Polyimide Precursor Research Articles

Carbon molecular sieve gas separation membranes derived from in-situ crosslinked polyimide containing bromine groups

The network polyimide (PI) precursor is a promising candidate to fabricate the advanced carbon molecular sieve (CMS) membrane since its robust crosslinked structure could prevent pore structure collapse during CMS formation. Exploring the relationship between network PI precursor structure and CMS membrane is highly significant. Herein, a novel brominated network PI precursor was fabricated via in-situ cross-linking technique firstly, and then the thermally induced bromination/debromination process was applied to tune the microporosity and gas transport properties of network PI precursor and its derived CMS membranes. After the bromination/debromination and carbonization at 550 °C, the resultant CMS membrane exhibited both high gas permeability and gas selectivities compared to its un-brominated network PI precursor derived CMS membrane. This is due to the bromination/debromination and carbonization enable the CMS membrane possesses large d-spacing values (11.06 Å), high BET surface areas (538.57 m2/g), and high percentage (∼71 %) of ultra-micropores. For instance, 6F-TA/TA-Br-550/30 membrane exhibits great CO2/CH4 separation ability, with a CO2 permeability of 6300 Barrer and a CO2/CH4 selectivity of 46.11, which is suppressed the latest 2019 trade-off curves. We anticipate that the present bromination/debromination and carbonization could provide a fresh perspective on the rational design of network PI precursor and its derived CMS membrane with excellent gas separation performance.

3D printing carbon from aqueous all aromatic polyimides

All-aromatic polyimides serve as versatile precursors for carbon formation due to their high aromatic content and repeating unit planarity, which synergistically enables pyrolysis to ordered carbon. Recent publications disclosed facile synthetic methods for additive manufacturing (3D printing) of all-aromatic polyimides using a pendant salt approach for ultraviolet-assisted direct ink write (DIW) additive manufacturing. This manuscript describes the introduction of pendant sodium sulfonate functionality to the poly(amic acids), and water-soluble all-aromatic polyimide precursors displayed suitable rheological properties for DIW at room temperature and vat photopolymerization (VP) at 50 °C. These aqueous solutions enabled the formation of microporous polyimide structures with a direct freeze-casting method and dense structures with gradual heating under inert atmosphere to 200 °C and subsequent thermal post-processing to 400 °C. Furthermore, polyimide 3D structures function as efficient carbon precursors when pyrolyzed at 2000 °C under inert atmosphere. Raman spectroscopy revealed carbonized 3D structures with characteristic graphitic and disordered carbon bands, which was indicative of polycrystalline, disordered glassy carbon. Furthermore, electrical conductivity measurements suggest opportunities for the formation of 3D conductive structures.

Synergistic tuning of microstructure and morphology in carbon molecular sieve hollow fibers for propylene/propane separation

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro‐ and macro‐structural morphologies for energy efficient propylene‐propane separation are reported here. A sub‐glass transition temperature (sub‐Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS “skin” derived from the 6FDA:BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2‐doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.

Synergistic Tuning of Microstructure and Morphology in Carbon Molecular Sieve Hollow Fibers for Propylene/Propane Separation.

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro- and macro-structural morphologies for energy efficient propylene-propane separation are reported here. A sub-glass transition temperature (sub-Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS "skin" derived from the 6FDA : BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2-doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.

High-Performance Carbon Molecular Sieve Membranes Derived from a PPA-Cross-linked Polyimide Precursor for Gas Separation.

Carbon molecular sieve (CMS) membranes have emerged as attractive gas membranes due to their tunable pore structure and consequently high gas separation performances. In particular, polyimides (PIs) have been considered as promising CMS precursors because of their tunable structure, superior gas separation performance, and excellent thermal and mechanical strength. In the present work, polyphosphoric acid (PPA) was employed as both cross-linker and porogen, it created pores within the PI polymeric matrix, while it also effectively acting as a cross-linker to regulate the ultramicropores of the CMS membranes, thus simultaneously improving both permeability and selectivity of the CMS membranes. By employing PI/PPA hybrid with PPA content of 5 wt % as a precursor, the obtained CMS membrane exhibited a CO2 and He permeability of 1378.3 Barrer and 1431.4 Barrer, respectively, which was an approximately 10-fold increase compared to the precursor membrane. Under optimized conditions, the CO2/CH4 and He/CH4 selectivity of the obtained CMS membrane reached 81.5 and 89.9, respectively, which was 278% and 307% higher than that of the pristine PI membrane. In addition, the membrane exhibited good long-term stability during a one-week continuous test. This study clearly denoted PPA can be used for precisely tailoring the ultramicroporosity of CMS membranes.

