Method of producing polyetherester monomer and cement dispersants

A cement dispersant comprising water-soluble vinyl copolymer produced by a first step and a second step,

• said first step consisting of producing polyetherester monomer shown by Formula 3 by causing an esterification reaction of polyalkyleneglycol with a closed end shown by Formula 1 and unsaturated carboxylic acid shown by Formula 2 by using an acid catalyst under a heated and reduced-pressure condition in the absence of solvents and in the presence of one selected from the group consisting of p-benzoquinone, phenothiazine and a mixture thereof in an amount of 0.03-0.5 weight % of said polyalkyleneglycol with a closed end while distilling away generated water, wherein said Formula 1, said Formula 2 and said Formula 3 are respectively:
• where R1 and R2 are each H or methyl group, R3 is one selected from the group consisting of alkyl groups with 1-22 carbon atoms, benzyl group, phenyl group and alkylphenyl groups each having alkyl group with 1-12 carbon atoms, and A is residual group produced by removing all hydroxyl groups from polyalkyleneglycol with repetition number of oxyalkylene units 5-250, said oxyalkylene units consisting either only of oxyethylene units or of both oxyethylene units and oxypropylene units;
• and
• said second step consisting of
• producing said water-soluble vinyl copolymer by radical copolymerization of said polyetherester monomer produced in said first step and vinyl monomer inside an aqueous solution, said vinyl monomer being copolymerizable with said polyetherester monomer.