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Presence of Two Maxima in the Isothermal Free-Radical Polymerization Rate of Isobornyl Methacrylate Retarded by Oxygen

机译:等温自由基聚合中两种千里马的存在   氧气阻滞异丙基甲基丙烯酸酯的速率

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摘要

The kinetics of the free-radical polymerization of isobornyl methacrylate(IBoMA) at 80C, initiated by benzoyl peroxide (BPO), was determined bydifferential scanning calorimetry (DSC), using sample pans previously sealed inair or in nitrogen. The polymerization was arrested by vitrification at a finalconversion close to 0.80. The kinetics in nitrogen could be fitted usinginitiation and propagation rate constants reported in the literature, afunctionality of the termination rate constant controlled by translationaldiffusion based on the free-volume model, and an efficiency factor for theinitiator decomposition that decreased with conversion in the medium-highconversion range. The presence of oxygen led to a significant decrease in thepolymerization rate, an effect that was enhanced when decreasing the samplesize (increasing the surface-to-volume ratio). The original finding was thepresence of two maxima in the isothermal polymerization rate (a double geleffect), a fact that was confirmed by replicating experiences in two differentDSC devices and changing the amount of initiator in the formulation. The firstmaximum in the polymerization rate was explained by the decrease of thediffusion rate of macromolecular radicals to the oxygen-rich boundary, aneffect that starts at low conversions. The second maximum was related to thedecrease in the solubility/diffusion of oxygen in the reaction medium, aphenomenon that is particularly severe at high conversions.
机译:甲基丙烯酸异冰片酯(IBoMA)在80°C由过氧化苯甲酰(BPO)引发的自由基聚合动力学是通过差示扫描量热法(DSC)使用预先密封在空气中或氮气中的样品盘测定的。在接近0.80的最终转化率下通过玻璃化阻止聚合。氮气中的动力学可以使用文献中报道的引发和传播速率常数,基于自由体积模型由平移扩散控制的终止速率常数的功能以及中高转化率下引发剂分解的效率因数降低来拟合。范围。氧的存在导致聚合速率显着降低,当减小样品尺寸时(增加表面体积比),这种作用得到了增强。最初的发现是等温聚合速率中存在两个最大值(双重凝胶效应),这一事实已通过在两个不同的DSC设备中复制经验并更改配方中引发剂的量得到了证实。聚合速率的第一个最大值是由大分子自由基向富氧边界的扩散速率降低所解释的,这种影响始于低转化率。第二个最大值与氧气在反应介质中的溶解度/扩散的降低有关,这种现象在高转化率下尤为严重。

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