Unzipping Reaction Research Articles

Visualizing Ribbon-to-Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire-Based Tip-Enhanced Raman Scattering Microscopy.

Graphene nanoribbons (GNRs), a quasi-one-dimensional form of graphene, have gained tremendous attention due to their potential for next-generation nanoelectronic devices. The chemical unzipping of carbon nanotubes is one of the attractive fabrication methods to obtain single-layered GNRs (sGNRs) with simple and large-scale production. The authors recently found that unzipping from double-walled carbon nanotubes (DWNTs), rather than single- or multi-walled, results in high-yield production of crystalline sGNRs. However, details of the resultant GNR structure, as well as the reaction mechanism, are not fully understood due to the necessity of nanoscale spectroscopy. In this regard, silver nanowire-based tip-enhanced Raman spectroscopy (TERS) is applied for single GNR analysis and investigated ribbon-to-ribbon heterogeneity in terms of defect density and edge structure generated through the unzipping process. The authors found that sGNRs originated from the inner walls of DWNTs showed lower defect densities than those from the outer walls. Furthermore, TERS spectra of sGNRs exhibit a large variety in graphitic Raman parameters, indicating a large variation in edge structures. This work at the single GNR level reveals, for the first time, ribbon-to-ribbon heterogeneity that can never be observed by diffraction-limited techniques and provides deeper insights into unzipped GNR structure as well as the DWNT unzipping reaction mechanism.

Unzipping polymers significantly enhance energy flux of aluminized composites

This paper describes a new approach to enhancing the energy delivery rate of pyrotechnics by employing an unzipping polymer. The basic strategy is to localize the heat feedback to just near the reaction front by driving the endothermic chemistry of unzipping. This should then liberate gas near the flame front and propel particles away from the burning surface, to minimize agglomeration and sintering. In this study, polypropylene carbonate (PPC) is employed to load 90 wt% Al and CuO nanoparticles (NPs) via direct ink-writing. The results show a >1500% faster energy release rate from the aluminothermic reaction compared to a conventional polymer binder. Through in-operando microscopy, we observed a 6X thinner flame front and smaller combustion products, revealing significantly lower agglomeration of Al NPs with the unzipping polymer. Fast-heating Time-of-Flight Mass Spectrometry confirms that the unzipping polymer decomposes to low-molecular-weight gasses at a relatively low temperature, which significantly reduces the sintering of Al NPs. The thinner flame implies that heat feedback to the unreacted materials is more localized and drives the endothermic unzipping reaction for gas generation. This study provides a new approach to substantially increasing the energy release rate of nanoscale metallic fuels.

Tracking the complete degradation lifecycle of poly(ethyl cyanoacrylate): From induced photoluminescence to nitrogen-doped nano-graphene precursor residue

Poly(ethyl cyanoacrylate) (PECA) is a commercial polymer which degrades easily at temperatures between 150 - 200 °C via an unzipping reaction where volatile monomer is produced. In this report, the complete moderate-temperature degradation lifecycle is delineated, which also includes formation of a carbonaceous by-product where the ester side groups are lost and ring formation between the backbone and cyano side group occurs. Degradation-induced photoluminescence is observed at an intermediate point where the remaining PECA (or re-polymerized oligomers) has sp3 carbons but sp2-carbon-containing clusters of the by-product that will ultimately form aromatic structures are also present. This observation supports the hypothesis that degradation-induced photoluminescence in polymers, which has been observed widely, is connected to the formation of such sp2 containing clusters, and that this process is relatively independent of the original polymer chemistry, as PECA dominantly degrades through a mechanism distinctly different than the thermo-oxidative cascade associated with many thermoplastic materials. As degradation further advances, a residue of approximately 8% of the original mass is produced which is no longer photoluminescent and can ultimately transform into nitrogen-substituted nano-graphene. Observing the entire lifecycle further solidifies the previously-proposed connection between degradation-induced luminescence in polymers and photoluminescence in hydrogenated amorphous carbon. The low degradation temperature of PECA also provides a bridge between classic polymer degradation and waste-to-graphene strategies that generally involve much more aggressive processing.

