 u00b0 c allowed to cool down to room temperature and left to stand for 4 d then 10 g of this hydrophilic urethane acrylate and 0 2 g of ammonium peroxodisulphate were dissolved in 40 g of water and separately another 10 g of the hydrophilic urethane acrylate and 1 g of ascorbic acid were dissolved in 40 g of water to which 10 u03bcl of a 3 percent solution of iron ii chloride had been added then the two portions were combined by brief stirring.