writer：Zhengfang Chen, Bin Wang, Jian Kang, Jinyao Chen, Feng Yang, Ya Cao, Huilin Li, Ming Xiang
keywords：β-nucleated isotactic polypropylene; crystallization behavior; crystalline morphology
source：期刊
specific source：Polymers for Advanced Technologies
Issue time：2013年
Aiming  at  further  investigate  the  combination  effect  of  concentration  of 
β-nucleating  agent  (β-NA)  and  stereo-defect  distribution  on  the  crystallization 
behavior  of  β-nucleated  isotactic  polypropylene  (β-iPP),  in  this  study,  the 
crystallization behavior and polymorphic morphologyof twoβ-iPP resins with nearly 
same average isotacticity (PP-A and PP-B) but different uniformities of stereo-defect 
distribution were investigated by differential scanning calorimetry (DSC), wide angel 
X-ray  diffraction  (WAXD)  and  polarized  optical  microscopy  (POM).  The  results  of DSC  and  WAXD  showed  that  the  addition  of  TMB-5  increases  the  crystallization temperature and  decreases  the  spherulite sizes  of  both  PP-A  and  PP-B, and  reduces their  crystallization energy  barriers as  well;  however,  the  polymorphic  behaviors  of PP-A and PP-B exhibit different dependence on the TMB-5 concentration. For PP-A with less uniform distribution of stereo-defects, β-phase can be observed only when the TMB-5 concentration is no less than 0.1wt%, while for PP-B with more uniform stereo-defect  distribution,  addition  of  0.01wt%  TMB-5  can induce  the formation  of β-phase. Moreover, the analysis of POM indicated that the crystalline morphologies of both PP-A and PP-B change greatly with the TMB-5 concentration, and the variation features  of  PP-A  and  PP-B  are  quite  different  from  each  other.  PP-B  with  more uniform  stereo-defect  distribution  was  more  favorable  for  the  formation  of  large amount  of  β-phase  in  the  presence  of  wide  concentration  range  of  TMB-5.  The different  polymorphic  behaviors  and  their  different dependences  on  the  β-NA concentration were related to the different uniformities of stereo-defect distribution of the samples, since the distribution of stereo-defects could restrain the regular insertion of  molecular  chains  during  crystallization  and  thus determine  the  tendency  the α-phase crystallization of the sample.