Isomerisation-copolymerisation

Styrene, which can be treated formally as an a-olefin branched in the 3-position, forms copolymers with ethylene and a-olefins (as well as with /i-olefins, involving isomerisation copolymerisation). Both heterogeneous Ziegler-Natta catalysts and a single-site metallocene catalyst promote the copolymerisation. 

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] ... 

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]. 

Coordination polymerisation via re complexes comprises polymerisation and copolymerisation processes with transition metal-based catalysts of unsaturated hydrocarbon monomers such as olefins [11-19], vinylaromatic monomers such as styrene [13, 20, 21], conjugated dienes [22-29], cycloolefins [30-39] and alkynes [39-45]. The coordination polymerisation of olefins concerns mostly ethylene, propylene and higher a-olefins [46], although polymerisation of cumulated diolefins (allenes) [47, 48], isomerisation 2, co-polymerisation of a-olefins [49], isomerisation 1,2-polymerisation of /i-olcfins [50, 51] and cyclopolymerisation of non-conjugated a, eo-diolefins [52, 53] are also included among coordination polymerisations involving re complex formation. 

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],... 

Under most conditions, only the simple polypropylene ketone) is formed in propylene/carbon monoxide alternating copolymerisation. Isomerisation of poly(ketone) to poly(spiroketal) can occur, and it may be assisted by cationic palladium species and protonic acids. It must be emphasised that a low reaction temperature favours the formation of a spiroketal structure [107]. At a temperature above the ceiling temperature, the poly(spiroketal) depolymerises to the more flexible and entropically favoured poly (ketone) [481]. 

How can one explain the occurrence of steric defects in tactic poly(ot-olefin)s Explain why high-resolution nuclear magnetic resonance is the most convenient method for determining the chain micro structure in poly(a-olefin)s. Consider how 3H and 13C NMR spectroscopy can provide stereochemical information concerning a-olefin polymer chains on the diad level (m, r) and the triad level (mm, rr, mr). Explain why /1-olefins, which do not homopolymerise (without isomerisation) in the presence of Ziegler-Natta catalysts, undergo copolymerisation with ethylene in the presence of these catalysts. 

As in the case of homopolymerisation, no problem of isomerisation of propagating species exists in the copolymerisation of norbornene with carbon monoxide and hence 2,3-bicyclo[2.2.1]hept-2-ene units, as the only norbornene monomeric units appear in alternating copolymers with carbon monoxide [27] ... 

A very interesting group of random copolyethers is obtained by anionic copolymerisation of EO (a highly hydrophilic monomer) with BO (a highly hydrophobic monomer). Because EO does not isomerise to double bond structures and BO has a much lower tendency to isomerise to allyl structures than PO (see Chapter 12.2), the BO-EO copolyethers have a very low unsaturation level compared to PO homopolymers or even PO-EO copolymers [82]. This variant of polyether polyols synthesis in the form of BO-EO copolymers is a very interesting way to obtain low unsaturation polyether polyols directly from synthesis. Another group of low unsaturation polyether polyols, obtained directly from synthesis, are the tetrahydrofuran (THF)-EO and THF-PO copolymers synthesised with cationic catalysts (see Chapter 7.3). 

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