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Radical formation was observed in purified ois-1.4-poly(butadiene) after irradiation in vucuo at 77'K with UV light from a medium pressure mercury lamp. The free radicals were studied by electron spin resonance (ESR). The ESR spectra obtained were interpreted as due mainly to radicals formed by scission of the C-C bond midway between the double bonds : 0 -CHz-CH=CH-HZ t-+ -CH2-CH-CH=CHz A minor part was assigned to radicals formed by hydrogen abstraction from one of the a-methylene groups. These radicals are believed to be twisted, resulting in bad overlapping between the x-electron cloud and the p-orbital of the unpaired electron, i.e. the radicals give spectra of the alkyl type : =CH-CH-CHz-.In addition the spectra contained a weak signal interpreted as due to polyenyl radicals -(CH=CH),-CHz.At liquid nitrogen temperatures all radicals formed were stable, but at temperatures near the glass transition range, the radicals disappeared rapidly. One radical type showed much less stability and rearranged on heating the sample to 114'K; these radicals were formed by hydrogen abstraction from the cc-methylene groups. The changes in the infrared and ultraviolet absorption spectra observed by other authors are discussed in relation to the radicals identitied here. 0 ZUSAMMENFASSUNG: I n gereinigtem cis-1.4-Polybutadien wurde nach Bestrahlung mit ultraviolettem Licht einer Mitteldruck-Quecksilberlampe Radikalbildung beobachtet. Die freien Radikale wurden rnit Hilfe der Elektronenspinresonanz (ESR) untersucht. Die erhaltenen ESR-Spektren werden hauptsiichlich auf die Gegenwart von Radikalen zuriickgefiihrt, die durch die Aufspaltung einer C-C-Bindung entstehen, die in der Mitte zwischen zwei benachbarten Doppelbindungen des Polymeren liegt ; 0 -CHz-CH=CH-CH2 W -CH2-CH-CH=CH2 ein kleinerer Anteil wird Radikalen, die bei Wasserstoffabspaltung von einer der a-Methylengruppen entstehen, zugeschrieben. Es wird angenommen, dal3 diese Radikale gedreht *) Present address: Chemical Research Lab., NKT, 2000 Copenhagen F, Denmark. P. CARSTENSENsind, was eine schlechte nberlappung zwischen der n-Elektronenwolke und dem p-Orbital des ungepaarten Elektrons zur Folge hat; das heifit, die Radikale geben Spektren vom Alkyltyp : =CH-CH-CHz-. AuBerdem enthielten die Spektren ein schwaches Signal, das auf Polyenylradikale -(CH=CH),-CHz schlieBen laat.Bei Temperaturen des fliissigen Stickstoffs sind alle gebildeten Radikale stabil, w a r e n d sie in der Nahe des Glasumwandlungsgebietes rasch verschwinden. Einer der Radikaltypen zeigt vie1 geringere Stabilitat und lagert sich urn, sobald die Probe auf 114'K erwarmt wird; diese Radikale bilden sich durch Wasserstoffabspaltung aus den ol-Methylengruppen.Die hderungen in den IRund UV-Absorptionsspektren, die von anderen Autoren beobachtet wurden, werden uuter Bezugnahme auf die hier identifizierten Radikale erortert. 0

During the manufacture of cross-linked polyethylene cables the insulation material experiences temperature protocols which vary with the radial position. The time-temperature scheme has, however, a major influence on microstructure of the insulation and chemical composition of the peroxide by-products. Thus it could be expected that the electrical properties of the insulation would vary with the spatial position within the cable. The purpose of the present work is to identify if there is a difference in the DC-electric properties at different radial depths of an extruded high voltage direct current (HVDC) cable insulation. In this study, DC electrical resistivity and DC breakdown strength measurements were carried out on samples taken from the insulation regions close to the inner and outer the semi-conductive screens. The obtained results show no significant difference of the investigated electric properties between the two regions. Hence, the DCelectric properties of the bulk insulation are constant within the accuracy of measurements.

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