Mechanism of Propylene Oxide Polymerization Promoted by N-Heterocyclic Olefins

Type
Article

Authors
Alghamdi, Miasser
Cavallo, Luigi
Falivene, Laura

KAUST Department
Chemical Science Program
KAUST Catalysis Center (KCC)
Physical Science and Engineering (PSE) Division
Research Computing

Online Publication Date
2017-01-25

Print Publication Date
2017-02-09

Date
2017-01-25

Abstract
We report a mechanistic DFT investigation of the organopolymerization of propylene oxide (PO) promoted by N-heterocyclic olefins (NHOs) in combination with benzylic alcohol (BnOH). Calculations support the experimentally based hypothesis of two competing pathways, namely, the anionic and zwitterionic pathways. The former is based on an acid–base cooperativity between BnOH and the NHO, promoting ring opening of PO by BnO–. The latter occurs through the formation of a zwitterionic adduct by nucleophilic attack of the exocyclic carbon atom of the NHO on the PO, with the concerted ring opening of PO. The two initiating species cannot interconvert, and chain elongation can proceed from both initiation adducts. Potential energy surfaces were computed for a set of NHOs to clarify the effects of the steric and electronic properties of the NHO on the system reactivity. The results achieved represent useful insight toward the synthesis of PPO with better properties with respect to the polymer obtained with the experimental tested systems because the computationally proposed NHO system is the only one that favors the mechanism leading to higher molecular weight.

Citation
Al Ghamdi M, Cavallo L, Falivene L (2017) Mechanism of Propylene Oxide Polymerization Promoted by N-Heterocyclic Olefins. The Journal of Physical Chemistry C 121: 2730–2737. Available: http://dx.doi.org/10.1021/acs.jpcc.6b10977.

Acknowledgements
This work was supported by funding from King Abdullah University of Science and Technology (KAUST).

Publisher
American Chemical Society (ACS)

Journal
The Journal of Physical Chemistry C

DOI
10.1021/acs.jpcc.6b10977

Additional Links
http://pubs.acs.org/doi/full/10.1021/acs.jpcc.6b10977

Permanent link to this record