Correlation of Microstructure, Rheological and Morphological Characteristics of Synthesized Polypropylene (PP) Reactor Blends Using Homogeneous Binary Metallocene Catalyst.

Javid Vaezi,Hossein Khonakdar,Mehdi Nekoomanesh,Alireza Mojarrad,Seyed Jafari

doi:10.3390/polym9030075

Abstract

A novel binary homogeneous catalyst system based on (I): rac-Me2Si(2-Me-4-PhIn)2ZrCl2 and (II): (2-PhIn)2ZrCl2 catalysts at various molar ratios was utilized for the synthesis of polypropylene (PP) reactor blends with bimodal molecular weight distribution (MWD). The results of gel permeation chromatography analyses revealed that the catalyst (I) was responsible for the production of i-PP with high molecular weight (MW) while the individual use of catalyst (II) led to the production of an elastomeric PP with relatively low MW. However, application of the binary catalyst system led to high MW bimodal MWD products being highly dependent on the catalysts’ molar ratios. Increasing the molar ratio of catalyst (II) to catalyst (I) resulted in a notable enhancement of the products’ complex viscosity due to the increased MW, a higher level of chains’ entanglements and formation of amorphous blocks along the polymer chains. All products exhibited a single relaxation that shifted towards longer times upon changing the catalysts’ molar ratios. Scanning electron microscopy results revealed that the fracture surface of the blends, synthesized by the binary catalyst system, became more heterogeneous in comparison with the products obtained by the individual use of the catalyst (I). The observed heterogeneity was found to increase by increasing the amount of catalyst (II). Such morphological change was further corroborated by the dynamic rheological data, indicating a promising correlation between the linear rheological results and the morphological features of the synthesized PP reactor blends.

Highlights

Polypropylene (PP) is one of the most commonly used plastics which is increasingly being utilized worldwide due to its rather low price, good processability and its ease of modification for different applications
The and 973 cm and absorption bands techniques are characteristic bands assigned to helices is one of the common, simple economical for indirect measurement of the chain conformation related to the isotactic segments that have different numbers of repeating units
The molecular weight distribution (MWD) curves of synthesized products by the individual use of catalysts (I) and (II) and their binary systems show that MWD was broadened and became bimodal for products obtained binary systems show that MWD was broadened and became bimodal for products obtained from from the catalysts’ mixtures

Summary

Introduction

Polypropylene (PP) is one of the most commonly used plastics which is increasingly being utilized worldwide due to its rather low price, good processability and its ease of modification for different applications. Recent researches have been conducted with the aim of synthesizing polyolefins with improved microstructure and properties, and to this end, novel catalyst systems were designed. Of the new strategies to synthesize polyolefins with optimum properties, one could mention the alloy, hybrid and multi-component catalyst systems [8,9,10,11,12,13,14,15,16]. In those systems, each catalyst produces a polymer with a unique structure and properties. Due to the occurrence of chain transfer reactions from one active site to another, in the presence of a chain transfer agent such as trimethyl aluminum (TMA) or triisobutyl aluminum (TIBA), the final product is a reactor blend of two or more polymers possessing stereoblock copolymer microstructures, which exhibit different properties as compared to the polymers produced from the individual use of catalysts [17,18,19,20]

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