Faculty of Chemistry, University of Gdańsk, Poland.
J Phys Chem A. 2010 Apr 1;114(12):4296-303. doi: 10.1021/jp907031x.
The mechanism of polymerization of p-xylylene and its derivatives is analyzed at the theoretical level. The polymerization reaction takes place in vacuo without any catalyst. The first step is a pyrolytic decomposition of starting material for polymerization, p-cyclophane, a cyclic dimer of p-xylylene, into biradical linear dimer and finally into two quinonoid monomeric molecules of p-xylylene. The quinonoid monomer is diamagnetic; i.e., it has a singlet ground state. The monomers after pyrolysis, when the temperature is lowered, do not re-form cyclic dimers but instead polymerize into long chain molecules. The initiation of polymerization requires dimerization of two monomers leading to formation of a genuine noncoupled biradical dimer. The chain molecules grow through the propagation reaction only one unit at a time, by the attachment of a monomer to a radical chain end. In this work the pyrolysis reaction, the initiation reaction and the first propagation steps of parylene polymerization (up to pentamer) are studied in details using different quantum chemical methods: AM1 and PM6 semiempirical methods and density functional theory (DFT) approach using B3LYP functional with two basis sets of different size (SVP and TZVP).
对 p- 亚二甲苯基及其衍生物的聚合机理进行了理论分析。聚合反应在真空中进行，无需任何催化剂。第一步是聚合起始原料 p- 环戊二烯（p- 亚二甲苯基的环状二聚体）的热解分解，生成线性双自由基二聚体，最终生成两个 p- 亚二甲苯基的醌式单体分子。醌式单体是抗磁性的，即它具有单线态基态。热解后，当温度降低时，单体不会重新形成环状二聚体，而是聚合成长链分子。聚合的引发需要两个单体的二聚化，从而形成真正的非耦合双自由基二聚体。链分子通过仅一次一个单元的增长反应，通过单体附着在自由基链末端来生长。在这项工作中，使用不同的量子化学方法详细研究了聚对二甲苯的热解反应、引发反应和聚合的第一个扩展步骤（最多五聚体）：AM1 和 PM6 半经验方法以及密度泛函理论（DFT）方法，使用 B3LYP 函数和两个不同大小的基组（SVP 和 TZVP）。
