Method for producing aqueous solution of polymer having phosphorylcholine groups

A method for producing an aqueous solution of a polymer having a phosphorylcholine group comprising the steps of:

• polymerizing a polymerizable composition containing a polymerizable monomer having the phosphorylcholine group represented by the formula (I) in an organic medium or without a medium in the presence of a non-metal polymerization initiator soluble in a water-containing medium, to obtain crude polymer having the phosphorylcholine group, wherein said non-metal polymerization initiator is selected from the group consisting of succinic peroxyglutarate, t-butyl peroxymaleate, t-butyl peroxypivalate, di-2-ethoxyethyl peroxydicarbonate, 3-hydroxy-1,1-dimethylbutyl peroxypivalate, 1-((1-cyano-1-methylethyl)azo)formamide, 2,2′-azobis (2-methyl-N-phenylpropionamidine)dihydrochloride,2,2′-azobis (N-(4-chlorophenyl)-2-methylpropionamidine)dihydrochloride,2,2′-azobis (N-(4-hydroxyphenyl)-2-methylpropionamidine)dihydrochloride, 2,2′-azobis(N-(4-aminophenyl)-2-methylpropionamidine)tetrahydrochloride, 2,2′-azobis(2-methyl-N-(phenylmethyl)propionamidine)dihydrochloride, 2,2′-azobis(2-methyl-N-2-propenylpropionamidine)dihydrochloride, 2,2′-azobis(2-methylpropionamidine)dihydrochloride, 2,2′-azobis(N-(2-hydroxyethyl)-2-methylpropionamidine)dihydrochloride, 2,2′-azobis(2-(5-methyl-2-imidazolin-2-yl)propane)dihydrochloride, 2,2′-azobis(2-(2-imidazolin-2-yl)propane)dihydrochloride, 2,2′-azobis(2-(4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl)propane)dihydrochloride, 2,2′-azobis(2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane dihydrochloride, 2,2′-azobis(2-(5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl)propane)dihydrochloride, 2,2′-azobis(2-(1-(2-hydroxyethyl)-2-imidazolin-2-yl)propane)dihydrochloride, 2,2′-azobis(2-(2-imidazolin-2-yl)propane), 2,2′-azobis(2-methyl-N-(1,1-bis(hydroxymethyl)-2-hydroxyethyl)propionamide), 2,2′-azobis(2-methyl-N-(1,1-bis(hydroxymethyl)ethyl)propionamide), 2,2′-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2′-azobis(2-methylpropionamide)dihydrate,4,4′-azobis(4-cyanopentanoic acid), 2,2′-azobis(2-hydroxymethyl)propionitrile), and mixtures thereof,
• adding a water-containing medium to said crude polymer to obtain a crude polymer aqueous solution containing the polymer having the phosphorylcholine group at a concentration of 0.5 to 80 wt % thereof, and then
• purifying said crude polymer aqueous solution with a separation membrane:
• (wherein X denotes a divalent organic residue, Y denotes an alkyleneoxy group having 1 to 6 carbon atoms, and Z denotes a hydrogen atom or R5 —CO—(wherein R5 denotes an alkyl group having 1 to 10 carbon atoms or a hydroxyalkyl group having 1 to 10 carbon atoms), R1 denotes a hydrogen atom or a methyl group, R2, R3 and R4 are the same or different groups and denote a hydrogen atom, or a hydrocarbon or hydroxy substituted hydrocarbon group having 1 to 6 carbon atoms and m denotes 0 or 1.