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Activated carbon (AC) was treated with nitric acid, hydrogen peroxide, and urea. The obtained products were then used as supports for the preparation of palladium/activated carbon (Pd/AC) catalysts. The characterization results revealed that the AC textural structure and surface properties were selectively modified via different treatments, and the surface functional groups of the supports could affect the particle size, dispersion, and chemical states of the Pd nanoparticles. The surface of the urea-treated AC (AC-U) contained more carbonylic groups and nitrogenous species but fewer hydroxylic and carboxylic groups than the surfaces of the ACs subjected to other treatments. Consequently, in the hydrogenation synthesis of meropenem, the Pd/AC-U catalyst provided a higher meropenem yield and lower amounts of impurities in the meropenem product than the other catalysts. The nitrogenous groups not only provided efficient anchoring sites for Pd nanoparticles, improving the reaction activity, but also reduced the side reactions, decreasing the impurity content in the product.

The present work reports the construction of polypyrrole (PPy) hydrogels directly with the as-synthesized PPy nanotubes (PPy-NTs) through infiltration of poly vinyl alcohol (PVA) and poly(acrylic acid) (PAA) solutions. This method avoids the time-consuming purification of the in-situ formed conducting hydrogels and provides a facile way to incorporate nanostructured conducting polymers evenly into the hydrogel matrix. PPy-NTs/PVA/PAA hydrogels with dual cross-linking networks were prepared through multiple freeze-thawing cycles followed by coordination with iron (III) ions. The tensile and compression strength of the hydrogels are ca. 54 kPa and 160 kPa, respectively. The PPy-NTs/PVA/PAA hydrogel was mainly electronic conducting dominated, and it showed the highest conductivity of ca. 0.04 S/cm after swollen in 0.2 M HCl (with 2wt% of PPy-NTs). Benefited from the high aspect ratio and high conductivity of PPy nanotubes, it is probable to mediate the PPy content and the integrity of the electronic conducting pathways to develop high-performance hydrogel materials used as strain sensors.

Introducing B–O bonds into traditional polymer networks can produce polymer materials with novel structures and unique properties. In particular, the higher bond energy of B–O bonds can significantly improve the thermal stability of the polymers, meanwhile, their sensitivity to heat and media can realize the reprocessing and recycling of the polymer materials with cross-linked structures. In recent years, cross-linked polymers based on B–O bonds with different structural characteristics and functions have been developed, which has greatly enriched the field of boron-containing crosslinked polymers. Over the past decade, our research has focused on boric/boronic acid and their derivative modified phenolic resins, and a series of ablative resistant polymers and dynamic crosslinked polymers with excellent properties have been developed. In this review, the progress of research on cross-linked polymers based on B–O bonds with different structures and functions, and the synthesis, structure and properties are highlighted. The basic principles for improving the thermal stability of the polymers and achieving the regeneration of crosslinked polymers based on the B–O bonds are elaborated. Future challenges and development trends for cross-linked polymers based on B–O bonds are also critically discussed.

Boron-containing polymers have many applications resulting from their prominent properties. Organoboron species with reversible B-O bonds have been successfully employed for the fabrication of various self-healing/healable and reprocessable polymers. However, the application of the polymers containing boronic ester or boroxine linkages is limited because of their instability to water. Herein, we report the hydrolytic stability and dynamic covalent chemistry of the nitrogen-coordinating cyclic boronic diester (NCB) linkages, and a new class of vitrimers based on NCB linkages is developed through the chemical reactions of reactive hydrogen with isocyanate. Thermodynamic and kinetic studies demonstrated that NCB linkages exhibit enhanced water and heat resistance, whereas the exchange reactions between NCB linkages can take place upon heating without any catalyst. The model compounds of NCBC-X1 and NCBC-X2 containing a urethane group and urea group, respectively, also showed higher hydrolytic stability compared to that of conventional boronic esters. Polyurethane vitrimers and poly(urea-urethane) vitrimers based on NCB linkages exhibited excellent solvent resistance and mechanical properties like general thermosets, which can be repaired, reprocessed, and recycled via the transesterification of NCB linkages upon heating. Especially, vitrimers based on NCB linkages presented improved stability to water and heat compared to those through conventional boronic esters because of the existence of N → B internal coordination. We anticipate that this work will provide a new strategy for designing the next generation of sustainable materials.

The mechanical durability, especially wear-resistance seriously restricts the practical application of superhydrophobic surfaces. Lots of efforts have been put to improve the mechanical durability of superhydrophobic surfaces. However, due to the lack of a standard evaluation criterion, it is inaccurate to evaluate the mechanical durability of superhydrophobic surfaces by merely comparing the abrasion cycles or distance it can stand before losing superhydrophobicity. In this paper, the wear-resistance of superhydrophobic surfaces against sandpaper abrasion was evaluated based on a typical resin-hydrophobic filler formula. The mechanical strength, coefficient of friction and evolution of superhydrophobicity with growing abrasion cycles of as-prepared superhydrophobic surfaces were carefully studied by considering the hydrophobic filler sizes. In spite that superhydrophobic surfaces can all be achieved with hydrophobic fillers from nano-meter scale particles to micro-meter scale clusters at a certain content, the larger the filler size, the better the wear-resistance. For superhydrophobic coatings with a given surface roughness, its superhydrophobicity can be preserved when abraded against items which were rougher than coating itself. Furthermore, drag reduction performance of the developed superhydrophobic surfaces was evaluated against the polymer solution. This work will provide useful clues for establishing the standard to evaluate the wear-resistance of superhydrophobic coatings.

