Ring-opening Polymerization Of Benzoxazine Research Articles

Evaluation of optical, thermal and hydrophobic properties of sustainable stilbene-based benzoxazines for high-performance utilization

Currently there is a growing interest in the field of photosensitive benzoxazines synthesized from sustainable raw materials. An attempt has been made to synthesize nine structurally different benzoxazines through Mannich condensation reaction. The formation of the expected structure of the synthesized benzoxazine monomers were ascertained using spectroscopic methods. The ring-opening polymerization of benzoxazines was studied using DSC and found that THS-imp benzoxazine monomer exhibits the lowest value of curing temperature (Tp) of 179oC than the rest of the benzoxazine monomers. Thermal stability of polybenzoxazines were analyzed using thermogravimetric analyzer. Among the different polybenzoxazines studied, poly(THS-a) possesses the higher thermal stability with char yield of 53% than that of other benzoxazines. The band gap values of benzoxazines calculated from optical studies are ranged between 3.92-4.71 eV. The hydrophobic behavior of the polybenzoxazines assessed using the water contact angle obtained from goniometer for both neat polymer matrix and benzoxazine coated cotton fabric. Results from the water contact angle infer that the benzoxazines coated cotton fabric exhibited 152o, which shows the superhydrophobic behavior. The corrosion resistant properties of all the polybenzoxazines coated over MS specimen has been tested. Among them poly(THS-pfsa) and poly(THS-imp) have higher Icorr value and corrosion inhibition efficiency of 99%. Data obtained from different studies indicate that the benzoxazines developed from sustainable stilbene can be utilized in the form of coatings, adhesives, sealants, and matrices for composites for wide range of industrial and engineering applications, where high thermal stability and are required.

Synthesis, ring-opening polymerization, and properties of benzoxazines based on o- and p-hydroxybenzyl alcohols

Two series of bifunctional benzoxazines were synthesized from o- and p-hydroxybenzyl alcohols ( oHBA and pHBA), three aliphatic diamines containing ether linkage (Jeffamines D230 and D400 and 4,7,10-trioxa-1,13-tridecanediamine (TTDDA)), and paraformaldehyde. The chemical structures of the benzoxazines were confirmed by 1H and 13C nuclear magnetic resonance and Fourier transform infrared (FTIR) spectroscopy. The ring-opening polymerization of the benzoxazines was studied by differential scanning calorimetry and FTIR, respectively. oHBA-based benzoxazines respectively exhibit lower onset temperatures of ring-opening polymerization than pHBA-based counterparts due to the O–H∙∙∙O intramolecular hydrogen-bonding interaction between the hydrogen of ortho-methylol group and the oxygen in oxazine ring, and oHBA-based polybenzoxazines respectively show lower glass transition temperatures ( Tgs) than pHBA-based counterparts due to the difference in crosslinking density caused by the steric hindrance effect of the position of methylol group on the polymerization of benzoxazine monomers. In each of the two series of benzoxazines, the onset temperature of ring-opening polymerization of D230-based benzoxazine is close to that of TTDDA-based analogue and lower than that of D400-based counterpart owing to the steric effect of the chain length and chain volume of the bridging structure between the oxazine rings on the polymerization, and the Tg of D230-based polybenzoxazine is close to that of TTDDA-based analogue and much higher than that of D400-based counterpart owing to the difference in crosslinking density caused by the steric hindrance effect of the bridging structure on the polymerization of benzoxazine monomers. In addition, all the polybenzoxazines exhibit thermally induced shape memory effect. In each of the two series of polybenzoxazines, the shape recovery rate and ratio of D400-based polybenzoxazine are respectively close to those of D230-based counterpart and higher than those of TTDDA-based analogue due to the difference in network architecture.

