Trans-vinylene groups polyethylene

The first-order rate constants for terminal vinyl groups and for trans-vinylene groups in linear polyethylene were observed by Dole and Williams (8) to be 20 to 30 times higher than our corresponding rates in the amorphous trans- and vinyl polybutadienes (Table III). On the other hand, the initial yields were lower than our G0 values because of the... 

Similar effects are observed in y-irradiated n-C H (530 kGy) in the molten state. Three new structures are identified as a) one-bond crosslinks (H-structure), b) trans-vinylene groups and c) long branches (T- or Y-structure)144). However, highly crystalline polyethylene y-irradiated in the solid state at low doses (up to 40 kGy) yields predominantly the branched Y-structure. A failure to detect the cross-linked H-structure could arise from a) insufficient abundance of crosslinks to give a detectable signal and b) insufficient mobility of crosslinked chains in the polyethylene gel which results in very broad resonance lines, not observable during normal data acquisition in the solution 13C NMR experiment145). 

The relative susceptibilities of the crystalline and amorphous portions of polyethylene to high energy radiation has been a moot question. Present evidence indicates that for linear polyethylenes without vinyl end groups the G-values for the production of hydrogen, cross-links, and trans-vinylene groups are identical for the melt at 133 °C and the crystalline state at 130°C (I). (Scission is now believed to be essentially nil at least, its occurrence is not demonstrated). 

The dosimetry utilization of polyethylene films in the 10 -10 Gy dose range is based on ultraviolet at 240 nm (Chen et al. 1980) or infrared measurement of carbonyl or trans-vinylene groups formed upon irradiation and analyzed at 5,800 nm or 10,600 nm, respectively (Charlesby et al. 1964 McLaughlin et al. 1999). 

The main products of polyethylene photo-oxidations are hydroxyl (OH), carbonyl (C=0) and vinyl groups, whereas trans-vinylene groups are formed but only in small amounts. 

The results of Table II are interesting from several standpoints. In the first place the vinylene groups in polyethylene (PE) are all trans,... 

Figure 1 shows a comparison of the vinyl bond content of polyethylenes produced with several catalysts. In addition to the vinyl end groups, the polymers contained trans-vinylenes and a very small number of vinylidene double bonds [46, 51, 66]. 

The data of Table II indicate that the etch rates for CB and its "homologues"—TP, CO (or TO), and EPM—tend to increase monotonically with a decrease in vinylene (-CH=CH-) unsaturation. The elastomeric EPM was chosen instead of crystalline polyethylene as a model for the fully saturated CB to avoid a morphology factor in etch rates, as was observed with crystalline TB. The difference in etch rates for the partially crystalline TO and the elastomeric CO (ratio of about 1.2 1.0) is attributable more to a morphology difference between these polyoctenamers than to the difference in their cis/trans content. Cis/trans content had likewise no perceptible effect on etch rates in the vinyl-containing polybutadienes (see Table I) if there was a small effect, it was certainly masked by the dominant effect of the vinyl groups. 

Inasmuch as the production of tram-vinylene unsaturation is one of the important processes occurring during the y-ray irradiation of polyethylene, it is interesting to compare G(t—Vl) in polyethylene with G(Vl) values in other substances. Data are presented in Table II where G(Vl) represents a monoene group, whether cis or trans. 

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