Effect of the nature and content of branched α-olefin units on the physico-chemical characteristics of linear polyethylene

• Published in: Polymer science USSR 1991, Vol.33 (11), p.2318-2326
• Main Authors: Dreval', V.Ye, Artamonova, S.D., Bobrov, B.N., Kleiner, V.I., Barancheyeva, V.V., Litvinov, I.A., Kechek'yan, A.S.
• Format: Article
• Language: English
• ISSN: 0032-3950; 1878-268X
• DOI: 10.1016/0032-3950(91)90083-3

The structure, phase transitions, density, linear thermal expansion and strength of binary copolymers of ethylene with four α-olefins (vinylcyclohexane, 3-methylbutene, 1,3-methylpentene-1 and 3-ethylpentene-1) containing non-linear side-chain substituents, were studied by the methods of X-ray structural analysis, DSC, dilatometry and mechanical testing. The relation between the size and shape of the substituent and the physico-chemical characteristics of the copolymer was investigated. It was found that starting from some critical content (1.5–2 mol%), the introduction into the chain of small amounts of the α-olefins studied leads to a loosening of the crystal lattice. This effect is independent of the volume of the substituent, but may change with its changing shape. Substituents of two sufficiently long branches have a stronger distorting effect on the PE crystal lattice, and at the same time lead to the production of larger crystals. The obtained results can be explained on the assumption that the non-linear substituents affect not only the crystalline, but also the amorphous component of the copolymer structure. This evidently is the cause of the extreme variation of the low-temperature strength of the copolymer at low concentrations of α-olefins.