Thermal Ring-opening Polymerization Research Articles

Green and Heavy-Duty Anticorrosion Coatings: Waterborne Epoxy Thermoset Composites Modified through Variation of Zinc Dust Loading and Incorporation of Amine-Capped Aniline Trimer and Graphene Oxide.

In this study, an array of environmentally friendly and heavy-duty anticorrosion composite coatings were prepared. The synthesis involved amine-capped aniline trimer (ACAT) produced by an oxidative coupling reaction and graphene oxide (GO) prepared based on Hummer's method, and later, the waterborne epoxy thermoset composite (WETC) coatings were prepared by thermal ring-opening polymerization of EP 147w, a commercial waterborne epoxy resin, in the presence of ACAT and/or GO with zinc dust (ZD). A synergistic effect was observed by replacing a significant amount of the ZD loading in the WETC by simultaneously incorporating a small amount of ACAT and GO. The electrochemical corrosion measurements of the as-prepared WETC coatings indicated that incorporating 5% w/w ACAT or 0.5% w/w GO separately replaced approximately 30% w/w or 15% w/w of the ZD, respectively. Moreover, the WETC coatings containing 5% w/w ACAT and 0.5% w/w GO simultaneously were found to replace 45% w/w of the ZD. A salt spray test based on ASTM B-117 also showed a consistent trend with the electrochemical results. Incorporating small amounts of ACAT and GO in WETC coatings instead of ZD not only maintains the anticorrosion performance but also enhances adhesion and abrasion resistance, as demonstrated by the adhesion and abrasion tests.

Card-bisphenol based bio-silica reinforced poly(urethane-co-benzoxazine) foam for an electrical insulation

Agricultural waste by-products such as cashew nut shell liquid and rice husk ash were utilized for the syntheses of card-bisphenol (C) and precipitated bio-silica (S), respectively. A hydroxyl terminated card-bisphenol based benzoxazine resin (CHB) was synthesized and then converted it into soft-foam namely benzoxazine-co-urethane pre-polymer (CHB-UF) by polymerizing with hexamethylene diisocyanate (HMDI) in the absence of any catalysts or foaming agents. Subsequent thermal ring opening polymerization of CHB-UF at 200 °C provides poly(benzoxazine-co-urethane) hard-foam (PCHB-UF) with little shrinkage. Similarly, different weight ratios of precipitated bio-silica (0–15 wt%) reinforced bio-based PCHB-UF hard-foam composites (PCHB-UFS) were prepared to utilize them for high-k dielectrics and hydrophobic applications. The foam microstructure was ascertained through the field emission scanning electron microscopy (FE-SEM). The reinforcement of bio-silica into the CHB-UF foam increases the value of dielectric constant according to the increase in weight percentage concentration, which might be due to the reduction in volume of voids. The neat PCHB-UF possesses the value of dielectric constant of 7.04 with lower value of dielectric loss of 0.01. Similarly, the values of dielectric constant and dielectric loss of 15 wt% bio-silica reinforced composites (PCHB-UFS15) are 10.1 and 0.08 respectively. The PCHB-UFS15 has shown hydrophobic nature with the value of water contact angle of 135°. Data obtained from different studies suggest that the bio-foam composites obtained from sustainable sources can be considered as an efficient dielectric materials used for electronics insulation.

High-Thermal Stable Epoxy Resin through Blending Nanoarchitectonics with Double-Decker-Shaped Polyhedral Silsesquioxane-Functionalized Benzoxazine Derivatives.

A series of di-functional benzoxazine (BZ) monomers was synthesized, specifically the double-decker silsesquioxane (DDSQ) cage structure (DDSQ-BZ). Comparative analyses were conducted between DDSQ-BZ monomers and the most commonly utilized bisphenol A-functionalized bifunctional benzoxazine (BPA-BZ) monomer. DDSQ-BZ compounds possess better thermal properties such as high char yield and high thermal decomposition temperature (Td10) after thermal ring-opening polymerization (ROP) because the inorganic DDSQ cage nanostructure features a nano-reinforcement effect. In addition, blending inorganic DDSQ-BZ compounds with epoxy resin was explored to form organic/inorganic hybrids with enhanced thermal and mechanical properties following thermal ROP. The improvement in mechanical properties is primarily attributed to the network structure formed by the cross-linking between DDSQ-BZ and the epoxy resin during thermal ROP, as well as hydrogen bonding interactions formed between the hydroxyl groups generated during thermal ROP and the Si-O-Si bonds in the DDSQ structure.

