Infrared spectra, with both unpolarised and polarised radiation, have been obtained for a series of Phillips type high density polyethylenes of varying stress crack resistance. They were examined after cold drawing, by neck propagation, under standard conditions, and the presence of uniaxial orientation was confirmed by X-ray pole figure measurements. Intensity measurements with unpolarised radiation on the bands at 1080, 1352, and 1894cm-' showed that with samples of bad stress crack resistance both the folds and the tie chains increase in concentration at the expense of the regularly folded chains in crystalline regions, whereas only the tie chains increase with samples having good stress crack resistance. Dichroic measurements on nine bands, the majority of them characteristic for methylene groups in gauche and trans conformations in amorphous regions, show that there is no marked degree of orientation of the chain folds or tie chains with samples of good stress crack resistance. However, there is significant orientation, particularly of the tie chains, for samples with poor stress crack resistance. ZUSAMMENFASSUNG :Fur eine Reihe wenig vermeigter Polyathylene (vom Phillips-Typ) verschiedener Spannungsrififestigkeit wurden sowohl mit unpolarisierter als auch mit polarisierter Strahlung IR Spektren aufgenommen. Die Polymere wurden unter Standardbedingungen kalt verstreckt; danach wurden rnit Hilfe der Rontgenstreuung (Messung der Reflex-Indices, ,,pole figures") uniaxiale Orientierungen festgestellt. Intensitatsmessungen mit unpolarisierten Strahlen an den Banden bei 1080, 1352 und 1 894 cm-' zeigten, daB bei den Proben rnit geringer Spannungsrififestigkeit sowohl die Faltungen als auch die diese verbindenden Ketten (,,tie chains") auf Kosten der regelmafiig gefalteten Ketten in kristallinen Gebieten zunehmen, wohingegen bei Proben rnit hoher SpannungsriBfestigkeit nur die Konzentration der ,,tie chains" zunimmt. Messungen des Dichroismus an 9 Banden (wobei die meisten Banden charakteristisch sind fur Methylengruppen in trans und gauche Konformationen in amorphen Bezirken) zeigen, daB fur Polymere rnit hoher SpannungsriBfestigkeit kein erheblicher Orientierungsgrad der Kettenfaltungen und ,,tie *) Part 3: M.
SynopsisInfrared dichroic measurements have been made on a number of blown polyethylene films for which x-ray diffraction pole figure studies are reported in the three preceding papers; they complement them in some respects, and lead to several conclusions. Gauche chain conformations in loose chain folds in amorphous regions, characterized by bands a t 1303,1352, and 1368 cm-', show appreciable orientation in films with high-stress orientation but very little with low-stress orientation. Conversely, extended tie chains in amorphous regions, assessed by the band a t 1080 cm-', are appreciably orientated with the more normal type of low-stress film but not with high-stress films. It is therefore possible, rapidly and inexpensively, to distinguish between the two types of orientation. The method for studying the orientation of extended tie chains is capable of further development. There is probably an empirical correlation between the dichroic ratios a t 720 and 730 cm-I and the tear strengths and balances of the films with low-stress orientation.
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
Results for the rates of bromination of vinyl, vinylidene, and trans vinylene groups in various types of polyethylene are reported and interpreted. It is shown that for two Phillips type vinyl-containing polymers, one near-linear and the other ethyl branched, the uptake of vapour phase bromine at ambient temperature is rapid, because the unsaturation lies largely in amorphous regions. Plots of log(A,/A,) against time, where A . and A , are the absorbances at 910cm-' initially and after time t, are linear until bromination is almost complete, indicating that it is a diffusion controlled process. The subsequent slower bromination is tentatively interpreted in terms of vinyl groups sited in defective surface layers of the crystalline lamellae. Both types of bromination occur more readily with the ethyl branched polymer than with the linear material. Bromination of the residual unsaturation in wholly crystalline regions occurs only in the molten state. X-ray diffraction measurements confirm that the majority of the vinyl groups are sited in amorphous regions.Similar conclusions are drawn for vinylidene and trans vinylene groups, but the rate of bromination of polymers containing the latter type of unsaturation does not wholly correlate with the amorphous content. From this evidence and from measurements on a thicker film of the ethyl branched vinyl polymer it is concluded tentatively that there are differences in the amorphous regions which lead to varying rates of diffusion of bromine vapour. ZUSAMMENFASSUNG:Es werden Ergebnisse uber die Bromierung von Vinyl-, Vinyliden-und trans-Vinylengruppen in verschiedenen Typen von Polyathylenen berichtet und interpretiert. Es wird gezeigt, darj fur 2 Phillips-Polyathylene (das eine fast linear und das andere mit Athylzweigen) mit Vinylgruppen, die Aufnahme von gasformigem Brom bei Raumtemperatur sehr schnell erfolgt, weil die ungesattigten Gruppen hauptsachlich in amorphen Bereichen *) Part 2: cf.').liegen. Auftragungen von log(A,/A,) gegen die Zeit ( A , und A , sind die Absorptionen bei 9 1 0 m -' zur Zeit t=O und zur Zeit I) sind bis zur fast vollstandigen Bromierung linear. Dies zeigt, daB es sich um diffusionskontrollierte Vorgange handelt. Die sich anschlieBende langsame Bromierung wird versuchsweise Vinylgruppen, die sich in gestorten Oberflachenschichten von Kristall-Lamellen befinden, zugeordnet. Beide Arten der Bromierung erfolgen leichter bei dem athylvermeigten als bei dem linearen Polyathylen. Die iibrigbleibenden ungesattigten Gruppen in den vollstandig kristallinen Bereichen werden nur bei geschmolzenem Polymerem bromiert. Rontgenstreumessungen zeigen, daB der. Hauptanteil der Vinylgruppen in den amorphen Bereichen liegt.Ahnliche Schliisse werden fur Polymere gezogen, die Vinyliden-b m . Vinylengruppen enthalten. Im letzteren Fall kann die Bromierungsgeschwindigkeit jedoch nicht ganzlich mit dem Gehalt an amorphem Polymeranteil korreliert werden. Daraus sowie aus Messungen an dickeren Filmen des athylvermeigten Polymeren wird versuchsweise geschlossen, daB in d...
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