Zwitterionic
Polymerization to Generate High Molecular Weight Cyclic Poly(Carbosiloxane)s
- Publication date
- Publisher
Abstract
The zwitterionic ring-opening of
2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (TMOSC) with <i>N</i>-heterocyclic carbenes generates high molecular weight
cyclic p(TMOSC). The NHC-mediated polymerization of TMOSC with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene
(IMes, <b>1</b>) generates the poly(carbosiloxane) p(TMOSC)
with molecular weights from 27 000 < <i>M</i><sub>n</sub> < 80 000 Da (1.4 < <i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> < 2.2) within 30 min at room temp.
With the more nucleophilic carbene 1,3,4,5-tetramethyl-imidazol-2-ylidene
(<b>4</b>), the ring-opening polymerization occurs within minutes
at room temperature to generate cyclic p(TMOSC) with molecular weights
up to <i>M</i><sub>n</sub> = 940 000 Da (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> = 3.2). The
resulting p(TMOSC)s are predominantly cyclic as evidenced by dilute
solution viscosity studies and MALDI-TOF MS. DFT calculations provide
support for both zwitterionic and neutral, cyclic intermediates