Bio-based polybenzoxazines as an efficient coatings to protect mild steel surfaces from corrosion

New types of mono and bi-functional benzoxazine monomers were synthesized using cardanol (C) and 4-aminobenzonitrile (abn), p-phenylediamine ( ppda) along with paraformaldehyde. The synthesized benzoxazine monomers structure was elucidated by 1H, 13C-NMR and FTIR spectroscopic techniques. The polymerization temperature (Tp) of C-abn and C- ppda are noticed at 280oC and 237oC, respectively. It was also noticed that bi-functional benzoxazine (C- ppda) possesses lower curing temperature than mono-functional benzoxazine (C-abn). The ring opening polymerization of benzoxazine was confirmed by FTIR spectroscopy. Thermal analyses indicate that, benzoxazine [poly(C- ppda)] possesses higher thermal stability than poly(C-abn). The surface roughness of the benzoxazine coated MS specimen was analysed by atomic force microscope. The values of water contact angles obtained for poly(C-abn) and poly(C- ppda) are 145o and 148o, respectively. It was noticed that the mild steel specimen coated with bio-based benzoxazine C-abn exhibit excellent resistance to corrosion.

Structurally Designed Imine Skeletal Pyrenyl Pendant Pyridine Core Polybenzoxazine nSiO2/PBZ Hybrid Polymer Nanocomposites

Novel polybenzoxazine-silica (nSiO2/PBZ) hybrid nanocomposites were designed and synthesized using carbazole terminal pyrenyl pyridine core imine skeletal benzoxazine monomer (PYCBZ) and nanosilica (nSiO2) through in situ sol-gel method. The FT-IR and Raman spectral studies ascertained the formation of nanosilica reinforced polybenzoxazine hybrid nanocomposites. The nSiO2/PBZ hybrid nanocomposites exhibited excellent thermal stability and higher char yield than that of neat PBZ. The elevation in glass transition temperature of the nanocomposites was evidenced by the limited motion of the polymeric network with the introduction of nanosilica particles in the PBZ matrices. The hydrophobic nature of a less polar nSiO2 in the composites zipped the water uptake behaviour of (nSiO2/PBZ) hybrid nanocomposites to low percentage. The shift in the absorption peak reveals that the nanosilica particles were successfully incorporated through thermal ring opening polymerization of benzoxazine. The homogeneous reinforcement of nSiO2 particles retains the fluorescent properties of polybenzoxazine. The uniform molecular level dispersion of nano SiO2 onto polybenzoxazine networks were confirmed from transmission electron microscope and scanning electron microscope images.

Development of sustainable and antimicrobial film based on polybenzoxazine and cellulose

A new class of bio based polymer blends have been prepared from a modified chitosan based benzoxazine precursor (E-ch) and amino cellulose (AC). AC was derived from cellulose with excellent film-forming, biocompatibility and biodegradability property. E-ch was synthesized from eugenol, modified chitosan and paraformaldehyde. The chemical structure was confirmed by FT-IR and 1H NMR analyses. Bio films were prepared by mixing E-ch and AC with diluted acetic acid, in different ratios. These films were further cross-linked by applying heat, via ring-opening polymerization of benzoxazine without any curing agent. FT-IR and DSC were used to study the effects of AC on E-ch to form cross-linked network polymer films [poly(E-ch)/AC]. Hydrogen bonding interactions were found to exist between poly(E-ch) and AC. These kinds of interactions considerably improve the mechanical and thermal properties and char yield of the polymer films. Additionally, these biofilms; poly(E-ch) and poly(E-ch)/AC have been examined for bio-activity with S. aureus. It is confirmed that these bio-films are effective in inhibiting bio-film related infection. In a similar way, both the bio-films act against C. albicans and thus avoid the formation of mycological infection. These results expose that poly(E-ch) and AC bio-films are capable to act as anti-microbial and anti-fungal agents.

