Review Article A review on the development of liquid chromatography systems for polyolefins Polyolefins are the most widely produced synthetic polymer commodity and are found in countless applications ranging from bottles, packaging films to bullet-proof jackets, etc. Such widely different applications rely on high variability in the physical properties of polyolefins, which is a result of variations in microstructure, chemical composition and molar mass. Though polyolefins contain only carbon (C) and hydrogen (H) atoms, the microstructures of polyolefins are extremely variable, differing in the nature of the monomers (e.g. ethylene versus propylene), the degree of branching, chemical composition in the case of copolymers and finally their molar masses. Production, research and development of polyolefins require the analysis of polyolefin samples in terms of all these parameters. Development of efficient and robust analytical techniques based on the interactive LC is reviewed. The needed computational/theoretical studies to understand the retention mechanism in the newly developed chromatography systems are discussed. Keywords: Interactive chromatography / Modeling / Polyolefins DOI 10.1002/jssc.201000516 1 Short history of polyolefins Polyolefins, i.e. polyethylene (PE), polypropylene (PP), poly- 1-butene, ethylene/1-alkene copolymers (also known as linear-low density PE) and propene/alkene copolymers, are the world’s most widely used synthetic polymers. Their productions exceed 100 million metric tons per year and continue to grow exponentially [1]. The history of their discovery and production is long and is a result of many excellent chemists, physicists and other specialists working in the field, as documented by the book ‘‘History of polyolefins’’ [2]. Naturally occurring polyolefins are compo- nents of bitumen and similarly solid parafin waxes have been known for centuries, but these were not known to be polymers. Synthetic polyolefins were first synthesized by decomposition of diazomentane by Hinderman [3]. Liquid oligomers of isobutylene were prepared by Butlerov and Goriainov [4]. Solid samples of isobutylene were synthesized by Otto [5]. Staudinger prepared polyolefins by hydrogena- tion of natural rubber [6]. At the time, these materials were essentially laboratory curiosities and they could not be produced economically. The commercial production of LDPE began in England in 1939 and its use as an insulator in coaxial cable was essential for the Britain’s World War II radar system for detecting enemy aircraft. The discovery of new catalysts by Ziegler, Breil, Holzkamp and Martin in 1953 [7] was an unprecedented break-through in polyolefin industries. The new catalysts led to a drastic reduction of the production costs and made the synthesis of new types of polyolefins such as linear PE, ethylene/alkene copolymers as well as PP and propene/1-alkene copolymers possible [8]. A new era in controlled synthesis of polyolefins started in 1979 after Sinn, Kaminsky and Brintzinger discovered the metallocene catalysts [9]. As a consequence of the above- outlined progress, the industrial production of polyolefins increased and these polymers have found thousands of applications in our daily lives. 2 Molecular characterization of polyolefins The majority of polyolefin materials has melting tempera- ture above 1001C and is resistant against most common liquids. Such properties are useful for practical applications; however, they lead to problems in characterization. Due to their semi-crystalline structures, polyolefins are soluble only after heating above their melting temperatures and require Tibor Macko 1à Robert Bru ¨ ll 1 Yutian Zhu 2 Yongmei Wang 2 1 German Institute for Polymers, Darmstadt, Germany 2 Department of Chemistry, The University of Memphis, Memphis, TN, USA Received July 14, 2010 Revised September 12, 2010 Accepted September 13, 2010 Abbreviations: CRYSTAF, crystallization analysis fractionation; DSC, differential scanning calorimetry; EGMBE, ethylene glycol monobutyl ether; ELSD, evaporative light-scattering detection; EVA, ethylene–vinylacetate; FTIR, Fourier transform infrared spectroscopy; LCCC, LC under critical condition; PE, polyethylene; PP, polypropylene; PS, polystyrene; SEC, size exclusion chromatography; TCB, 1,2,4-trichlorobenzene; TREF, temperature rising elution fractionation à Additional correspondence: Dr. Tibor Macko E-mail: tmacko@dki.tu-darmstadt.de Correspondence: Dr. Yongmei Wang, Department of Chemistry, The University of Memphis, Memphis, TN 38154, USA E-mail: ywang@memphis.edu Fax: 1901-678-3447 & 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com J. Sep. Sci. 2010, 33, 3446–3454 3446