Phase Structure and Crystallization Behavior of Polypropylene in-Reactor Alloys:  Insights from Both Inter- and Intramolecular Compositional Heterogeneity

Abstract

Systematic investigation on the compositional heterogeneity, phase structure, the crystallization and subsequent melting behavior of two commercial in-reactor alloys EB-P and EP-P (ethylene-co-butylene polypropylene and ethylene-co-propylene polypropylene) from Basell were conducted. The composition of the alloys and the chain structure of each component were characterized by combinatorial using of preparative TREF and 13 C NMR technique. The compositional heterogeneities of both samples were further studied by SSA technique, and possible thermal fractionation mechanisms were then inferred. Correlations between the mechanical properties and the molecular architectures and phase structures were discussed. The results show that the excellent balance between toughness and rigidity of sample EB-P primarily benefits from the crystalline polyethylene homopolymer (HPE) phase and the amorphous ethylene-R-olefin copolymer (EC) component, which is proved to be enriched at the interface between the dispersed polypropylene homopolymer phase (HPP) and the matrix (HPE). As for EP-P sample, the very high amorphous EC content, and the homogeneous and interpenetrating cocontinuous phase structure in the alloy are considered to be mainly responsible for the outstanding low-temperature impact toughness.

The dynamic crystallization and multiple melting behavior of polypropylene in the in‐reactor alloy: A differential scanning calorimetry study

“…The composition of the alloy was characterized in our previous paper. 7 Three components have been identified from the combination of solution NMR, analytical TREF and SEM results: homo polypropylene (HPP), ethylene-propylene segmented copolymer with crystallizable ethylene and propylene blocks, and ethylene-propylene random (EPR) copolymer which is not crystallizable.…”

“…An in-reactor alloy system generally shows very complicated microstructures and typically heterophasic morphology, which consists of ethylene-propylene random copolymer, ethylene-propylene segmented copolymers with different sequence lengths of polyethylene (PE) and polypropylene (PP) segments, and homo polypropylene (HPP). 6,7 It is understandable that the mechanical properties of PP in-reactor alloy are related to both the microphase-structure of the blend system and the crystallization behavior of each component. However, most of previous studies, if not all, mainly focus on the phase structure and the composition of the alloy, and try to correlate them with either the polymerization mechanisms or the mechanical properties of the material.…”

“…The crystallization and melting behavior of PP in the alloy should be different from that of the pure iPP because of the presence of block copolymer which are partially miscible with PP matrix and served as a compatibilizer between the PP matrix and dispersed rubber phase. In our previous publication in this series, 7 we have systematically studied the compositional heterogeneity and phase structure of the polypropylene in-reactor alloy. In this article, particular attention is served to the nonisothermal crystallization and the subsequent melting behavior of PP in the in-reactor alloy, trying to achieve a complete understanding of the thermal dynamic mechanism behind the crystallization and melting phenomenon.…”

Effect of Copolymerization Time on the Microstructure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys

“…Definitely, these two melting peaks were segregated not only by the molecular chain defects but also by some contribution from the meltingrecrystallization-remelting process during heating. 18 By combining the results of FT-IR, NMR, and DSC analysis, we obtained a clear map for the chain structure and structure distribution of these PP/EPR in-reactor alloys. In these alloys, the ethylene-propylene random copolymer was available at room temperature fraction (fraction 1), and the PP homopolymer with a very low content of ethylene was included in over 100 C fraction (fractions 4 and 5), these three fractions totally occupied more than 80 wt % of the alloy.…”

“…18,19 Recently, thermal fractionation methods, such as stepwise isothermal crystallization (SIC) and successive selfnucleation and annealing (SSA) by differential scanning calorimetry (DSC), have been developed to analyze the structural heterogeneity of molecular chains. [20][21][22] SSA is based on the sequential application of self-nucleation and annealing steps to a polymer sample.…”