Z-type and R-type macro-RAFT agents in RAFT dispersion polymerization – another mechanism perspective on PISA
Z-type and R-type macro-RAFT agents in RAFT dispersion polymerization – another mechanism perspective on PISA
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DOI：
10.1039/c6py00605a
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发表时间：
2016-05
影响因子：
4.6
通讯作者：
Mingguang Yu;Jianbo Tan;Jianwen Yang;Z. Zeng
中科院分区：
文献类型：
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作者：
Mingguang Yu;Jianbo Tan;Jianwen Yang;Z. Zeng
在常见的RAFT分散聚合诱导自组装（PISA）配方中，通常使用左基侧带有亲溶剂链的r型宏观RAFT剂来介导聚合，而z基侧带有亲溶剂链的z型宏观RAFT剂很少使用。在本文中，我们尝试使用z型宏观RAFT剂（mPEG113-BTPA）介导苯乙烯的RAFT分散聚合，发现该过程表现出较差的PISA倾向和较弱的分子量控制。相比之下，我们用r型宏观raft剂（mPEG113-DDMAT）进行了相同的过程，发现该配方表现出典型的PISA过程，并且纳米颗粒在原位产生。进一步的实验表明RAFT基团的位置对RAFT分散聚合的PISA过程起着关键作用。当使用r型宏RAFT试剂时，RAFT基团将嵌入到生成的颗粒中，而在z型宏RAFT试剂的情况下，RAFT基团位于颗粒表面。我们尝试利用mPEG113-BTPA稳定颗粒表面的RAFT基团对颗粒表面进行修饰，并通过破坏RAFT基团成功去除亲溶剂嵌段，通过表面引发RAFT聚合生成聚二甲基丙烯酰胺嵌段。基于上述机理视角，我们设计了初步实验，发现mPEG113-BTPA介导的1,4-二氧六环苯乙烯预聚合合成的z型宏观RAFT嵌段共聚物通过非均相RAFT分散聚合可以制备出定义良好的单分散纳米球。
In a common RAFT dispersion polymerization induced self-assembly (PISA) formulation, R-type macro-RAFT agents with a solvophilic chain attached at the leaving group side are normally used to mediate the polymerization, meanwhile Z-type macro-RAFT agents with a solvophilic chain attached at the Z-group side are seldom employed. In this paper, we have tried to use a Z-type macro-RAFT agent (mPEG113-BTPA) to mediate RAFT dispersion polymerization of styrene, and found that the process exhibited a poorer PISA tendency and weaker molecular weight control. In comparison, we have conducted the same process mediated with an R-type macro-RAFT agent (mPEG113-DDMAT), and found that the formulation exhibited a typical PISA process, and nanoparticles were produced in situ. Further experiments suggest that the location of RAFT groups plays a key role for the PISA process in RAFT dispersion polymerization. The RAFT groups will be embedded in the produced particles when an R-type macro-RAFT agent is employed, but locate on the particle surface in the case of the Z-type macro-RAFT agent. We have tried to employ the RAFT groups on the surface of the mPEG113-BTPA stabilized particles to modify the particle surface, and successfully removed the solvophilic block via breaking the RAFT group, and generated the poly(dimethylacrylamide) block by surface-initiated RAFT polymerization. Based on the above mechanism perspective, we have designed a preliminary experiment, and found that well-defined monodisperse nanospheres could be prepared by heterogeneous RAFT dispersion polymerization mediated with a Z-type macro-RAFT agent-based block copolymer which was synthesized via pre-polymerization of styrene in 1,4-dioxane mediated with mPEG113-BTPA.