Polymer having dispersing function, oil well cement dispersant, and preparation method therefor and use thereof

A method for preparing a polymer, comprising:

• subjecting a monomer mixture to polymerization in water under the solution polymerization conditions in the presence of an initiator, wherein the monomer mixture comprises a monomer A, a monomer B, a monomer C and a monomer D, the monomer A being an unsaturated polyether and/or polyester, the monomer B being an unsaturated carboxylic acid and/or anhydride and/or salt thereof, the monomer C being a silane that contains a polymerizable group, and the monomer D being an unsaturated sulfonic acid and/or a salt thereof;
• and the molar ratio of monomer A:
• monomer B:
• monomer C:
• monomer D is 1:(0.5-6):
• (0.01-4):
• (5-15);
• and
• controlling the solution polymerization conditions so that the resulting polymer has a weight average molecular weight of 20,000-120,000,
• wherein the silane is of formula (IV):
• in formula (IV), each of R1, R2, R3, R1′ and R2′ is independently selected from H and C1-C4 alkyl;
• Ra, Rb and Rc are each independently selected from H and C1-C4 alkyl or alkoxyl, and n is an integer from 5 to 25.