A different route to functional polyolefins: olefin–carbene copolymerisation

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 olefin-carbene polymerisation reactions provide a viable alternative to more traditional olefin polymerization techniques. Rh(III)-catalyst precursors, while active in the homopolymerisation of either olefins or carbenes, proved to be virtually inactive in olefin-carbene copolymerization. Conversely, the use of Rh(I)(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)Rh(III)-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.

Synthesis of functional ‘polyolefins’: state of the art and remaining challenges

“…Copolymerisation of functionalised carbenes with ethene is also possible, albeit leading to quite inhomogeneous polymer mixtures. 273 These results emphasise the potential of this new technique for the development of new materials that are up to now inaccessible via traditional olefin polymerisation.…”

An Efficient Method for the Synthesis of 2′,3′-Nonsubstituted Cycloalkane-1,3-dione-2-spirocyclopropanes Using (2-Bromoethyl)diphenylsulfonium Trifluoromethanesulfonate

“…12) 2,3-Nonsubstituted 1,1-diacylcyclopropanes can be prepared from 1,3-dicarbonyl compounds by double alkylation using 1,2-dibromoethane. For example, the reaction of acetylacetone (6a) and 1,2-dibromoethane with potassium carbonate in dimethyl sulfoxide (DMSO) afforded the corresponding cyclopropane 7a in 61% yield 13) (Chart 2).…”

One-pot catalyst-free synthesis of down- and upconversion fluorescent oligopyrazolines from diazoacetates and maleic anhydride

“…The constitutional units of the resulting oligomers are accurately identified by the MALDI-TOF-MS. 10 An m/z difference of 130 between series A and B is recorded, For the oligomer with [1a] : [2a] = 0.1 : 1 (Fig. 3.…”