“Cr^(2+)+BPO”体系引发的活性自由基聚合

Living Radical Polymerization Initiated by the Aged “Cr^(2+)+BPO” Complex System

以“Cr^(2+)+BPO”体系,在0～40℃下,引发了一系列烯类单体的聚合。该体系引发的活性自由基聚合反应对单体结构有如下的选择性:α-甲基丙烯酸酯类单体在不高于30℃时能进行活性自由基聚合;其它烯类单体,如丙烯酰胺、丙烯腈、苯乙烯以及α-碳原子上不带甲基的丙烯酸酯类单体,均不能进行;而丙烯酸和α-甲基苯乙烯则不能被引发聚合。当温度高于30℃时,α-甲基丙烯酸酯类单体只能进行一般的自由基聚合。根据聚合结果,讨论了该体系引发活性自由基聚合反应的机理。利用“Cr^(2+)+BPO”体系,使MMA与丙烯腈进行嵌段共聚,共聚产物经分离,得到了较纯的嵌段共聚物,并予以表征。采用ESR和可见光谱,探讨了“Cr^(2+)+BPO”体系陈化反应的机理。

Polymerization of various vinyl monomers initiated by the aged 'Cr^(2+)+BPO' complex system was carried out in DMF at 0～40℃. The dependence of living radical polymerization on monomer structures has been discovered. It was found that the living radical polymerization of methlacrylate initiated by the aged 'Cr^(2+)+BPO' complex system occured at 30℃ or below, but the polymerization of other vinyl monomers, such as acrylamide, acrylonitrile, styrene and acrylate without methyl group on α-carhon did not show the living character regardless of the reaction temperature. When the reaction temperature rose above 30℃, the polymerization of methylacrylate did not show the living character, either. Acrylic acid and α-methylstyrene could not be polymerized by the aforementioned initiation system. The mechanism of the living radical polymerization initiated by 'Cr^(2+)+BPO' was discussed in terms of a transition metal complex with free radicals and stereo-hindrance. By the living radical polymerization of MMA initated by the aged 'Cr^(2+)+BPO' complex, the block copolymerization of MMA with AN was carried out. The PMMA-b-PAN was purified and characterized. The ESR and the visible spectra of the aged 'Cr^(2+)+BPO' complex system were studied and the mechanism of the aging process of Cr^(2+) and BPO in DMF was also discussed.