Developing recyclable, self-healable, and highly malleable thermosets is one of the keys to relieve environmental pollution and meet our increasing demand for "greener" materials. Hindered urea bonds (HUBs) have been successfully incorporated in preparing dynamic covalent networks with those desirable properties. However, one key drawback is the low thermal stability and poor mechanical performance of previously reported systems. In this work, we demonstrated that the incorporation of aromatic moiety-containing diamine-based HUBs can greatly improve the thermal and mechanical performance of the poly(urethane-urea)s (PUUs) while still maintaining the desirable recycling, self-healing, and reprocessing properties. Studies on model compounds revealed the origin of the thermal stability and demonstrated the dynamic property. The aromatic-containing diamine-based HUBs were then used to prepare a series of catalyst-free PUUs with improved thermal and mechanical properties. The dynamic HUBs significantly reduced the relaxation timescale and allowed the PUU networks to be recycled multiple times. The healed and recycled PUUs regained most of the mechanical strength and integrity of the original material. Therefore, this unique and simple approach is expected to open up new avenues to design PUUs with optimal performance for various applications.

Easily oxidized group of traditional phenolic resin (PF) results in poor oxidation resistance at high temperature, which is unable to satisfy the requirements of advanced aerospace vehicles for high-performance application, especially ablation resistance. In order to improve the oxidation resistance of PF, a SiO2/RGO binary hybrid nanomaterial assisted anti-oxidation for PF was designed. Here, we reported a simple sol-gel process and high temperature reduction for synthesis of dispersed SiO2 nanoparticles on graphene (G-S). The designed structure of G-S was confirmed by FTIR, XRD, SEM and TEM. Introduction of G-S into PF (P-G-S) was beneficial to enhancement of oxidation resistance in whole temperature range (0–1000 °C). P-G-S-3 (3 wt.% of G-S) exhibits both lower thermal oxidative decomposition rate and higher termination temperature of thermal oxidative decomposition (increase from about 750 °C up to 900 °C) than those of neat PF in air. In addition, P-G-S-3 decomposed by thermal oxidation in air (at 557 °C, weight loss> 30 wt.%) later than neat PF (at 519 °C, weight loss> 20 wt.%). What's more, compared to the collapse of skeleton structure and few residual fragments of neat PF, P-G-S-3 showed greater oxidation resistance which resulted in the retention of a large number of aromatic C-C, methylene and different kinds of ether bond at temperature from 550 °C to 700 °C by FTIR and XPS. The section of P-G-S-3 expresses skin lamination that can act as a barrier to slow down the diffusion of oxygen into resin matrix. And SiO2 on the surface protected the matrix continually as indicated from the SEM analysis.

Resin based superhydrophobic coatings are effective to construct robust superhydrophobic surfaces on large scale without limitation of substrates. However, for most of the common resin based superhydrophobic coatings, it is inevitable to deteriorate environmental or health problems due to release of a large amount volatile solvents. In this work, a kind of water-based organic/inorganic hybrid consisted of acrylate copolymers and superhydrophobic silica nanoparticles were synthesized. The highly water-repellent silica nanoparticles were successfully involved into the aqueous dispersion of acrylate copolymers without additional surfactants. The as-synthesized hybrids simultaneously retain the excellent film-forming property of acrylate resins and amplify the contributions of low surface energy nanoparticles to the superhydrophobicity. Robust superhydrophobic coatings (CA > 160°, CA

Boron carbide (B4C) is an attractive material for numerous applications including vehicle armor, cutting tools, blasting nozzles, and abrasive powder, owing to its extreme hardness, high melting point, high Young’s modulus, and excellent thermoelectric properties. However, the application of B4C is limited by the high-temperature synthesis process. The present work aims to explore a low-temperature manufacturing process for synthesizing B4C with a small amount of free carbon. Poly(resorcinol borate) with an aromatic structure and high char yield was chosen as the aromatic polymeric precursor. A combination of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy was performed to investigate the influences of the reaction temperature and holding time on the changes in the precursor microstructure. The results indicate that the rod-like structure of crystalline B4C is successfully synthesized at 600 °C, and the free carbon can be reduced to about 0.8 wt% in the final product. This is because the pyrolysis temperature controlled the carbon content of the B4C, which led to an enlarged contact domain between B2O3 and carbon, and a relatively low-temperature synthesis of B4C.

The objective of the current work is to synthesize novel boron-containing polymers with excellent thermal resistance, and reveal the structure and the reason for the high char yield. Thus, poly (dihydroxybiphenyl borate) (PDDB) with a more rigid molecular chain, was successfully synthesized using 4,4′-dihydroxybiphenyl and boric acid. Structural characterizations of the prepared PDDB were performed via NMR, FTIR, XPS, and XRD analyses. The results reveal that PDDB consists of aromatic, Ph O B and B O B structures as well as a small number of boron hydroxyl and phenolic hydroxyl groups. PDDB shows good solubility in strong polar solvents, which is of great importance for the modification of thermosetting resins. TGA combined with DSC were employed to evaluate the thermal properties of PDDB, and increases in the glass transition temperature (Tg) and char yield were observed with increased boron content. Tg and char yield of PDDB (800 °C, nitrogen atmosphere) reached up to 219 °C and 66.5%, respectively. PDDB was extensively characterized during pyrolysis to reveal the high char yield of PDDB. As briefly discussed, the boron oxide and boron carbide that formed during pyrolysis play a crucial role in the high char yield of PDDB, which reduces the release of volatile carbon dioxide and carbon. This research suggests that PDDB has great potential as a novel modified agent for the improvement of the comprehensive performance of thermosetting resins to broaden their applicability in the field of advanced composites.

