1 -butene copolymerisation

Ethylene can be copolymerised with several monomers like propylene, 1-butene, vinyl acetate, ethyl acrylate, etc. 

Kinetic studies of migratory insertion reactions of the ligands that are involved as (P-P)Pd" fragments in either the propagation cycle of ethene/CO copolymerisation or ethene dimerisation to butenes have been reported by Brookhart [28] and Bian-chini [5e, fj. 

Bci dcr Copolymerisation von Athylcn und cis-Buten-2 liefem Katalysa-toren, die bei der Polymerisation von Propylen (76) keine taktischen Polymcren synthctisicren, wic Vanadiumacctylacctonat und Diathyl-aluminiumchlorid, ebenfalls keine kiistallinen Copol5Tnercn. Copol3unere von Athylen und trans-Buten-2 sind mit alien verwendeten Katalysato-ren nicht kristallin crhaltcn worden. 

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]. 

Also, the copolymerisation of ethylene and a-olefins can be readily performed using Phillips catalysts. The copolymerisation of ethylene with 1-butene or 1-hexene is the basis of the large expanding linear low-density polyethylene market [28,37,43,237]. 

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). 

Copolymerisations of propylene [68,458-460] and 1-butene [47] with higher a-olefins have also been carried out in order to obtain copolymers offering a range of properties not available from the homopolymers alone. As regards the copolymerisability of a-olefins, which decreases with increasing size of the alkyl substituent at the double bond, it results mainly from steric effects [458]. 

The different reactivities of the olefins are important for the copolymerisation. The comonomer reactivity ratio, rj, in copolymerisation with ethylene appears to decrease with increasing steric hindrance around the double bond in the a-olefin in to the following order [250] ethylene > propylene > 1-butene > linear a-olefin > branched a-olefin. 

Normally, propylene reacts 5-100 times more slowly than ethylene, and 1-butene 3-10 times more slowly than propylene [37], Relative copolymerisation... 

It should be mentioned that some Ziegler-Natta catalysts containing Ni(II) compounds, which are capable of inducing /i-olefin isomerisation to the corresponding a-olefin, e.g. 2-butene to 1-butene, readily promote the copolymerisation of the a-olefin formed with ethylene [464 166],... 

Styrene/a-olefin copolymers containing a predominant amount of styrene units can be easily formed through the monomer isomerisation-copolymerisation of styrene and /i-olefin such as m-2-butene in the presence of heterogeneous Ziegler-Natta catalysts such as TiCl3—AlEt3. Styrene appeared to be a favourable comonomer for monomer isomerisation-copolymerisation with internal olefins, since only the isomerisation of /i-olefin to a-olefin, and not the isomerisation of styrene (in contrast to the olefin), occurs in the presence of Ziegler Natta catalysts [119] ... 

By adding NiCl2 to the TiCl3—AlEt3 catalyst (Ni/Ti/Al molar ratio 1 1 3), the contents of 1-butene units in the copolymer were increased at the same comonomer feed as compared with the copolymerisation system without added... 

NiCl2. It is interesting that copolymers consisting almost entirely of styrene units are produced easily via monomer isomerisation-copolymerisation of styrene and czx-2-butene, contrary to the ordinary copolymerisation of styrene and 1-butene [119]. 

Another interesting monomer for copolymerisation with carbon dioxide is isomeric 2-butene oxide. In copolymerisation in a ternary comonomer system consisting of 2-butene oxide, 1-butene oxide and carbon dioxide with the diethylzinc-water catalyst, m-2-butene oxide was incorporated in the copolymer, while trans-2-butene oxide hardly underwent an enchainment [230]. Thus, the smaller steric hindrance for the r/.v-isomer than for the irans-isomer throughout the coordination copolymerisation with carbon dioxide is to be taken into account. 

Mazzanti, G., a. Valvassori, G. Sartori, and G. Pajaro Anionic coordinate copolymerisation of pnipylene with butene-1. Chim. Ind. (Milan) 42.468 (1960). 

Dall Asta,G., Mazzanti, G., Ciampelli, F. Stereospezifische alternierende Copolymerisation von Athylen mit Buten-2. Kolloid-Z. 182, 50-60 (1962). 

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