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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.

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.

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.

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.

Using a noncovalent functionalization strategy, hyperbranched polyborate (HBb) acts as a solubilizer for carbon nanotubes (CNTs), and a stable HBb-CNT dispersion in N-methyl-pyrrolidone was produced. The thermal properties of the resulting HBb-CNT/polybenzoxazine (B-BOZ) composites and their carbonized structures were investigated. Scanning electron microscopy demonstrated that the fracture surface of HBb-CNT/B-BOZ composites was rather rough and plenty of plastic deformation was exhibited. Thermogravimetric analysis indicates an improvement in the thermal stability of the composite with CNTs, especially that of 2.0 wt% CNT modified composite. The increase in the thermal stability is due to the good nanotube dispersion and the effective polymer-CNT interaction. Graphite-like boron carbonitride ceramic compounds were found after the composites were carbonized at 1,100°C for 2 h, and there was more B-C, B-N, and C-N bonds in the carbonized HBb-CNT/B-BOZ composite than that of HBb/B-BOZ composite. The result implied that CNTs can promote the ceramic process of HBb/B-BOZ composite, and the strategy of introducing ceramic precursor into polymer composites may be useful to improve their ablation properties. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

During aniline chemical oxidative polymerization which accompanies a falling pH, the initial acidity as well as the early stage pH profile actually plays an important role in the formation of polyaniline (PANI) micro/nanostructures. By utilizing an interfacial polymerization system, transfer and dosage of the reactants were controlled to change acidity profile during the early stage of reaction, without introducing any extra electrolytes. The results showed that, even for the polymerization systems with identical conditions, significant increase on the early stage pH profile induced by accelerated reactants’ transfer had led to PANI exhibiting molecular structures and morphologies typically belonging to those synthesized with weak acidity. Effects of the early stage acidity profile on the final PANI products can be attributed to the initially formed oligomeric products, which can direct the self-assembly of subsequently produced polymers.

Hyperbranched polyborate (HBPB) is a new hyperbranched polymer with excellent thermal resistance, which can be used to improve the thermal stability, especially carbon yield, of phenolic resin (PR). In the present paper, thermal properties and curing degrees of the blends of PR and HBPB (PR–HBPB blends) are investigated. It is found that the curing degrees of PR–HBPB blends would be decreased, and the decrease of curing degree can be attributed to the improper ratio of phenol groups of HBPB to hydroxymethyl groups of PR. Paraformaldehyde (PFM) is introduced to remedy the deficiency of hydroxymethyl groups in PR–HBPB blends. The curing degrees of PR–HBPB blends are improved and the carbon yields of the blends of PR, HBPB, and PFM (PR–HBPB–PFM blends) can be up to 75–80% at 800°C in nitrogen. PR–HBPB–PFM blends can be explored as novel precursors for carbon materials with excellent properties, ease of preparation and low cost. Copyright © 2010 John Wiley & Sons, Ltd.

With unique structure and extraordinary electronic, thermal, and mechanical properties, graphene fascinates the scientific community. Due to its hydrophobic feature, preparation of a stable and highly concentrated graphene dispersion without the assistance of dispersing agents has generally been considered a challenge. Chemical reduction of graphene oxide (GO) is one of the most important methods for preparing a graphene dispersion. The aggregation of graphene sheets is a key reason to destabilize the resulting dispersion during conversion of aqueous GO dispersion to graphene. In this study, by replacing mechanical stirring with ultrasonic irradiation, the aggregation of various intermediates is effectively suppressed during the process of reduction of GO. Hence, a stable graphene dispersion with a high concentration of 1 mg.mL(-1) and relatively pure graphene sheets are achieved, and the as-prepared graphene paper exhibits a high electric conductivity of 712 S.m(-1). Ultraviolet-visible absorption spectroscopy and X-ray photoelectron spectroscopy show that ultrasound is the essence of enhancing chemical reaction rate. Fourier transformed infrared spectra and Raman spectra indicate that ultrasound has less damage to the chemical and crystal structures of graphene.

