Hayley A. Brown, Young A. Chang, and Robert M. Waymouth, Stanford University, CA, USA, synthesized via zwitterionic ring-opening polymerization high molecular weight cyclic p(TMOSC). They used carbosiloxane monomers 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (TMOSC) and different N-heterocyclic carbenes.

A NHC-mediated polymerization of TMOSC with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) generates the poly(carbosiloxane) p(TMOSC) with molecular weights from 27,000 < M_n < 80,000 Da within 30 min at room temp. The more nucleophilic carbene 1,3,4,5-tetramethyl-imidazol-2-ylidene generated cyclic p(TMOSC) with molecular weights up to M_n = 940,000 Da within minutes at room temperature.

The results show the diversity of zwitterionic ring-opening polymerization for generating cyclic macromolecules.

• Zwitterionic Polymerization to Generate High Molecular Weight Cyclic Poly(Carbosiloxane)s,
  Hayley A. Brown, Young A. Chang, Robert M. Waymouth,
  J. Am. Chem. Soc. 2013.
  DOI: 10.1021/ja409843v