Construction of three-dimensional porous organic polymers with enhanced CO2 uptake performance via solid-state thermal conversion from tetrahedral benzoxazine-linked precursor

Porous organic polymers (POPs) with three-dimensional (3D) linkages have drawn great interest due to their potential applications in separation, adsorption, and sensing fields. Herein, a new 3D benzoxazine (BZ)-linked porous organic polymer (TPM-BZ-Py POP) was synthesized by linking a tetrahedral benzoxazine (TPM-BZ-Br4) with tetraethynylpyrene (Py-T) via Sonogashira coupling. Specifically, the synthesis of the tetrahedral benzoxazines with four oxazine rings in a single monomer involved the utilization of Schiff base formation, NaBH4 reduction as well as Mannich condensation reactions. To confirm the chemical structure of the benzoxazine monomers and their corresponding polybenzoxazines, Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and carbon nuclear magnetic resonance (13C NMR) spectroscopy techniques were employed. The pore volume and specific surface area of the 3D TPM-BZ-Py POP were determined through N2 adsorption/desorption isotherms, and they were found to be 0.52 cm3/g and 185 m2/g, respectively. In addition, the solid-state chemical transformation occurred during thermal ring-opening polymerization (ROP), and the resulting 3D poly(TPM-BZ-Py) POP displayed higher CO2 capture ability (1.81 mmol/g) compared with TPM-BZ-Py POP (0.60 mmol/g) at room temperature. Such enhancement observed in poly(TPM-BZ-Py) POP was proposed to be caused by the formation of phenolic units and Mannich bridges within the polymer network by taking into consideration the structural transformation during the ring-opening polymerization (ROP). The functionalities in poly(TPM-BZ-Py) have great potential to interact with CO2 molecules through strong intermolecular hydrogen bonding or acid/base interactions, which further supports the benefit of incorporating oxazine rings into POP frameworks.

The Preparation of Electrolyte Hydrogels with the Water Solubilization of Polybenzoxazine.

Polybenzoxazine (PBZ) exhibits excellent heat resistance, and PBZ derivatives have been designed and synthesized to achieve high performance. However, the application range of PBZ is limited by the strong interactions between molecular chains and its low solubility in organic solvents, thereby limiting its processability. This study focused on the benzoxazine structure as the molecular backbone of new hydrogel materials that can be applied as electrolyte materials and prepared functional gel materials. Here, we prepared hydrogels by water-solubilizing PBZ derivatives, which typically exhibit low solubility in organic solvents. Although studies on the hydrophilization of PBZ and its complexation with hydrophilic polymers have been conducted, no studies have been performed on the hydrogelation of PBZ. First, the phenol in the organic solvent-insoluble PBZ thin film obtained after the thermal ring-opening polymerization of the monomer was transformed into sodium phenoxide by immersion in a NaOH aqueous solution to water-solubilize it and obtain a hydrogel thin film. Although the hydrogel thin film exhibited low mechanical strength, a free-standing hydrogel film with improved strength was obtained through the double network gelation method with an acrylamide monomer system. The physical properties of the polymer composite hydrogel thin film were evaluated. The ionic conductivity of the hydrogel thin films was in the order of 10-4 S cm-1, indicating the potential of PBZ as an electrolyte hydrogel material. However, improving its ionic conductivity will be undertaken in future studies.

Design and Synthesis of Amphiphilic Graft Polyphosphazene Micelles for Docetaxel Delivery.

