Distribution Kinetics of Radical Reactions

摘要-麦考伊-9810194自由基反应在聚合、解聚、石化裂化和齐聚等工业应用中很常见。PI计划研究在复杂混合物中量化这些大分子反应的机理和动力学的基本和一般模型。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被模拟为半连续分子量分布中的基本反应的组合。这一假设将通过理论和实验研究得到验证，其共同特点是，将通过凝胶渗透色谱等手段监测大分子分布，并与数学模型进行比较。基元反应，如引发、吸氢、断链、耦合传播和终止，将构成机理。最近的结果表明，当众所周知的长链和准静态近似被应用于自由基时，这些反应步骤导致了实验验证的聚合物随机链和链端裂解过程的速率表达式。计划将分析范围扩大到氢供体和大分子自由基的混合物。大多数已发表的连续分配动力学结果都是基于速率系数k与相对分子质量x无关的假设。对于只持续几个小时的聚合物分解实验，这是一个有效的近似值。实验时间越长，平均相对分子质量的变化越大，需要用k(X)模型来解释。将测试k(X)的多项式或幂定律表达式来描述这样的实验。计划用于实验研究的自由基过程包括氢给体辅助裂解、聚合物混合物反应和纤维素降解。理论研究将与实验并行进行，以求出径向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，如支化和分子量。与相似解相关的精确数学解将被开发出来，以显示分子量分布在更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.