Modified polyvinyl acetate and preparation method and use thereof and oil-based drilling fluid

A method of preparing a modified polyvinyl acetate including:

• (1) subjecting a mixed liquor L1 comprising a functional monomer to a first reaction with a first vinyl acetate monomer, then adding a first initiator to carry out a second reaction to obtain a mixed liquor L2;
• (2) subjecting an acrylate monomer, a second vinyl acetate monomer, a second initiator and the mixed liquor L2 to carry out a third reaction to obtain a mixed liquor L3;
• (3) subjecting a third initiator and the mixed liquor L3 to carry out a fourth reaction under the airtight and ultrasonic conditions, subsequently heating products produced by the fourth reaction to a fifth reaction to obtain a mixed liquor L4;
• (4) subjecting the mixed liquor L4 to a product extraction treatment to prepare a modified polyvinyl acetate;
• wherein the functional monomer is selected from acrylic acid, oleic acid or butenedioic acid.