Stereoselective Ring-Opening Polymerization of Lactones with a Fused Ring Leading to Semicrystalline Polyesters

Abstract

Monomer design is vital in the development of polymers with desired thermal and mechanical properties. Here, we prepared two monomers (M1, trans-octahydro-2H-benzo [b][1,4]dioxepin-2-one and M2, trans-octahydro-2H-benzo[b][1,4]oxathiepin-2-one) based on 1,5-dioxepan-2-one (DXO) and 1,4-oxathiepan-7-one (OTO) by incorporating trans-fused cyclohexyl rings. These monomers featured living ring-opening polymerization-yielding polymers with predictable molecular weights while maintaining low D̵ values. To gain a better understanding of the influence of polymer tacticity on polymer properties, a series of polymers with variable tacticities were prepared under various conditions. Their thermal property studies revealed that increasing the P r value to 91% of P(M2) led to an emerging melting-transition temperature of 101 °C. Copolymerization of M1 and M2 allowed us to obtain a well-defined diblock polymer P(M2)-b-P(M1) and random copolymer P(M1-co-M2) with distinct thermal behaviors. Excitingly, oxidation of P(M2) resulted in an increase of the glass transition temperature from 18 to 112 °C. Hydrolysis of these polymers to corresponding hydroxyl acids and subsequent lactonization reactions enabled a closed-loop life cycle of P(M)s.

Ring‐Opening Polymerization of a Benzyl‐Protected Cyclic Ester towards Functional Aliphatic Polyester†

“…A novel monomer 2‐((benzyloxy)methyl)‐1,4‐oxathiepan‐7‐ one (BTO) was synthesized via a simple 2‐step reaction of benzyl glycidyl ether and 3‐mercaptopropionic with a 66% overall yield on 20 g scale (Scheme S1). [ 29,46 ] A hydroxyl acid A1 was first synthesized by ring opening of benzyl glycidyl ether with 3‐mercaptopropionic acid as a nucleophile. Monomer BTO was then obtained by cyclization of A1 in the presence of ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDCI), hydroxybenzotriazole (HOBt), and triethylamine (Et 3 N) at room temperature.…”

“…The hydrolysis of aliphatic polyesters into precursor intermediate of monomer followed our previous report. [ 29 ] P(BTO) was treated with LiOH in a THF/H 2 O solution and the hydroxyl acid intermediate A1 was obtained by simple extraction from the mixed solution upon acidification of the reaction solution. Subsequently, the monomer BTO was resynthesized via the cyclization of the recovered A1 (Figure 5).…”

“…[ 28 ] Recently, our group has developed a synthetic method to construct monomers 5,6‐T6GDXO and 5,6‐T6GOTO with fused‐rings, which underwent stereoselective living polymerization to afford aliphatic polyesters with well‐controlled molecular weights and high tacticity. [ 29 ] However, post‐polymerization modification of the resulting polymers is challenging, which further restricted the scope of its application.…”

(Bipyridine bisphenolate)-aluminum/onium salt pair: a highly active binary catalyst for ring-opening polymerization of lactide with improved thermostability and protic tolerance

“…34–36 Besides, organometallics can achieve a high degree of control over the stereoregularity of the polymer chain, compared with organocatalysts and Lewis pairs. 9,37–45…”

“…[34][35][36] Besides, organometallics can achieve a high degree of control over the stereoregularity of the polymer chain, compared with organocatalysts and Lewis pairs. 9, [37][38][39][40][41][42][43][44][45] Salen-metal complexes have prevailed in the ROP of lactone, because the steric and electronic effects of the ligand can be easily modulated by chemical modification. In addition, the ONNO tetradentate structure in the salen-type ligand reduces the possibility of ligand exchange, which is beneficial for improving the stability of the catalyst.…”