Huge improved gas separation performance of carbon molecular sieve membrane by forming a double crosslinked polyimide precursor

A vital issue in searching for advanced gas separation membranes is understanding the precursor structure-gas separation properties of carbon molecular sieve (CMS) membranes. Here, we reported two crosslinked polyimides and used as CMS precursors, in which, the DCPI-4 is a double cross-linkable polyimide with 4 % triptycene triamine as a crosslinker (Type I) and COOH group that can be crosslinked at 350 °C by decarboxylation (Type II), whereas the DCPI-0 with COOH (Type II). After pyrolysis at 550 °C, the DCPI-4-CMS showed a higher SBET (812 vs 713 m2g-1), larger ultra-microporosity ratio (26.6 % vs 17.8 %), larger d-spacing (4.08 vs 3.94 Å), less graphitization (sp3/sp2 of 0.156 vs 0.118), 5.5 times higher CO2 permeability (7573 vs 1391 Barrer) and same CO2/CH4 selectivity (∼62) than DCPI-0-CMS. We consider this is due to the type I crosslinking enhances the rigidity of the polyimide backbone, and inhibits the collapse of micropores during the carbonization, which causes improved ultra-microporosity and ultra-micropore ratio that both enhances the gas diffusion and solubility coefficient as well activation energy difference of gas pairs. Conclusively, this double crosslinking method provides a good perspective for achieving CMS membranes with excellent gas separation performance.

Thermally Rearranged (TR) Polybenzoxazoles from o-Substituted Precursor Polyimides with Phenyl Pendant Groups: Synthesis, Properties, and Thermal Rearrangement Conditions.

A series of polyimides (PIs) was synthesized from 6FDA and two o-OH substituted diamines having bulky pendant phenyl, Ph, and trifluoromethyl, CF3, groups as precursors for thermally rearranged polybenzoxazole, TR-PBO, membranes. One diamine had two pendant Ph substituents; in the other, the substituents were Ph and CF3. Applying azeotropic and chemical cyclizations allowed the obtention of four o-hydroxy (o-OH) or/and o-acetoxy (o-OAc) substituted PIs depending on the imidization method. The PIs were labeled as 3Ph-OH, 4Ph-OH, or 3Ph-OAc and 4PH-OAc, respectively. Thermal rearrangements of all four precursors were investigated in the interval from 350 to 450 °C. The conversions to TR-PBO increased with temperature, and almost quantitative conversions were obtained at temperatures close to 450 °C, although o-OH substituted PIs reached conversions slightly higher than those of o-OAc PIs at a given temperature. The TR-polymers' fractional free volume (FFV) also increased with conversion but was higher for the o-OAc substituted precursors. Despite the high TR-PBO conversions, self-supported uniform TR membranes with reasonable mechanical properties were obtained, except for 4Ph-OH. Gas separation behavior of the membranes significantly improved after the thermal treatment, and the final CO2/CH4 permselectivities lay between the 1991 and 2008 Robeson upper bounds. Particularly, TR-membranes derived from o-OAc precursors and with pendant CF3 group demonstrated better gas transport properties with values of P (CO2) = 1121 barrer and αCO2/CH4 = 29 for 3Ph-OAc derived membrane, which positioned it beyond the 2008 upper limit.

Metalized Plastic Current Collectors Incorporated with Halloysite Nanotubes toward Highly Safe Lithium‐Ion Batteries

AbstractMetalized plastic current collectors (MPCCs) have shown potential in improving the energy density and safety of lithium‐ion batteries (LIBs). However, the poor mechanical strength, weak interfacial adhesion force, and surface metal corrosion have impeded the practical application of MPCCs. Here, an innovative engineering of MPCCs is proposed by incorporating halloysite nanotubes (HNTs) as fillers into polyimide (PI) polymer layer, which is further coated with two thin copper (Cu) layers. Because of the strong bonding between HNTs surface and the PI precursor, HNTs improve the mechanical strength of PI‐HNTs composite film, reinforce the interfacial adhesion force between the PI‐HNTs film and the coated Cu layer, and suppress the Cu corrosion by electrolyte. The prepared MPCCs exhibit a low mass density and only account about one‐fifth of the density of commercial Cu CCs. Furthermore, the PI‐HNTs‐Cu composite demonstrates significantly enhanced interfacial adhesion force doubled to 4 N cm−1 along with prolonged stability under electrolyte immersion and electrochemical reaction conditions, and delivers a high fracture strength of 125 MPa. LIBs assembled with MPCCs deliver a twice higher discharge capacity compared to battery with Cu CCs and reach a long‐term cycle capacity retention as high as 92.9% at 0.5 C after 500 cycles.