Hyperbranched polyborate (HBPB) is a new polymer with highly branched structures, plenty of functional end groups and excellent thermal resistance, which can be used as a positive modifier for phenolic resin (PR) to greatly increase the carbon yield of PR. In the present article, thermal properties and structural changes of HBPB modified PR (PR-HBPB) during the pyrolysis are studied. The pyrolysis mechanism of PR-HBPB is proposed to explain the increase of the carbon yield of PR-HBPB. It is found that the carbon yields of PR-HBPBs containing 10 and 20 wt% of HBPB are 71.3 and 73.1 % at 800°C in nitrogen, which are higher than those of PR and HBPB but not the sum of the carbon yields of PR and HBPB in consideration of their mixing ratio. The increase of carbon yield of PR-HBPB can be attributed to the combined effects of the excellent thermal stability of HBPB, the formation of BC 3 and B 2 O 3 , promoted graphitization by HBPB and the protection of B 2 O 3 on the edges of the graphite microcrystallites. POLYM. ENG. SCI., 50:1382-1388, 2010. © 2010 Society of Plastics Engineers.

Polyaniline (PANI) nanofibers were chemically prepared through ultrasonic irradiated polymerization with varying ultrasonic power, frequency, and reaction temperature. It was found that PANI nanofibers with smoother surfaces and uniform diameters can be achieved by increasing the ultrasonic power or the reaction temperature in the studied ranges; a higher reaction temperature was also beneficial for producing PANI nanofibers with larger aspect ratios. With the ultrasonic power set to 250 W, although the polymer prepared at higher frequencies showed higher purity as well as smoother surfaces than those at lower frequencies, the one prepared at 50 kHz with uniform diameters of about 80 nm and lengths of about 700 nm performed best. With the ultrasonic power and frequency fixed and aniline polymerization carried out between 0 and 75°C, PANI nanofibers exhibiting larger aspect ratio and less agglomeration were obtained under a higher reaction temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

In the present paper, polyaniline (PANI) was polymerized by ammonium persulphate using a chemically oxidative process under mild tempertures ranging from −5–20°C. Electrical conductivity of as synthesized PANI got enhanced gradually owing to the increase in molecular weight and crystallinity with decrease in synthesis temperature. Extraction with tetrahydrofuran (THF) was employed as the purification method of emeraldine base (EB) to enhance the electrical conductivity of PANI effectively attributed to the removal of the low molecular weight fractions and defective molecular chains. Methanesulfonic acid (MSA) was used to dope EB due to its strong acidity and small molecular size, and the amount of dopant versus EB was also optimized. Using a novel “synergistic doping” process with m-cresol, electrical conductivity of PANI is further enhanced owing to more regular molecular chains which resulted in better interchain charge carriers' conduction. The emeraldine salts obtained finally have high electrical conductivity reaching up to 32.5 S cm−1, which is much higher than that of the conventionally synthesized sample reported previously. Copyright © 2008 John Wiley & Sons, Ltd.

Novel boron modified phenolic resins (PR) were prepared by blending PR with boric acid terminated hyperbranched polyborate (HBb). In order to reveal the effect of HBb on the structure of the carbonized PR, several experimental tools were employed such as X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Both the XRD and Raman spectroscopy analyses indicated that the boron incorporation resulted in an increase in the crystallite height and a decrease of interlayer spacing. Moreover, the C1s XPS of PR and HBb modified PR revealed that the graphite carbon decreased from 54.50% to 42.85% after incorporating boron atoms in that some of carbon atoms are substituted with boron atoms by forming B–C bonds. The presence of the B–C bonds indicated that part of boron atoms have been introduced into the structure of carbonized PR. These findings revealed that HBb exhibited obvious effects both in promoting the graphite crystallite and in improving the thermal stability.

Polyaniline (PANI) nanofibers were successfully prepared by a sonochemical way with hydrogen peroxide as the oxidant. In comparison with the polymerization performed with mechanical stirring, the polymerization rate of aniline was greatly enhanced and PANI nanofibers were achieved instead of the particulate PANI, though the yield was decreased relatively, indicating the positive effect of ultrasound in producing PANI nanostructures. The uniformity and lengths of the PANI nanofibers were greatly improved as compared with the PANI nanofibers synthesized with ammonium peroxydisulfate (APS) as oxidant under the same conditions, rendering hydrogen peroxide a better oxidant in producing high-quality PANI nanofibers. The PANI nanofibers exhibited similar FTIR spectra, XRD patterns, and dispersibility, but different UV–vis spectra, to their counterpart synthesized with APS as oxidant. UV–vis spectra showed only the head-to-tail structured PANI molecules were produced in the high-quality PANI nanofibers. The findings will be of some help to elucidation of the formation mechanism of PANI nanofibers.

