Crystalline Stereoregular Poly(ether-ester) via MeAl[Salen]-Catalyzed Well-Controlled Ring-Opening Polymerization of Enantiopure Cyclic Ether-Ester Monomer

Abstract

The development of chemically recyclable polymers with closed-loop life cycles is believed to be the most attractive strategy in creating the circular plastic economy. Here, we successfully prepared a pair of enantiopure O-heterocyclic lactones bearing with pendent phenyl substituent, which are named (2S,7R)-7-methyl-2-phenyl-1,4-dioxepan-5-one (SR-M1) and (2R,7R)-7-methyl-2-phenyl-1,4-dioxepan-5-one (RR-M2), respectively, by using the methanolysis product of poly(3-hydroxybutyrate) (P3HB) as the raw material. The well-controlled ring-opening polymerizations of SR-M1 and RR-M2 were achieved in the presence of MeAl[salen] as the catalyst to produce poly(ether-ester)s with controlled molecular weights, narrow dispersities, and well-defined terminal groups. The monomer stereoconfiguration has a big impact on their polymerization kinetics and thermodynamics as well as the thermal and mechanical properties of resultant polyesters. Both the resultant P(SR-M1) and P(RR-M2) exhibited closed-loop recyclability. The depolymerization of resultant polyesters back to pristine monomers can be easily realized using stannous octoate as the catalyst in solution.

Ring-Opening Polymerization of Lactones to Prepare Closed-Loop Recyclable Polyesters

“…In the presence of MeAl[salen]/BnOH catalytic system, the enantiopure monomers of M22 and M23 with δ-substituted phenyl group achieved controlled ROPs at RT to prepare polyesters with well-defined chain-end groups, high M n s and narrow Đs. 179 M22 had a higher polymerization activity and a lower T c than M23. Even though both polyesters had similar chemical structures, PM22 was an amorphous polymer with a T g of 19 °C, while PM23 was a semicrystalline polymer with a crystallinity of 34% and a T m of 85 °C.…”

“…Reineke and co-workers reported the synthesis and polymerization of a novel disubstituted valerolactone, β-acetoxy-δ-methyl­valerolactone, which was derived from the renewable feedstock triacetic acid lactone (TAL). The ROP thermodynamic behavior was examined, and the resultant amorphous material displayed a T g of 25 °C (Table , run 15). Li et al prepared a series of poly­(ester–amide)­s (PEAs) by the ROP of morpholino-2,5-dione derivatives (MDs), which can be synthesized from α-hydroxy acids and α-amino acids. , These amorphous PEAs can also be directly depolymerized to pristine MDs under an amberlyst 15 ion-exchange resin.…”

“…Recently, our group reported the synthesis of substituted DXOs and corresponding poly­(ether- alt -ester)­s by upcycling of P3HB (Figure a). ,− First, P3HB was degraded to high-purity 3-hydroxybutyrate by alcoholysis using sulfuric acid as the catalyst. The obtained 3-hydroxybutyrate was selectively reacted with cyclohexene oxide (CHO) to synthesize intermediates that was transformed into fused-ring lactone (4-MOHB) with a high purity and high yield through facile saponification and ring-closing reaction.…”

“…(a) Upcycling of P3HB to prepare closed-loop recyclable poly­(ether- alt -ester)­s, (b) chemical structures of O -heterolactones and (c) ROP thermodynamic parameters of O -heterolactones, ,− and (d) upcycling P3HB into N -heterolactone and recyclable poly­(amine- alt -ester) …”

Organocatalytic Group Transfer Polymerization of N,N-Diethylsorbamide Leading to trans-1,4-Addition Polymer: Controlled/Living Nature Applied to the One-Pot Synthesis of Block Copolymer with Poly(N,N-dimethylacrylamide)

“…The use of organocatalysts, also known as metal-free catalysts, has considerably progressed in organic chemistry since 2000. − In polymer chemistry, the ring-opening polymerization of lactide using 4-(dimethylamino)­pyridine as a catalyst was reported in 2002 as the first living polymerization using an organocatalyst . Organocatalytic polymerization has been widely expanded to use applicable cyclic monomers, such as cyclic esters, cyclic carbonates, and epoxides, and copolymerization of epoxide with CO 2 . − These new precision polymerization systems require improvement in terms of polymerization activity, chemical selectivity, and polymer structure control. As a different type of polymerization, the group transfer polymerization (GTP) of polar monomers using 1-trimethylsiloxy-1-methoxy-2-methyl-1-propene (silyl ketene acetal, SKA Me ) enables the controlled/living system. − Taton et al and Waymouth et al reported that N -heterocyclic carbene efficiently organocatalyzed the GTPs of methyl methacrylate and tert -butyl acrylate and the block GT copolymerization (GTcoP) of n -butyl acylate, N , N -dimethylaminoethyl acrylate, N , N -dimethylaminoethyl methacrylate, N , N -dimethylacrylamide (DMAm), and methacrylonitrile. − We have reported that several types of organic molecules categorized as strong Bro̷nsted acids of trifluoromethanesulfonimide (Tf 2 NH) and pentafluorophenylbis­(triflyl)­methane (C 6 F 5 CHTf 2 ), strong Lewis acids of N -(trimethylsilyl)­bis­(trifluoromethanesulfonyl)­imide (Me 3 SiNTf 2 ) and tris­(pentafluorophenyl)­borane (B­(C 6 F 5 ) 3 ), and organic superbases of 1- tert -butyl-4,4,4-tris­(dimethylamino)-2,2-bis­[tris­(dimethylamino)­phosphoranylidenamino]-2Λ5,4Λ5-catenadi­(phosphazene) ( t -Bu-P 4 ) and 2,8,9-triisobutyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]­undecane (T i BP) have effectively catalyzed the controlled/living GTP of (meth)­acrylate and acrylamide monomers. − An optimal organocatalyst/initiator combination is crucial to achieving a controlled/living GTP.…”