HSA fibrillar networks assembled and stabilized in the condensed phase of thermoset polybenzoxazine

Abstract

12-hydroxystearic acid (HSA) was introduced into the thermoset benzoxazine, we expected that the stable ordered structures could be introduced into the thermoset three-dimensional network through the self-assembly of HSA and the polymerization-induced phase separation of benzoxazine monomers. To better understand the structural effects attributed to the introduction of HSA, some model compounds possessing the chemical structure-like HSA were also involved into the study. HSA and benzoxazine (Ba-bz) mixed with different weight ratios, an isotropic solution could be formed after the mixture melted, indicating that HSA molecules in Ba-bz monomers could assemble into ordered structures like in other organic solvents. The study found that the HSA molecules did not aggregate together in the form of individual molecule which completely distinguished from the model compounds. A conjunction of observation of macroscopic structure picture and characterization of microstructure of the samples, the results showed that HSA molecules spontaneously assembled into the fibrillar networks (SAFINs) in Ba-bz. Nanometric spherical micelles consist of HSA could be formed in the molten isotropic solution of HSA and Ba-bz and aggregate into tubes upon cooling. Due to the high concentration of HSA, the nanometric spherical micelles were easier to self-assembly into the large scale fibrillar tubes. During the polymerization, the fibrillar tubes could be stacked further under the action of the polymerization-induced and the rapid formation of the cross-linking network of polybenzoxazine stabilized the tubes. The tubular structure of HSA aggregation was filled with the polybenzoxazine, contributing to the formation of the interpenetrating structure.