The cross-linked structures of traditional thermosetting resins not only endow carbon fibre-reinforced polymer (CFRP) composites with excellent performance, but also make their efficient recovery a real challenge. The goal of this paper is to create reversible thermosets using dynamic boronic ester bonds as cross-links in replacement of traditional irreversible covalent bonds. Specifically, we used phenylboronic acid (PBA) to crosslink traditional novolac resin (NR), namely PBNR. By combining the reprocessability of thermoplastics with the desirable chemical and thermal stability of conventional thermosets, controlled degradation and full recycling of cross-linked resins and CFRP composites under ambient conditions were realized through a gentle alcoholysis process. The PBNR/CFRP composites fabricated by hot-pressing showed excellent mechanical properties. The multiple recycling experiments revealed near-total recovery of the clean fibre cloth and binder materials, which could be reprocessed into composites with similar mechanical properties to fresh materials. Dynamic boronate bonds have been demonstrated to open up a new pathway for full recycling of thermosetting resins and CFRP composites, which has a great impact in aeronautical, astronautics, adhesive, coating, or electronic packaging fields.

The cross-linked polystyrene (PS) are commonly used plastic materials, however, the greater brittleness and the difficulties in recycling severely limit their applications. In this work, we provide a new strategy for the crosslinking of PS based on the nitrogen-coordinating cyclic boronic ester (NCB) linkages. PS vitrimers are synthesized from PS with hydroxyl groups and isocyanate-terminated NCB oligomer. Incorporating NCB linkages can greatly improve the solvent resistance, thermal stability and mechanical properties of PS without sacrificing its dielectric properties. PS vitrimers exhibit rapid stress relaxation and improved creep resistance due to the stable NCB linkages. PS vitrimers were able to withstand multiple reprocessing cycles via the exchange reactions of NCB linkages without catalyst. The recycled PS vitrimers were shown to regain the structural integrity, mechanical strength and dielectric properties as the original. The glass fibre reinforced PS vitrimer composites were prepared to explore the application in copper clad manufacture, which showed good mechanical properties and can be conveniently recycled to resin solution and clean glass fibre. This work provides a new strategy for the development of the green dielectric polymer materials for copper clad laminates, and may serve as a guide for rational design of dynamic materials based on general-purpose plastics.

With the rapid development of the fifth-generation mobile communication, stringent requirements have been put forward for the dielectric properties of polymer-based copper-clad laminates. However, thermally and mechanically robust materials with low dielectric loss (Dr) are very scarce. Herein, we propose a simple method to prepare cyclic polyolefin (COC)/polystyrene vitrimers (PSVMs) from semi-interpenetrating polymer networks with low Dr. The topological rearrangement of PSVMs caused by the transesterification of nitrogen-coordinating cyclic boronic ester (NCB) linkages under heat helped uniformly disperse the COC in the PSVM. As a result, the COC-PSVM and its quartz glass fiber reinforced COC-PSVM composites exhibited excellent thermal, mechanical, and dielectric properties. Specifically, the dynamic reversibility of the NCB linkages under heat facilitated the complete recovery of the COC-PSVM composites. This study provides a new strategy for the preparation of resin matrix with low Dr for printed circuit boards, which is conductive to reducing the environmental pollution from e-waste.

Phenylboronic acid (PBA) modified phenolic resin (PBPR) is one of the most important phenolic resins (PR) due to its good processability and high char yield. However, the pyrolysis mechanisms of PR and PBPR still remain poorly understood, which imposes limits on the synthesis, development and application of these materials. In this work, the pyrolysis process of PBPR has been studied through novolac resin (NR) and PBA crosslinked NR (PBNR) at high temperatures, and the reasons for the high char yield of PBPR were explored, as well. According to the results, the pyrolysis of NR begins with the cleavage reaction of the covalent single bonds in the molecular backbone. The release of volatile organic compounds (VOCs) such as monophenols and bisphenols formed by the cleavage of C—C single bonds is the major cause of the decreased char yield of NR at elevated temperatures. Meanwhile, increasing NR molecular weight and crosslinking NR could reduce the formation probability of VOCs, which is beneficial to obtaining the high char yield resin. In PBPR, the boronic ester linkages make the formation of VOCs more difficult and contribute to the high char yield of resin. The present work provides guiding significance for deeply understanding the pyrolysis mechanism of PR and PBPR to ensure their high thermal stability and char yield at high temperatures.

