Characterization of Functionalized Polyolefns by High-Temperature Two-Dimensional Liquid Chromatography by Anton Ginzburg, Tibor Macko, and Robert Brüll Application Note F unctionalized polyolefns, such as copolymers of ethylene vinyl ace- tate (EVA), are a commercially important polymer commodity. Depending on their comonomer con- tent, these materials find application in the production of foams, films, and hot melt adhesives. The polyolefn market is growing by 5–6% annually due to its ver- satile physical and mechanical properties, low cost, and easily available raw materi- als. 1 As a result, the characterization of functionalized polyolefns has become an important area in polymer research. 2 Olefn copolymers are generally distributed with regard to various parameters such as chemical composition, molar mass, func- tionality, degree of branching, block length, and tacticity. Comprehensive characteriza- tion of the interrelationship between these distributions is therefore essential to under- standing the catalyst performance, as well as to optimizing the synthesis and structure– property relationships. In the case of func- tionalized polyolefns, the most important distributions are molar mass distribution (MMD) and chemical composition distri- bution (CCD), and their interrelationship is referred to as chemical heterogeneity. A number of fractionation techniques are commonly used in polyolefn analysis. High- temperature-size exclusion chromatogra- phy (HT-SEC) is the established method to determine the MMD. SEC separation is based on the size of the molecules in solu- tion (hydrodynamic volume) and the extent to which they are excluded from the pores of a stationary phase. The MMD and cor- responding molar mass averages can be obtained from a calibration curve that relates the molar mass to the elution volume, or by using on-line molar mass detectors such as light scattering or viscosimetry. However, the size of a macromolecule in solution is also infuenced by its molecular architecture, such as branching, and by the chemical com- position via affnity toward the used solvent. This means that macromolecules having the identical hydrodynamic volume but different chemical composition may coelute at the same elution volume in SEC. Crystallization fractionation (CRYSTAF) and temperature-rising elution fraction- ation (TREF) are commonly used to deter- mine the CCD of semicrystalline olefin copolymers. Both techniques utilize the relationship between comonomer content and the crystallizability from a hot dilute solution, which is derived from Flory’s the- ory. 3 TREF can also be hyphenated with SEC to reveal the full chemical heteroge- neity. 4,5 This can be done either off-line 4 or on-line. 5 However, the entire approach is limited to well-crystallized samples; thus samples with a higher content of comono- mer (>10 wt%) cannot be studied in this way. Another drawback is that TREF is a relatively time-consuming technique. The method of choice when it comes to sepa- rating complex polymers with regard to their chemical composition is HPLC. Separation in HPLC can be achieved via different mecha- nisms, including adsorption–desorption and precipitation–redissolution. 6 However, HPLC has thus far been limited to polymers that are soluble at room temperature. The authors’ group developed the first interactive HPLC systems for the separation of functionalized polyolefins at high temperatures. 7–9 It was shown that EVA copolymers, 7–9 ethylene methyl acrylate copolymers, 8 and ethylene butyl acrylate 8 can be separated according to their chemical composition at a temperature of 140 °C using silica gel as stationary phase and gradients of nonpolar/polar solvents as mobile phase. To characterize the chemi- cal heterogeneity, i.e., the relationship of CCD and MMD (hyphenation of interac- tive HPLC with SEC), 2D-LC separation is required. The advantages and disadvantages of using either HPLC-SEC or SEC-HPLC sequences have been discussed in detail by van der Horst et al. 10 At present, standard 2D-LC procedures and instruments are limited to separation at ambient temperatures, 11 and therefore cannot be applied to the characterization of semicrystalline polyolefns. This paper describes the coupling of the interac- Figure 1 HT-2D-LC schematic. Reprinted from American Laboratory January 2011