Conducting polyaniline (PANI) nanofibers doped with sulphuric acid were synthesized by a sonochemical method and dispersed in methyl isobutyl ketone (MIBK) with ultrasonicating. The dispersion was mixed with poly(methyl methacrylate) (PMMA) solution in MIBK and cast to fabricate transparent conductive films with evaporation of the solvent. With only a mixing procedure and without any dispersant added, the PANI nanofibers were well dispersed in the matrix polymer as indicated by scanning electron microscopy (SEM) examination. The conductive composite films showed a percolation threshold at ca. 2.2 wt% owing to the relatively larger one-dimensional aspect ratios of the nanofibers. With loadings of PANI nanofibers in the range of 5–20 wt%, composite coatings in thickness of 1 μm with conductivities of 10 −4 to 10 −2 S/cm and transmittances higher than 40% in the visible spectrum can be achieved. The composite coatings showed good stability in air and solvents like water and isopropanol. Combined with their relatively easy preparing procedures, the PANI nanofibers based transparent conductive films can be great promise in practical applications.

The effects of pH profile and “soft template” during aniline chemical oxidative polymerization (COP) were investigated and evaluated simultaneously with diethylene triamine pentaacetic acid (DTPA) as a structural directing agent. Formation of PANI nanotubes and nanoparticles, smooth microspheres, and urchin-like microspheres were illustrated by evaluating the pH profile during aniline COP while considering the “soft template” effects of DTPA. PANI nanosheets with two semicurled edges were found in the system producing nanotubes, which provides an evidence for the “curling mechanism” of PANI nanotube formation. With different pH profiles, chemical structures and aggregation structures of the as-synthesized PANI micro/nanostructures are similar, whereas their conductivity, wettability, Cr (VI) adsorption, and electrochemical behaviors are distinct. The present study indicates that if properly conducted, pH profile adjustment is more effective than “soft template” to control the morphology and to optimize the performance of PANI micro/nanostructures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42403.

Polyaniline (PANI) was synthesized by chemical oxidative polymerization of aniline (ANI) in the presence of sulfonated crosslinked polystyrene (SCPS) particles in neutral water. The polymerization of ANI occurred preferentially on the surfaces of the SCPS particles, resulting in core/shell structured SCPS/PANI particles. The conductivities of the SCPS/PANI particles increased with increasing degree of sulfonation of the SCPS and with increasing ANI/SCPS weight ratios in the reactants. Conductive epoxy-based composites were prepared by curing the blend of SCPS/PANI particles and epoxy resin with an aromatic amine curing reagent, indicating the core/shell structured particles were stable, to some extent, to alkaline environments, which will be of significant importance for the practical application of PANI in many cases. Copyright © 2006 Society of Chemical Industry

Anodic electrodes for ozone generation were prepared with lead dioxide particles of various diameters. The lead dioxide particles were characterized with X‑ray diffraction analysis and the electrodes were characterized and performed for ozone generation. It was revealed that both the diameters of the lead dioxide particles and the con‑ tents of the pore forming agent have great effect on the performance of the electrodes. With decreasing of the diameters of the lead dioxide particles from the range of 55‑74 µm to the range of 15‑35 µm the performance of the electrodes improved. But no further improvement was found with further decreasing of the particle diameters to the range of 5‑15 µm. However by employing an appropriate amount of pore forming agent during the elec‑ trode preparations the performance of the anodic electrode can be improved. The optimized weight ratio of ammonium oxalate to lead dioxide is 1.33/100.

Lightweight and flexible composite coatings of p-toluene sulfonic acid doped polyaniline (PANI–TSA) with various mass fractions and polyacrylate were prepared for electromagnetic interference (EMI) shielding. Both the volume and surface conductivities of the composite coatings increased with increasing PANI–TSA; furthermore, the volume conductivity showed a typical percolation behavior with a percolation threshold at about 0.21. The EMI shielding effectiveness (SE) of the PANI–TSA/polyacrylate coatings over the range of 14 kHz to 15 GHz increased with increasing PANI–TSA as the direct-current conductivity did. EMI SE of the coatings at the low frequencies (14 kHz to 1 GHz) was around 30–80 dB, higher than that at the high frequencies (1–15 GHz); this indicated possible commercial application of the coatings for far-field EMI shielding. The highest EMI SE value was 79 dB at 200 MHz with a coating thickness of 70 ± 5 μm. The moderate SE, light weight, and easy preparation of the coating are advantages for future applications for EMI shielding. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2149–2156, 2005