Distribution Kinetics of Radical Reactions

摘要-麦考伊-9810194 自由基反应在工业应用中很常见，如聚合，解聚，石化裂化和低聚等。PI计划研究基本和通用模型，量化复杂混合物中这些大分子反应的机理和动力学。 大多数应用涉及许多组分的分布，这些组分可以通过分布动力学进行数学描述。 PI假设这些自由基过程可以建模为半连续分子量分布之间的基元反应的组合。 这一假设将通过理论和实验研究进行测试，其共同特征是大分子分布将被监测，例如，通过凝胶渗透色谱法，并与数学模型进行比较。 基元反应，如引发、夺氢、断链、耦合增长和终止，将构成机理。 最近的研究结果表明，这些反应步骤导致实验验证的速率表达式的随机链和链端裂解过程的聚合物时，众所周知的长链和准稳态近似施加到自由基。 计划将分析扩展到包括氢供体和大分子自由基的混合物。 大多数已发表的连续分布动力学结果都是基于速率系数k与分子量x无关的假设。 这对于仅持续几个小时的聚合物分解实验是有效的近似。 实验时间越长，平均分子量的变化越大，需要用k（x）模型来解释。 将测试k（x）的多项式或幂律表达式以描述此类实验。 计划用于实验研究的激进过程是氢供体辅助裂解、聚合物混合物反应和纤维素降解。 理论研究将与实验平行进行，以发展自由基机构基本平衡方程的数学解。 PI将扩展当前的模型，以包括多变量分布，如分支和分子量。 将开发与相似性解决方案相关的精确数学解决方案，以显示分子量分布在较长时间范围内的演变。

Abstract - McCoy - 9810194 Free-radical reactions are common in industrial applications such as polymerization, depolymerization, petrochemical cracking and oligomerization, etc. The PI plans to investigate fundamental and general models that quantify the mechanisms and kinetics of these macromolecular reactions in complex mixtures. Most of the applications involve distributions of many components that can be mathematically described by distribution kinetics. The PI hypothesizes that these radical processes can be modeled as combinations of elementary reactions among semi-continuous molecular weight distributions. This hypothesis will be tested by theoretical and experimental investigations with the common feature that macromolecular distributions will be monitored, for example, by gel permeation chromatography, and compared with mathematical models. Elementary reactions, such as initiation, hydrogen abstraction, chain scission, propagation by coupling, and termination, will constitute the mechanisms. Recent results indicate that these reaction steps lead to experimentally verified rate expressions for random chain and chain-end cleavage processes for polymers when the well-known long-chain and quasi-stationary-state approximations are applied to radicals. Extending the analysis to include hydrogen donors and mixtures of macromolecular radicals is planned. Most published results in continuous distribution kinetics are based on the assumption that rate coefficient, k, are independent of molecular weight, x. This is a valid approximation for polymer decomposition experiments that last only a few hours. Longer experiments yield a larger shift in average molecular weight and need to be interpreted by a model with k(x). Polynomial or power-law expressions for k(x) will be tested to describe such experiments. The radical processes planned for experimental study are hydrogen-donor assisted cracking, polymer mixture reactions, and cellulose degradation. Theoretical investigations to de velop mathematical solutions to the fundamental balance equations for the radical mechanisms will be conducted in parallel with experiments. The PI will extend current models to include multivariable distributions, such as branching and molecular weight. Exact mathematical solutions that are related to similarity solutions will be developed to show the evolution of molecular weight distributions over a longer time range.