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

Automated summary

Compared to polypropylene homopolymer, the presence of a beta-nucleating agent usually leads to a lower amount of beta-phase in polypropylene random copolymer with comonomer inserted. The insertion of comonomer reduces the formation of beta-nuclei and weakens the growth rate of beta-phase, leading to the decreased content of beta-phase in polypropylene random copolymer. The study provides important insights into the control of polymorphism in polymers.