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Theoretical study of polymerization mechanism of p-xylylene based polymers.

Authors
  • Smalara, Krzysztof
  • Giełdoń, Artur
  • Bobrowski, Maciej
  • Rybicki, Jarosław
  • Czaplewski, Cezary
Type
Published Article
Journal
The Journal of Physical Chemistry A
Publisher
American Chemical Society
Publication Date
Apr 01, 2010
Volume
114
Issue
12
Pages
4296–4303
Identifiers
DOI: 10.1021/jp907031x
PMID: 20201543
Source
Medline
License
Unknown

Abstract

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).

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