Main-chain benzoxazine oligomers: Effects of molecular weight on the thermal, mechanical, and viscoelastic properties

With the intent to study materials processing properties during the curing process, oligomeric benzoxazines of different molecular weight and distribution were obtained from 4-tert-butylphenol, bisphenol A, 4,4-diaminodiphenylmethane and paraformaldehyde by varying the amounts of phenolic compounds. Average molecular weight and distribution of prepared mixtures of polybenzoxazine precursors were determined by gel permeation chromatography analysis. By knowing the molecular weight distribution of prepared mixtures of polybenzoxazine precursors its effect on thermal, mechanical, and viscoelastic properties of the resin during processing and polymerization could be investigated. Mixtures of polybenzoxazine precursors of higher average molecular weight and broader molecular weight distribution displayed faster curing, lower curing conversions, and higher crosslinking densities of cured resins leading to polybenzoxazines with improved properties. This investigation was oriented towards the material processing aspects with the focus on the effect of molecular weights and viscoelastic properties of starting materials on the proceeding of the curing, including changes in material properties, and sample molding. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46659.