A facile method to prepare high molecular weight bio-renewable poly(γ-butyrolactone) using a strong base/urea binary synergistic catalytic system

Abstract

Biorenewable poly(γ-butyrolactone) with a high molecular weight was prepared with a base/urea binary synergistic catalyst.

Chemoselective Ring-Opening Polymerization of Bio-Renewable α-Methylene-γ-Butyrolactone via an Organophosphazene/urea Binary Synergistic Catalytic System Toward a Sustainable Polyester

“…26,27 Very recently, we and others successfully prepared high molecular weight PγBL with a strong base/(thio)urea binary synergistic catalytic system, in which (thio)urea anions were demonstrated to effectively activate γBL ring as well. [28][29][30] According to the previous studies, we believe that urea anions can also effectively promote the ROP of MBL through activation of γBL ring. On the other hand, the VAP pathway of MBL is proposed to proceed via the generation of a carbanion intermediate, which requires catalysts with considerably stronger basicity than those suitable for the ROP pathway.…”

“…As a proof-of-concept, a series of ureas with a cyclohexyl group and a substituted phenyl group was designed and screened for the chemoselective ROP of MBL since ureas with asymmetric structures were proven to be more effective at activation of γBL ring (Scheme 1b, Figure S1-S5). 30 The experiments were first conducted at low temperature (-50 °C) and high monomer concentration (8 M) in tetrahydrofuran (THF) to favor the ROP of MBL in the presence of benzyl alcohol (BnOH) as initiator. As a control experiment, the polymerization conducted with CTPB in the absence of urea achieved a low MBL conversion of 20%, producing exclusively VAP product P(MBL)VAP (Table 1, run 1).…”

“…The deprotonation of U4 by CTPB to generate urea anion was evidenced by the disappearance of half amount of urea protons ( Figure S13) and the concomitant shift of other proton resonances of U4 (d, e, g, h) to upfield, which was consistent with the previous reports. 30,33 Upon addition of BnOH, the formation of hydrogen bonding between BnOH and U4 anion rather than formation of BnOanion was indicated by the downfield shift of the methylene proton resonance (b) from 4.55 to 4.65 ppm as well as the broadening of hydroxyl proton (c) signal ( Figure S14). The addition of excess U4 led to reduced deshielding effect to methylene proton (b) of BnOH as evidenced by the slightly upfield shift of proton resonance (b) from 4.65 to 4.62 ppm.…”

DFT Modeling of Organocatalytic Ring-Opening Polymerization of Cyclic Esters: A Crucial Role of Proton Exchange and Hydrogen Bonding

“…The thioimidate catalyst demonstrated good catalytic activity in lactide polymerization, but lower activity in TMC ROP and low productivity in polymerization of lactones. The novel simple and promising catalysts, the close structural analogs of TU-derived thioamidate, were studied in the few past years [138][139][140][141][142]. These catalysts, which represent the metal derivatives of disubstituted ureas, demonstrated high activities in ROP of cyclic esters of all actual structure types-lactide, lactones, TMC, and ethylene phosphates.…”

Ring-opening (co)polymerization of γ-butyrolactone: a review

“…23 Working in tetrahydrofuran (THF) at -50 °C was even worse as only 4% conversion was reached. 25 PEG-b-PγBL block copolymers could be also prepared in low yields starting from poly(ethylene glycol) macroinitiator deprotonated by NaH followed by polymerization of γBL in dichloromethane/THF (DCM/THF) mixture.…”