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.