The structural versatility of polydichlorophosphazene derived from the inestimable possibilities to functionalize the two halogens, attached to each phosphazene main chain unit, attracted increasing attention in the last decade. This uncountable chemical derivatization is doubled by the amphiphilic roleplay demonstrated by polyphosphazenes containing twofold side-chained hydrophilic and hydrophobic moieties. Thus, it is able to encapsulate specific bioactive molecules for various targeted nanomedicine applications. A new amphiphilic graft, polyphosphazenes (PPP/PEG-NH/Hys/MAB), was synthesized via the thermal ring-opening polymerization of hexachlorocyclotriphosphazene, followed by a subsequent two-step substitution reaction of chlorine atoms with hydrophilic methoxypolyethylene glycol amine/histamine dihydrochloride adduct (PEG-NH2)/(Hys) and hydrophobic methyl-p-aminobenzoate (MAB), respectively. Fourier transform infrared spectroscopy (FTIR) and 1H and 31P-nuclear magnetic resonance spectroscopy (NMR) have been used to validate the expected architectural assembly of the copolymer. Docetaxel loaded micelles based on synthesized PPP/PEG-NH/Hys/MAB were designed by dialysis method. The micelles size was evaluated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The drug release profiles from the PPP/PEG-NH/Hys/MAB micelles were established. In vitro cytotoxicity tests of PPP/PEG-NH/Hys/MAB micelles loaded with Docetaxel revealed that designed polymeric micelles exhibited an increased cytotoxic effect on MCF-7 cells.

Highly Thermally Stable, Reversible, and Flexible Main Chain Type Benzoxazine Hybrid Incorporating Both Polydimethylsiloxane and Double-Decker Shaped Polyhedral Silsesquioxane Units through Diels-Alder Reaction.

This work synthesizes a new bifunctional furan derivative (PDMS-FBZ) through a sequence of hydrosilylation of nadic anhydride (ND) with polydimethylsiloxane (PDMS), reaction of the product with p-aminophenol to form PDMS-ND-OH, and its subsequent Mannich reaction with furfurylamine and CH2 O. Then, the main chain-type copolymer PDMS-DABZ-DDSQ is prepared through a Diels-Alder (DA) cycloaddition of PDMS-FBZ with the bismaleimide-functionalized double-decker silsesquioxane derivative DDSQ-BMI. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy confirm the structure of this PDMS-DABZ-DDSQ copolymer; differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA) reveal it to have high flexibility and high thermal stability (Tg = 177 °C; Td10 = 441 °C; char yield = 60.1 wt%); contact angle measurements reveal a low surface free energy (18.18 mJ m-2 ) after thermal ring-opening polymerization, because the inorganic PDMS and DDSQ units are dispersed well, as revealed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This PDMS-DABZ-DDSQ copolymer possesses reversible properties arising from the DA and retro-DA reactions, suggesting its possible application as a functional high-performance material.

Mussel‐Inspired, Underwater Self‐Healing Ionoelastomers Based on α‐Lipoic Acid for Iontronics

Weak adhesion and lack of underwater self-healability hinder advancing soft iontronics particularly in wet environments like sweaty skin and biological fluids. Mussel-inspired, liquid-free ionoelastomers are reported based on seminal thermal ring-opening polymerization of a biomass molecule of α-lipoic acid (LA), followed by sequentially incorporating dopamine methacrylamide as a chain extender, N,N'-bis(acryloyl) cystamine, and lithium bis(trifluoromethanesulphonyl) imide (LiTFSI). The ionoelastomers exhibit universal adhesion to 12 substrates in both dry and wet states, superfast self-healing underwater, sensing capability for monitoring human motion, and flame retardancy. The underwater self-repairabilitiy prolongs over three months without deterioration, and sustains even when mechanical properties greatly increase. The unprecedented underwater self-mendability benefits synergistically from the maximized availability of dynamic disulfide bonds and diverse reversible noncovalent interactions endowed by carboxylic groups, catechols, and LiTFSI, along with the prevented depolymerization by LiTFSI and tunability in mechanical strength. The ionic conductivity reaches 1.4 × 10-6 -2.7 × 10-5 S m-1 because of partial dissociation of LiTFSI. The design rationale offers a new route for creating a wide range of LA- and sulfur-derived supramolecular (bio)polymers with superior adhesion, healability, and other functionalities, and thus has technological implications for coatings, adhesives, binders and sealants, biomedical engineering and drug delivery, wearable and flexible electronics, and human-machine interfaces.

Reprocessable Polybenzoxazine Thermosets with High Tgs and Mechanical Strength Retentions Using Boronic Ester Bonds as Crosslinkages.

