The third component of 5-sulfoisophthalic acid dihydroxy propyl ester sodium salt (SIPP) and the fourth component of poly(butylene adipate) (PBA) or polyethylene glycol (PEG) were added respectively in the process of esterification and polycondensation for the polymerization of 1

3-propanediol (or trimethylene glycol) and terephthalic acid.Three kinds of cationic dyeable poly(trimethylene terephtalate) copolyesters (PTTs) were synthesized by direct esterification-polycondensation process

and were characterized by differential scanning calorimetry (DSC)

1H-nuclear magnetic resonance (1H-NMR) and thermogravimetric analysis (TGA)

respectively.Compared to PTT

the thermal degradation properties for PTTs modified by SIPP

PBA and PEG almost kept invariant.DSC was used to further investigate the nonisothermal crystallization properties of PTT and the cationic dyeable PTTs

and the experimental results indicated that the Avrami exponents for PTT were from 4.24 to 4.50

suggesting that nonisothermal crystallization mechanism for PTT was simultaneously controlled by homogeneous and heterogeneous nucleation

and the nonisothermal crystallization for PTT was very complex.The Avrami exponents for PTTs modified by SIPP

PBA and PEG were from 1.72 to 2.64

and it was assumed that the nonisothermal crystallization mechanism for cationic dyeable PTTs was the heterogeneous nucleation.The crystallization activation energy of cationic dyeable PTTs was higher than that of PTT

suggesting that the crystallization was more sensitive to the temperature.Therefore

it was of great importance to control the temperature in spinning process.