A fully recyclable phenolic resin (TDNR) with dynamic cross-linked network was facilely prepared without any catalyst using commercial novolac and toluene diisocyanate by forming hindered urethane bonds. TDNRs not only preserved the intrinsic mechanical strength of classic phenolic resin, but also displayed efficient stress relaxation behaviour. The bulk TDNR exhibited a glass transition temperature up to 200 °C and tensile strength up to 55 MPa. Both the chemical and mechanical features of TDNR were effectively preserved after five recycle circulations. The recyclable TDNR can serve as a universal resin matrix either for molding compounds which are easily repairable or for fiber-reinforced composites with good processibility. The exchangeable network of TDNR ensures good processibility for long fiber prepregs, which are suitable for hand molding and reshape of composites. By utilizing a “simple” chemistry mechanism, the close-loop recycle of phenolic resin with high working temperature and good mechanical properties are successfully achieved.

In this study, phenolic resin (PR) that is modified with poly (dihydroxybiphenyl borate) (PDDB) is prepared. The chemical structure, thermal properties and structural evolution at high temperatures for cured PDDB/PR are investigated to understand the reason for high char yields. The results show that the phenylborates that are formed during curing are attributed to the high char yield of PDDB/PR (74%, 800 °C). Phenylborates can block parts of phenolic hydroxyl and effectively inhibit their thermal decomposition reaction. By tracking the resin residue and volatiles that are released during pyrolysis, it is determined that boron oxide and boron carbide are formed via pyrolysis and help reduce carbon loss. Introducing PDDB into PR improves the graphitization degree and graphite crystallites of carbonization products, which promotes the formation of ordered glassy carbon during pyrolysis. Additionally, the CF/PDDB/PR composites show excellent mechanical and ablation properties due to good interfacial adhesion between resin matrix and fibre. This method makes it possible for using PDDB to enhance the thermal properties of the polymer with lower cost, more functions and broader applications.

In this work, 2-phenyl-1,3,2-benzenediolborane (PBO) with a five-membered cyclic phenylboronate structure was introduced into a benzoxazine resin to improve its processability and thermal resistance. PBO catalysis was beneficial at accelerating the curing reaction of PBO modified BZ (PBOZ), leading to a lower exothermal peak temperature (186 °C) and a shorter gelation time than for BZ (238 °C). PBO was successfully incorporated into the network structure of the BZ and phenylboronate structures formed during curing. The TGA and DMA results showed that the cured PBOZs exhibited excellent thermal stability and a higher crosslinking density than cured PR. The char yield and glass transition temperature of the cured PBOZ increased by 12% and 38 °C, respectively, relative to the BZ. The interlaminar shear strength of the high silica glass cloth-reinforced PBOZ composites were higher than that of the BZ composite due to the good interfacial adhesion properties between the PBOZ and glass fiber observed in the SEM results. This work provides a new strategy to develop BZs with excellent comprehensive properties.

Novel epoxide-terminated hyperbranched polyurethanes (EHPU) with different epoxy values were prepared through functionalization of hyperbranched polyurethane with glycidol. Fourier transformed infrared (FTIR) and nuclear magnetic resonance analyses were conducted and confirmed the successfully synthesis of EHPU. Differential scanning calorimetry measurements were carried out for thermal and kinetic studies of EHPU and benzoxazine (BZ) hybrid. Specifically, through kinetic study using advanced isoconversional method, it was found that EHPU can catalyze the polymerization of BZ oligomers when degree of curing is below 0.7 with the apparent activation energy dropped 8.3 kJ/mol. Whereas, the epoxide groups of EHPU can join the curing reaction of BZ at 180 °C, which was further confirmed by FTIR analysis.

In this work, poly (bisphenol A borate) (PBAB), which has excellent thermal resistance and a high char yield, was synthesized via a convenient A 2 + B 3 strategy by using bisphenol A (BPA) and boric acid (BA). The chemical reaction between BPA and BA and the chemical structure of PBAB were investigated. The results demonstrate that PBAB consists of aromatic, Ph–O–B and B–O–B structures, as well as a small number of boron hydroxyl groups and phenolic hydroxyl groups. The thermal properties of PBAB were studied by DMA and TGA. The results indicate that the glass transition temperature and char yield are gradually enhanced by increasing the boron content, where the char yield of PBAB at 800 °C in nitrogen (N 2 ) reaches up to 71.3%. It is of particular importance that PBAB show excellent thermal resistance in N 2 and air atmospheres. By analysing the pyrolysis of PBAB, the high char yield of PBAB can be attributed to the formation of boron oxide and boron carbide at high temperatures, which reduced the release of volatile carbon dioxide and improved the thermal stability of the carbonization products. This study provides a new perspective on the design of novel boron-containing polymers and possesses significant potential for the improvement of the comprehensive performance of thermosetting resins to broaden their applicability in the field of advanced composites.

Supercapacitors fill the gap between batteries and conventional solid state and electrolytic capacitors. Polypyrrole (PPy) is a very important electrode material for supercapacitors. However, the repeated volume changes usually damage PPy structure and result in PPy poor stability during a long-term charging/discharging process. PPy/carbon material composites were prepared to overcome the defects of pure PPy electrodes, and significant enhancement for the specific capacitance, charging/discharging rate and electrodes stability was demonstrated thereafter. The development of composite electrodes based on PPy and carbon materials is reviewed in this paper.

