A soluble aromatic polyimide was chloromethylated to produce a new starting material.Chloromethyl group was used as a functional reactive group to graft poly（propylene glycol） side-chain

and we attained polyimide with PPG side-chain modification

the structure of the product was identified by FTIR and 1H NMR.Dielectric Constant and BET characterizations revealed that the dielectric constant reduced obviously

from 3.147 to 2.976;the specific surface area and the pore volume increased after the polyimide had been modified by PPG side-chain which had large volume.Besides

the polymer that we had prepared had good solubility;such property made the polyimide easy processing and well application in microelectronic industry.