BF₃·OEt₂ in alcoholic media, an efficient initiator in the cationic polymerization of phenyl‐1,3‐benzoxazines

Abstract

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.

Fatty acid-derived α,ω-bis-benzoxazines through hydrosilylation; curing and thermoset properties

“…Water and IPA in the catalyst were found to have a negative effect. 1 H NMR spectra of the reaction product after 24 h show a decrease in the intensity of the benzoxazine ring methylene signals and the appearance of new signals at 4.4, 4.2 and 3.8 ppm, which can be related with ring opening products [46,47]. According to these results the rest of the study was carried out using Karstedt's catalysts.…”

Advances in the Synthesis of Methylated Products through Indirect Approaches

“…[76] In peptide chemistry,r eductiono ft he N,O-acetal derivatives of amino acids has been aw ell-known approach to access Nmethylated amino acids.T he methodology also works well to make N-methylated amino alcohols. Table 16 [77][78][79][80][81][82] illustrates some recent examples under different reducing conditions.…”

“…The methodology also works well to make N‐methylated amino alcohols. Table illustrates some recent examples under different reducing conditions.…”

Ring Opening Reaction of 3,4‐Dihydro‐2H‐1,3‐Benzoxazine with Amines at Room Temperature

“…found that the polymerization of benzoxazine can proceed at room temperature with the assistance of Lewis acids such as PCl 5 , and the polymer with N,O‐acetal‐type structure was formed. Andreu et al . found that under the combined effect of BF 3 ⋅OEt 2 and methanol, the polymerization of benzoxazine can be effectively initiated at 60 °C.…”