Preparation of High Purity Samples, Effect of Purity on Properties, and FT-IR, Raman, 1H and 13C NMR, and DSC Data of Highly Purified Benzoxazine Monomers

QICHAO RAN; HATSUO ISHIDA; SEISHI OHASHI; CARLOS R. ARZA; KAN ZHANG; PABLO FROIMOWICZ

Advanced and Emerging Polybenzoxazine Science and Technology

Elsevier

Año: 2017; p. 1053 - 1082

As the interest in benzoxazine becomes wide spread, the number of papers published increased exponentially every year in the past twenty years and this trend still continues. Multiple papers have been published on the same benzoxazine monomer, yet the results vary from paper to paper, due in part to the variation of the purity of samples prepared. In order to further advance the fundamental understanding of benzoxazine chemistry, it is important that researchers share common data or information so that quantitative comparison of the results is possible and helps to establish reliable standard data. For this purpose, this chapter is prepared with high purity compounds only, mostly with single crystals of benzoxazine monomers, in order to provide standard structural and spectral information. For a specific case, a sample preparation method, including synthesis to minimize the impurity that interferes with the purification, is provided. Based on this method, we have prepared the largest single crystal of the bisphenol A/ aniline based benzoxazine (abbreviated as BA-a) ever reported. Quite often different papers provide rather similar NMR spectra for the same monomer they studied. Yet, their differential scanning calorimetric (DSC) results vastly differ. This is the reflection of very strong effect of a small amount of cationic impurities on the polymerization process. The effect of such cationic impurities is amplified by the autocatalytic polymerization mechanism of benzoxazine resins. Therefore, this chapter also discusses the effect of varying purity on DSC thermograms, highlighting the strong effect of the impurity on polymerization kinetics. Finally, this chapter presents the Raman and Fourier transform infrared (FT-IR) as well as 1H and 13C NMR spectra, and DSC thermograms of benzoxazine monomer single crystals, with the exception of a few samples being multiple crystals, which are identified as such for clarity.