Effect of composition on crystallization behavior for polypropylene catalloys (PP-cats)was studied by using differential scanning calorimetry (DSC)and polarized optical microscopy (POM).The decrease of melting point for PP-cats indicates the existence of stronger interaction between the propylene homopolymer and the ethylene-propylene random copolymer (EPR)in PP-cats.The isothermal crystallization kinetics of PP-cats in the early stage could be described by the Avrami model

and a comparison with that of pure iPP was carried out.It is found that the crystallization of PP-cats proceeds with instantaneous nucleation and three-dimensional growth.The overall crystallization rate of PP-cats is higher than that of pure iPP and increases with the increase of the EPR content.However

the spherulite growth rate of PP-cats appears slower than that of pure iPP and decrease with the increase of the EPR content

which is ascribed to the difficulty in moving of propylene chains due to the higher viscosity of PP-cats melt.Furthermore

the results of morphology observation reveal that the nucleation density of PP-cats is rather higher than that of pure iPP.It is suggested that the higher overall crystallization rate of PP-cats is a result of the nucleation effect of the EP content.