Control of free-radical emulsion polymerization of methyl methacrylate by oxygen injection. II. Experimental study

Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.     

液压系统噪声的现场诊断与处理

分析了液压系统噪声产生的原因,提出了在现场维修过程中故障的判断方法及处理手段.     

Morphology and properties of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene]/silica nanoparticle hybrid films

Poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene] (MEH‐PPV)/silica nanoparticle hybrid films were prepared and characterised. Three kinds of materials were compared: parent MEH‐PPV, MEH‐PPV/silica (hybrid A films), and MEH‐PPV/coupling agent MSMA/silica (hybrid B films), in which MSMA is 3‐(trimethoxysilyl) propyl methacrylate. It was found that the hybrid B films could significantly prevent macrophase separation, as evidenced by scanning electron and fluorescence microscopy. Furthermore, the thermal characteristics of the hybrid films were largely improved in comparison with the parent MEH‐PPV. The UV‐visible absorption spectra suggested that the incorporation of MSMA‐modified silica into MEH‐PPV could confine the polymer chain between nanoparticles and thus increase the conjugation length. The photoluminescence (PL) studies also indicated enhancement of the PL intensity and quantum efficiency by incorporating just 2 wt% of MSMA‐modified silica into MEH‐PPV. However, hybrid A films did not show such enhancement of optoelectronic properties as the hybrid B films. The present study suggests the importance of the interface between the luminescent organic polymers and the inorganic silica on morphology and optoelectronic properties. Copyright © 2004 Society of Chemical Industry     

生态平衡的伦理学意蕴解读

20世纪以来，人类采用技术工程治理、法律制裁和经济惩罚等措施，一定意义上改善了局部的生态环境，但是未能遏制住全球环境问题的恶化态势。生态危机的根本解决，关键在于人类自身必须进行深刻的利益观念和价值观念的变革。重新审视人与自然界的关系，对自然进行伦理关怀，寻求和建立以保护地球环境和人类生存与可持续发展的生态平衡理念。     

比较法在房地产开发中的应用

对"比较法"原理和应用情况进行了分析,说明其在房地产开发中能够科学地预测房地产的价格和收益,从而提高财务分析的科学性和权威性,为项目决策提供科学依据,以促进"比较法"在房地产开发中的应用。     

喷墨打印相纸及打印图像质量的分析

喷墨打印相纸随着数码相机的发展近几年在国内发展迅速。针对目前产品质量没有测量标准的现状,提出喷墨相纸的质量指标主要为4个,即白度、光泽度、油墨吸收性和防水性。给出了相应的测量方法。并指出相纸上油墨点的面积是衡量质量的第一重要指标,其次是点的圆度。另外对图像输出的质量介绍了一种科学的评价方法,即图像的逼真性分析。说明图像的打印墨点直径不应小于方形像素的对角线长,图像才能真实再现。