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Abstract. The target of the present study was to investigate the structure-property relationships of heterophasic ethylenepropylene (EP) copolymers based on a single-site (metallocene) catalyst (SSC) supported with an emulsion technology developed by Borealis. The structure of these copolymers, their morphology evolution, as well as resulting mechanical properties were studied by varying the composition of the dispersed phase, i.e. the amorphous ethylene-propylene copolymer or rubber (EPR), in a systematic series of bench-scale products. Next to composition effects, an attempt was made to understand the key differences between products based on Ziegler-Natta catalysts (ZNC) and single-site catalysts (SSC) in terms of polymer structure and property profile. A remarkably different phase morphology with very good phase coupling to the matrix PP and the absence of crystallizable polyethylene in the ethylene-rich copolymers (EPR) was observed for the SSCbased grades, resulting in a high level of impact strength over a wide composition range.

Keywords: polymer synthesis, polypropylene, morphology, single-site catalyst, mechanics

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1. Introduction

Among the wide range of polypropylene (PP) grades, the class of heterophasic ethylene-propylene (EP) copolymers has conquered a wide range of applications from seemingly trivial packaging uses to technically complex parts, for example in the automotive area. Initially produced by melt mixing PP homopolymers with different amounts of externally produced elastomers like ethylene-propylene rubbers (EPR) or ethylene-propylene-diene elastomers (EPDM), products commonly referred to as 'block copolymers' (correctly 'heterophasic copolymers', HECOs) were later developed in multi-reactor gas phase plants (e.g. Novolen process) or in bulk/gas phase combinations (Spheripol or Borstar PP process). These combine a crystalline PP matrix (produced in the first 1-2 reactors) with embedded particles of EPR and PE (produced in 1 or more following reactors) [1]. Structural and compositional aspects of such heterophasic EP copolymers (EP-HECOs ) have been studied extensively in the past and are reported e.g. in papers of Doshev and coworkers [2, 3] and Grein and coworkers [4, 5]. The key influence factors on performance can be summarized as amount [6], composition and molecular weight of the disperse (EPR) phase as well as the properties of the matrix phase like crystallinity and ductility.

Aspects of their synthesis have been studied e.g. by Cecchin et al. [7], highlighting process and catalyst effects on the possible composition and property...

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