Abstract
Today's olefin metathesis catalysts show high reactivity, selectivity, and functional group tolerance and allow the design of new syntheses of precisely functionalized polymers. Here the synthesis of a new end-capping reagent is investigated allowing the introduction of a highly reactive activated ester end-group at the polymer chain end as well as its prefunctionalization to directly introduce functional moieties. The versatility of this new end-capping reagent is demonstrated by utilizing it to synthesize a so-called termimer (a monomer with termination capabilities). Copolymerization of a norbornene derivative with the termimer leads to hyperbranched ring-opening metathesis polymerization polymers as proven by gel permeation chromatography and MALDI-ToF-(matrix-assisted laser desorption/ionization time of flight) mass spectrometry.
Highlights
Over the past two decades many new methods have been developed to introduce functionality during ruthenium catalyzed living ring-opening metathesis polymerization (ROMP).[1,2,3,4] The ruthenium carbene complexes developed by Grubbs et al show a high tolerance toward polar functional groups.[5]
With the aim of designing a highly reactive and functionalizable end-capping reagent the synthesis of a substituted cis-vinyl ether was addressed as cis olefins typically react faster than the corresponding trans olefins in olefin metathesis reactions
An activated ester was chosen as the functionalizable moiety as these are tolerated by the olefin metathesis reaction[23] and can be functionalized pre or postpolymerization
Summary
Over the past two decades many new methods have been developed to introduce functionality during ruthenium catalyzed living ring-opening metathesis polymerization (ROMP).[1,2,3,4] The ruthenium carbene complexes developed by Grubbs et al show a high tolerance toward polar functional groups.[5] The preparation of functional polymers can be achieved polymerizing functional monomers Another approach is the synthesis of linear end functional polymers carrying exactly one functional group at the end of the chain. Activated ester groups in polymers were previously shown to be excellent functionalities for postpolymerization functionalization.[16] To exemplify the versatility of such an end-capping reagent, we used it to build a so-called termimer, a reagent that can propagate (like a monomer) and at the same time terminate a polymerization reaction. To the best of our knowledge this is the first report of branched ROMP polymers exclusively prepared by olefin metathesis
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