Boron-containing organic polymers have excellent thermal stability and flame retardancy. Hyperbranched polymers, in which boron atoms are introduced in the form of borates, exhibit superior performance and have more applicability. This work focuses on the boron-containing polymer poly (resorcinol borate) (PRB). The chemical structure of PRB and its structural evolution at high temperatures are investigated in order to clarify the reason for its high char yield. The results indicate that the molecular skeleton of PRB mainly consists of aromatic structures, borates, B O B structures, and a small number of boron hydroxyl groups and phenolic hydroxyl groups. During pyrolysis, boron oxide is formed by the cleavage of borate O C bonds at about 400 °C. This process effectively avoids the formation and release of volatile carbon dioxide, reducing carbon loss. A large fraction of the carbon from aromatic rings is converted to amorphous carbon via pyrolysis, which possesses higher thermal stability. These results can guide the design and synthesis of novel boron-containing polymers and can provide a strategy for modifying the thermal properties of phenolic resins in order to broaden their applicability in the field of ablative-resistant composites and coatings.

In this paper, the initial stage of the pyrolysis process of phenolic resin has been simulated by ReaxFF (reactive force field) molecular dynamics simulation under various temperatures (3000 K, 3250 K, and 3500 K), to study the behavior of phenolic hydroxyl groups and to investigate the correlation between the production of small oxygen-containing molecules (including H 2 O, CO and CO 2 ) and the quantity of hydroxyl radicals at different temperatures. We observed that the highly active phenolic hydroxyl groups would be easily turned into phenoxyl radicals and hydroxyl radicals in primary evolution. And also, both the phenoxyl radicals and hydroxyl radicals had remarkable impact on the following process of pyrolysis in secondary evolution: the formation of phenoxyl radicals reduced the stability of the benzene ring and damaged backbone of phenolic resin accompanying with the release of CO molecules, while the hydroxyl radicals increased the amount of CO molecules and converted them into CO 2 molecules, to reduce the char yield of resin. We found that the amounts of small oxygen-containing molecules increased with the rise in the number of phenolic hydroxyl groups or the rise in the temperature. We also found that both the two evolution modes of phenolic hydroxyl groups (I. phenolic hydroxyl groups – phenoxyl radicals – small oxygen-containing molecules; II. phenolic hydroxyl groups – hydroxyl radicals – small oxygen-containing molecules) can reduce the thermal stability of the backbone of resin. The negative effect of phenolic hydroxyl groups on the thermal stability of cured PR is valuable to the understanding of the pyrolytic process and char forming mechanism, and also the enhancement of the thermal stability of resin.

Density functional theory (DFT) was applied to model molecules of phenolic resin (PR) to interpret the relationship between the atomistic structure and thermal properties of the cured PR. The bond dissociation energy (BDE) of C–C (in methylene bridges) and C–O bonds (in hydroxyls), as well as the Fukui function of hydroxyl, benzene and methylene groups, were calculated. The isomers of bisphenol-F and the methyl substituents have a slight effect on the BDEs of C–C and C–O bonds, while the oxidized structures, such as p-benzoquinone and aldehyde groups, lead to a drastic decrease in the C–C bond BDEs. The high reactivity of the carbon atoms in the benzene groups and the oxidized structures results in an increased possibility of being attacked by free radicals and protects the methylenes from being attacked, but it will also lead to ring-opening reactions and weight loss. These results provide a great opportunity to understand the relationship between the atomistic structure and the thermal stability of the cured PR, which plays a pivotal role in the design and optimization of thermal stable polymers.

Polypyrrole (PPy) synthesized by the oxidation of pyrrole with iron(III) chloride in the presence of sulfonic azo dyes exhibits fascinating nanometer-scale morphology and high conductivity, which are distinctly different from their counterparts prepared without dyes. The present work systematically studied the roles of sulfonic azo dye aggregates formed in acidic medium during the growth of PPy based on structural and elemental analysis. The formation of PPy nanostructures have been investigated by following the pH profile, by adjusting the precipitation rate of dye aggregates and by comparing the molecular structure of three azo dyes, viz. methyl orange, ethyl orange and Orange I. The results showed that the ethyl orange derived aggregates formed in iron(III) chloride solution and in hydrochloric acid solution had exactly the same structure as well as elemental composition. Aggregates derived from methyl orange formed in iron(III) chloride solution involved a trace amount of iron element. Orange I, another azo dye that can induce aggregates rapidly in iron(III) chloride solution, contributed negligibly to both the morphology and conductivity of PPy. The structure-directing effects of methyl orange/iron(III) complexes in directing PPy nanostructures seems to be unique and cannot be simply extended to other azo dyes, probably due to the dye interaction with iron ions.

In the present study, the density functional theory (DFT) was applied to investigate the influence of borate structure on the thermal stability of phenolic resin modified by boric acid (BPR) and phenylboronic acid (PBPR). The bond dissociation energy (BDE) and electronic structure, which represent the stability of chemical bonds and reactivity of functional groups respectively, were obtained with the BPW91, B3LYP, CAM-B3LYP and M06-2X method based on simplified models of BPR and PBPR. The BDE of B–O bond was higher than C–O and C–C bonds, which may contribute to the thermal stability of the resins. Moreover, the population analysis indicated that the formed borate structures from boric hydroxyls and phenolic hydroxyls could inhibit the active sites, such as phenolic hydroxyls and methylenes in PR. The inhibiting effect worked well in both BPR and PBPR, especially in the structures with eight-membered heterocycles formed by the borate and methylene bridges. These results provide useful clues for understanding the roles of borate structure in improving the thermal stability of PR, which are of practical importance in the design and optimization of thermal stable resins.

