1-octene, copolymerisation

Coordination catalysts allowed for the first time the copolymerisation of ethylene with other olefins such as 1-butene, 1-hexene or 1-octene, which, by introducing side branches, reduces the crystallinity and allows a linear low-density polyethylene to be produced at comparatively low pressures [136], Figure 2.3 shows schematic structures for the three polyethylenes, with the main features exaggerated for emphasis [46]. 

Extensive efforts have also been made to develop olefin polymerisation catalysts based on metallocenes with only one ligand of the cyclopentadienyl type. Ethylene-,dimethylsilylene- or tetramethyldisilylene-bridged mono(l-tetra -methylcyclopentadienyl), mono(l-indenyl) or mono(9-fluorenyl)-amidotita-nium complexes, such as dimethylsilylene(l-tetramethylcyclopentadienyl)(t-butyl)amidotitanium dichloride [Me2Si(Me4Cp)N(/-Bu)TiCl2] (Figure 3.10), have recently attracted both industrial and scientific interest as precursors for methylaluminoxane-activated catalysts, which polymerise ethylene and copolymerise ethylene with 1-butene, 1-hexene and 1-octene [30,105,148-152]. 

Random ethylene copolymers with small amounts (4-10 wt-%) of 7-olefins, e.g. 1-butene, 1-hexene, 1-octene and 4-methyl- 1-pentene, are referred to as linear low-density polyethylene, which is a commercially relevant class of polyolefins. Such copolymers are prepared by essentially the same catalysts used for the synthesis of high-density polyethylene [241]. Small amounts of a-olefin units incorporated in an ethylene copolymer have the effect of producing side chains at points where the 7-olefin is inserted into the linear polyethylene backbone. Thus, the copolymerisation produces short alkyl branches, which disrupt the crystallinity of high-density polyethylene and lower the density of the polymer so that it simulates many of the properties of low-density polyethylene manufactured by high-pressure radical polymerisation of ethylene [448] (Figure 2.3). 

Styrene undergoes copolymerisation with ethylene and various a-olefins in the presence of heterogeneous Ziegler-Natta catalysts. Its reactivity in the copolymerisation is quite low, which is illustrated by the values of the relative reactivity ratios, r and r2, presented in Table 4.5 [118]. One may note, however, a considerably high relative reactivity of styrene in copolymerisation with vinyl-cyclohexane. The copolymerisation of styrene with small amounts of a-olefin, such as 1-octene or 1-decene, yields copolymers of reduced crystallinity and thus reduced brittleness compared with the homopolymer of styrene. 

Ethylene may be copolymerised with vinyl acetate to make ethyl-vinyl acetate, offering high seal integrity and clarity for frozen food applications where a high degree of toughness is required. Ethylene copolymers with other olefins such as propylene, 1-hexene and 1-octene allow a range of properties to be achieved. Linear low density polyethylene (LLDPE) has a... 

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