Resveratrol-based tri-functional benzoxazines: Synthesis, characterization, polymerization, and thermal and flame retardant properties

A series of thermally stable resveratrol-based tri-functional benzoxazine resins have been synthesized using resveratrol, different amines (aniline, 4-chloroaniline and 3-aminophenylacetylene) and paraformaldehyde. The molecular structures of these benzoxazines have been characterized by 1H and 13C NMR spectroscopy and FT-IR spectroscopy. The assignments for the characteristic protons and carbons in oxazine rings are confirmed using two-dimensional (2D) NMR techniques, including 1H–1H NOESY and 1H–13C HMQC. Moreover, the ring-opening polymerization of benzoxazines is studied using in situ FT-IR and differential scanning calorimetry (DSC), and the thermal stability and the flammability of the polybenzoxazines are also investigated by thermogravimetric analysis (TGA) and micro-scale combustion calorimetry (MCC), respectively. In addition to the advantages of lowest melting and polymerization temperatures amongst these resveratrol-based, tri-functional benzoxazines, the corresponding polybenzoxazine derived from benzoxazine containing acetylene shows highest thermal stability with a Tg temperature higher than 350 °C, initial degradation temperature at 10% weight loss at 465 °C, and char yield of 74% at 800 °C in nitrogen atmosphere. Furthermore, this polybenzoxazine also exhibits exceptionally low heat release capacity (30.7 J g−1 K−1) and total heat release value (6.0 kJ/g).

Studies on the ring-opening polymerization of benzoxazines: Understanding the effect of the substituents

A wide set of differently substituted 3-phenyl-3,4-dihydro-2H-1,3-benzoxazine derivatives (models of thermosetting benzoxazine resins) were synthesized and their polymerization temperature was studied using Differential Scanning Calorimetry (DSC). The effect of the electronic properties of different substituents in different positions of the alkoxyphenyl ring on the polymerization temperature was analyzed by the Hammett equation. A non-linear Hammett plot was obtained indicating a change in the polymerization mechanism. Based on these results, different ring-opening polymerization (ROP) mechanisms are proposed to operate depending on the electronic character of the substituents. Thus, the previously unpredictable dependence of the polymerization temperature with the electronic character of the substituents in the alkoxyphenyl ring can be now understood and even advanced for future developments.

Copolymerization of mono and difunctional benzoxazine monomers with bio-based phthalonitrile monomer: Curing behaviour, thermal, and mechanical properties

The eugenol based phthalonitrile (EPN) monomer was successfully copolymerized with mono and difunctional benzoxazine (P-a and BA-a) monomers via concerted catalysis polymerization. The loading of EPN in benzoxazine monomers was varied from 10 to 40 wt% and impacts of loading on thermal, thermomechanical and mechanical properties were studied. The FTIR analysis confirmed that both poly(P-a/EPN) and poly(BA-a/EPN) copolymers can be completely cured without the addition of curing additive. The addition of the bio-based EPN monomer enhanced the curing peak temperatures and reduced the curing reaction enthalpies. Initially, OH groups were produced from the oxazine ring opening polymerization of benzoxazine and they enhanced the curing of EPN. The thermal stabilities, as well as the stiffness and Tg of the copolymers, were much higher as compared to the neat polymers. Highest values were seen on the 40 wt% loading of EPN monomer in the copolymers. Moreover, the difunctional benzoxazine based copolymer showed higher enhancements in the properties as compared to the mono-functional benzoxazine based copolymer. The decline was seen in the flexural properties as EPN monomer contains the flexible chain in the structure. The morphological changes supported all the claims for the copolymers. The prepared copolymers can be used as a high performance thermosetting resin.

SYNTHESIS AND CHARACTERIZATION OF MONOFUNCTIONAL BENZOXAZINE FROM CARDANOL

A novel thermoplastic polybenzoxazine was synthesized based on agrochemical renewable cardanol–a by–product of cashew nut shell liquid (CNSL). A solventless synthesis of monofunctional benzoxazine monomer based on cardanol, aniline and paraformaldehyde was carried out. The liquid benzoxazine monomer was characterized by 1HNMR and FTIR spectroscopy. Curing characteristics at different temperatures were studied and monitored by differential scanning calorimeter (DSC). The appearance of two exothermic peaks associated with reaction of double bonds of the aliphatic side–chain and ring opening polymerization of benzoxazine. High thermal stability of the polymer sample was confirmed by thermogravimetric analysis (TGA).

