Ethylene carbonate/cyclic ester random copolymers synthesized by ring-opening polymerization

Abstract

International audienceThe diaminophenolate and β-diketiminate zinc complexes [(NNO)ZnEt] ((NNO)− = 2,4-di-tert-butyl-6-{[(2′-dimethylaminoethyl)-methylamino]methyl}phenolate)) and [(BDIiPr)Zn{N(SiMe3)2}] (BDIiPr = CH(CMeNC6H3-2,6-iPr2)2), respectively, the Lewis acidic triflate salt Al(OTf)3, and the guanidine TBD (= 1,5,7-triazabicyclo[4.4.0]dec-5-ene), combined to a protic source as initiator, typically benzyl alcohol (BnOH), enabled the successful copolymerization of ethylene carbonate (EC) with various cyclic esters such as β-butyrolactone (BL), δ-valerolactone (VL), ε-caprolactone (CL) or L-lactide (LLA). The random copolymerizations proceeded smoothly under mild operating conditions, preferentially from [(NNO)ZnEt]/BnOH at 60 °C in toluene within a few hours, affording the corresponding copolymers void of ether units, with Mn,SEC values in the range ca. 6000–93 350 g mol−1 and with unimodal, moderately broad dispersity values (ĐM = 1.3–2.1). Under the same experimental conditions, the homopolymerization of EC did not proceed. The first EC/BL random copolymers were thus synthesized with up to 26 mol% of EC inserted within the polyester, while the second example of P(EC-co-VL) was isolated. P(EC-co-VL), P(EC-co-CL), and P(EC-co-LLA) copolymers were prepared with higher than previously reported EC content, namely 23, 37, and 17 mol% vs. 10, 31, and 4 mol%, respectively. In contrast to other catalyst systems, the Al(OTf)3/BnOH system promoted CO2 elimination from the copolymers, thereby leading to ether defects. Microstructural analysis of the copolymers by 13C{1H} NMR spectroscopy revealed the presence of signals previously never described and possibly arising from consecutive EC units within the random copolymers. Thermal transition temperatures measured by DSC further supported the random nature of these copolymers

Recent Trends in Catalytic Polymerizations

“…More particularly, recent efforts have focused on transposing the organocatalysts developed for the ROP of lactones to carbonates as they are more biocompatible than their metal counterparts (Chart ). ,− Today, the organocatalyzed ROP of carbonates achieves high levels of control over molecular weight.…”

Zinc Complexes with an Ethylene-Bridged Bis(β-diketiminate) Ligand: Syntheses, Structures, and Applications as Catalysts in the Borylation of Aryl Iodides

“…These ligands could be easily synthesized, and their steric demands can be readily tuned by varying the organic substituents attached to the imine groups. Consequently, a number of zinc complexes have been synthesized by the utilization of a large variety of β-diketiminate ligands. − They behaved as highly active catalysts for the ring-opening polymerization (ROMP) of lactides. − Particularly, Harder and co-workers reported a series of dinuclear zinc complexes supported by bridged β-diketiminate ligands . In studies of the copolymerization of epoxides and CO 2 , they found that there existed an equilibrium between the active dimer and inactive monomer (both are adducts of a catalyst, CO 2 , and epoxide), and the coexistence of the dimer and monomer decreased the efficiency of polymerization reactions.…”

Sequence‐Controlled Alternating Copolyesters Synthesis via Selective Ring‐Opening Polymerization

“…On the other hand, different kinds of monomers often show largely different activities in copolymerization, then the copolymerization reaction of these monomers tends to result in a copolymer with block, gradient or random sequence instead of alternating sequence. [11,[51][52][53][54][55][56] Current reports mainly focus on the copolymerization of the same kind of monomers but with different pendant groups. Therefore, alternating copolymerization of cyclic ester monomers of different ring sizes is another challenge, which will provide access to hybridize the advantages of multiple homopolyesters into one copolyester and broaden the potential applications of copolyesters.…”