3 years ago

Metal and Counteranion Nuclearity Effects in Organoscandium-Catalyzed Isoprene Polymerization and Copolymerization

Metal and Counteranion Nuclearity Effects in Organoscandium-Catalyzed Isoprene Polymerization and Copolymerization
Tracy L. Lohr, Shuoyan Xiong, Yanshan Gao, Massimiliano Delferro, Jiazhen Chen, Tobin J. Marks
The binuclear organoscandium half-sandwich complexes (Me3SiCH2)2(THF)Sc[C5Me4–Si(CH3)2–(CH2)n–Si(CH3)2-C5Me4]Sc(CH2SiMe3)2(THF) (n = 0, Sc-C0-Sc; n = 2, Sc-C2-Sc) and monometallic C5Me4SiMe3Sc(CH2SiMe3)2(THF) (Sc1) were prepared and fully characterized by conventional spectroscopic, analytical, and diffraction techniques. These complexes are active catalysts for isoprene polymerization and ethylene/isoprene copolymerization upon activation by the co-catalysts trityl perfluoroarylborate (Ph3C+)B(C6F5)4 (B1) and trityl bisperfluoroarylborate (Ph3C+)2[1,4-(C6F5)3BC6F4B(C6F5)3]2– (B2). Marked catalyst and co-catalyst nuclearity effects on product polymer microstructure are achieved in isoprene polymerization. Thus, the percentage of cis-1,4- units in the polyisoprene products increases from 24% (Sc1) to 32% (Sc-C2-Sc) to 48% (Sc-C0-Sc) as the catalyst nuclearity increases and the Sc···Sc distance contracts. The binuclear catalysts regulate the isometric unit distributions and favor 3,4–3,4–3,4 blocks. Furthermore, the percentage of polyisoprene trans-1,4- units increases ∼5 times when binuclear co-catalyst (B2) is used, in comparison to B1. In ethylene/isoprene copolymerizations, the binuclear catalysts produce polymers with higher molecular weights (Mn = (3.4–6.9) × 104; polydispersity of Đ = 1.4–2.0) and with comparable isoprene enchainment selectivity versus Sc1 under identical reaction conditions. However, isoprene incorporation is curiously reduced by ∼50% when B2 is used versus B1. These results highlight the importance of both ion pairing and imposed nuclearity in these polymerizations, and these results indicate that both catalyst and co-catalyst nuclearities can be used to access specific polyisoprene polymer/copolymer microstructures.

Publisher URL: http://dx.doi.org/10.1021/acscatal.7b01621

DOI: 10.1021/acscatal.7b01621

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.