Preparation and characterization of a novel benzoxazines/bismaleimide/2,2′-diallylbisphenol A blend with multiphase structures

Novel benzoxazine (BOZ)/bismaleimide (BMI)/2,2′-diallylbisphenol A (BA), with a multiphase structure, was successfully prepared under the catalysis of methyl p-toluenesulfonate (PTSM) through reaction-induced phase separation. The curing reaction of BOZ with BMI and ring-opening polymerization of BOZ under the catalysis of PTSM were studied by Fourier transform-infrared spectroscopy and differential scanning calorimetry analyses, respectively. Mechanical measurements, thermogravimetric analysis, and microanalyses were conducted to assess the toughness and morphology of the composite. The reaction between BOZ and 4,4′-bismaleimidodiphenyl methane (BDM) occurs at a relatively high temperature. The ring-opening reaction of BOZ starts at a low temperature of 100°C because of the catalysis of PTSM. The BOZ/BDM/BA system with an appropriate amount of BOZ significantly improves the impact strength and flexural strength compared with those of the BA/BDM resin. The BOZ/BDM/BA system with PTSM also features high impact strength and flexural strength. Scanning electron microscopy images and energy-dispersive spectroscopy results show that BOZ-rich phase is dispersed in BDM-rich phase in the BOZ/BDM/BA system with PTSM. Thermogravimetric data show that the BOZ/BDM/BA blend with a multiphase structure exhibits superior thermal resistance to those of the BOZ/BDM/BA and BA/BDM resins. The formation mechanism of the ternary system under the catalysis of PTSM is elucidated with Gibbs free energy theory.

Carbon Aerogels with Excellent CO2 Adsorption Capacity Synthesized from Clay-Reinforced Biobased Chitosan-Polybenzoxazine Nanocomposites

The present study reports for the first time the use of biobased chitosan-polybenzoxazine (CTS-PBZ) as a precursor for high CO2 adsorbing carbon aerogels (CAs). Montmorillonite (MMT) is used to reinforce the CTS-PBZ aerogel. MMT-CTS-PBZ nanocomposite aerogels are synthesized using the freeze-drying technique and then cross-linked via ring-opening polymerization of benzoxazine followed by carbonization at 800 °C. Polybenzoxazine improves the structural stability for removing CO2 from the environment even at a high pressure. The properties of polymeric and nanocomposite aerogels have been evaluated using X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The microstructure of the CAs is characterized by N2 adsorption–desorption measurements. The CAs exhibit mesoporous materials with pore sizes in the range of 2–7 nm and high BET surface area. The total pore volume of CAs is as large as 0.296 cm3 g–1, and the maximum BET surface area is 710 m2 g–1. Breakthrough curves of CO2 adsorption show high CO2 adsorption capacity at ambient conditions and excellent CO2 adsorption–desorption reversible performance with a maximum of 5.72 mmol g–1. Adsorption isotherms and thermodynamic properties of CO2 adsorption are described.

Arbutin-based benzoxazine: en route to an intrinsic water soluble biobased resin

A novel benzoxazine monomer containing a carbohydrate moiety was synthesized using a solventless approach from the reaction of arbutin, a naturally occurring phenolic compound, furfurylamine and formaldehyde. The chemical structure of this fully bio-based benzoxazine monomer was confirmed by 1H NMR and FTIR. Its polymerization has been investigated and monitored by DSC showing the ring opening polymerization of benzoxazine functions with a network densification thanks to the reaction of the furan group. The high hydroxyl content of the monomer allows its easy solubilisation in water paving the way to a wide range of possible “environmentally friendly” applications especially in the fields of coatings, paintings and adhesives.

Design and Development of Allyl Terminal Triaryl Pyridine Core Skeletal Modified Benzoxazines Based Polybenzoxazine-Silica (PBZ-SiO2) Hybrid Nanocomposites.