Benzoxazine resins (BZs) as a novel type of phenolic resin are high-performance matrix resin for advanced composites. Yet there still exist some deficiencies when used as ablative material in aerospace applications, such as high curing temperature and poor thermal stability. In the present study, the phenylboronic acid (PBA) modified BZs (PBBZs) exhibiting excellent processibilities and thermal properties were prepared by incorporating PBA into BZ. The viscosity, gel time and curing behaviors were examined to demonstrate that PBBZs possessed better processibilities than the BZ, representing the catalytic effect of PBA in this case. The incorporation of PBA accelerated the ring-opening polymerization of BZ, leading to the lower curing temperature. TGA results reveal that the cured PBBZs exhibit excellent thermal properties, where the char yield at 800 °C (nitrogen atmosphere) reaches 63.7% and is increased by 14.1 percentage points than that of BZ. The formed phenylboronates during curing act as additional cross-linking points and increase the cross-linking density of the cured resin, which results in the enhancement of the glass transition temperature of BZ ranging from 165 °C to 219 °C. This study provides a new vision for the preparation of high-performance matrix resin for ablative materials by introducing aryl-boron backbone.

Boron-containing phenolic resin (BPR) is a kind of the ablative resins with high-performance. Due to the lack of the exact knowledge concerning the pyrolysis mechanism of BPR, its development and application are greatly impeded. In the present paper, the chemical structure of the cured BPR and its structural evolution at high temperatures are investigated to clarify the reason for the high char yield of BPR. The results indicate that the high char yield of BPR is mainly attributed to the phenyl borates formed during curing, which can block parts of phenolic hydroxyl groups, and effectively inhibit their thermal decomposition reaction. Boron oxide is formed on the surface of carbonization products by the cleavage of O–C bonds from phenyl borates via pyrolysis, which avoids the release of volatile carbon dioxide and reduces the development of micro-structural defects of carbonization products. Introducing boron into PR improves the graphitization degree and graphite crystallites of carbonization products, which promotes the formation of a more ordered glassy carbon during pyrolysis. This study provides a new vision for the understanding of the high char yield of BPR, which makes it possible to develop a new ablative resin through molecular design.

A superhydrophobic (SH) surface is usually constituted by a combination of low surface energy substances and micro- and nanometer scale roughness structures. The latter, however, always have poor mechanical strength and require complicated fabrication procedures, seriously hindering the large-scale preparation and industrial application of SH surfaces. In this study, by introducing fluoroalkyl silane modified silica nanoparticles into hydroxyl acrylic resin using a simple spray-coating method, an SH acrylic polyurethane (SAPU) coating with good abrasion resistance and stable adhesion was obtained after cross-linking with polyisocyanate at room temperature. By virtue of the reaction between the silanol groups in silica NPs and the isocyanate groups in the curing agent, the hydrophobic silica NPs were stably anchored into the SAPU resin matrix while constructing hierarchical micro- and nanometer scale roughness structures on the coating surface. The dual characters ensure that the SAPU coating has a static water contact angle (CA) of >160°, a sliding angle of ∼10° and good mechanical properties, which exhibits CAs of >150° after wearing with sandpaper and maintains strong adhesion even after cross-cutting or impacting tests. Moreover, the SAPU coating retains an excellent water-repellent property after 12 h of immersion in hydrochloric acid with pH = 1, and can recover its water-repellent property after 12 h of immersion in sodium hydroxide solution with pH = 14 through hot air blowing. The facile spray-coating method as well as a mild room temperature curing process make this kind of SH coating especially suitable for non-wetting protection or modification of large-scale parts, providing a novel pathway for the development of a high performance SH surface.

Limited by the knowledge of the structure and pyrolysis mechanism of cured phenolic resin (PR), the influence of cross-link density (CLD) on the heat resistance of PR remains unclear. The objective of this work is to characterize the structure of PR and understand the relationship between structure and heat resistance. The CLD of cured PR is characterized by theoretical and experimental approaches based on the full understanding of the chemical structure. The influence of CLD on the heat resistance is studied by analyzing the pyrolysis behavior of cured PR, and the results reveal that cross-link can improve the thermal stability and char yield of cured PR simultaneously. A novel pyrolysis mechanism and a quantitative relationship between the CLD and residual weight of PR are proposed. The results of our paper provide a theoretical basis to develop resins with good heat resistance.

Purpose – This paper aims to disclose the evolution of pendulum hardness of two-component acrylic polyurethane coatings during the cure process and attempts to describe the quantitative relationship between pendulum hardness and curing time. These findings are helpful for the study of fast curing acrylic polyurethane coatings. Design/methodology/approach – The pendulum hardness method was used to monitor the hardness of two-component acrylic polyurethane coatings during curing. The quantitative relationship between pendulum hardness and curing time can be obtained with Avrami equation. Findings – The evolution of coating pendulum hardness can be divided into three stages. By using the Avrami equation that explained the influence of both the acid value and the curing temperature on the drying speed of hydroxyl acrylic resin, the evolution of coating pendulum hardness during curing can also be accurately described. Research limitations/implications – It should be noted that the physical meaning of the Avrami exponent, n, is not yet clear. Practical implications – The results are of great significance for the development of fast-curing hydroxyl-functional acrylic resins, with the potential to improve the drying speed of the coatings used in automotive refinish. Originality/value – It is novel to divide the pendulum hardness into three stages, and, for the first time, the Avrami equation is utilized to describe the evolution of coating pendulum hardness during curing.