Feasibility of unzipping polymer polyphthalaldehyde for extreme ultraviolet lithography

Background: Polyphthalaldehyde (PPA)-based systems can be interesting candidates for extreme ultraviolet (EUV) lithography as dry development resists with simple chemistry. Aim: We present EUV-induced mechanistic and contrast curve studies for the end-capped PPA. Approach: Fourier transform infrared (FTIR) spectroscopy and desorption studies were conducted to understand the EUV-induced mechanistic pathway. Although, contrast curve analysis was used to check its feasibility for EUV-patterning. Results: First, FTIR and desorption studies confirmed that the EUV-radiation is capable to remove the end-capping group and induce unzipping (direct depolymerization) reaction in the PPA polymer chain. Second, contrast curve analysis showed a gradual decrease in the film thickness with respect to the EUV dose, which is due to the low EUV sensitivity of the PPA polymer. A post exposure bake step is important to improve the contrast curve, as it helps to depolymerize any residual polymer remaining after exposure. Further, even though the polymer sublimates when exposed to the EUV radiation, eliminating the need to apply a wet development step, crosslinking at high doses causes deposition of residual film onto the wafer surface. Therefore, a thin film (below 20 nm) and a wet development process might be important to get clean patterns. Conclusion: This study confirms that the end-capped PPA, with a simple patterning mechanism, can be a useful system for the development of new dry development resists for EUV lithography.

Unzipping and scrambling reaction‐induced sequence control of copolymer chains via temperature changes during cationic ring‐opening copolymerization of cyclic acetals and cyclic esters

AbstractA temperature change‐dependent sequence transformation of copolymer chains was demonstrated by a method based on tandem depolymerization and transacetalization reactions during the cationic ring‐opening copolymerization of cyclic acetals and cyclic esters. In this study, the position of polymerization‐depolymerization equilibrium was controlled by the reaction temperature rather than by the decrease in monomer concentration under vacuum conditions, as in our previous study. First, the conditions for efficient copolymerization were optimized, with a particular focus on the structures of cyclic acetals and cyclic esters. Subsequently, sequence transformation induced by temperature change was examined during the copolymerization of 2‐methyl‐1,3‐dioxepane (generated in situ from 4‐hydroxybutyl vinyl ether) and δ‐valerolactone using EtSO3H. The homosequence length of cyclic acetals decreased during depolymerization (unzipping) at the oxonium chain ends upon increasing the temperature from 30 to 90 °C, while transacetalization (scrambling) of the main chain transferred midchain cyclic acetal homosequences to the oxonium chain ends. As a result of the cycle of unzipping and scrambling reactions, an alternating‐like copolymer was obtained. Interestingly, the possibility of reversible sequence transformation upon heating and cooling was also demonstrated.

Top-down synthesis of graphene nanoribbons using different sources of carbon nanotubes

Graphene nanoribbons (GNR) have shown great promise for applications in electronics, sensors, energy-conversion/storage devices, conductive composite materials, and biological fields. Commercialized GNR are mostly produced by unzipping high-quality carbon nanotubes (CNT), predominantly Mitsui CNT. Since the remaining stock of Mitsui CNT is running out, there is an urgent need for a reliable, cost-effective substitute. We studied three different brands of CNT as potential CNT sources in place of Mitsui CNT for making GNR. The NTL CNT and the Saratoga CNT were demonstrated to be well unzipped under both oxidative and reductive conditions based on scanning electron microscopy analysis. Raman and X-ray photoelectron spectroscopy were used to verify the efficacy of the unzipping reactions. The resulting GNR showed improved dispersibility in multiple solvents and similar electrical conductivity compared to the original CNT. The NTL CNT and the Saratoga CNT are expected to become a good substitute for Mitsui CNT in the large-scale production of GNR.

