Constructing ABA- and ABCBA-Type Multiblock Copolyesters with Structural Diversity by Organocatalytic Self-Switchable Copolymerization

Abstract

Self-switchable ring-opening copolymerization of epoxides, cyclic anhydrides, and cyclic esters catalyzed by an organocatalyst has been proved to be a promising approach to sequence-controlled (multi)­block copolymers. However, the scope of the cyclic esters is only limited to lactide, and selection of some anhydrides usually produced random copolymers with an ill-defined sequence. To overcome these challenges, we investigated the one-pot selective polymerization of O-carboxyanhydrides (OCAs)/cyclic anhydrides/epoxides and established an alternative pathway for well-defined multiblock copolyesters with structural diversity and functionality. A potential organocatalyst for self-switchable copolymerization was optimized using ring-opening polymerization of OCA and ring-opening alternating copolymerization of cyclic anhydrides/epoxides as model reactions. Subsequently, the chemoselectivity in terpolymerization was investigated by kinetic studies, and the formation of the sequence-defined triblock copolymer was identified by NMR and GPC analysis. Density functional theory (DFT) calculations for model reactions were also conducted to illustrate the excellent chemoselectivity in terpolymerization. The newly established self-switchable pathway exhibited broad monomer adaptability, and the structures of the monomer (including some challenging anhydrides) have no effect on the chemoselectivity. Finally, one-step synthesis of ABCBA-type pentablock copolyester without external monomer addition was explored from a self-switchable quadri-polymerization of OCAs, cyclic anhydries, epoxides, and lactide.

Construction of triblock copolyesters via one-step switchable terpolymerization of epoxides, phthalic anhydride and ε-caprolactone using dual urea/organic base catalysts

“…Therefore, it is always desired to develop advanced metal-free, simple, and greener catalysts toward switchable polymerization. 25–30…”

Simple and Precision Approach to Polythioimidocarbonates and Hybrid Block Copolymer Derivatives

“…In recent years, alternating copolymerization of epoxides and cyclic anhydrides has been ingeniously used in a series of studies fulfilling one-step block copolymerization, also widely referred to as self-switchable polymerization, using both metallic , and organic catalysts. , The key to these successes is that the electrophilicity of cyclic anhydride, especially PA, toward the reaction with alkoxide species well-exceeds that of the third monomer, such as CO 2 , cyclic esters, and epoxides, thus facilitating the construction of sequence-defined (AB) n (CB) m -, (AB) n C m -, and (AB) n B m -type polyester-poly­(carbonate/ester/ether) block ter-/copolymers in one synthetic step. In this study, we are interested to test the feasibility of involving the alternating copolymerization of ITC/epoxide in this realm ( i.e ., with ITC as the third monomer) and fulfilling one-step sequence-selective synthesis of the polyester-PTC block copolymer.…”

“…In recent years, alternating copolymerization of epoxides and cyclic anhydrides has been ingeniously used in a series of studies fulfilling one-step block copolymerization, also widely referred to as self-switchable polymerization, using both metallic 87,88 and organic catalysts. 89,90 The key to these successes is that the electrophilicity of cyclic anhydride, especially PA, toward the reaction with alkoxide species wellexceeds that of the third monomer, such as CO 2 , cyclic esters, 3) and from t BuP 2 /Et 3 B with excess Et 3 B to t BuP 2 /Et 3 B with excess t BuP 2 (b: homopolymerization of first order; entry 2 in Table 3).…”

One‐Step Sequence‐Selective Synthesis of Block Copolyester from Mixed Phthalic Anhydride, Cyclohexene Oxide, and δ‐Valerolactone

“…Similarly, (AB) n C m type block terpolymers have been one-step synthesized from the mixtures of an epoxide, a CA or CO 2 , and a homopolymerizable heterocyclic compound such as a lactone or lactide. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] It has also been reported that after the alternating copolymerization of CA and epoxide, the excess epoxide can act as the third monomer to deliver (AB) n B m type polyester-polyether block copolymers. [46][47][48][49] An analogous mechanistic pathway is followed in these cases.…”

“…[32] On the other hand, 𝛿-valerolactone (𝛿-VL) and 𝜖-caprolactone (𝜖-CL), the most commonly used lactone monomers for producing biodegradable aliphatic polyesters, have barely been involved in the terpolymerization with CA and epoxides, most probably because of the stronger nucleophilicity of the primary hydroxyl chain ends of poly(𝛿-valerolactone) (PVL) and poly(𝜖caprolactone) (PCL) that are more prone to inducing transesterification, especially in the presence of the alternating polyesters formed in the first stage. [36,50,51] In this work, we have developed sequence-selective terpolymerization from the mixture of phthalic anhydride (PA), cyclohexene oxide (CHO), and 𝛿-VL with greatly suppressed transesterification and epoxide ROP using a metal-free Lewis pair catalyst with excess Lewis base, which provides a new option for one-step controlled synthesis of (AB) n C m type block copolyesters (Figure 1).…”