Abstract: Using lanthanum nitrate, monocarboxylic acid, dicarboxylic acid and tricarboxylic acid as the precursors, six carboxylic lanthanums were synthesized, which were used in PVC as thermal stabilizers. By Congo red and torque rheometer, the static and dynamic thermal stability of the modified PVC was tested. It showed that the thermal stabilizers based on mono or dicarboxylic acid behaved better than those based on tricarboxylic acid. FTIR showed that when heated, lanthanum ion could coordinate with the chlorine atoms and thus the thermal stability was provided. In addition, HCl released during the degradation of PVC could be absorbed by lanthanum.

Key words: carboxylic acid, poly(vinyl chloride), lanthanum, thermal stabilizer