Dimethyl 2

6-naphthalate (DMN) and sodium of o-chlorobenzoate (SOCB) were used as model compounds to simulate the chemical reaction between poly(ethylene naphathalate) (PEN) and carboxylic acid alkali salt；and the reaction was studied by using DSC

polarized optical microscopy with a hot-stage (HPOM)

Fourier transform infrared spectrometry(FTIR) and high performance liquid hromatograpby (HPLC)．By means of DSC and HPOM

the reaction between PEN and SOCB was also proved at high temperature．Therefore

the chemical nucleation mechanism of carboxylic acid alkali salts in PEN was proposed．Carboxylic acid alkali salt reacts with the ester linkages of PEN at high temperature and PEN ionic chain-ends were produced．The ionic chain-ends act as a true nucleating agent to improve the crystallization rate of PEN．