e) gradually adding a portion of an entire amount of alkylene oxide to said initial charge amount of said acrylic acid in said vessel until an amount of {HEAD ~ alkylene oxide} is in a range of 0.8 to 2.0 in terms of molar ratio to said initial charge amount of said acrylic acid, with said portion of alkylene oxide and a residual amount of alkylene oxide being equal to said {TAIL ~ entire amount} of alkylene oxide to be supplied to the batch reaction, with acrylic acid not being added in this step “e”; and then 
e ) gradually adding a portion of an entire amount of alkylene oxide to said initial charge amount of said acrylic acid in said vessel until an amount of { HEAD ~ alkylene oxide } is in a range of 0.8 to 2.0 in terms of molar ratio to said initial charge amount of said acrylic acid , with said portion of alkylene oxide and a residual amount of alkylene oxide being equal to said { TAIL ~ entire amount } of alkylene oxide to be supplied to the batch reaction , with acrylic acid not being added in this step “ e ” ; and then
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