Modeling Spin-Forbidden Monomer Self-Initiation Reactions in Spontaneous Free-Radical Polymerization of Acrylates and Methacrylates

详细信息    查看全文

• 作者：Shi Liu ; Sriraj Srinivasan ; Jianmin Tao ; Michael C. Grady ; Masoud Soroush ; Andrew M. Rappe
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：October 9, 2014
• 年：2014
• 卷：118
• 期：40
• 页码：9310-9318
• 全文大小：380K
• ISSN：1520-5215

文摘

A spin-forbidden reaction is a reaction in which the total electronic spin-state changes. The standard transition-state theory that assumes a reaction occurs on a single potential energy surface with spin-conservation cannot be applied to a spin-forbidden reaction directly. In this work, we derive the crossing coefficient based on the Wentzel鈥揔ramers鈥揃rillouin (WKB) theory to quantify the effect of intersystem crossing on the kinetics of spin-forbidden reactions. Acrylates and methacrylates, by themselves, can generate free radicals that initiate polymerization at temperatures above 120 掳C. Previous studies suggest that a triplet diradical is a key intermediate in the self-initiation. The formation of a triplet diradical from two closed-shell monomer molecules is a spin-forbidden reaction. This study provides a quantitative analysis of singlet鈥搕riplet spin crossover of diradical species in self-initiation of acrylates and methacrylates, taking into account the effect of intersystem crossing. The concept of crossing control is introduced and demonstrated computationally to be a new likely route to generate monoradicals via monomer self-initiation in high temperature polymerization.