Intact Crystalline Semiconducting Graphene Nanoribbons from Unzipping Nitrogen-Doped Carbon Nanotubes.

Unzipping carbon nanotubes (CNTs) may offer a valuable route to synthesize graphene nanoribbon (GNR) structures with semiconducting properties. Unfortunately, currently available unzipping methods commonly rely on a random harsh chemical reaction and thereby cause significant degradation of the crystalline structure and electrical properties of GNRs. Herein, crystalline semiconducting GNRs are achieved by a synergistic, judiciously designed two-step unzipping method for N-doped CNTs (NCNTs). NCNTs are effectively unzipped by damage-minimized, dopant-specific electrochemical unzipping and subsequent sonochemical treatment into long ribbon-like nanostructures with crystalline basal planes. Owing to the nanoscale dimension originating from the dense nucleation of the unzipping reaction at highly NCNTs, the resultant GNRs demonstrate semiconducting properties, which can be exploited for chemiresistor-type gas-sensing devices and many other applications.

Effect of polyurethane sizing agent on interface properties of carbon fiber reinforced polycarbonate composites

ABSTRACTThis work is aimed at investigating how molecule structure of polyurethanes (PUs) as sizing agents influence the interface properties of carbon fiber (CF) reinforced polycarbonate (PC) composites. Effects of four PUs as sizing agents for CF on the interlaminar shear strength (ILSS) of CF reinforced PC composites are investigated. It is found that the three PUs except PC–PU as sizing agents on oxidized CF (OCF) made the ILSS of their reinforced PC composites increase up to 62.9 MPa by more than 24.8%. The chemical interaction between PU sizing agents and CF are attributed to high reactivity of isocyanate, but carbonate groups on PC–PU may have a chain unzipping reaction due to active groups on the surface of OCF. The chemical interaction between PU sizing agents and PC are attributed to transesterification. As a result, PUs containing isocyanate or polyester groups are ideal sizing agents for CF reinforced PC composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47982.

Study on Thermal Decomposition Behaviors of Terpolymers of Carbon Dioxide, Propylene Oxide, and Cyclohexene Oxide.

The terpolymerization of carbon dioxide (CO2), propylene oxide (PO), and cyclohexene oxide (CHO) were performed by both random polymerization and block polymerization to synthesize the random poly (propylene cyclohexene carbonate) (PPCHC), di-block polymers of poly (propylene carbonate–cyclohexyl carbonate) (PPC-PCHC), and tri-block polymers of poly (cyclohexyl carbonate–propylene carbonate–cyclohexyl carbonate) (PCHC-PPC-PCHC). The kinetics of the thermal degradation of the terpolymers was investigated by the multiple heating rate method (Kissinger-Akahira-Sunose (KAS) method), the single heating rate method (Coats-Redfern method), and the Isoconversional kinetic analysis method proposed by Vyazovkin with the data from thermogravimetric analysis under dynamic conditions. The values of ln k vs. T−1 for the thermal decomposition of four polymers demonstrate the thermal stability of PPC and PPC-PCHC are poorer than PPCHC and PCHC-PPC-PCHC. In addition, for PPCHC and PCHC-PPC-PCHC, there is an intersection between the two rate constant lines, which means that, for thermal stability of PPCHC, it is more stable than PCHC-PPC-PCHC at the temperature less than 309 °C and less stable when the decomposed temperature is more than 309 °C. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analysis/infrared spectrometry (TG/FTIR) techniques were applied to investigate the thermal degradation behavior of the polymers. The results showed that unzipping was the main degradation mechanism of all polymers so the final pyrolysates were cyclic propylene carbonate and cyclic cyclohexene carbonate. For the block copolymers, the main chain scission reaction first occurs at PC-PC linkages initiating an unzipping reaction of PPC chain and then, at CHC–CHC linkages, initiating an unzipping reaction of the PCHC chain. That is why the T−5% of di-block and tri-block polymers were not much higher than that of PPC while two maximum decomposition temperatures were observed for both the block copolymer and the second one were much higher than that of PPC. For PPCHC, the random arranged bulky cyclohexane groups in the polymer chain can effectively suppress the backbiting process and retard the unzipping reaction. Thus, it exhibited much higher T−5% than that of PPC and block copolymers.