In order to obtain reprocessable polybenzoxazine thermosets with high heat resistance and mechanical strength retentions, network structures without irreversible parts were constructed via crosslinking benzoxazine oligomers using boronic ester cross-linkers. Firstly, the benzoxazine monomer containing carbon–carbon double bonds was synthesized via the Mannich reaction. After thermal ring-opening polymerization, the benzoxazine oligomer containing carbon–carbon double bonds (OBZ) was yielded. Through the thiol-ene click reaction of the OBZ and dithiol cross-linker bearing boronic ester bonds, the polybenzoxazine thermosets using boronic ester bonds as crosslinkages (OBZ-BDB) were successfully synthesized. The structures of OBZ and OBZ-BDB were characterized by SEC, 1H NMR, and FT-IR measurements. Reprocessing experiments showed that OBZ-BDB has remarkable reprocessability. The retention rates of the tensile strengths through three generations of reprocessing were 98%, 95%, and 84%, respectively. Meanwhile, OBZ-BDB cross-linked by boronic ester bonds had brilliant thermal properties. The Tg of the original OBZ-BDB was 224 °C. With the increase of the reprocessing generations, the Tgs basically remained unchanged.

Cover Image, Volume 139, Issue 21

This cover image by Takashi Doi and co-authors shows the development of a novel, non-reversible surface relief (SR) system using photoreactive bis- or tris-cinnamate derivatives containing thermally curable benzoxazine moieties. Not only does their photodimerization and thermal ring-opening polymerization contribute to this phenomenon, but also local mass transfer driven by concentration gradient of unreacted molecules. This image depicts that the thermally stable SR structure can be formed easily through a twostep development-free process of ultraviolet exposure under a photomask and subsequent heat treatment. This system is promising an alternative technology to photolithography. DOI: 10.1002/app.52173

Metal Complexes of the Porphyrin-Functionalized Polybenzoxazine.

New porphyrin-functionalized benzoxazine (Por-BZ) in high purity and yield was synthesized in this study based on 1H and 13C NMR and FTIR spectroscopic analyses through the reduction of Schiff base formed from tetrakis(4-aminophenyl)porphyrin (TAPP) and salicylaldehyde and the subsequent reaction with CH2O. Thermal properties of the product formed through ring-opening polymerization (ROP) of Por-BZ were measured using DSC, TGA and FTIR spectroscopy. Because of the rigid structure of the porphyrin moiety appended to the benzoxazine unit, the temperature required for ROP (314 °C) was higher than the typical Pa-type benzoxazine monomer (ca. 260 °C); furthermore, poly(Por-BZ) possessed a high thermal decomposition temperature (Td10 = 478 °C) and char yield (66 wt%) after thermal polymerization at 240 °C. An investigation of the thermal and luminescence properties of metal–porphyrin complexes revealed that the insertion of Ni and Zn ions decreased the thermal ROP temperatures of the Por-BZ/Ni and Por-BZ/Zn complexes significantly, to 241 and 231 °C, respectively. The metal ions acted as the effective promoter and catalyst for the thermal polymerization of the Por-BZ monomer, and also improved the thermal stabilities after thermal polymerization.

Cyclic (phenylene sulfide) treated carbon fiber for facile preparation of high performance PEEK based anti-wear composites

Improving the surface activity of carbon fiber (CF) via a sizing agent is an efficient approach to enhance the performance of CF reinforced polymer composites. However, the conventional sizing agents usually readily decompose at high temperature. In this work, a novel heat resistant sizing agent is coated directly on the CF surface by in-situ thermal ring-opening polymerization of cyclic phenylene sulfide oligomers (CPS) in air. Studies indicate that the novel sizing agent is oxygenated poly (phenylene sulfide) (PPS), possessing high temperature stability. Properties of the PPS sized CF (CF-CT) filled PEEK based composite are investigated by using the original CF/PEEK composite as a reference. The results reveal that the CF-CT composite exhibit significantly higher tensile strength, lower average friction coefficient and wear rate when CF content exceeds 20 wt%. It is reasonably ascribed to the stronger interface interaction between the PPS sized CF and PEEK, which effectively promotes the enhancement effect of CF in the composite material.