A series of skeletal modified novel allyl terminal benzoxazines (BZ-als) have been successfully designed and developed using triaryl pyridine core diamines via conventional one-pot Mannich reaction. The polybenzoxazine-silica (PBZ-SiO2) nanocomposites were prepared by thermal ring-opening polymerization of benzoxazines with different weight percentages of 3-methacryloxypropyltrimethoxysilane through in-situ sol-gel method. The formation of hybrid nanocomposites was confirmed by FT-IR. The substantial enhancement in the glass transition temperature was remarked for PBZ-SiO2 hybrids than their respective neat PBZ systems. The dielectric constant of the nanocomposites was found decreased with an increment in the silica content. The shift in the characteristic absorption/emissions corresponding to the neat PBZs toward lower wave-length ascertains the successful formation of PBZ-SiO2 nanocomposites. The discernible phase behaviour observed morphological studies reveals the molecular-level dispersion of silica particles over the organic networks.

Thiol reactive polybenzoxazine precursors: A novel route to functional polymers by thiol-oxazine chemistry

Thermally activated ring opening polymerization of benzoxazines plays an important role in the fabrication of high performance phenolic thermosets with enhanced thermal and mechanical properties. In the present work, a novel synthetic strategy based on 1,3-benzoxazine-thiol ring opening reaction for the functionalization of polymers is reported. For this purpose, thiol reactive main chain benzoxazine polymer (PBZ) was synthesized by the reaction of bisphenol-A, 1,6-diaminohexane and paraformaldehyde in toluene:methanol mixture (2:1, v:v) following the monomer synthesis procedure. The obtained polybenzoxazine precursor was then reacted at room temperature with various thiol compounds, namely thiophenol, 2-ethanethiol and 1-butanthiol in CH3OH/CHCl3 for 24h. Successful incorporation of the thiol compounds to PBZ was confirmed by spectral and molecular weight characterizations. The thermally activated curing of the remaining benzoxazine rings occurs at lower temperatures than that reported for the conventional benzoxazines. The described strategy represents a unique approach not only for the polymer modifications but also for the preparation of high performance thermosets.

Study on the Ring-Opening Polymerization of Benzoxazine through Multisubstituted Polybenzoxazine Precursors

To discuss the mechanism of ring-opening polymerization (ROP) of benzoxazine, a bisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-0M), o-dimethylbisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-2M), and o-dimethylbisphenol A/o-tetramethyldiaminodiphenylmethane-based polybenzoxazine precursor (PBz-6M) were prepared. Among the polybenzoxazine precursors, free ortho positions to the O of oxazine are available for PBz-0M. No free ortho or para position to the O of oxazine is available for PBz-2M, but free ortho position to the N of oxazine is available. No free ortho positions to the O or N of oxazine are available for PBz-6M. According to DSC, IR, and thermal analysis, we found that the ROP of PBz-2M can be carried out even though no free ortho or para position to the O of oxazine is available. We conclude that the ROP is carried out through the ortho position to the N of oxazine and propose a reaction mechanism to explain the polymerization.

A novel high efficiency benzophenone based polymeric photoinitiator from ring-opening polymerization of benzoxazine

A novel polymeric photoinitiator based on benzoxazine was synthesized by introducing 4-hydroxy benzophenone, diglycolamine and paraformaldehyde into the macromolecular chain. Its molecular structure was characterized by 1H NMR, FTIR, and UV-Vis spectroscopy. Photopolymerization of tripropylene glycol diacrylate and trimethylolpropane triacrylate initiated by polybenzoxazine, benzoxazine, and benzophenone was studied by real time FTIR spectroscopy. The results obtained are discussed.

