Rational Optimization of Bifunctional Organoboron Catalysts for Versatile Polyethers via Ring-Opening Polymerization of Epoxides

Abstract

Quaternary ammonium and phosphonium borane bifunctional catalysts have shown high catalytic performance in ring-opening polymerization (ROP) of epoxides to produce polyether. Herein, we systematically investigate a series of well-defined organoboron catalysts by varying the electronic and steric properties of the Lewis acidic boron (B) centers, manipulating the steric hindrance on the ammonium cation (N+), adjusting the distance between B and N+, and regulating the nucleic B number of the catalysts. The investigation on the dinuclear catalysts indicated that the reactivity of a given catalyst could be speculated by its B–N–B angle and the B···B distance. We found that the increase of Lewis acidity and the number of B centers of the organoboron catalysts are useful for a high catalytic activity for ROP of epoxides. The Lewis acidity of the B centers was determined using the acceptor numbers, showing an order of borinane (23.4) > BBN (21.7) > BCy2 (18.8) > Bpin (15.5). Moreover, we demonstrated the production of various telechelic polyols in the presence of different chain transfer agents using the organoboron catalysts. The produced telechelic samples have a well-defined terminal functionality with controllable molecular weight. Lastly, these organoboron catalysts were utilized to produce block copolymers, allyl-terminated macromonomers, and random copolymers.

Borane catalysis for epoxide (co)polymerization

“…Coherently, computational studies have shown that the energy barrier for adopting an ideal conformation is lowered by a high steric demand around the nitrogen atom. 154 Finally, in accordance with previous results, it was confirmed that catalyst activity multiplies with the number of boron groups, that is tri- and tetranuclear structures outperformed the dinuclear ones.…”

“…A systematic variation of L = 3, 4, 5 and 6 revealed a stepwise decrease of activity in this order, with an observed TOF of 585 h −1 , 380 h −1 , 325 h −1 and 113 h −1 . 154 A very comparable trend was also found for EO monomer (TOF = 24 600 h −1 , 16 150 h −1 , 12 900 h −1 and 7750 h −1 , respectively). Thus, gradually activity of the dinuclear catalysts decreases as the linker length increases.…”

“…Yang, Wu and co-workers set themselves to the important task of systemizing the impact of the various catalyst tuning sites on performance in epoxide homopolymerization. 154 They focused on four aspects, namely (a) electronic and steric situation of the borane functionality, (b) steric hindrance around the ammonium nitrogen atom, (c) the B-N distance and (d) the number of boranes in the catalyst molecule.…”

Advances in the Synthesis of Chemically Recyclable Polymers

“…The produced PCPC can be recycled to the pristine CPO in 99% NMR yield and 95% isolated yield. A combination pathway of random chain scission and chain unzipping the depolymerization of PCPC was provided [131–136] …”

“…A combination pathway of random chain scission and chain unzipping the depolymerization of PCPC was provided. [131][132][133][134][135][136] 1,4-cyclohexadiene extracted from renewable vegetable oils (e. g. linoleic acid) is oxidized by mCPBA or oxycodone to produce 1,4-cyclohexadiene oxide (1,. This epoxide can be hydrogenated to obtain cyclohexene oxide (CHO), which can be selectively copolymerized with CO 2 to produce polycyclohexene carbonate (PCHC) in the presence of a metal Zn catalyst in toluene under 8 atm CO 2 pressure at room temperature.…”