The relation of structures and properties with modification technology of BMI resin is studied. A new method for increasing toughness of BMI resin

so called preinsitu polymerization (PISP) is employed. Three kinds of rigid oligmers (PI) used as modifier are polymerized in RS that can react with BMI and use as solvent in PISP

and we do not need to separate the mixture PI/RS. BMI is dissolved in the RS with PI to obtain modified BMI homogenous prepolymer (PI/RS/BMI). Curing reaction is studied by means of DTA and a gel characteristics analysis. In final step we cured the modified BMI system and obtained cured modified BMI resin and the properties of cured resin were investigated. PI/RS/BMI has good reactivity at high temperature and has good stability at low temperature

and the gel time of PI/RS/BMI resin is longer than RS/BMI at same temperature. PI/RS/BMI cured resin has excellent heat resistance as their HDT exceeds 270 ℃. PI/RS/BMI cured resin by PISP has excellent toughness and PI/RS/BMI cured resin by simplly melting mixture has poor toughness. The more toughness of PI

the more toughness of PI/RS/BMI cured resin.