四臂双亲性PEMA-b-PMAA嵌段共聚物的合成

Synthesis of 4-Arm Amphiphilic Block Copolymer PEMA-b-PMAA

由2-溴异丁酰溴和季戊四醇反应合成了四臂引发剂,以CuCl为催化剂,N,N,N′,N″,N″-五甲基二亚乙基三胺（PMDETA）为配体,在N,N-二甲基甲酰胺（DMF）中分步引发甲基丙烯酸乙酯（EMA）和甲基丙烯酸叔丁酯（tBMA）进行原子转移自由基聚合（ATRP）,得到了四臂型嵌段共聚物PEMA-b-PtBMA。改变聚合反应条件,可将四臂大分子引发剂PEMA-Br的平均分子量控制在0.8×104~2.2×104之间。通过FT-IR和1H-NMR证明,在三氟乙酸存在的条件下PtB-MA链段上的叔丁基可定向水解,其水解率在99%以上,转变为四臂双亲性嵌段共聚物PEMA-b-PMAA。采用LLS和TEM对四臂PEMA-b-PMAA自组装形成的胶束粒径及分布进行表征发现,其大小在200 nm左右,分布较均匀。

The 4-arm initiator was prepared by the esterification reaction between pentaerythritol and 2-bromoisobutyryl bromide.The 4-arm poly（ethyl methacrylate）-b-poly（tert-butylmethacrylate） copolymer was prepared by atom transfer radical polymerization（ATRP） using the 4-arm initiator,CuCl and N,N,N′,N″,N″-pentamethyldiethylenetriamine（PMDETA） as catalyst and ligand in N,N-dimethylformamide（DMF）.The molecular weight of the 4-arm PEMA can be controlled in range of 8000 to 22 000 by change reaction time.Then the 4-arm amphiphilic block copolymer of poly（ethyl methacrylate）-block-poly（methyl acrylic acid）（PEMA-b-PMAA） was obtained by hydrolysis from 4-arm PEMA-b-PtBMA copolymer in trifluoroacetic acid solution.In this case,the hydrolytic ratio of tBMA segment can be up to 99%.The molecular weight and structure of the copolymer were characterized by using gel permeation chromatography（GPC）,Fourier transform infrared（FT-IR） spectroscopy and nuclear magnetic resonance（1H-NMR）.The micellization of 4-arm PEMA-b-PMAA was investigated by using laser light scattering （LLS） and transmission electron microscopy（TEM）.It is found that the micelle size is about 200 nm.