Quantifying short chain branching microstructures in ethylene 1-olefin copolymers using size exclusion chromatography and Fourier transform infrared spectroscopy (SEC-FTIR)

A rapid method for the SEC-FTIR analysis of short chain branching distribut ion (SCBD) across the molecular weight distribution (NWD) is described and its application demonstrated using ethylene 1-olefins copolymers. Chromatog rams. are generated using the root mean square absorbance over the 3000-270 0 cm(-1) spectral region (i.e. FTIR serves as a concentration detector), Sp ectra from individual time slices of the chromatogram are subsequently anal yzed for comonomer branch levels using chemometric techniques. Furthermore, we are able to estimate error in the reported SCB content of each slice. U sing the appropriate training sets, chemometric models can be constructed w hich provide SCB versus MWD profiles with sufficient precision to detect tr ends resulting from catalyst and process changes in LDPE and/or HDPE sample s. We demonstrated the method by showing the results of a model that has en abled us to accurately quantify branching levels in polyolefins within +/-0 .5/1000 total carbons (i.e. ca. 0.1 mol%) in samples with relatively low le vels of SCB (i.e. < 10 SCB/total carbons) and mixed branch types. (C) 2001 Published by Elsevier Science Ltd.