Tuning a robust system: N,O zinc guanidine catalysts for the ROP of lactide

P.M. Schafer, P. McKeown, M. Fuchs, R.D. Rittinghaus, A. Hermann, J. Henkel, S. Seidel, C. Roitzheim, A.N. Ksiazkiewicz, A. Hoffmann, A. Pich, M.D. Jones, S. Herres-Pawlis*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

17 Citations (Web of Science)

Abstract

Non-toxic, highly active and robust complexes are the holy grail as ideal green catalysts for the polymerisation of biorenewable and biodegradable polylactide. Four new zinc guanidine complexes [ZnCl2(TMG4NMe(2)asme)], [ZnCl2(TMG5Clasme)], [ZnCl2(TMG5Measme)] and [ZnCl2(TMG5NMe(2)asme)] with different electron-donating and electron-withdrawing groups on the ligand's aromatic backbone have been synthesised. Ligands are derived from low-cost commercially available compounds and have been converted by a three- or four-step synthesis process into the desired ligand in good yields. The compounds have been fully characterised and tested in the ROP of rac-LA under industrially relevant conditions. The complexes are based on the recently published structure [ZnCl2(TMGasme)] which has shown high activity in the polymerisation of lactide at 150 degrees C. Different substituents in the para-position of the guanidine moiety significantly increase the polymerisation rate whereas positioning substituents in the meta-position causes no change in the reaction rate. With molecular weights over 71000 g mol(-1) being achievable, the best system produces polymers for multiple industrial applications and its polymerisation rate approaches that of Sn(Oct)(2). The robust systems are able to polymerise non-purified lactide. The initiation of the polymerisation is suggested to occur due to impurities in the monomer.
Original languageEnglish
Pages (from-to)6071-6082
Number of pages12
JournalDalton Transactions
Volume48
Issue number18
DOIs
Publication statusPublished - 14 May 2019

Keywords

  • cationic-polymerization
  • copper-complexes
  • cyclic esters
  • ligands
  • mechanism
  • polylactic acid
  • ring-opening polymerization
  • substitution
  • x-ray structures
  • zn(ii) complexes
  • CYCLIC ESTERS
  • SUBSTITUTION
  • COPPER-COMPLEXES
  • MECHANISM
  • ZN(II) COMPLEXES
  • CATIONIC-POLYMERIZATION
  • POLYLACTIC ACID
  • LIGANDS
  • RING-OPENING POLYMERIZATION
  • X-RAY STRUCTURES

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