锌卟啉共价有机框架和共轭微孔聚合物的光催化可逆加成-断裂链转移聚合

Zinc Porphyrin-based Covalent Organic Framework and Conjugated Microporous Polymer as Heterogeneous Photocatalysts for Reversible Addition-fragmentation Chain Transfer Polymerization

制备基于锌卟啉共价有机框架(COFs)和共轭微孔聚合物(CMPs)的异相光催化剂用于催化光诱导电子转移可逆加成-断裂链转移(PET-RAFT)聚合.这些光催化剂可以高效地将电子转移到链转移剂制备得到具有窄分子量分布(<1.20)和高链端保真度的聚丙烯酰胺和聚丙烯酸酯,聚合速率高于具有相似构建单元的卟啉或镍卟啉光催化体系.同时,对于锌卟啉COF和CMP材料,不同堆积模式和共轭程度影响了光催化剂的结构和光物理性质.比较两者的结构性质和催化性能,说明了在光控聚合中选择高效催化性质的构建单元是催化剂设计的关键要素.此外,相比于COF,CMP光催化剂具有更高的化学稳定性,可以被有效分离并循环使用.这项工作阐明了多孔有机聚合物在光控聚合中的设计要素,为实现异相的光聚合提供重要借鉴.

Zinc porphyrin-based covalent organic framework(COF)DhaTph-Zn-COF and conjugated microporous polymer(CMP)DhaTph-Zn-CMP as heterogeneous photocatalysts were prepared to activate photoinduced electron transfer-reversible addition-fragmentation chain transfer(PET-RAFT)polymerization under broad-range wavelengths.They could efficiently transfer electrons to chain transfer agents to synthesize polyacrylamides and polyacrylates with controllable molecular weight,narrow molecular weight distribution(<1.20),and high chain-end fidelity.The apparent polymerization rate constants were 0.0522 h^(-1) and 0.0621 h^(-1) for polymerization of N,N-dimethacrylamide with 2.5 mg/mL DhaTph-Zn-COF or DhaTph-Zn-CMP,respectively,under yellow light irradiation.The different stacking patterns and the degree of conjugation for the freshly prepared COF and CMP materials affected structure and photophysical properties,such as crystallinity,specific surface area,band gap,fluorescence lifetime,charge transfer resistance,etc.Although DhaTph-Zn-COF had an ordered stacking with better electron transfer properties,their similar catalytic properties indicated that the stacking patterns were not the primary factor to enhance the performance of photocatalysts.Meanwhile,the difference in photocatalytic polymerization of metalloporphyrin-based COFs displayed that a building block(zinc porphyrin)with high photocatalytic efficiency in a homogenous system is vital to the design of the heterogeneous photocatalysts for polymerization.Besides,the stability of photocatalysts directly affected the efficiency of catalytic cycles.Compared with DhaTph-Zn-COF,the amorphous DhaTph-Zn-CMP showed more robust chemical stability after several rounds of polymerization and could be used at least five times.The reduced efficiency of DhaTph-Zn-COF after recycling resulted from the loss of active components.The scanning electron microscopy(SEM)revealed the morphological difference between the COF and CMP photocatalysts.Better stability could be credited to the tight-packed particles formed by the disorderly stacked structure,which avoided the destruction by external factors such as monomers,solvents,and stir.This work provides insights into the design factors of heterogeneous POP photocatalysts for photopolymerization and promotes the development of efficient semiconductors and heterogeneous photocatalysts.