Miscibility of isotactic polypropylene with random and block ethylene-octene copolymers studied by atomic force microscopy-infrared

• Published in: Polymer (Guilford) Vol. 259; p. 125354
• Main Authors: Zhong, Zhenxing, Peng, Li, Zhang, Na, Su, Juanxia, Ye, Nanbiao, Luo, Zhongfu, Han, Charles C., Huang, Xianbo, Su, Zhaohui
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 27.10.2022
• Subjects: AFM-IR; Blends; Ethylene-octene copolymers; Miscibility; Polypropylene; Miscibility; Blends; Ethylene-octene copolymers; Polypropylene; AFM-IR
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2022.125354

Ethylene-octene random copolymers (EOCs) and block copolymers (OBCs) have been used extensively in toughening isotactic polypropylene (iPP). In this work, the miscibility of iPP/EOC and iPP/OBC blends has been investigated quantitatively using an atomic force microscopy-infrared (AFM-IR) technique. A blend of a partially deuterated iPP and EOC at 80/20 mass ratio was found to phase separate, and in situ AFM-IR analysis revealed the presence of deuterated iPP in both phases, indicating partial miscibility between the two components. Quantitation methods for phase compositions of iPP/EOC and iPP/OBC blends using AFM-IR were established, and phase separation kinetics for a solution-mixed iPP/OBC 50/50 blend at 200 °C was investigated using AFM-IR. The phase compositions reach an equilibrium state in ∼4 h, and each component exhibits a solubility of ∼10 wt% in the other one in the molten state. Moreover, an interphase of ∼1 μm thickness and transitional composition is present in between the iPP-rich and the OBC-rich phases, indicative of good compatibility between iPP and OBC. In contrast, an iPP/EOC 50/50 blend under the same conditions contains two co-existing phases, with an EOC content of 4.9 and 93.2 wt% for the iPP-rich and EOC-rich phase, respectively, with a sharp interface between, implying poorer compatibility of EOC with iPP than for OBC. Composition analyses for iPP/EOC 80/20 and iPP/OBC 80/20 blends prepared by melt-blending support these observations. [Display omitted] •Miscibility of iPP/POE blends is investigated quantitatively.•OBC and iPP each exhibits a solubility of ∼10 wt% in the other.•An interphase exists between the two phases in iPP/OBC blends.•OBC is more compatible with iPP than EOC.