Infrared spectroscopy is the premier analytical tool for determining the composition and structure of polyolefin products. The coupling of IR spectroscopy with size exclusion chromatography (SEC) through an automated solvent removing interface provides a map of changing composition across the molecular weight distributions. The characterization of polyolefin products by FTIR has many aspects, and calls for examination/measurement of adsorption bands across the full range (4000-650 cm-1) of the infrared spectrum. This poster describes a number of composition and configuration aspects of polyolefins that can be characterized by utilizing the whole of the mid-infrared spectral region. Examples include: Short chain branch analysis; Identification of polyethylene types; Resolution of blended polyolefin products; Crystallinity analysis; Polyolefin copolymer compositional drifts; Polymer degradation and Additive analysis. The FT infrared detector/analyzer, coupled with SEC, is a powerful tool for revealing composition and structural characteristics of the many polyolefin products in use. The technique consists of two consecutive injections. The first injection is made with standard conditions using trichlorobenzene TCB solvent at high temperature (145oC) at 1ml/min elution rate. A 100 ml injection and a disk speed of 3mm/min captures FTIR spectra suitable for traditional Short Chain Branching analysis using the major absorbance bands from 2800-3000 cm-1 or 1500-1300 cm-1 region. The second injection uses the same chromatographic conditions, but the ZnSe sample disk rotation is slowed by a factor of 10, resulting in a layer 10 times thicker in the IR beam. The resultant high intensity IR spectra provide a wealth of information within the fingerprint region throughout the MWD deposit track, very useful to characterize polyolefin compositional drifts (3 case studies) and to de-formulate complex polyolefin blends (1 case study).

Characterizing polyolefin copolymers and blends by high temperature SEC-IR with full mid-IR spectra

243rd National Meeting (2012)

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