Comparison of High-Temperature HPLC, CRYSTAF and TREF for the Analysis of the Chemical Composition Distribution of Ethylene-Vinyl Acetate Copolymers

The chemical composition distribution (CCD) is a fundamental molecular parameter of copolymers. High-temperature interactive liquid chromatography (HT-HPLC) has recently emerged as a new analytical technique for determination of the CCD of semicrystalline copolymers of ethylene and polar comonomers. With the aim of comparing the results of HT-HPLC with those from the traditionally used temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) techniques, three ethylene-vinyl acetate (EVA) copolymers were fractionated by TREF and the fractions were analyzed by HT-HPLC. HT-HPLC-Fourier transform-infrared (FT-IR) spectroscopy showed that individual fractions of different VA-content coelute in the HPLC. While the separation in TREF and CRYSTAF is mainly the result of the overall effect of alkyl branches and VA-comonomer units, in HT-HPLC it is the polar comonomer that selectively contributes to the adsorption. Thus, HT-HPLC leads to a much more detailed knowledge of the distribution of the structured units; in addition, it saves time.