Promoting effect of thiophenols on the ring‐opening polymerization of 1,3‐benzoxazine

ABSTRACTThiophenol and p‐nitrothiophenol were evaluated as promoters for the ring opening polymerization of benzoxazine. The ring‐opening polymerization of p‐cresol type monofunctional N‐phenyl benzoxazine 1a with 10 mol % of thiophenols proceeded at 150 °C, leading to the high conversion of 1a more than 95% within 5 h, whereas the polymerization of 1a without thiophenols did not proceed under the same conditions. The promotion effect of the thiophenols on curing of bisphenol‐A type N‐phenyl benzoxazine 1b was also investigated. In the differential scanning calorimetric (DSC) analysis of the polymerization of 1b at 150 °C without using any promoters, an exothermic peak attributable to the ring‐opening reaction of benzoxazine was observed after 8 h. In contrast, in the DSC analysis of the polymerization of 1b with addition 20 mol % of p‐nitrothiophenol, an exothermic peak was observed within 2 h, to clarify the significant promoting effect of p‐nitrothiophenol. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2523–2527

Mechanistic Pathways for the Polymerization of Methylol-Functional Benzoxazine Monomers

The polymerization mechanism of methylol-functional benzoxazine monomers is reported using a series of monofunctional benzoxazine monomers synthesized via a condensation reaction of ortho-, meta-, or para-methylol–phenol, aniline, and paraformaldehyde following the traditional route of benzoxazine synthesis. A phenol/aniline-type monofunctional benzoxazine monomer has been synthesized as a control. The structures of the synthesized monomers have been confirmed by 1H NMR and FT-IR. The polymerization behavior of methylol monomers is studied by DSC and shows an exothermic peak associated with condensation reaction of methylol groups and ring-opening polymerization of benzoxazine at a lower temperature range than the control monomer. The presence of methylol group accelerates the ring-opening polymerization to give the ascending order of para-, meta-, and ortho-positions in comparison to the unfunctionalized monomer. Furthermore, rheological measurements show that the position of methylol group relative to b...

Mechanistic Studies on Ring-Opening Polymerization of Benzoxazines: A Mechanistically Based Catalyst Design

Ring-opening polymerization behavior of a model p-cresol–aniline-based benzoxazine under various conditions was investigated in detail by 1H NMR analysis in deuterated DMSO. An improved mechanistic scheme was proposed to explain the observed experimental results. In light of this mechanistic scheme, several bifunctional catalysts were studied, and lithium iodide was found to be a very active and effective catalyst. Lithium cation is the Lewis acid part and effectively coordinates with oxygen or nitrogen atoms and promotes ring-opening of benzoxazines. Iodide ion is the nucleophilic part with good leaving ability and can react with the ring-opened imminium intermediates to prevent its rapid recombination with the phenolate.

Preparation and Properties of Polybenzoxazinepoly(dimethylsiloxane-co-diphenylsiloxane) Hybrids as High Performance Polymers

Polybenzoxazine, poly(B-a), was hybridized with polysiloxanes by synchronizing two reactions; ring-opening polymerization of benzoxazine (B-a) and the sol—gel process of diethoxysilanes. As diethoxysilanes, mixtures of diethoxydimethylsilane and diethoxydiphenylsilane in various ratios were used to prepare polysiloxane copolymers, poly(dimethylsiloxane- co-diphenylsiloxane), P(DMS/DPS). The effect of diphenylsiloxane (DPS) content of polysiloxane copolymer on the optical, mechanical, and thermal properties of the hybrids was studied. The progress of the sol—gel process was confirmed by IR, 1H-NMR and size exclusion chromatography. Opaque poly(B-a)-P(DMS/DPS) hybrid films were obtained at high dimethylsiloxane (DMS) content corresponding to the phase separation. The domain size of the polysiloxane was evaluated from the scanning electron microscope. Meanwhile, transparent hybrid films were obtained at high DPS content, corresponding to the homogeneous phase as observed from the scanning electron microscope. The hybrid films revealed higher tensile strength and elongation at break than pristine poly(B-a) as a function of DPS content. Dynamic viscoelastic analyses of the hybrids at high DMS content revealed two glass transition temperatures ( Tg) corresponding to polysiloxane and poly(B-a) components, while one Tg was observed at high DPS content. Thermogravimetric analysis of the hybrids revealed that the thermal stability of the poly(B-a)-polysiloxane hybrids was higher than pristine poly(B-a) depending on the DPS content.