A new multidimensional fractionation technique, temperature rising elution fractionation (TREF) combined with high temperature size exclusion chromatography FTIR (HT-SEC-FTIR), HT-SEC-DSC and high temperature two-dimensional liquid chromatography (HT-2D-LC) is used for the comprehensive analysis of a commercial impact polypropylene copolymer. HT-SEC-FTIR provides information regarding the chemical composition and crystallinity as a function of molar mass. Thermal analysis of selected SEC fractions yields the melting and crystallization behavior of these fractions which is related to the chemical heterogeneity of this complex copolymer. The thermal analysis of the fractions is conducted using a novel DSC method  high speed or high performance differential scanning calorimetry (HPer DSC) -that allows measuring of minute amounts of material down to micrograms. The most interesting and complex "midelution temperature" TREF fraction (80 °C) of this copolymer is a complex mixture of ethylene-propylene copolymers (EPC's) with varying ethylene and propylene contents and sequence length distributions, as well as iPP. High temperature solvent gradient HPLC has been used to show that there is a significant amount of PE homopolymer and EPC's containing long ethylene sequences in this TREF fraction. High temperature 2D-LC analysis reveals the complete separation of this TREF fraction according to the chemical composition of each component along with their molar mass distributions.

For the first time, the complex composition of a two-reactorproduced impact polypropylene copolymer (IPC) has been fully revealed by advanced thermal analysis, using the combination of fast scanning DSC (HPer DSC, flash DSC, and solution DSC) with SEC fractionation subsequent to TREF fractionation. The dual TREF-SEC separation provided fractions of a few micro-or nanograms that were used to correlate the molecular structure of the polymer chains and their thermal properties (melting and crystallization behavior of the different macromolecules under a variety of different conditions). The SEC fractions were collected using the LC transform interface and subjected to FTIR and fast scanning DSC analysis. The SEC curves showed mono-, bi-, and multimodal molar mass distributions. The SEC fractions collected were analyzed by HPer DSC at 50 °C/min by which the thermal properties of the fractions could be established and salient details revealed. The findings were confirmed by structural information that was obtained using FTIR measurements. These results confirmed that even after TREF fractions were obtained they were complex regarding molar mass and chemical composition. By applying HPer DSC at scan rates of 5−200 °C/min and flash DSC at scan rates of 10−1000 °C/s, the metastability of one of the fractions was studied in detail. The high molar mass part of the material appeared to be constituted of both highly isotactic PP and low to medium propylene content ethylene copolymers (EPC). The medium molar mass part consisted of high to medium isotactic PP and of low propylene content EPC. The low molar mass part did not show ethylene crystallinity; only propylene crystallinity of medium to low isotacticity was found. DSC measurements of TREF-SEC crossfractions at high scan rates in p-xylene successfully connected reversely to the slow scan rate in TREF elution, if corrected for recrystallization. All EPC's show only ethylene-type crystallization. The wealth of information obtainable from these method combinations promises to be extremely useful for a better understanding of the melting and crystallization processes of such complex materials. The ability to run DSC experiments at very high scan rates is an important prerequisite to understanding the melting and crystallization behavior under conditions that are very close to melt processing of these key commodity polymers.

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Summary: Three propylene‐ethylene random copolymers, of varying ethylene content, were fractionated using preparative TREF. The TREF fractions were subsequently analysed offline by CRYSTAF, DSC, 13C NMR spectroscopy, HT‐GPC, and WAXD. The effect of the ethylene comonomer on the crystallisability of the propylene was investigated, along with the effect of the comonomer on the type of crystal phase formed during the crystallisation. The results show that the comonomer inhibits the crystallisation of the copolymer and that as the ethylene content increases, the crystallisation and melting points decrease. It was also shown that the higher the ethylene content, the more of the γ‐phase crystal type is formed. The inter‐molecular distribution of the ethylene comonomer and stereo errors vary between the samples analysed, and this accounts for the relative differences in crystallisation behaviour of the samples.13C NMR of propylene‐ethylene random copolymer.magnified image13C NMR of propylene‐ethylene random copolymer.

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