Amidine-Mediated Zwitterionic Ring-Opening Polymerization of N-Alkyl N-Carboxyanhydride: Mechanism, Kinetics, and Architecture Elucidation
Amidine-Mediated Zwitterionic Ring-Opening Polymerization of N-Alkyl N-Carboxyanhydride: Mechanism, Kinetics, and Architecture Elucidation
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DOI：
10.1021/acs.macromol.5b02611
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发表时间：
2016-02-23
期刊：
影响因子：
5.5
通讯作者：
Zhang, Donghui
中科院分区：
文献类型：
--
作者：
Li, Ang;Lu, Lu;Zhang, Donghui
采用双环酰胺引发剂1,8-重氮杂环癸烯（DBU），研究了n -丁基-羧基氢化物（Bu-NCAs）的两性离子开环聚合（ZROP）。结果表明，通过系统地改变初始单体与引发剂的投料比，可以得到分子量（M-n）在3.5 ~ 32.4 kg mol（-1）范围内，多分散性指数（PDI）在1.02 ~ 1.12范围内的聚n -丁基甘氨酸（PNBGs）。聚合反应表现出可控聚合的特点，聚合物分子量随转化率呈线性增加，并成功进行了链结实验。动力学研究表明，该反应是一级反应，取决于单体和DBU浓度。起始速率与繁殖速率相当。通过dbu介导的Bu-NCA和n -丙基n -羧基氢化物（Pg-NCA）的共聚合成了聚[（n -丙基甘氨酸）-r-（n -丁基甘氨酸）]s [P-(npg -r- nbg)s]的随机共聚肽。随后接枝叠氮端聚乙二醇（PEG）产生瓶刷共聚物。利用原子力显微镜（AFM）对瓶刷共聚物样品进行分析，发现其表面形貌为环形纳米结构，与具有环状结构的多肽骨架相一致。溶液中瓶刷聚合物系的小角中子散射（SANS）表征也证实了多肽骨架的循环结构。
Zwitterionic ring-opening polymerization (ZROP) of N-butyl N-carboxyanhydrides (Bu-NCAs) has been investigated using 1,8-diazabicycloundec-7-ene (DBU), a bicyclic amidine initiator. It was found that poly(N-butylglycine)s (PNBGs) with molecular weight (M-n) in the 3.5-32.4 kg mol(-1) range and polydispersity index (PDI) in the 1.02-1.12 range can be readily obtained by systematically varying the initial monomer to initiator feed ratio. The polymerization exhibits characteristics of a controlled polymerization, as evidenced by the linear increase of polymer molecular weight with conversion and the successful enchainment experiments. Kinetic studies revealed that the reaction is first-order dependent on the monomer and the DBU concentration. The rate of initiation is comparable to that of the propagation. Random copolypeptoids of poly[(N-propargylglycine)-r-(N-butylglycine)]s [P-(NPgG-r-NBG)s] were also synthesized by DBU-mediated copolymerization of Bu-NCA and N-propargyl N-carboxyanhydride (Pg-NCA). Subsequent grafting with azido-terminated poly(ethylene glycol) (PEG) produces bottlebrush copolymers. Analysis of bottlebrush copolymer samples using atomic force microscopy (AFM) revealed a surface morphology of toroid-shaped nanostructures, consistent with the polypeptoid backbone having cyclic architecture. Small-angle neutron scattering (SANS) characterization of the bottlebrush polymer ensemble in solution also confirms the cyclic architecture of the polypeptoid backbones.