Copolymerisation with Heterocumulenes

An extremely interesting extension of the cyclopolymerisation of a, co-diacetylenes is the new Ni(0)-catalysed dialkyne cycloaddition copolymerisation with heterocumulenes (0=C=0, RN=C=0, RN=C=NR), unsaturated compounds (RC=N) and carbene-type compounds (C = 0, C=NR) [90]. The 1 1 cycloaddition copolymerisation of internal dialkynes R C C (CH2)X C C R (R=Et x 6, x 2), e.g. 3,11-tetradecadiyne, with carbon dioxide in the presence of the (R3P)2Ni(Cod)2 complex (R -CxHn) led to high molecular weight poly(2-pyrone) [91]  

The dialkyne/carbon dioxide copolymerisation is controlled by the relative rate of inter- and intramolecular cyclisations of the dialkyne the former is favoured when the number of methylene groups in the monomer R C C (CH2)X C = C—R is equal to 3,4 or 5 (x 3—5), but the intermolecular cyclisation of the dialkyne is favoured to effect 1 1 cycloaddition copolymerisation of the dialkyne and CO2 to a poly(2-pyrone) when the number x has other values [91 96]. 

Analogously, aromatic high molecular weight poly(pyridone)s have been obtained using terminal and internal aromatic diynes, e.g. 1,4-diethynylbenzene [98] and l,4-bis(phenylethynyl)benzene [99] respectively, for 1 1 cycloaddition copolymerisation with isocyanates. 

The ladder copolymers are preferentially formed (by the intermolecular reaction) because the formation of a tricyclic heterocycle by intramolecular cyclisa-tion is difficult for steric reasons [100]. 

The mechanism of ring formation from monoalkyne and heterocumulenes, catalysed by Ni(0) complexes, Lx Ni(0), has been proposed to involve one-step cycloaddition scheme (10) [103] and scheme (11) [104, 105] show the formation of the 2-pyrone ring in the alkyne reaction with carbon dioxide and the 2-pyridone ring in the alkyne reaction with isocyanate respectively  

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However, the most important goal that might be reached by the application of coordination catalysts for the polymerisation of heterounsaturated monomers is the possibility of the enchainment of heterounsaturated monomers, not susceptible to homopropagation, via their copolymerisation with heterocyclic monomers. This concerns primarily the coordination copolymerisation of carbon dioxide and oxacyclic monomers such as epoxides, leading to aliphatic polycarbonates [8 12]. Representative examples of the copolymerisations of heterocyclic monomers and hardly homopolymerisable heterocumulenes, in the presence of coordination catalysts, are listed in Table 9.4 [1]. 

Table 9.4 Copolymerisation of heterocyclic monomers with heterocumulenes in the presence of coordination catalysts 2...

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