Pyrolysis mechanism of Poly(lactic acid) for giving lactide under the catalysis of tin

In order to obtain the mechanisms of the pyrolysis reaction that poly (lactic acid) (PLA) gives lactide in the presence of Sn, the four types of low molecular weight PLAs (L-PLA) with different end-groups were prepared, including HO-L-PLA-COOH, R-L-PLA-OH, R-L-PLA-COOH, and R-L-PLA-R, and depolymerized by thermogravimetry at different heating rates. As for the pyrolysis reactions of the L-PLAs, their activation energy (Ea) were estimated by the several isoconversional model-free methods and their kinetic models were also explored by the Malek method. The random degradation behavior of L-PLAs was determined by the plots of ln{−ln[1−(1−w)0.5]}vs. 1/T for experimental data from TG for L-PLAs and model reactions. The experimental results showed that the Ea values and the possible kinetic models for the pyrolysis reactions of the L-PLAs were different due to the different end-groups and thereof the mechanisms for the pyrolysis reactions of PLA that give lactide were proposed under the catalysis of Sn. The pyrolysis reactions of R-L-PLA-OH and R-L-PLA-R trend to be controlled by a single kinetic model. The pyrolysis reactions of HO-L-PLA-COOH and R-L-PLA-COOH are more complex and controlled by not less than two kinetic processes. The pyrolysis reaction of PLA selectively produces lactide through the unzipping and intramolecular transesterification reactions, including the backbiting reaction caused by the Sn-carboxylate and Sn-alkoxide chain ends, which are directly formed from the hydroxyl and carboxyl end-groups of PLA, and the lactide selective elimination at the random position of the polymeric backbone.

Elastic Properties of DNA as the Entropic Driving Force for Dehybridization Transitions

Through the use of a coarse-grained lattice model informed from all-atomic simulations near equilibrium, we obtain a theoretical estimate of the sequence-dependent slow melting rates (> nanoseconds) of DNA duplexes with activation free energies accurate within 3kT. We show that the change in elastic properties of short DNAs is the key entropic driving force for DNA melting and hybridization. Using a vibration and torsional continuum model, we relate this entropy to the bending and torsional persistence lengths captured from the phonon spectra in all-atomic simulations, near equilibrium, by capturing both the momentum and configuration degrees of freedom simultaneously. A key to the theory is the cooperative melting of all but one base pair at the transition state. This hinge transition state allows us to replace the hydrogen bond vibration modes with a set of out/of-phase bending modes with a much higher vibration entropy (lower phonon frequencies). A multidimensional version of Kramers transition state theory allows us to assign this change to an effective vibrational entropy term that counters the enthalpic gain required to break the hydrogen bonds, leading to an elastic theory for the melting rate of short DNAs. As the hydrogen bond enthalpies are thermodynamic quantities, we estimate them from the classical nearest-neighbor theory. The vibration entropy of the hinge transition state is strictly kinetic but, as it relates only to the persistence lengths, we are able to capture it from near-equilibrium simulations of the duplex. This theory allows us both to make quantitative estimates of the melting rates of short DNAs as well as to differentiate between unzipping and other reaction pathways that may be followed in the presence of secondary structures or mismatches. It represents the first theory for DNA melting with quantitative accuracy.

