Living Initiator-Transfer Anionic Polymerization of Isocyanates by Sodium Diphenylamide

Abstract

Access to protein-inspired polyisocyanates with high molecular weights (MWs) from anionic polymerization of isocyanates is challenging as it requires exceptional livingness. For this purpose, a dimerically self-associated sodium diphenylamide (NaDPA) was introduced as a robust chain-end-protective initiator in the anionic polymerization of n-hexyl isocyanate (HIC) in the absence or presence of sodium tetraphenylborate (NaBPh 4 ) additive. At [NaDPA] 0 /[NaBPh 4 ] 0 = 5, unusual one-half initiation efficiency and one-half order of reaction kinetics were observed. Accordingly, initiator-transfer anionic polymerization (ITAP), a mechanism driven by the dimer of NaDPA ((NaDPA) 2 ) in a dual role is proposed, in which one unimer initiates the polymerization and the other reversibly deactivates the propagating chain end through its repetitive cycles of 1:1 cross-association/dissociation. Living ITAP by NaDPA with NaBPh 4 was proven by X-ray crystallography, density functional theory calculation, and quantitative yield of poly(n-hexyl isocyanate)s with an expanded range of controlled MWs (M n = 6.09−47.8 kDa and Đ = 1.07−1.16).

Synthetic Control of Helical Polyisocyanates by Living Anionic Polymerization toward Peptide Mimicry

“…Later, sodium N-phenethyl-3-phenylpropanamide (Na-PEPPA) 55 was developed as an aliphatic chain-end-mimic initiator to solve the slow initiation of aromatic NaBA. In addition to the chain-end-mimic initiators, sodium benzhydroxide (NaBH), 69 sodium deoxybenzoin (NaDB), 70 sodium diphenylmethane (NaDPM), 72 and sodium diphenylamide (NaDPA), 73 with different anionic structures, were also introduced as initiators in the anionic polymerization of HIC. These initiators have shown characteristic initiation efficiencies in the absence and presence of NaBPh 4 (Table 1).…”

“…Meanwhile, a series of kinetic studies of living anionic polymerization of isocyanates were begun by Lee and coworkers. 55,72,73 The first effort was made by using NaDPM ((C 6 H 5 ) 2 CHNa) as a carbanionic initiator. 72 The polymerization of HIC was performed in the absence or presence of The nonliving characteristics completely disappeared by adding NaBPh 4 to the initiator (Scheme 7a).…”

“…193−198 Furthermore, its high livingness allows the sequential addition of comonomer mixtures, thereby accumulating a number of monosequences in a polymer chain. 199,200 Accordingly, polyisocyanates produced by living anionic polymerization 46,55,[66][67][68][69][70]72,73,87 can evolve into peptide-mimicking polymers with multisequences. The sequence control of polyisocyanates has been accompanied by kinetic studies of living coordination and anionic copolymerization of binary mixtures of isocyanates.…”

“…However, many previous polymerization systems categorized into the “classical chain-growth polymerization of isocyanates” had limitations in kinetic studies due to their lack of livingness. ,,,,,,− In particular, these systems cannot avoid substantial competition between propagation reactions and side reactions (cyclotrimerization and uncharacterized irreversible termination). For this reason, reliable kinetic studies were possible only under the living polymerization mechanisms that were well established by Novak − and Lee. ,,− ,,, …”

“…Another kinetic study was attempted to verify the dual function of self-associated initiators . NaDPA ((C 6 H 5 ) 2 NNa) was chosen as a self-associated initiator with a dimeric structure ((NaDPA) 2 ) .…”