High temperatures required for the polymerization of benzoxazines (Tp &gt; 180 oC) is one of the main drawbacks for the synthesis and applications of polybenzoxazines. Monomeric 1,3-benzoxazines undergo decomposition at high temperature and hydrolysis. Production of volatile compounds during polymerization can induce foaming, and voids in the materials, together with contamination of the working place by toxic volatile organic compounds.1 The presence of different substituents in the phenolic ring of benzoxazines can affect the Tp due to electronic effects.2 As far as we know, no studies on the effects of substituents in the meta position have been previously reported and will be described here. Hammett analysis lend to the conclusion that probably different rate determinant steps are involved. Many different catalysts have been attempted to reduce Tp.3 Among them, phenols have been studied. These compounds can be present even as contaminants from the synthesis of benzoxazines. The combination of different substituted benzoxazines and phenols as catalyst has been deeply studied, being able to reduce the polymerization temperatures in some cases up to 70 oC. The nature of the final polymers is modified by the use of these catalysts, being possible to observe the changes by studing Tg, TGA, gel content and DMA. Finally, a photochemical approach has been preliminary tested in water media being able to generate oligomers of different benxozazines at room temperature. Once more, the presence of different substituents on the phenolic ring defines clearly the type of reactions observed.

Three different approaches to reduce the polymerization temperature of benzoxazines

255th National Meeting (2018)

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