Synthesis of a novel hydantoin-containing silane and its effect on the tracking and bacteria resistance of addition-cure liquid silicone rubber

A novel hydantoin-containing silane, [3-(5,5-dimethylhydantoinurethano) propyl] ethoxyallyloxysilane (DMHURPAS), was synthesized and the structure was characterized by FTIR and 1H NMR. The effect of DMHURPAS was investigated on the anti-tracking and antibacterial properties of addition-cure liquid silicone rubber (ALSR) after surface chlorination. It was found that ALSR containing only 1.5phr of DMHURPAS passed 1A 4.5kV level and erosion mass decreased from 0.843g to 0.037g. The thermal stability of ALSR was significantly improved and the mechanical properties were also enhanced. From thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), ALSR/DMHURPAS showed significant decrease of carbonyl compounds and cyclic oligomers but increase of CH4 and CO2 during thermal degradation, indicating that DMHURPAS could inhibit oxidation of methyl groups and unzipping reaction, and promote the cleavage of methyl groups in ALSR. The antibacterial rates of ALSR containing 2.0 phr of DMHURPAS against Escherichia coli and Staphylococcus aureus were 95.7% and 83.4%, respectively.

Pyrolysis kinetic analysis of poly(methyl methacrylate) using evolved gas analysis-mass spectrometry

The results of evolved gas analysis-mass spectrometry (EGA-MS) analysis were used for the kinetic analysis of poly-methyl methacrylate (PMMA) pyrolysis for the first time. Various kinetic methods, such as model-free, integral master-plots, and model-fitting methods, have been applied to derive the kinetic parameters (activation energy, pre-exponential factor and reaction model). The PMMA pyrolysis reaction mechanism was suggested to occur via a single step unzipping reaction producing methyl methacrylate (MMA) as the main pyrolyzate from the kinetic analysis results and mass spectrum obtained from the EGA-MS measurements. The kinetic parameters derived from model-free method combined with the integral master-plots method were comparable to those obtained from the peak property method (PPM). The theoretical curve derived from the kinetic results by the PPM was also well matched with the experimental thermal conversion curve using the EGA-MS measurements.

Quantitative Evaluation of Chemical Degradation of Polymer Electrolyte Membrane for Fuel Cells and the Method of Lifetime Prediction

A fuel cell vehicle (FCV) is a vehicle that utilizes fuel cells as its power source. Development of fuel cells for FCV is always aimed at a more compactsize by means of higher power density and longer driving range through enhanced energy efficiency. Fuel cells also require endurance reliability comparable to internal combustion engines, and cost reductions will be required to encourage widespread consumer use. The power generating part of a fuel cell is called the membrane electrode assembly (MEA), which consists of a polymer electrolyte membrane (PEM) and electrodes with a catalyst. The performance of the fuel cell is mainly determined by the activity of the catalyst on each electrode and by the proton conductivity of the PEM. Because the performance, energy efficiency, durability, and cost of fuel cells are all related and involve trade-offs, optimization of the PEM design cannot be readily achieved. A particular issue that has faced optimization of the PEM design is the amount of time it takes to estimate PEM durability. The only method available has been to test it over a long period of time, and this is why FCV has had such an extended development period. In order to optimize the PEM design in less time, a new method capable of estimating durability without durability testing must be developed. To this aim, we first made it possible to quantitatively evaluate the rate of chemical degradation of PEM to estimate durability and predict its lifetime. Next, we developed a mathematical formula for the rate of chemical degradation of the PEM to predict its service life. Two possible reaction mechanisms have been proposed as the chemical degradation of the perfluorosulfonic acid (PFSA) membrane. One is the scission of the main chains of the polymer and the other is an unzipping reaction in which the end groups of the main chains progressively degrade. In order to quantitatively estimate the rate of chemical degradation of the PFSA membrane, we numerically modelized these two reaction mechanisms. When a scission of the main chain occurs, the location of the split becomes two new end groups, which suggests that the number of points of origin for an unzipping reaction increases exponentially. The fluoride release behavior was calculated based on this model. As a result, we confirmed that the experimental fluoride release data can be explained by these two reaction mechanisms of chemical degradation. In order to describe the fluoride release quantity F as a function of duration time t, exponential function Eq. (1) was formulated to closely match the experimental results. F(t) = a [exp(b･t) - 1] (1) One of the factors that influence the chemical degradation rate of the PEM is contamination by metal ions. Adding a radical quencher is a well-known method to assure durability of the PEM by mitigating chemical degradation. In order to estimate the acceleration of PEM degradation caused by metal ion contamination or the mitigation effects offered by a radical quencher, durability testing was carried out using different levels of metal ion contamination or radical quencher additives. The results of these tests show that fluoride release behavior can be represented by Eq. (1) by fixing coefficient b and varying only coefficient a. Coefficient ais therefore defined as the accelerating factor of chemical degradation. The accelerating factor can be obtained by making Eq. (1) fit the experimental fluoride release data, and it can be used as an indicator of the severity of chemical degradation. Introducing the concept of accelerating factor to represent the fluoride release rate made it possible to deal quantitatively with the effect of factors that accelerate or mitigate chemical degradation. Moreover, the size of acceleration or mitigation effect caused by multiple factors can be indicated with a single variable. We confirmed changes in accelerating factor during FCV operation with bench testing, which demonstrated the driving modes of an actual vehicle using a fuel cell stack with the same specifications as stacks installed in actual vehicles. The fluoride release rate was calculated from the accelerating factor envisioning actual FCV operation. Fluoride release behavior can be converted into membrane thickness loss. In this way, decrease in membrane thickness during FCV operation and the lifetime of the PEM can be predicted using calculations.