In-situ crosslinking of a novel conjugated dialkynyl-based polyimide for high performance carbon molecular sieve membrane

High-performance and reliable membranes for efficient gas separation and their design strategies are key points for membrane-based carbon capture. Here, we reported a high-performance carbon membrane design protocol from a microporous, highly rigid polyimide precursor (6FBD1-CR), which was produced by in-situ crosslinking a polyimide (6FBD1) containing conjugated dialkynyl group at 300 °C. The possible crosslinking mechanisms are the [2+2+2] trimerization of three ethynyl groups to form a benzene ring and the Diels-Alder reaction between the ethynyl bond and phenylacetylene to generate the fused naphthalene ring. After crosslinking, the membrane shows a ∼ 8-fold improved microporosity (37.1–298 m2 g−1). When pyrolyzed at 550 °C, the resulting 6FBD1-CMS demonstrates very high pure- and mixed-gas separation performance. E.g., the CO2 permeability reaches 7661 Barrer and CO2/CH4 selectivity of 44, additionally, even at the CO2/CH4 mixed-gas pressure of 30 bar, the PCO2 can still reach 4920 Barrer combined with a αCO2/CH4 of 28, which is well above the latest CO2/CH4 mixed-gas Upper Bound line. We consider this is due to the acetylene crosslinking induced a very stable microporous structure composed of rigid fused rings that alleviate the micropore collapse during the carbonization process, and thus, resulting in a relatively higher BET surface area, larger d-spacing, relatively higher concentration of continuous disordered phase (higher sp3/sp2) and small activation energy (Ep) for gas transport than the CMSM derived from polyimide without pre-crosslinking. This finding provides new opportunity for the structural design of high-performance CMSMs.

Solvent-guided nanoarchitecturing of heterodiatomic carbon superstructures for high-performance zinc-ion hybrid capacitors

Designing well-structured carbon nanomaterials is crucial for promoting zinc-ion hybrid capacitors with high-kinetics and large-current Zn2+-storage viability. Herein we report the solvent-guided nanoarchitecturing of polyimide precursor to customize versatile heterodiatomic carbon superstructures (CS). Modulating the solvent-precursor interaction through a solubility parameter model and molecular dynamic simulation optimizes the thermodynamic solubilization (–2.14 eV) and growth kinetics (–9.22 eV) of polymeric intermediates with a minimum energy obstruction. The solvent-optimized CS exhibit well-defined spherical topology, ion-compatible pore channels and favorable dual-function motifs, affording more ample-exposed zincophilic platforms and high-speed ion transport routes. As a consequence, the assembled Zn||CS hybrid capacitor activates superior electrochemical activity and durability, including superior rate capacities (240 mAh g−1 at 0.5 A g−1, 108 mAh g−1 at 100 A g−1), high energy density (145 Wh kg−1) and ultralong lifespan (300,000 cycles at 50 A g−1). Marriage of experimental studies and theoretical calculations unravel the alternate storage of opposite charges in CS cathode, which involves high-kinetics physical Zn2+/CF3SO3− uptake at zincophilic sites and chemical redox of Zn2+ ions with carbonyl/pyridine motifs to initiate O−Zn−N bonds. Molecular dynamics simulations demonstrate that diffusion kinetics of Zn2+ ions is greatly facilitated by > 10 Å micropores with low energy barriers, but is blocked by < 7 Å micropores. This work provides new insights into the structural engineering of carbon superstructures for advanced energy storage.

Preparation of polyimide hollow particles using chemical imidization

Abstract Hollow polyimide (PI) particles were successfully prepared using chemical imidization with acetic anhydride and pyridine as the chemical imidization reagents. The imidization reagents were added to the dispersion in which N,N-dimethylformamide (DMF) droplets with dissolved poly(amic acid) (PAmA, the precursor of PI) were dispersed in a cyclohexane medium. In the absence of poly(n-butyl methacrylate) (P[n-BMA]) in PAmA/DMF droplets, approximately 10% of the PI particles had hollow structures. Conversely, in the presence of a small amount of P(n-BMA) in PAmA/DMF droplets (0.2∼1 wt%), all PI particles had hollow structures. The P(n-BMA) would affect the phase separation of the PI in the droplets, thereby promoting the formation of a hollow structure.

