A new innovative synthetic approach for the preparation of maleimidobenzoxazines was developed. For the first time the phenolic diversity in maleimidobenzoxazine compounds was enabled, opening many possibilities for tailoring properties of maleimidobenzoxazines through phenolic diversity. The key in a successful implementation of a novel synthetic approach was utilization of aminomaleimide compound prepared by modified synthetic path, without the need for chromatographic purification. Yields of prepared maleimidobenzoxazines reached up to 95%, which is a significant improvement prior to previous studies dealing with the maleimidobenzoxazines. Aminomaleimide and all novel maleimidobenzoxazine substances were characterized by 1H NMR, 13C NMR and FTIR spectroscopies. The curing behaviour of prepared maleimidobenzoxazines was investigated by DSC analysis and mechanical properties by DMA analysis. Novel maleimidobenzoxazines showed similar properties comparing to the already presented in the literature showing high glass transition temperature values over 240 °C. Thermogravimetric analysis proved improved thermal stability of maleimidobenzoxazines compared to anilinobenzoxazines. Finally, the use of prepared maleimidobenzoxazines was investigated by the means of Diels-Alder reaction as a possible benzoxazine bearing maleimide group precursor for self-healing purposes.
COBISS.SI-ID: 1537432771
The Diels-Alder reaction between N-phenylmaleimide and benzoxazine bearing furan group was investigated for the purpose of successful appliance of self-healing in benzoxazine polymer networks. The reaction as a function of temperature/time was performed in molten state and in a solution, where also the kinetic study was performed. The Diels-Alder reaction leads to a mixture of two diastereomers: endo presented at lower cyclo-reversion temperature and exo at higher. Therefore, the conversion rates and exo/endo ratio were studied in detail for both systems. The study of the kinetics in a solution revealed that the Diels-Alder reaction followed typical bimolecular reversible second-order reaction. This study shows detailed investigation of Diels-Alder reaction and provides beneficial knowledge for further use in self-healing polymer networks.
COBISS.SI-ID: 1536888771
Epoxidized cardanol was used as a starting material for the development of a novel bio-based benzoxazine surfactant (BOX). The designed surfactant was used as a stabilizer for epoxy aqueous emulsions. As dispersed phase two epoxy resins were used; synthetic bisphenol A diglycidy ether type epoxy resin (EP) and bio-renewable epoxidized soybean oil (ESO). Formation and stability of aqueous emulsions were studied by investigating particle size and distribution and rheological behavior. Copolymer films (coatings), produced by drying the emulsions, were cured at elevated temperature. To ensure a highly crosslinked structure of thermosetting films amine curing agent (AM) was used. Benzoxazine surfactant showed excellent compatibility with both epoxy resins and effectively copolymerized with both of them. The introduction of polybenzoxazine into the epoxy network improved the thermomechanical properties (higher value of storage modulus and higher crosslink density) of neat epoxy resins. The glass transition temperature was reduced only slightly.
COBISS.SI-ID: 1536970435
Curing kinetics of guaiacol based benzoxazine synthesized from guaiacol, furfurylamine and formaldehyde forming bio-based polybenzoxazine was investigated. Curing process showed complex polymerization behavior, since the exothermal signal consisted of several overlapped peaks. Differentiation and fitting of overlapped peaks was performed by PearsonVII distribution obtaining two separate exothermal signals further associated to stage 1 and stage 2. The apparent activation energies of both stages were determined to be 113.8 kJ mol–1 and 117.5 kJ mol–1, respectively, according to Kissinger. The first could be explained by benzoxazine ring-opening and electrophilic substitution, whereas the second stage corresponds to the rearrangement and diffusion-controlled step. Kinetics of each stage was studied separately. As a result, the first stage was described by Šesták–Berggren autocatalytic model, whereas the second stage appeared to follow nth order kinetics proved by Friedman method. Application of both kinetic models demonstrated that the predicted curves fit well with the non-isothermal DSC thermograms and as such sufficiently describes the complex curing behavior of guaiacol based benzoxazine.
COBISS.SI-ID: 1536750531