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Issue 25, 2013
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A different route to functional polyolefins: olefincarbene copolymerisation

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Abstract

Copolymerisation of carbenes and olefins (ethene), mediated by Rh-based catalyst precursors, is presented as a new, proof-of-concept methodology for the controlled synthesis of functional polymers. The reactions studied show that olefincarbene polymerisation reactions provide a viable alternative to more traditional olefin polymerization techniques. RhIII-catalyst precursors, while active in the homopolymerisation of either olefins or carbenes, proved to be virtually inactive in olefincarbene copolymerization. Conversely, the use of RhI(cod) catalyst precursors allows the synthesis of high molecular-weight, highly functionalized copolymers. The reactions yield a mixture of copolymers and some carbene homopolymers, which proved to be difficult to separate. Polyethylene was not formed under the applied reaction conditions. The average ethene content in this mixture could be increased up to 11%, although analysis of the mixture revealed that the ethene content in fractions of the copolymer mixture can be as high as 70%. Attempts to increase the ethene content by increasing the ethene pressure unexpectedly led to lower average ethene contents, which is most likely due to changes in the ratio of copolymers vs. carbene homopolymer. This behaviour is most likely a result of the reactivity difference of different active Rh-species formed under the applied reaction conditions. Apparently, higher ethene concentrations slow down the copolymerisation process (mediated by yet unidentified Rh-species) compared to the formation of homopolymers (mediated by different Rh-catalysts; most likely (allyl)RhIII-alkyl species), thereby changing the product ratio in favour of the homopolymer. The average ethene content in the copolymer mixture therefore decreases, while the ethene content within the copolymer fraction has likely increased at higher ethene concentrations (but simply less copolymer is formed). The obtained copolymers exhibit a blocky microstructure, with the functional blocks being highly stereoregular. Branching does occur and the functional groups are present in the polymer backbone as well as at the branches. Formation of copolymers was confirmed by Maldi-ToF analysis, which revealed incorporation of several ethene units into the copolymers.

Graphical abstract: A different route to functional polyolefins: olefin–carbene copolymerisation

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Publication details

The article was received on 07 Dec 2012, accepted on 14 Jan 2013 and first published on 16 Jan 2013


Article type: Paper
DOI: 10.1039/C3DT32941K
Citation: Dalton Trans., 2013,42, 9058-9068
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    A different route to functional polyolefins: olefincarbene copolymerisation

    N. M. G. Franssen, J. N. H. Reek and B. de Bruin, Dalton Trans., 2013, 42, 9058
    DOI: 10.1039/C3DT32941K

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