A base–conjugate-acid pair for living/controlled ring-opening polymerization of trimethylene carbonate through hydrogen-bonding bifunctional synergistic catalysis

Abstract

The ring-opening polymerization (ROP) of trimethylene carbonate (TMC) using a base-acid binary organocatalyst system of 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) and Brønsted acid trifluoromethanesulfonic acid (TFA) with benzyl alcohol (BnOH) as the initiator has been investigated. The MTBD and its conjugate-acid pair H-bonding bifunctional synergistic activation mechanism was demonstrated by NMR measurements, and the living/controlled nature of MTBD/TFA catalyzed ROP of TMC was confirmed by the kinetic and chain extension experiments. The controlled ROP of TMC with the optimal molar ratio of MTBD/TFA = 2/1 proceeded to afford well-defined PTMC with narrow molecular weight distributions (M w /M n ∼ 1.1). The molecular weights determined by 1 H NMR are in precise agreement with the theoretical values. 1 H NMR, SEC, and MALDI-ToF MS measurements confirmed the structure of the obtained homopolymer PTMC. In addition, a diblock copolymer consisting of poly(trimethylene carbonate) and poly(L-lactide) (PTMC-b-PLLA) was synthesized successfully by the MTBD/TFA binary catalyst system.

Solvent‐free ring‐opening polymerization of lactones with hydrogen‐bonding bisurea catalyst

“…Here, a synergistic catalytic mechanism was proposed, in which the bisurea activated the carbonyl group of monomer and MTBD facilitated the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding (Scheme ) . Kiesewetter expounded that (thio)urea/MTBD mediated ROP of VL proceeded through one of two mechanisms, (thio)‐imidate mechanism and classic H‐bond mediated mechanism.…”

Bifunctional Squaramides as Organocatalysts for Lactide Polymerization: Catalytic Performance and Comparison with Monofunctional Analogues

“…To date, the squaramide‐mediated ROP of lactide was reported on one occasion using a squaramide/(−)‐sparteine two‐component catalytic mixture . While the present study was in progress, a Pt‐functionalized aminosquaramide was also reported to oligomerize lactide …”

Thiourea binding with carboxylic acid promoted cationic ring-opening polymerization

“…Three strategies of 5 hydrogen-bonding activation existed in the ROP of cyclic carbonyl-containing monomers: (i) the simultaneous activation of an alcohol group and a carbonyl function by a unique bifunctional catalyst provided with a hydrogen bond donor and an acceptor, for example thiourea-amine catalysts were used to catalyze the ROP of lactide by Waymouth and Hedrick in 2005 [33]; (ii) the catalytic system consisted of two separate species with one of them acted as hydrogen bond 10 donor and the other as hydrogen bond acceptor, which was demonstrated by thiourea/amine [34][35][36]; (iii) the single activation of an alcohol group by a hydrogen bond acceptor, such as phosphazene [37,38]. In continuation of our interest in organocatalysis in ROPs [36, [39][40][41][42], we envisioned the concept of multicatalysis [43] should pioneer in an HBD cooperating with BA model in polymerizations. 15…”