Synthesis, spectral, and thermal studies on eugenol based hydrophobic polybenzoxazines

ABSTRACT A new class of the thermally stable, hydrophobic, sustainable, and renewable eugenol (E)-based benzoxazines is synthesized using 4-aminobenzonitrile (abn) isophoronediamine (ipda) separately. Polybenzoxazines were formed by thermal ring-opening polymerization of respective monomers and confirmed by spectral analyses. TGA results indicated that the residual char yield value obtained at 850°C for poly(abn) and poly(ipda) are 36% and 32%, respectively. Poly(E-abn) showed better thermal stability than poly(E-ipda) due to the presence triazine cross-linkages in the matrix system. The water contact angle studies showed that poly(E-ipda) possesses better hydrophobic character than poly(E-abn) due to the presence of isophorone (alicyclic) group and allyl substitutions.

Solid state chemical transformations through ring-opening polymerization of ferrocene-based conjugated microporous polymers in host–guest complexes with benzoxazine-linked cyclodextrin

Herein, we describe two ferrocene-derived conjugated microporous polymers (FFCCMPs) prepared through Sonogashira couplings of 9-ferrocenylidene-2,7-dibromo-9H-fluorene (FFC) with tetraethynylpyrene (Py-T) and tetrakis(4-ethynylphenyl)ethene (TPE-T), respectively, and their properties determined using various spectroscopic techniques. These two FFC CMPs formed inclusion complexes (ICs) with a benzoxazine-linked β-cyclodextrin (CD-BZ), with host-guest interactions occurring between the ferrocene and β-CD units. We used Fourier transform infrared spectroscopy, X-ray diffraction, two-dimensional nuclear Overhauser enhancement NMR spectroscopy, solid-state 13C CP/MAS NMR spectroscopy, and thermogravimetric analysis to characterize these FFCCMP/CD-BZ ICs. The BZ units in the FFCCMP/CD-BZ ICs underwent thermal ring-opening polymerization to form new Mannich bridges featuring both intermolecular (OH···O) and intramolecular (OH···N) hydrogen bonds; the resulting TPE-FFCCMP/poly(CD-BZ) and Py-FFCCMP/poly(CD-BZ) ICs exhibited outstanding thermal stability, with the latter having the higher CO2 uptake ability (1.42 mmol g–1) and capacitance (46 F g–1 at 0.5 A g–1).Background: Host–guest complexes formed from macrocyclic hosts possessing hydrophobic cavities such as cyclodextrins (CDs) and various guest molecules have been studied widely for their fascinating characteristics. The interaction of ferrocene-containing CMPs with hydrophobic cavities of CDs to form inclusion complexes materials with excellent thermal properties and these materials can be used in different fields including energy storage and gas capture.Methods: Two ferrocene-based fluorene CMPs—TPE-FFC CMP and Py-FFCCMP—through Sonogashira couplings of 9-ferrocenylidene-2,7-dibromo-9H-fluorene (FFC), as the main block, with tetraethynylpyrene (Py-T) and tetrakis(4-ethynylphenyl)ethene (TPE-T), were successfully synthesized through Sonogashira couplings. Then, the two FFC CMPs were attached to a benzoxazine-functionalized β-cyclodextrin (CD-BZ) through host-guest complexation. The successful synthesis of two FFC CMPs and FFCCMP/CD-BZ ICs was investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, two-dimensional nuclear Overhauser enhancement NMR spectroscopy, solid-state 13C CP/MAS NMR spectroscopy, and thermogravimetric analysis.Significant Findings: The present work offers a new and facile strategy for the preparation CMPs/CD inclusion complexes through supramolecular chemistry and using these materials as an electrode in the energy devices and CO2 uptake.

Bisbenzylidene cyclopentanone and cyclohexanone-functionalized polybenzoxazine nanocomposites: Synthesis, characterization, and use for corrosion protection on mild steel

