Molecular Origin of the Induction Period in Photoinitiated Cationic Polymerization of Epoxies and Oxetanes

Sungmin Park, Landon J. Kilgallon, Zheqin Yang, Du Yeol Ryu, Chang Y. Ryu

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4 Citations (Scopus)

Abstract

We investigated how the reactivity of epoxide and oxetane monomers in photoinitiated cationic polymerization is strongly influenced by their ability to form intramolecular hydrogen-bonding complexes with the Brønsted acids produced by the photoinitiator. In this paper, we highlight the importance of the thermal stability of the hydrogen-bonded complexes of the protonated monomers. We observed that the glycidyl ether structural motif (and its oxetane analog) is key for the formation of the complexes. Using temperature-controlled Fourier transform infrared (FTIR) with in situ ultraviolet irradiation, we performed a series of real-time FTIR experiments which support the hypothesis that the induction period is due to the thermal stability of the hydrogen-bonded complex. In particular, we focused on the photoinitiated cationic polymerization of bis(1-ethyl(3-oxetanil)methyl) ether ("di-oxetane", DOX) for the thermal stability study because it exhibits a prolonged induction period. Furthermore, it was possible to delay the cationic polymerization of DOX without causing autocatalytic polymerization if the temperature is kept lower than 30 °C. This is because the protonated monomer is stable and propagates very slowly at temperatures below 30 °C. On subsequent heating, the hydrogen-bonded complex of DOX loses its thermal stability, and the autocatalytic cationic polymerization of DOX occurs.

Original languageEnglish
Pages (from-to)1158-1165
Number of pages8
JournalMacromolecules
Volume52
Issue number3
DOIs
Publication statusPublished - 2019 Feb 12

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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