Electrochemical behavior of hybrid carbon nanomaterials: the chemistry behind electrochemistry

The unzipping of temperature-induced multi-walled carbon nanotubes (MWCNTs) to yield graphene oxide nanoribbons (GONRs) has been studied. These carbon nanomaterials consisting of MWCNTs and unzipped MWCNTs have been synthesized, thoroughly characterized, and subsequently evaluated for electrochemical sensing. Three temperatures (55, 65 and 75°C) yielding three carbon nanomaterial termed as GONR-55, GONR-65 and GONR-75, respectively, were carefully studied. Interestingly, GONR-65 became the most suitable material for the electrochemical sensing of a wide range of model analytes displaying the best electrochemical response with independence of the analysed molecule. This electrochemical behaviour seems to be associated to the progress of the unzipping reaction that influences the balance between the Csp2/Csp3 ratio, the graphitic fraction and the type of functional groups introduced. These results revealed the importance of the temperature in the synthesis process, for tailoring carbon nanomaterials which could be used in a particular molecular detection application opening new opportunities for electrochemical sensing applications.

Dopant-specific unzipping of carbon nanotubes for intact crystalline graphene nanostructures.

Atomic level engineering of graphene-based materials is in high demand to enable customize structures and properties for different applications. Unzipping of the graphene plane is a potential means to this end, but uncontrollable damage of the two-dimensional crystalline framework during harsh unzipping reaction has remained a key challenge. Here we present heteroatom dopant-specific unzipping of carbon nanotubes as a reliable and controllable route to customized intact crystalline graphene-based nanostructures. Substitutional pyridinic nitrogen dopant sites at carbon nanotubes can selectively initiate the unzipping of graphene side walls at a relatively low electrochemical potential (0.6 V). The resultant nanostructures consisting of unzipped graphene nanoribbons wrapping around carbon nanotube cores maintain the intact two-dimensional crystallinity with well-defined atomic configuration at the unzipped edges. Large surface area and robust electrical connectivity of the synergistic nanostructure demonstrate ultrahigh-power supercapacitor performance, which can serve for AC filtering with the record high rate capability of −85° of phase angle at 120 Hz.