Covalent Introduction of Plasma-Treated carbon nanotubes into polyimide nanocomposites at Ultra-Low content

In this paper, the effect of plasma treatment on the structure of carbon nanotubes (CNTs) and the structure/properties of polyimide (PI) nanocomposites with CNTs at ultra-low content (0.001 wt% ∼ 0.004 wt%) were investigated. Plasma treatment of CNTs under the mixture-gas of N2 and CO2 resulted in introducing isocyanate group on the surface of CNTs. PI nanocomposites with non-treated CNTs (nCNTs) or plasma-treated CNTs (pCNTs) were synthesized by in-situ polymerization, where PI as well as polyamic acid (precursor of PI) was polymerized under the presence of fillers. The structural studies revealed that pCNTs were highly dispersed in the nanocomposites with the strong interfacial interaction of covalent bond at the interface between PI and pCNTs. As a result, the excellent reinforcement effect of CNTs was successfully exploited to the PI nanocomposites at ultra-low content. For example, the Young’s modulus, tensile strength and toughness increased by 83 %, 51 % and 41 % by the incorporation of only 0.001 wt% of pCNTs, while the nanocomposite with nCNTs showed brittle behavior caused by poor interfacial interaction. Here in, we show that the characteristics of polymer matrices can be drastically changed by the addition of ultra-low content of nanofillers where the surface chemistry is optimized.

Excellent gas separation performance of hybrid carbon molecular sieve membrane derived from polyimide/10X zeolite for hydrogen purification

Membrane-based gas separation is attracting more and more attention in hydrogen purification and CO2 separation. One critical challenging remaining for large-scale production is fabricating a high-performance membrane with both inexpensive and excellent separation performance. In this work, a novel hybrid-carbon molecular sieve (CMS) membranes were reported for hydrogen purification by pyrolysis of commercial polyimide precursor (PMDA-ODA) with incorporation of modified 10X zeolite. The addition of modified 10X zeolite provided additional gas transport channels to the CMS mixed matrix membrane (MMM), and contained a significant fraction of micropores within the 0.6–0.8 nm range, which greatly enhance hydrogen adsorption capacity. Interestingly, despite this, the selectivity for H2/N2 and H2/CH4 also increases with higher zeolite content. This unexpected phenomenon may be attributed to the partial blocking of zeolite pores by CMS strand, which narrows the 10X pore size to a dimension smaller than CH4 and N2, enabling differentiation between H2 and CH4 gas pairs. Therefore, the permeability and selectivity of H2 was significantly enhanced. The CMS/10X-7.5 (with 7.5 wt % 10X zeolite) exhibited an advanced H2 permeability (1709 Barrer) and high gas selectivity of 551 for H2/CH4 and 105 for H2/N2, respectively, which is higher than other samples and exceed the 2015 trade-off lines. Furthermore, the CMS/10X-7.5 delivered excellent stability after 20 cycles. Therefore, this hybrid CMS/10X-7.5 obtained by carbonization of zeolite-doped polymer precursors has great potential for larger industrial applications.

Water vapor sorption and transport in carbon molecular sieve membranes

Carbon Molecular Sieve (CMS) membranes have been extensively studied for gas separations. Many gas separation applications involve humidified streams, but reports on water vapor transport in CMS membranes are limited. In this study, water permeability, diffusivity, and solubility were determined as a function of water activity for CMS membranes. Water transport properties of membranes synthesized at different pyrolysis temperatures (550 °C and 800 °C) and with different polyimide precursors were examined. Water sorption followed Type V isotherms as previously observed for the adsorption of water in microporous carbons. Water permeability was much higher at all water activity values for CMS samples prepared at lower pyrolysis temperature. Water permeabilities as a function of water activity of the three different polyimides pyrolyzed at 800 °C were very similar. Water permeability of CMS membranes was high compared to many other polymeric materials, showing potential for dehydration applications. Finally, the steady-state water vapor diffusivity (Dss), estimated from steady state permeability and equilibrium sorption measurements, was compared to the experimental transient diffusivity (D), matching reasonably well.

Numerical modeling of the carbonization of polyimide fibers in a cylindrical furnace

Carbon fiber is widely used as a reinforcing material in polymer composite such as carbon fiber reinforced plastic (CFRP) due to its high specific strength, elastic modulus and lightweight. The majority of the industrial carbon fiber is produced from synthetic precursor polymer such as polyacrylonitrile (PAN), pitch and polyimide. While relatively many studies have been published for the carbonization of PAN, little studies have been found on the heat transfer during carbonization of polyimide precursors. In this study, we numerically analyzed the carbonization process of a polyimide (PI) precursor for carbon fibers in a lab-scale cylindrical furnace. Gas flow, temperature distribution and concentration profiles including the off-gases from the precursor fibers were included in the analyses. First, we established mathematical models for the off-gases behavior from the precursor fibers. The models were incorporated into computational fluid dynamics in order to find behavior of the mixture gas of the working nitrogen gas and the off-gases. And then, numerical simulation results using the model were obtained and compared to the experimental results to verify the model. Finally, we evaluated the application scalability of the established numerical model through changes in wall temperature and precursor fiber moving speed. The results showed that the model can be used to study the PI carbonization process in the industrial size carbonization furnace.

