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Highly branched (DUPONT) and nearly unbranched ( Marlex 50) polyethylenes were investigated. The samples were partly crystallized. Marlex was also prepared in pure crystalline form. Dilatometric investigations revealed a sharp melting point and practically no relaxation phenomena in pure crystals. Nuclear magnetic resonance absorption spectra of branched samples definitely show remains of narrow line even at – 170°C., but it disappears completely with Marlex . In pure crystals the narrow line is extremely weak below 70°C. and changes reversibly with temperature. After heating over 70°C. irreversible changes occur, the samples approaches the structure of Marlex crystallized from melt.
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Peterlin et al. (1960) studied this question.
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