Cross-linked polymers, such as phenolic resin and its composites are widely used in industrial practice, but the absence of clear understanding on their thermal expansion behaviors in glassy state limits their applications, especially in the occasions where dimensional accuracy are addressed. The coefficients of thermal expansion (CTEs) of cured phenolic resin and inorganic particles filled phenolic resin at glassy state at different temperatures are analyzed in this article. The results show that the CTEs of glassy cross-linked polymers change with temperature, and exhibit a strong dependence on the temperature. By modifying the state equation of linear amorphous polymer, the equation that can be used to quantitatively describe the temperature dependence of CTEs of cross-linked polymers is established. By analyzing the temperature dependence of CTE, an equation is proposed to predict the CTEs of filled phenolic resins with different filler loadings at a specific temperature. The results of this study have contributed to a better understanding of the thermal expansion behaviors of glassy cross-linked polymers, and are of great significance in industrial practice. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers

A postsynthetic self-assembly system was designed to investigate a construction process from suspended polyaniline (PANI) molecules to condensed aggregates. The conventionally synthesized PANI was dissolved in polar solvent and introduced into acidic medium with electrolytes similar to the aniline chemical oxidative polymerization (COP) medium. In this way, reaction interference that is usually encountered in the COP process could be avoided, and influences of medium conditions including organic electrolytes on the self-assembly behaviors of PANI were studied. It was discovered that, in a static aqueous medium with moderate pH and rich electrolytes, PANI molecules composed of bulk aggregates could self-assemble into well-dispersed nanoparticles with few structural changes. Electrostatic force is considered to dominate the self-assembly of PANI molecules as compared with other noncovalent interaction or the effect of soft templates such as ionic liquid and surfactant. The results are supposed to provide better understanding on the formation mechanism of micro/nanostructured PANI.

As far as the longitudinal relaxivity (r1) is concerned, gadolinium ions (Gd3+)-based MRI contrast agents modified by traditional carriers do not appear to be far superior to the clinically used Magnevist. In this study, a type of MRI contrast agent (Gd3+@CGO) possessing a significantly high r1 value was easily prepared using a carboxyl-functionalized graphene oxide (CGO) as a nanocarrier to directly interact with GdCl3·6H2O. With 2.8 wt% of Gd3+ loaded on CGO, the prepared Gd3+@CGO shows good dispersibility in water and possesses r1 of 63.8 mM−1 S−1, which is 14 times higher than that of Magnevist. It is exciting to note that Gd3+ anchored on CGO remains stable at least for one year, probably relying on the electrostatic adsorption and physical encapsulation effect of CGO towards Gd3+.

This work reports an aryl boron-containing phenolic resin (PR) exhibiting an extremely high thermal decomposition temperature and char yield and formed by reacting phenylboronic acid (PBA) with PR. DSC was used to study the curing behaviour of the PBA modified PR (PBPR). The structure and thermal properties of the cured PBPR were investigated by FTIR, XPS, 11 B NMR and TGA. Phenylboronates were formed during the curing of PBPR, which reduced the distance between benzene rings. The TGA indicates that the temperature with the maximum decomposition rate increased for the cured PBPR by 56 °C, and the charring yield increased by 13.4 per cent (800 °C, nitrogen atmosphere) relative to PR. FTIR, XPS, XRD, 11 B NMR and Raman analyses were used to study the structural evolution of the cured PBPR during pyrolysis. Boron oxide was formed during the char formation from the cleavage of B–C and B–O–C bonds via pyrolysis, which effectively avoided the release of volatile carbon oxides and retained the carbon. In addition, incorporating boron into the carbon lattice increases the crystallite height and decreases the interlayer spacing. These findings reveal that PBA exhibited obvious effects in improving the thermal stability and promoting the graphite crystallites of PR during carbonization.

Phenolic resins (PRs) play an important role in aerospace due to their low cost, outstanding chemical resistance, mechanical properties, thermal properties and ablative properties. However, the industrially produced PRs are often mixtures of polyphenolic compounds with different structures and molecular weights, among which the low molecular weight components are detrimental to the properties of PRs, especially the thermal stability. In this paper, the dihydroxydiphenylmethane (DHDM) contents in several typical industrial novolac resins (NRs) were measured by liquid chromatography and gel permeation chromatography, and the effect of DHDM content on the viscosity, curing process, glass transition temperature (Tg) and thermal stability of NRs was investigated. The results showed that a significant reduction in viscosity and Tg was observed for the NRs with higher DHDM content. The existence of DHDMs reduced the gel point and crosslinking density of the cured NRs by hexamethylenetetramine, leading to a significant decrease in the 5% weight loss temperature, the maximum weight loss temperature, as well as the char yield at 800 °C. Therefore, in addition to the free phenols, we should pay more attention to the DHDMs existed in the NRs. This study provides an important insight for NR manufacturers that the DHDM contents should be reduced through the proper control of process parameters to further expand their wider application scope.