In this study, we synthesized and investigated bisbenzylidene cyclopentanone and cyclohexanone-functionalized polybenzoxazine nanocomposites as anti-corrosion coatings. The chemical structures of CP-BZ and CH-BZ were confirmed using Fourier transform infrared (FTIR) spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy. Differential scanning calorimetry (DSC) revealed that the thermal polymerization temperature of the uncured CH-BZ (198 °C) was significantly lower than that of the monomer 3-phenyl-3,4-dihydro-2H-benzoxazine (263 °C). We used DSC and FTIR spectroscopy to study the curing behavior of these monomers. The degradation temperature of poly(CH-BZ) (326 °C) was higher than that poly(CP-BZ) (249 °C), based on thermogravimetric analysis. We used solution dispersion and thermal ring-opening polymerization to prepare a new class of bisbenzylidene-based polybenzoxazine (PBZ; CP-BZ or CH-BZ) composites with epoxidized soybean oil (E-SBO; 10 or 20 wt%) and E-SBO/bentonite (nanoclay; 3 or 5 wt%) for use as corrosion-protection coatings for mild steel (MS). We employed salt-spray and electrochemical measurements to investigate the influence of the epoxy and nanoclay contents, respectively, on the corrosion-resistance of these coatings. A 20 wt% epoxy content in the PBZ/E-SBO coatings provided corrosion-resistance superior to those of pure PBZs. Furthermore, the addition of 20 wt% E-SBO and 3 wt% of nanoclay decreased the corrosion rate by one order of magnitude (2.653 × 10−3 mm year–1) when compared with that of pure poly(CH-BZ) (1.292 × 10-2 mm year–1) and two orders of magnitude when compared with blank(MS) (1.094 × 10-1 mm year–1) with protection efficiency (98.16 %), revealing markedly increased barrier properties of the composite coatings towards corrosive species. Thus, these materials function as excellent corrosion-resistance coatings for MS.

A tetraphenylethylene-functionalized benzoxazine and copper(II) acetylacetonate form a high-performance polybenzoxazine

In this study, we synthesized TPE-BZ, a new tetraphenylethylene (TPE)-functionalized benzoxazine (BZ) monomer (1,1,2,2-tetrakis(3-phenyl-3,4-dihydro-2H-benzo[e] [1,3]oxazin-6-yl)ethane), through reduction of the Schiff base formed from TPE-4OH–CHO (1,1,2,2-tetra(3-formyl-4-hydroxyphenyl)ethylene) and aniline and subsequent reaction with paraformaldehyde. Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry confirmed the structure of the TPE-BZ monomer. We used differential scanning calorimetry (DSC), FTIR spectroscopy, and thermogravimetric analysis (TGA) to investigate the thermal ring opening polymerization (ROP) and thermal stability of the TPE-BZ monomer after thermal treatment at various temperatures (from room temperature to 250 °C). The TGA profiles revealed that thermal treatment at 250 °C under a N2 atmosphere gave a poly(TPE-BZ) that possessed excellent thermal stability and a high char yield (435 °C, 64.3 wt%). Furthermore, water contact angle measurements of the poly(TPE-BZ) obtained at 210 °C for 2 h indicated a relatively low surface free energy (18.6 mJ m−2), presumably because of strong intramolecular hydrogen bonding between the phenolic OH groups and the N-Mannich bridge in the polybenzoxazine matrix. We also employed DSC, FTIR spectroscopy, and TGA to examine the specific interactions in TPE-BZ/Cu(acac)2 complexes. DSC analysis revealed that blending the TPE-BZ monomer with various weight ratios of Cu(acac)2 lowered the thermal curing temperature of TPE-BZ from 250 to 239 °C, accompanied by a lower curing temperature at 189 °C. Using the Kissinger method, the activation energy of the TPE-BZ/Cu(acac)2 complex (127 kJ mol−1) was lower than that of the TPE-BZ monomer (141 kJ mol−1), suggesting that Cu(acac)2 functioned as a catalyst that initiated ROP of the oxazine units, while providing a product that retained high thermal stability.

Reprocessable polybenzoxazine thermosets crosslinked by mussel-inspired catechol-Fe3+ coordination bonds

The traditional thermosets cannot be reprocessed, which causes serious environmental pollution and resource waste. The catechol-Fe3+ coordination bonds existing in marine mussel byssal cuticle provide a reversible crosslinking structure for reprocessable thermosets. A reprocessable polybenzoxazine thermoset (PBOZ-dopa45-Fe3+) by catechol-Fe3+ coordination bonds was synthesized successfully based on mussel-inspired chemistry and benzoxazine chemistry. Firstly, benzoxazine monomers containing carboxyl groups were synthesized. Secondly, polybenzoxazine with carboxyl groups was obtained through thermal ring-opening polymerization. And then catechol groups were grafted onto the pendant groups of polybenzoxazine. Finally, the reprocessable polybenzoxazine was obtained by catechol groups coordinating with Fe3+. The structure of polybenzoxazine was characterized by NMR, FTIR and SEC measurements. The formation of reversible crosslinked network composed of catechol-Fe3+ coordination bonds is confirmed by UV–Vis absorbances, system color changes, and dissolution states in methanol solutions of different pH. Reprocessing experiments indicate that the reversible catechol-Fe3+ coordination bonds endow remarkable reprocessability of cured resin. Dynamic mechanical measurements and thermogravimetric measurements show that the PBOZ-dopa45-Fe3+ can still maintain excellent thermal properties. Cross-linking by catechol-Fe3+ coordination bonds provides a new way for the preparation of reprocessable thermosets.

