Baris Kiskan

Self-Curable Benzoxazine Functional Polybutadienes Synthesized by Click Chemistry

Novel side-chain benzoxazine functional polybutadiene (PB-benzoxazine) was synthesized by using click chemistry strategy. First, some of double bonds were brominated with Br2 in CCl4 and subsequently converted to azido groups by using NaN3 in DMF. Propargyl benzoxazine was prepared independently by a ring-closure reaction between p-propargyloxy aniline, paraformaldehyde and phenol. Finally, azidofunctionalized polybutadiene was coupled to propargyl benzoxazine with high efficiency by click chemistry. The spectral and thermal analysis confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that PB-benzoxazine undergoes thermally activated curing in the absence of any catalyst forming polybutadiene thermoset with high char yield.

Polybenzoxazine: A Powerful Tool for Removal of Mercury Salts from Water

A reusable macroporous polybenzoxazine resin with high specific surface area was prepared as sorbent material for the removal of mercury salts. For this purpose, allyl-functionalized bis-benzoxazine was cured in dimethyl sulfoxide by thermally activated ring-opening polymerization at 180 °C for 3 d followed by a freeze-drying process. The porous structure of the resin was confirmed by SEM analysis and N2 adsorption/desorption studies at 77.3 K. Among various metal ions, namely, Pb(II), Fe(II), Mn(II), Cu(II), Zn(II), and Cd(II), the porous polybenzoxazine resin exhibited a specific sorption behaviour towards Hg(II). Mainly chemisorption and to some extent adsorption mechanisms were proposed for the observed high loading capacity of the resin. As evidenced by FTIR spectral analysis, the chemisorption is attributed to the coordination system formed between free OH and tertiary amino groups in the polybenzoxazine structure and Hg(II) ions. It was also demonstrated that the porous polybenzoxazine can be regenerated simply by treatment with acids. The resin was recycled for up to seven cycles without any significant loss of activity, as proved by sorption and desorption experiments.

Thermally curable fluorinated main chain benzoxazine polyethers via Ullmann coupling

Fluorinated main chain benzoxazine polyethers were prepared by Ullmann coupling of fluorinated benzoxazines in the presence of a nano-copperoxide catalyst. Various parameters such as the monomer structure, temperature, and the effect of catalyst on the polymerization were studied. The benzoxazine groups present in the polyether structure were shown to readily undergo thermally activated ring-opening polymerization in the absence of an added catalyst forming cross-linked networks. The thermal stability of the cured polymers was investigated and compared to that of classical polybenzoxazines. The lower surface energy of the fluorinated polymers made ultrathin films (∼20 nm thick) stable against dewetting at curing temperatures and resulted in thermally cured smooth coatings on solid substrates.

Synthesis, Characterization and Thermally-Activated Curing of Azobenzene-Containing Benzoxazines

Two new benzoxazine monomers with aliphatic and aromatic substituents, as well as azobenzene moieties were synthesized and characterized by spectroscopic methods. Their thermal curing behavior in the absence of any catalyst was investigated by differential scanning calorimetry. The thermal properties of the cross-linked structures were also studied by thermogravimetric analysis. While the monomeric forms gave some indication of thermally-induced isomerization, the azo groups were shown to be fixed in the disordered form in the densely cross-linked matrix.

Electrochemical manipulation of adhesion strength of polybenzoxazines on metal surfaces: from strong adhesion to dismantling

A novel electrochemical redox process for the manipulation of adhesion of polybenzoxazine thermosets on metal surfaces is reported. The method pertains to the electrochemically driven hydroquinone–quinone redox couple. Several antraquinone based bisbenzoxazines possessing phenyl, benzyl and methyl furfuryl substituents were synthesized and characterized. The antraquinone bisbenzoxazines were shown to readily undergo thermally activated ring-opening polymerization in the absence of a catalyst forming cross-linked networks on metal surfaces. The substituent effect on thermal curing behaviour and thermal stability of the cured polymers were investigated. The strong binding affinities of phenolic hydroxyl groups of the anthraquinone moiety in the cured polymers promote adhesion on the metal surface. Electrochemical oxidation converts hydroquinone groups into quinone moieties resulting in the dismantling of the coated films. The generality of this electrochemical method is demonstrated by initial results on platinum electrodes as well as steel plates.

