Infrared spectroscopic studies on polyethylene, 2. The characterisation of specific types of alkyl branches in low‐branched ethylene polymers and copolymers

Abstract

Bands characteristic for some specific branches have been found in two regions of the IR spectra of near linear polyethylenes made by the Phillips process. Polymers with methyl branches give a band at 935 cm-', probably the methyl rocking mode. The intensity of this band is proportional to the methyl branch content, thus providing a quantitative method for its estimation. No band specific for ethyl branches has been found, but propyl and longer branches show one at 890cm-' and this is also assigned to the rocking mode. This band is observed more readily if the polymers are brominated at ambient temperature, to remove interfering unsaturation bands. The results for methyl and ethyl branched near linear polymers differ significantly from those obtained with polypropylene, poly( 1 -butene), and ethylene copolymers with high concentrations of methyl and ethyl branches. This is very probably the result of the presence of blocks of the repeating unit --CH 2<H(R)-in the latter materials. Methyl branched polymersshow a band at 1150cm-', assigned to the methyl wagging mode of branches present in the crystalline phase. Its intensity is proportional to the methyl branch content and it may be used for quantitative purposes. Ethyl and longer branches d o not give a methyl wagging band of detectable intensity. ZUSAMM ENFASSUNG :In den IR-Spektren von wenig verzweigten Polyathylenen (hergestellt durch den Phillips-ProzeB) wurden charakteristische Banden fur einige bestimmte Zweige gefunden. Polymere mit Methylzweigen geben eine Bande bei 935 cm ~ die wahrscheinlich der CH 3-Pendelschwingung (,,rocking") entspricht. Die Intensitat dieser Bande ist proportional dem Gehalt an Methylzweigen, der mit dieser Methode quantitativ bestimmt werden kann. Es wurde keine Bande gefunden, die den Athylzweigen spezifisch zukommt, wahrend Propyl-und langere Zweige eine ,,rocking"-Bande bei 890 cm ' aufweisen. Diese Bande kann leichter beobachtet werden, wenn die Polymeren bei Raumtemperatur bromiert werden, um uberlagernde *) Part 1 : cf.3'.Olefinbanden zu entfernen. Die Ergebnisse fur Polymere mit

Oxidation of solid polyethylene films: Effects of backbone branching

“…~'~ 5 Because of overlap of the 1378-1379cm -1 CH3-absorption with the 1368cm -1 absorption from amorphous --CH2-groups, the spectrum of the UHMWPE film was subtracted from the spectrum of each laboratorysynthesized and commercial PE studied as proposed by McRae & Maddams. 15 The subtraction was scaled on the FTIR computer to completely suppress the 1368 cm-1 absorption so that the 1378-1379 cm-1 absorption could be more accurately measured. This rapid procedure is equivalent to the laborious wedge compensation method proposed by ASTM.…”

Thermal and mechanical modification of LDPE in single‐screw extruder

“…Further, a small peak appears at 910 cm À1 on the shoulder of the 890 cm À1 peak when LDPE is extruded at 350 C. This small absorption peak, assigned as terminal vinyl group created by chain scission reaction, 23 is not detected in the samples extruded at lower temperatures. It is found that the peak intensity of the absorption peak at 890 cm À1 , attributed to propyl and longer branches, 24 is not affected by extrusion temperature. This indicates that the SCB structure is not affected by thermal degradation.…”

The effect of orientation on radiation‐induced degradation in high density polyethylene

“…Spectral changes in polyethflene upon drawing have been studied previously using polarized or unpolarized IR radiation (20)(21)(22)(23). We investigated changes in the intensities of the bands at 1894, 1080 and 1715 cm-'.…”