Chitosan/polybenzoxazine/clay mixed matrix composite aerogels: preparation, physical properties, and water absorbency

The present study reports development of chitosan/polybenzoxazine/clay mixed matrix composite aerogels (MMCAs) using freeze-drying of various sodium montmorillonite (Na-MMT) colloidal dispersions in chitosan/benzoxazine polymers blend in aqueous solution. Thermal treatment of aerogels leads to produce crosslinked MMCAs. The microstructure characteristics of the MMCAs were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal properties of the MMCAs were evaluated by thermal gravimetric analysis (TGA). The obtained MMCAs have ultra-low densities within a very small range (<0.073 g/cm3) and exhibited that their porosities higher than 93%. The effect of Na-MMT on thermal properties of the chitosan/polybenzoxazine MMCAs was investigated. The onset decomposition temperatures were significantly enhanced with clay-loading, implying the superior thermal stability of these composites. Due to the thermal ring-opening polymerization of benzoxazine, the effect of heat treatment on dimensional stability and water absorption of the chitosan/benzoxazine-based aerogels have also been investigated, which have not yet been studied elsewhere. The results demonstrated that polymerized aerogels are highly stable not only in neutral water, but also in acidic medium. The obtained MMCAs exhibit to be efficient water absorbents. The results revealed that the MMCAs are relatively high water absorption up to 2900 wt% at ambient conditions.

Thermal Stability Change of Insoluble Sulfur by a Heat Treatment and Its Mechanism Study.

Insoluble sulfur (IS), used as a vulcanizing reagent of rubber, is prepared by the thermal ring-opening polymerization of sulfur (S8). Enhancing its thermal stability and content ratio (yield) is important for the industrial production of IS. The post-heating process at a high temperature of 70 or 90°C of the mixture of IS and S8 enhanced the thermal stability of IS and reduced the yield of IS. Further, the process at 30°C enhanced its thermal stability and maintained its yield. Since the thermal stability of IS is considered to be closely related to the chain length of polymer sulfur, a method for determining the chain length of IS was investigated by quantifying the amount of electron spin of radicals from sulfur, estimated from electron spin resonance (ESR) measurements. We confirmed that the long-period post-heating process at 30°C induced high thermal stability without reducing the yield of IS due to growth of the sulfur polymer chains.

Benzoxazine monomers containing triphenylimidazole: Polymerization of monomers and properties of polybenzoxazines

In this study, two novel benzoxazine monomers containing triphenylimidazole (TBZ) and triphenylimidazolium (MTBZ) moieties are synthesized and fully characterized. The thermal ring-opening polymerization process of the two monomers is monitored by the 1H NMR and GPC analyses, which demonstrates that such a polymerization proceeds through a rearrangement of ketal-type linkage in the main chain into Mannich-type polymer along with the fast increasing in molecular weight. The structures of the triphenylimidazole-containing polybenzoxazines, poly-TBZ and poly-MTBZ, are verified by 1H NMR and FT-IR spectroscopies, and the thermal and mechanical properties of such polybenzoxazines are investigated by TGA and DMA analyses. Owing to the good solubility of poly-TBZ and poly-MTBZ in common organic solvents, poly-TBZ can be easily converted into poly-MTBZ through a facile post-modification approach. More importantly, the poly-TBZ shows the acid-dependent spectral properties due to formation of amine salts, whereas poly-MTBZ can be used as a chemodosimeter for the detection of Ag+, which exhibits high selectivity, good linearity and naked-eye distinguishable color change. This strategy can be utilized to prepare triphenylimidazole-containing polybenzoxazines with good solubility and tunable spectral properties, thereby extending their functionalities and applications.