[中文文摘]研究了以 2 ,2 ,6 ,6 -四甲基 - 1-哌啶氧化物 (TEMPO)作为稳定自由基 ,过氧化苯甲酰(BPO)为引发剂 ,丙二腈 (MN)为加速剂 ,极性单体甲基丙烯酸甲酯的聚合 .在丙二腈的促进下 ,聚合速率明显加快 ,4h可达 89%的转化率 .在聚合过程中 ,分子量变化不大 ,分子量分布较窄 .随着聚合体系温度提高 ,转化率随之升高 ,到达 12 0℃后 ,转化率反而下降 ,分散性变化不大 .12 0℃为其较理想的聚合温度 .通过对模型聚合物的核磁共振 (1HNMR)分析 ,发现氧氮自由基部分脱落 ,解释了极性单体不能在稳定自由基存在下进行活性聚合的原因 .对氧氮自由基易从主链脱落的可能解释是两个腈基的强吸电子效应削弱了C -O键 ,从而使氧氮自由基与主链的连接减弱 ,导致分子量不可控制。[英文文摘]Poly (methyl methacrylate) was synthesized starting from benzoyl peroxide and TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy). It was found that nitroxide mediated polymerization of methyl methacrylate was distinctly accelerated by the addition of small amount of malononitrile (MN). During the whole course, the polydispersities were narrow and the molecular weight didn't increase with conversion and time. When the reaction temperature was enhanced, the rates increased but when the temperature reached 120℃, they stopped increasing and began to drop and the polydispersities kept low. 120 ℃was the optimal temperature for this system. Through the 1H NMR analysis of PMMA , it was found TEMPO partly departed from the main chain , which explained that polar monomer couldn’t polymerize in a living manner in the presence of stable free radical .固体表面物理化学国家重点实验
