Separating ethylene-propylene-diene terpolymers according to the content of diene by HT-HPLC and HT 2D-LC Rajesh Chitta a , Anton Ginzburg a , Gerard van Doremaele b , Tibor Macko a , Robert Brüll a, * a Deutsches Kunststoff-Institut (German Institute of Polymers), Schlossgartenstr. 6, 64289 Darmstadt, Germany b Lanxess Elastomers B.V., PO Box 1130, 6160 BC Geleen, The Netherlands article info Article history: Received 26 August 2011 Received in revised form 13 October 2011 Accepted 26 October 2011 Available online 2 November 2011 Keywords: Ethylene-propylene-diene terpolymers (EPDM) High performance liquid chromatography (HPLC) Polyolefins abstract The separation of ethylene-propylene-diene terpolymers (EPDM) according to the three monomer units is an important task to understand the macroscopic properties of these technically important elastomers. In particular a separation with regard to the content of diene is of extreme value because the distribution of the latter along and across the molar mass axis determines the cross-linking behavior. In this study we show that high-temperature liquid chromatography (HT-HPLC) can be used for this purpose: the chro- matographic retention of EPDM on porous graphite using a gradient of 1-decanol/trichlorobenzene is a function of both the content of ethylene and diene. The contribution of the diene alone to the chro- matographic retention can be quantified by calculating the difference in elution volume between the EPDM and an EP copolymer having an equivalent content of ethylene. The chromatographic separation of fully hydrogenated EPDM indicates that the additional retention due to diene is the result of its geometrical nature. Coupling the HPLC separation according to the chemical composition with size exclusion chromatography (SEC) enables to reveal for the first time the complete molecular heteroge- neity, i.e. the relationship between the chemical composition distribution and the molar mass distri- bution of EPDM. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Ethylene-propylene-diene (EPDM) continues to be one of the most widely used synthetic elastomers having both specialty and general purpose applications. It is characterized by its outstanding resistance against ozone, oxidation, aging, weather and high- temperatures [1,2]. These properties can be attributed to the stable and saturated polymer backbone structure present in the material. Their unique features make EPDM useful for outdoor and elevated temperature applications, such as automotive profiles, roofing, electrical insulation, belts, window gaskets, and water seals. Commercial products contain an ethylene content ranging from 40 to 60 mol%. 5-ethylidene-2-norbornene (ENB), 5-vinyl-2- norbornene (VNB) and dicyclopentadiene (DCPD) are the dienes typically incorporated. On a molecular level the macroscopic properties of these elastomers, which include processing and vulcanizing behavior as well as the final properties of the cross- linked network, are largely controlled by the molar mass distribu- tion (MMD), the chemical composition distribution (CCD) and the way these distributions are related to each other, i.e. the molecular heterogeneity. Therefore, it is important to characterize these fundamental parameters to understand the structure4property relationships. Size exclusion chromatography (SEC) [3], which separates macromolecules according to hydrodynamic volume, is a well established technique to determine the molar mass distribution (MMD) and the average molar mass for polymers. SEC can be coupled to IR- [4] or NMR-spectroscopy [5,6] to yield the distri- bution of monomer units along the molar mass axis. The CCD of semicrystalline olefin copolymers is usually deter- mined by fractionation techniques like Crystallization Analysis Fractionation (CRYSTAF) [7] and/or Temperature Rising Elution Fractionation (TREF) [8]. Both discriminate the polymer chains on the basis of their crystallizability from a dilute solution in a temperature gradient and consequently fail in the case of amor- phous EP and EPDM samples. As a result there is no analytical technique available to characterize the CCD of these materials. High performance liquid chromatography (HPLC) is another well known technique to determine the CCD of polymers, but its application was for a long time limited to ambient temperature [9e11]. In the case of semicrystalline polyolefins, which only dissolve at high-tempera- tures, however, the first sorbent-solvent system for adsorption * Corresponding author. Tel.: þ49 6151 162305; fax: þ49 6151 292855. E-mail address: rbruell@dki.tu-darmstadt.de (R. Brüll). Contents lists available at SciVerse ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2011.10.050 Polymer 52 (2011) 5953e5960