To evaluate the influence of the electronic effects on the polymerization temperature, we looked at several 3-phenyl-3,4-dihydro-2-H-1,3-benzoxazine monomers with electron-withdrawing or electron-donating groups in the 6 and 4 0 positions. The monomers were synthesized and characterized using different synthetic methods to achieve the best possible results. The thermal polymerization of these benzoxazine monomers was analyzed by differential scanning calorimetry, and the polymerization behavior and the polymer characteristics were related to the electronic character of the substituent and the polymerization mechanism. V

The autocatalytic thermal polymerization behavior of three benzoxazine monomers containing carboxylic acid functionalities is reported. Several mixtures of these carboxylic monomers and 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine were prepared and their thermal polymerization behavior was analyzed by differential scanning calorimetry. The acid character of these reactive monomers increases the concentration of oxonium species, thus catalyzing the benzoxazine ring opening reaction. In this way the polymerization temperature decreased by as much as 100 °C in some cases. The existence of decarboxylation processes at high temperatures has been established by FTIR‐ATR and related to the increase in thermal stability observed by TGA in some cases. A relationship between the presence of carboxylic groups in the resulting materials and their flame retardancy behavior has also been established. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6091–6101, 2008

Benzoxazines derived from aniline and 4-hydroxybenzoic acid and from phenol and 4-aminobenzoic acid were prepared with two different synthetic approaches. When the carboxylic group reacted with epichlorohydrin, glycidylic derivatives M-1 and M-2, respectively, were obtained. The ring opening of benzoxazine and epoxy took place simultaneously with no catalyst for both monomers. Likewise, both ring-opening polymerizations took place when boron trifluoride monoethylamine (BF 3 ÁMEA) or 4-(N,N-dimethylamino)pyridine was used as a catalyst for M-1. However, for M-2, when BF 3 ÁMEA was used as a catalyst, the epoxy and benzoxazine ring openings could be distinguished, and a polyether intermediate containing benzoxazine side chains could be obtained.

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3-Phenyl-3,4-dihydro-2H-1,3-benzoxazine (m 1 ) underwent cationic ring opening polymerization using BF 3 ÁOEt 2 in alcoholic solution under mild conditions. The polymerization of m 1 proceeds through an intermediate hemiaminal ether leading mainly to the formation of polybenzoxazines with diphenylmethane bridges, and not only the classical Mannich-type ones. During the first stages of the reaction, low-molecular weight soluble oligomers containing benzoxazine rings are formed. At longer polymerization times, the propagation proceeds conventionally through the phenolic active sites. This polymerization mechanism is extensible to other substituted 3-phenyl-3,4-dihydro-2H-1,3-benzoxazines but fails in the case of 3-alkyl-3,4-dihydro-2H-1,3-benzoxazines or when the phenyl group in Position 3 have a substituent in the p-position. Spectroscopic studies and kinetic experiments using model reactions and deuterium labeled benzoxazines, allow proposing a plausible different polymerization mechanism. These soluble benzoxazinecontaining polymers can be conveniently processed and impregnated on appropriate substrates before underwent crosslinking producing materials with comparable properties to those of conventional bis-benzoxazines.