Recycling and Self-Healing of Polybenzoxazines with Dynamic Sulfide Linkages

In this work, a recycling and self-healing strategy for polybenzoxazines through both S–S bond cleavage-reformation reaction and supramolecular attractions is described. Both recyclable and self-healable polybenzoxazines can be prepared from low cost chemicals with a simple procedure in only 30 minutes. For this purpose, inverse vulcanization of poly(propylene oxide)benzoxazine (PPOB) and diallybenzoxazine (B-al) with elemental sulfur was performed at 185 °C. The obtained cross-linked polymer films exhibited thermally driven recycling ability up to 5 cycles. Moreover, the self-healing ability of a test specimen was shown. Spectral characterizations, thermal stability and fracture toughness of the films were investigated after each recycling.

Preparation of microporous organic polymer through Schiff base chemistry and its potential application

The uniform microporous organic polymer (MOP) was obtained in one-pot and one-step polymerization process through Schiff base chemistry under thermal conditions. The obtained anthraquinone–melamine based MOP (AM-MOP) displays high surface area (215 m2/g). AM-MOP was manually filled into a column with high pressure and used as packing material in the high-performance liquid chromatographic applications. The analysis of compounds such as polycyclic aromatic hydrocarbons, pesticides, flavonoids, and phenolic acids was performed to display a possible application by using AM-MOP packed column. Compared to the commercial columns, AM-MOP exhibits better selectivity factor and column efficiency arising from its strong π–π interaction activity. Furthermore, it has similar solvent uptake in both polar and nonpolar media, which explains good compatibility of the material with all mobile phases, from acetonitrile to methanol and water.

Main-chain benzoxazine precursor block copolymers

A novel strategy for the preparation of block copolymers of polymeric benzoxazine precursors with polyetheramines by one-pot two-step or stepwise pathways is described. The method pertains to the use of simple chemicals such as 4-hydroxyaniline, formaldehyde and polyetheramines (Jeffamines). The structures and molecular weights of the polymers were characterized by FTIR, 1H NMR, and GPC. Successful block copolymer formation was evidenced by the clear shift of the molecular weight of the block copolymer to the higher molecular weight region. Thermal properties of the polymers were also investigated by using DSC and TGA. Block copolymers were shown to undergo thermally activated curing by the ring-opening polymerization of the benzoxazine block. The thermal stability of the cured product drastically increased compared to the precursor polyetheramine.

Combining benzoxazine and ketene chemistries for self-healing of high performance thermoset surfaces

A novel strategy for the synthesis and characterization of self-healable polybenzoxazine-based high performance thermoset surfaces is presented. The method involves the preparation of polymeric benzoxazine precursors from simple chemicals such as bisphenol A, formaldehyde, polyetheramines (Jeff amines) and subsequent ring opening polymerization followed by light-induced oxoketene formation. The structure and molecular weights of precursor polymers were characterized by FTIR, 1H NMR, and GPC, respectively. Successful self-healable formulations were prepared using bisbenzodioxinone (5 wt%) in the precursors, which were shown to undergo thermally activated curing by the ring opening polymerization of benzoxazines. The thermal properties of the polymers were also investigated by using DSC and TGA. Light-induced self-healing on the surface of the cured specimens was demonstrated and quantified by AFM analysis. The thermal stability differences of the cured and healed products were also investigated and compared.

Chapter 13 – Thiol-Benzoxazine Chemistry for Macromolecular Modifications

This chapter deals with the synthetic pathways of obtaining materials with thermally curable benzoxazine moieties by using the catalytic opening of the lateral benzoxazine rings by thiols (COLBERT), or in other words the thiol-benzoxazine reaction to further improve special properties, particularly processibility and toughness or for designing new materials. The combination of COLBERT with photolytic thiol-ene, postpolymer modifications of main chain polybenzoxazines, synthesis of linear, block copolymers, and hybrid networks are presented. The advantages of the thiol-benzoxazine approach can be listed as fast and easy reaction conditions at ambient temperature or even below, 100% atom economy, and the availability of wide range of thiol compounds. Apart from these, the conventional benefits of benzoxazine chemistry, like the ease of benzoxazine synthesis and its design flexibility, can be considered additional virtues of thiol-benzoxazine chemistry.