Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W Green St., Urbana, IL, 61801, USA.
Department of Chemical Engineering, Virginia Polytechnic Institute and State University, 635 Prices Fork Rd., Blacksburg, VA, 24061, USA.
Angew Chem Int Ed Engl. 2016 Oct 10;55(42):13010-13014. doi: 10.1002/anie.201605508.
Recently O-carboxyanhydrides (OCAs) have emerged as a class of viable monomers which can undergo ring-opening polymerization (ROP) to prepare poly(α-hydroxyalkanoic acid) with functional groups that are typically difficult to achieve by ROP of lactones. Organocatalysts for the ROP of OCAs, such as dimethylaminopyridine (DMAP), may induce undesired epimerization of the α-carbon atom in polyesters resulting in the loss of isotacticity. Herein, we report the use of (BDI-IE)Zn(OCH(CH )COOCH ) ((BDI)Zn-1, (BDI-IE)=2-((2,6-diethylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene), for the controlled ROP of various OCAs without epimerization. Both homopolymers and block copolymers with controlled molecular weights, narrow molecular weight distributions, and isotactic backbones can be readily synthesized. (BDI)Zn-1 also enables controlled copolymerization of OCAs and lactide, facilitating the synthesis of block copolymers potentially useful for various biomedical applications. Preliminary mechanistic studies suggest that the monomer/dimer equilibrium of the zinc catalyst influences the ROP of OCAs, with the monomeric (BDI)Zn-1 possessing superior catalytic activity for the initiation of ROP in comparison to the dimeric (BDI)Zn complex.
最近，O-羧酸酐（OCAs）作为一类可行的单体出现，可以进行开环聚合（ROP），制备带有官能团的聚（α-羟基烷酸），这些官能团通常很难通过内酯的 ROP 来实现。OCAs 的 ROP 有机催化剂，如二甲氨基吡啶（DMAP），可能会导致聚酯中α-碳原子的非对映异构体异构化，从而导致立构规整性丧失。本文报道了（BDI-IE）Zn（OCH（CH ）COOCH ）（（BDI）Zn-1，（BDI-IE）=2-（（2,6-二乙基苯基）氨基）-4-（（2,6-二异丙基苯基）亚氨基）-2-戊烯），用于在没有非对映异构体异构化的情况下控制各种 OCAs 的 ROP。均聚物和具有受控分子量、窄分子量分布和立构规整骨架的嵌段共聚物可以很容易地合成。（BDI）Zn-1 还可以控制 OCAs 和丙交酯的共聚，有利于合成可能对各种生物医学应用有用的嵌段共聚物。初步的机理研究表明，锌催化剂的单体/二聚体平衡影响 OCAs 的 ROP，与二聚体（BDI）Zn 配合物相比，单体（BDI）Zn-1 具有更高的 ROP 引发催化活性。