Easily oxidized group and rigid structure of phenolic resin (PR) network can result in brittleness and low char yield at high temperatures, which limits the widespread applications of PR in harsh environment. Whilst organic-inorganic hybrid material, such as POSS-containing material was introduced to enhance PR, the microstructure and the thermo-mechanical properties of the hybrid material modified PR are not well understood. Therefore, in the work, a novel organic-inorganic hybrid networks (ENH) were prepared with epoxy-polyhedral oligomeric silsesquioxane (EPOSS) modified novolac phenolic resin (EN) and hexamethylenetetramine (HMTA) to further clarify the curing behavior and its relation to microstructure and the resulting thermal-mechanical properties. Here, the curing characteristics of ENH were discussed by usinag advanced isoconversional method and Fourier transform infrared spectroscopy (FTIR). It was revealed that a diversity of crosslinking networks was exhibited after curing ENH, including EPOSS-NR crosslinked, tethered structure, and self-polymerized structure of EPOSS as well as NH networks. When the substitution degree of EPOSS is relatively low, EPOSS serves as a junction point to further improve the crosslinking density of ENH networks, leading to better thermo-mechanical properties, thermal stability and tensile property as well as lower dielectric properties. However, as the self-polymerization of EPOSS increased, the NH network was dramatically disrupted and the thermo-mechanical properties, thermal stability and tensile property of ENH were deteriorated.

In the present study, a novel aryl-boron-containing phenolic resin named as PBPR has been synthesized from phenol and formaldehyde in the presence of phenylboronic acid. The chemical structure of the PBPR was confirmed by Fourier transform infrared, nuclear magnetic resonance and X-ray photoelectron spectroscopy. The molecular weight, viscosity and curing behavior were examined to demonstrate that PBPRs have better processability than common boric acid-modified phenolic resin. The thermal stability and fracture toughness of the cured PBPRs were greatly enhanced, where the char yield at 1000°C (nitrogen atmosphere) and the glass transition temperature reached 70.0% and 218°C, respectively. The excellent mechanical and ablative properties of the PBPR composites may have benefited from the good interfacial adhesion between the resin matrix and the reinforced fiber. The flexural strength and the linear ablative rate are 436.8 ± 5.2 MPa and 0.010 mm/sec, respectively. This study opens a new window for the preparation of high-performance ablative composites by designing a resin matrix containing an aryl-boron backbone. Copyright © 2013 John Wiley & Sons, Ltd.

By incorporating graphene oxide (GO) into phenolic resin (PR), GO/PR composites were prepared, and the effects of the content and reduction degree of GO on thermal resistance of GO/PR composites were studied. The peak degradation temperature of the PR was increased by about 14 °C with GO which was heat treated. The char yield of GO/PR composite at a GO weight fraction of 0.5% was about 11% greater than that of PR. The interactions such as covalent bonds and π–π stacking between GO and PR were regarded as the main reason for the enhancement. Located at the GO–PR interface, GO effectively anchored and structured PR molecular near the surfaces of GO sheets, and thus facilitated the formation of char. The superiority of GO/PR composites over PR in terms of thermal properties enhancement should also be related to the promoting graphitization by the addition of GO.

In order to improve the adhesion of electroless copper plating on phenolic resin matrix composite (PRMC), a new and efficient tin-free sensitization process has been developed. Electroless copper plating could be achieved in three steps, namely: (i) chemical etching with potassium permanganate solution; (ii) sensitization and activation with glucose and silver nitrate solution respectively; and (iii) electroless copper plating. Compared with the sample sensitized with stannous chloride (SnCl2), the copper plating obtained in the tin-free process showed excellent adhesion with the PRMC substrate, but had lower plating rate and conductivity. Additionally, the morphology of the copper plating was affected by the sensitization process, and the tin-free process was conducive to the formation of the large spherical copper polycrystal. Although the process is slightly complicated, the new sensitization process is so low-cost and environment-friendly that it is of great significance and could be applied into large-scale commercial manufacturing.

Pendulum hardness, which is widely used in the characterization of organic coatings, depends greatly on the thickness of the coating. However, it is still unclear whether a qualitative or quantitative relationship exists between pendulum hardness and coating thickness. In the present article, the pendulum hardness values of acrylic coatings with different thicknesses are measured using a Konig pendulum hardness tester to clarify the dependence of pendulum hardness on thickness of coating. The results show that the pendulum hardness of acrylic coatings decreases gradually with the increasing thickness of coating within a thickness range, and the sensitivity of pendulum hardness to thickness of coating depends greatly on the glass transition temperature of the coatings. An equation suitable for describing the relationship between logarithmic decrement of the amplitude of pendulum's oscillation and thickness of coating is presented, which can separate the contributions of substrate and coating on the logarithmic decrement. This study demonstrates that the measured value of pendulum hardness is not the bulk hardness value for the coating but the representative value of the system consisting of substrate and coating. An excellent correlation between pendulum hardness and thickness of acrylic coatings is obtained, which is fairly supported by the experimental data.

By introducing polyaniline nanofibers (PaniNFs) as a stabilizer during the conversion of graphene oxide to graphene in an aqueous medium under ultrasound, the aggregation of the intermediates and products was effectively suppressed. A stable dispersion of PaniNFs and graphene (G) with a high concentration was obtained. This method represents a convenient and potential route to prepare a PaniNF-G dispersion on a large scale, which may increase the applications of graphene. Vacuum filtration of the dispersion yields a high-quality self-supporting PaniNF/G composite film, whose electrical conductivity can be increased by rinsing with hydrochloric acid.