Toward a Further Understanding of the Decreased β-Phase Content in β-Nucleated Polypropylene Random Copolymer: From Nucleation and Growth Kinetics

Compared with polypropylene homopolymer (PPH), β-nucleating agent (β-NA) usually induces less β-phase in polypropylene random copolymer (PPR) with comonomer inserted. A widely held view is that unfavorable β-growth kinetically caused by the insertion of comonomer contributes to a decreased relative content of β-phase ( k β ) in PPR. To further understand the decreased k β in PPR, we separately investigated the nucleation and growth behavior of various isotactic polypropylenes (iPPs) nucleated with a β-NA, N, N ′-dicyclohexylterephthalamide (DCHT). With the aid of fractionated crystallization, the possibility of DCHT to form β-nuclei, i β / i, is calculated to be reduced in PPR with ethylene inserted, demonstrating fewer β-nuclei induced. As for growth, it is found that the insertion of comonomer decreases the relative growth rate of β-phase ( G β / G α ) and weakens the kinetic advantage of β-growth. The study reveals that both i β / i and G β / G α decrease with the insertion of comonomer. Fewer β-nuclei induced by DCHT and the subsequent unfavorable β-growth simultaneously contribute to the final decreased k β . Our fundamental insight provides a more comprehensive understanding of the decreased k β as comonomer is inserted into the iPP chain and could have important implications in the control of the polymorphism of polymers.