The Molecular Structure of Polyethylene. II. Determination of Short Chain Branching¹

Characterization and microstructure study of low‐density polyethylene by Fourier transform infrared spectroscopy and temperature rising elution fractionation

“…As shown in Figure 2, it is possible to distinguish between LDPE, HDPE, and LLDPE by their IR spectra. 19 The IR spectrum of LDPE shows a methylene rocking mode at 720/730 cm 21 , a methyl rocking band at 894.5 cm 21 (arising from butyl short branches), methylene wagging in the amorphous region at 1305 and 1353 cm 21 , a methyl deformation band (bending mode) at about 1380 cm 21 , and a methylene deformation band at about 1460 cm 21 .…”

“…Unfortunately, the absorption at 894.5 cm 21 , arising as a result of butyl branches, is highly covered by vinylidene and vinyl unsaturation bands at 888 and 910 cm 21 , respectively, so any quantitative use of Figure 3 FTIR spectra of an LDPE film before and after bromination and n-hexadecane (NaCl cell) in the methyl rocking region.…”

“…this band can be made only after the resolution of these interferences. This can be done by hydrogenation 21 or by bromination, 22 which eliminates double bonds in the resin. Hydrogenation converts the vinyl and vinylidene unsaturations into more methyl groups and takes place under more severe conditions.…”

“…In fact, the IR spectra of different types of polyethylene have been studied in greater detail than those of other polymers. 14 Many studies have been conducted to evaluate the branch types and contents in LDPE by IR spectroscopy, focusing on the methyl deformation band (symmetric) around 1377 cm 21 , the methyl rocking band region between 1200 and 800 cm 21 , and the methylene rocking region between 770 and 720 cm 21 . 15 Furthermore, in recent years, fractionation methods such as temperature rising elution fractionation (TREF) 16 and crystallization analysis fractionation 17 have also used for the determination of SCBD in semicrystalline polymers.…”

Structure and properties of polyethylene produced by γ‐radiation polymerization in flow system

“…The methyl group content in the polymer was determined from the absorption a t 1378 cm-' by the method of Bryant and Voter. 9 The melting point of the polymer was measured by a differential thermal analysis, melt index by a melt indexer according to ASTM-D-1238, and tensile properties by a Shimadzu Autograph IS-2000 according to ASTM D-638. Number-average molecular weight was determined from viscosity measurements on tetralin solution at 130°C by use of Tung's formula.…”