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

Abstract

Development of effective organocatalysts for the living ring‐opening polymerization (ROP) of lactones is highly desired for the preparation of biocompatible and biodegradable polyesters with controlled microstructures and physical properties. Herein, a new class of hydrogen‐bond donating bisurea catalysts is reported for the ROP of lactones under solvent‐free conditions. ROP of lactones mediated by the bisurea/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD) catalyst exhibits a living/controlled manner, affording the polymers and copolymers with the well‐defined structure, predictable molecular weight, narrow molecular weight distribution, and high selectivity for monomer at low catalyst loadings at ambient temperature. The possible mechanism of bisurea/MTBD‐catalyzed ROP of lactones is proposed, in which the bisurea activates the carbonyl group of lactones while MTBD facilitates the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding. Moreover, the poly(ε‐caprolactone‐co‐δ‐valerolactone) [P(CL‐co‐VL)] random copolymers with various compositions were synthesized using the bisurea/MTBD catalyst. The measurements of thermal properties and crystalline structure demonstrate that the CL and VL units are cocrystallized in the crystalline phase of P(CL‐co‐VL) copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 90–100

Bisurea and Bisthiourea H-Bonding Organocatalysts for Ring-Opening Polymerization: Cues for the Catalyst Design

“…The 2-O2 H-bond donor was insoluble in solvents relevant for ROP. Especially versus the rigid (thio)­urea tethers, our results here suggest that the most effective catalysis arises when the (thio)­urea moieties are allowed to interact with one another, lending credence to the originally proposed mechanism whereby bis­(thio)­urea moieties bring about ROP through an activated-(thio)­urea mechanism characterized by one (thio)­urea stabilizing through internal H-bond activation the (thio)­urea which activates the lactone for enchainment, Figure . , We propose that the increased efficacy of 2-S5 and 2-O5 plus MTBD (vs other linker lengths) arises from the stability of the pseudo-7-membered cycle (vs larger or smaller cycles in other bis-donors) formed by intramolecular H-bondingthe (thio)­urea moiety being largely rigid. The enhanced rates displayed by 2-O5 and 2-S5 are enhanced by a factor of two versus their respective “parent” 2-X3 H-bond donor, and this enhanced rate does not result in increased M w / M n .…”

Pathway to fully-renewable biobased polyesters derived from HMF and phenols

“…Further, we develop an organocatalytic polymerization of model FDHL monomers containing methoxymethyl and phenoxymethyl side chains using known acidic and basic catalysts under mild conditions. 58,59 The polymerizations show equilibrium behavior as expected for six-membered lactones due to low ring strain. Differential scanning calorimetry (DSC) analysis reveals that the T g can be controlled by incorporating different pendant groups.…”

Organocatalyzed Synthesis and Degradation of Functionalized Poly(4-allyloxymethyl-β-propiolactone)s

“…Therefore, chemical syntheses such as ring-opening polymerization, , directive carbonylative polymerization, − and step-growth polymerization have been investigated as alternative routes to synthesize PHAs. − Among these approaches, the controlled ring-opening polymerization of β-lactone allows the production of high-molecular-weight PHAs ( M n > 100 000) with excellent reactivity and productivity. ,, This polymerization process has been traditionally mediated by highly effective metal-based salts or discrete metal complexes, enabling to achieve a high stereochemical control of the microstructure or alternation with chiral racemic β-substituted β-lactones. − More recently, metal-free organocatalysts have been employed as an effective approach for the ring-opening polymerization of β-lactones under mild conditions with unique advantages, such as cost effectiveness, high chemical tunability, high stability, and high performance. ,− …”