Synthesis and characterization of a novel class of low temperature cure Benzoxazines

A series of a novel class of low cure benzoxazines (BZ-1 to BZ-12) based on phenol, bisphenol-A, bisphenol-F mixture and 4, 4 isomers of bisphenol-F were synthesized using aniline, N, N-dimethyl amino propyl amine (DMAPA) and caprolactam (CPL) modified DMAPA. The molecular structure of benzoxazine monomers was characterized by ¹H NMR, FT-IR, and LC mass spectrometry analysis. DSC and TGA analysis were carried out to study the polymerization process and stability of benzoxazines respectively. Among the benzoxazine systems studied, PBZ-5 is found to possess the reasonably lower cure temperature with good char yield, T_max and Tg values. The catalytic effect on curing behavior of BZ-5 with different types of catalysts such as mono hydroxy (C₁-C₆), polyhydroxy (C₇-C₉) and acidic catalysts (C₁₀ to C₁₃) was studied and discussed in detail. Among the catalysts used, 4,4-thiobisphenol (C₇) was found to be the most effective catalyst towards the ring opening polymerization and in turn lowers the cure temperature (amount, acidity, basicity and structural compatibility of the catalysts) than that of other catalysts (C₂-C₁₃). In addition, the catalytic behavior of starting materials (bisphenol-A and bisphenol-F) towards benzoxazines BZ-5, BZ-6, BZ-8 and BZ-9 were also studied and it can be found that bisphenol-A/F also acts as an effective catalyst which can bring down the cure exotherm to a significant extent.