Tuning morphology of siloxane bond‐based polybenzoxazines by controlling the sol–gel and curing processes

FORCHETTI CASARINO, AGUSTIN; BORTOLATO, SANTIAGO ANDRÉS; ESTENOZ, DIANA ALEJANDRA; SPONTÓN, MARISA ELISABET

POLYMER ENGINEERING AND SCIENCE

JOHN WILEY & SONS INC

Año: 2021

0032-3888

Novel polybenzoxazine/polysilsesquioxane nanocomposites were synthesizedwith uniform and reproducible structural morphology, high Tg, and good thermalstability. Polysilsesquioxane was oriented in a nanometer-size lamellarstructure. Benzoxazine monomer based on silane (BA-3aptms) was synthesizedby reaction between bisphenol A, 3-(trimethoxysilyl)propylamine, and paraformaldehydein a 1:2:4 molar ratio. Four experimental conditions of the twostage sol?gel process for polysilsesquioxane were studied, and their effect onthe material characteristics investigated. In the first stage, hydrolysis wasfavored, while the second stage mostly consisted of condensation. The reactioncondition with the longest hydrolysis time allowed the increase of the concentrationof silanol units and the selective condensation, favoring the formationof a higher amount of cage-like cyclic structures. In addition, this experimentalprocedure was well controlled so that the sol?gel and oxazine-ring openingreactions were extremely reproducible from batch to batch. All processes weremonitored by Fourier transform infrared spectroscopy (FTIR), thermogravimetricanalysis and dynamic mechanical thermal analysis, scanningelectron and transmission electron microscopies, and X-ray diffraction. Achemometric approach based on a multivariate curve resolution model wasapplied to the FTIR spectra, which allowed the identification of four reactioncomponents associated with the sol?gel and the curing processes.