Polycaprolactone/multi-wall carbon nanotube nanocomposites prepared by in situ ring opening polymerization: Decomposition profiling using thermogravimetric analysis and analytical pyrolysis–gas chromatography/mass spectrometry

Poly(ϵ-caprolactone) (PCL) was reinforced with amino-functionalized multi-walled carbon naonotubes (f-MWCNTs) by an in situ ring opening polymerization (ROP) procedure. Transmission electron microscopy (TEM) was initially utilized in order to observe the state of dispersion of MWCNTs in the matrix, which is known to affect heavily the physicochemical properties of the composite materials. Subsequently, a thorough investigation of the decomposition profiling of PCL and nanocomposites was performed by employing thermogravimetric analysis (TGA) and analytical pyrolysis–gas chromatography/mass spectroscopy (Py–GC/MS). The results from TGA revealed that the thermal stability of the matrix is not enhanced by f-MWCNTs, while the detailed study with Py–GC/MS showed that random chain scission via cis-elimination, intramolecular transesterification and unzipping reactions dominate the decomposition of PCL. It is noteworthy that the highest amount of filler was found to catalyze decomposition reactions without interfering with the detected mechanisms. In terms of the mechanical properties, the presence of f-MWCNTs improved the stiffness of the matrix, as evidenced through dynamic mechanical analysis (DMA).

Thermal degradation mechanism of poly(hexamethylene carbonate)

Thermal degradation behaviors of poly(hexamethylene carbonate) (PHC) were investigated by means of thermogravimetric analysis (TGA), proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC) and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). Six types of PHC samples with different end groups and molecular weights were synthesized to systematically investigate the thermal degradation mechanism. Thermal degradation behaviors of the PHC samples were examined under both isothermal and non-isothermal conditions. The PHC samples showed distinct thermal degradation behaviors from other aliphatic polycarbonates (poly(propylene carbonate), poly(trimethylene carbonate) and poly(butylene carbonate)). The results indicated that the chain-end structure makes a slight effect on the thermal stability of PHC regardless of the molecular weight. During the non-isothermal degradation of PHC, four main reactions were illustrated: unzipping, intramolecular transesterification, β-H transfer and decarboxylation reactions. Intramolecular transesterification reaction dominantly occurs below 300 °C accompanying with unzipping reaction which can only be induced by hydroxyl end group, and releasing cyclic hexamethylene carbonate monomer and dimer. Above 300 °C, the four degradation reactions take place simultaneously.

Morphological and Electronic Characterization of Functionalized Graphene Nanoribbons Obtained by the Unzipping of Single-Wall Carbon Nanotubes: A Scanning Tunneling Microscopy Study

A few layers of functionalized graphene (FLG) have been obtained by the oxidative unzipping reaction of single-walled carbon nanotubes. A detailed Scanning Tunneling Microscopy and Transmission Electron Microscopy study shows that several different morphologies are observed, depending on the substrate upon which they are deposited, thus providing useful hints for a “real world” application of these carbon nanostructures. In addition, a combined Scanning Tunneling Spectroscopy investigation has shown that the electronic properties of these FLG are affected by their functionalization degree, opening interesting perspectives for their use in sensor and biosensor devices.

Thermal degradation mechanism of poly(butylene carbonate)

Thermal degradation mechanism of poly(butylene carbonate) (PBC) was elucidated by means of thermogravimetric analysis (TGA), 1H nuclear magnetic resonance (1H NMR) and pyrolysis-gas chromatography mass spectrometry (Py-GC/MS). The results indicated that there are three main pathways for the thermal degradation of PBC, including unzipping, β-H transfer and decarboxylation reactions. The unzipping reaction can be facilely induced at low temperature of 200 °C, and all of the three reactions occur at high temperature above 300 °C. TGA results suggested the thermal stability order: hydroxyl-terminated PBC < acetyl-terminated PBC < methyl carbonate terminated PBC. The hydroxyl end group can induce the unzipping reaction, while methyl carbonate chain-end depresses the occurrence of it.