氮氧自由基研究(ⅩⅩⅢ)——哌啶氮氧自由基及其氧铵盐与N,N,N′,N′-四甲基对苯二胺在水溶液中的单电子转移反应

ESR波谱和流动-停止UV动力学研究表明,水溶液中2,2,6,6-四甲基-4-羟基哌啶-1-氧自由基1和相应氧铵澳盐2均可将N,N,N′,N′-四甲基对苯二胺(TMPD)氧化为相应自由基正离子TMPD+,2还能将TMPD+进一步氧化为二价正离子TMPD~(2+).TMPD+可发生可逆歧化,其稳定性强烈受介质酸碱性的影响。利用计算机对动力学曲线的模拟测得上述有关反应的速率常数,并讨论了反应机理。     

Main chain scission reaction of poly(methyl methacrylate) caused by two-photon ionization of dopant

The main chain scission reaction of poly(methyl methacrylate) (PMMA) doped with N,N,N,′,N′-tetramethyl-p-phenylenediamine (TMPD) was examined by ESR spectroscopy and GPC measurement, and the scission mechanism was analyzed. The two-photon ionization of TMPD with excimer laser excitation at 77 K produced an ester radical anion of PMMA (PMMA·m?), which becomes the main chain tertiary radical ? CH₂? C˙(CH₃)? CH₂? after the detachment of the ester side group by annealing of the sample at room temperature. The main chain scission radical ˙C(CH₃)(COOCH₃)? (PMMA˙) which was produced by the β-scission from? CH₂? ˙C(CH₃)? CH₂? showed the 13-line ESR spectrum instead of the ordinary 9-line, due to the fast quenching of the sample to 77 K. The change of the molecular weight distribution was measured by GPC after several irradiation-and-annealing operations. The simulation of the GPC curve confirmed that the scission re-action occurs at random in the PMMA chain in the solid and the main chain scission yield from the ester radical anion, [PMMA˙]/[PMMA·m?], is 0.30. © 1995 John Wiley & Sons, Inc.     

Acetalization of carbonyl compounds with 2, 2, 4-trimethyl-1, 3- pentanedio catalyzed by novel carbon based solid acid catalyst

The synthesis of 2, 4-diisopropyl-5,5-dimethy1- 1.3-dioxane through the acetalization of isobutyraldehyde with 2, 2, 4-trimethy1-1,3-pentanediol （TMPD） catalyzed by the novel carbon based acid was first carried out. High conversion （≥98%） and specific selectivity were obtained using the novel carbon based acid, which kept high activity after it was reused 5 times. Moreover. the catalyst could be used to catalyze the acetalization and ketalization of different aldehydes and ketones with superior yield. The yield of several products was over 90%. The novel heterogeneous catalyst has the distinct advantages of high activity, strikingly simple workup procedure, non-pollution, and reusability, which will contribute to the success of the green process greatly.     

HTEMPO和TMPD调控下MMA可控/活性光聚合研究

以HTEMPO(2,2,6,6-四甲基-4-羟基哌啶-1-氧自由基)和TMPD(2,2,6,6-四甲基哌啶酮)为调控介质, 以Irgacure 651为引发剂, 研究了甲基丙烯酸甲酯(MMA)光聚合体系的控制反应动力学, 比较了单分子(HTEMPO为调控介质)和双分子(HTEMPO和TMPD为调控介质)调控体系, 并讨论了HTEMPO和HTEMPO/TMPD在MMA光聚合体系中的调控作用、 光敏化作用和原位光氧化反应. 结果表明, 对MMA光聚合体系, 以HTEMPO/TMPD为控制介质的双分子调控体系是有效的, 获得了良好的ln(\[M0\]/\[M\])与时间, 数均分子量与转化率之间的线性动力学关系, 并且PMMA均聚物的多分散性指数(PDI)随着转化率的提高而减小. 在高转化率(>85%)下, 体系的多分散性指数(PDI)最小值可达到1.2.