Comparison of the physical properties of different polyimide nanocomposite films containing organoclays varying in alkyl chain lengths

Abstract Poly(amic acid) (PAA), a precursor of polyimide (PI), is synthesized by reacting dianhydride 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride with diamine 3,3′-dihydroxybenzidine in N,N′-dimethylacetamide. Organoclays with different alkyl chain lengths were dispersed in PAA, and the weight percentages (wt%) of the organoclays varied. The PI hybrid films were prepared over multiple steps under heat treatment conditions. Bentonite (BTN) was used as the pristine clay, and octylamine (C8) and hexadecylamine (C16) were used to chemically modify the surface of BTN to obtain the desired organoclay samples. Organoclays C8-BTN and C16-BTN were dispersed in a PI matrix, and the organoclay content varied in the range of 1–9 wt%. The thermal, morphological, and optical properties of the PI hybrid films were investigated based on the organoclay content. Although the thermal stability of the PI hybrid film improved when a small amount of organoclay was added, it decreased when the nano-filler content exceeded a certain critical content. Specifically, in the hybrid containing C8-BTN, the critical content is 5 wt%, while in the hybrid with C16-BTN, the critical content is 7 wt%. In addition, the morphology of the clay dispersed in the matrix at the critical content showed the best dispersed phase. The physical properties (thermal characteristics, dispersibility, and optical transparency) of the PI hybrid film containing C16-BTN were better than those of the hybrid film containing C8-BTN. However, the thermal expansion of the C8-BTN hybrid was lower than that of the C16-BTN film at the same content.

A long service life silicon-doped laser-etched polyimide anode materials for high-rate lithium-ion battery

Silicon (Si)-based materials emerge as promising anode materials owing to their theoretical capacity as high as 4200 mAh g−1. However, when Si-based materials are assembled into battery anode sheets, they face the dilemmas of severe volume expansion and poor electric conductivity. In this study, three-dimensional (3D) layered porous Si‑carbon (C) composites are designed and fabricated from a polyimide (PI) precursor through cyclization polymerization and laser etching. SiC particles are dispersed in the porous network structure, which reduces the volume expansion of the anode during charging and discharging, so that the electrode has good cycle life and specific capacity. The laser-etched Si-doped polyimide (L-Si-PI) anode achieves 1332 mAh g−1 capacity in the first discharge and a high capacity of 1057 mAh g−1 after 1500 cycles at 0.2 A g−1 for half lithium-ion batteries (LIBs). When the L-Si-PI is employed for full LIBs, it exhibits a specific capacity of 142 mAh g−1 at 0.1C with 800 cycles working life. And kinetic analysis reveals a diffusion-controlled lithium storage mechanism in the composite. In a word, such rational nanostructure design and multi-component synergic interaction system has a good application prospect in the field of LIB research.

Laser-synthesis of conductive carbon-based materials from two flexible commercial substrates: A comparison

One of the key challenges in the field of flexible electronics relies on finding conductive materials that can withstand bending and stretching stresses while maintaining their performance. In this context, this work presents a comparative study of laser-induced conductive materials from the direct laser-scribing of two commercial flexible films: the benchmark Kapton® HN polyimide (PI) precursor and the UltemTM 1000 polyetherimide (PEI) alternative contender. The synthesis process on both materials is optimized in terms of electrical conductivity using a high-performance galvanometric laser with a wavelength of 532 nm for the fabrication of multiple samples at different laser powers and speeds. The samples are structurally characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Fourier-Transform Infrared Spectroscopy (FTIR) aiming at understanding the chemical and physical changes of the ablated material. The results demonstrate that the proposed setup is feasible for the synthesis of uniform and reliable conductive patterns on the surface of both substrates with high reproducibility. In particular, it is proved that PEI is more suitable precursor for flexible electronics applications which demand high electrical conductivity, leading to a sheet resistance of 3.62 ± 0.35 Ω/sq at 0.8 W and 5 mm/s once the laser-synthesis process is optimized (against the 6.04 ± 0.63 Ω/sq at 0.6 W and 5 mm/s offered by the LIG on PI). The performance of both laser-induced patterns as electrodes for the fabrication of electrochemical capacitors is also studied and compared in terms of areal specific capacitance.

Improved selectivity and anti-aging ability for 6FDA type carbon molecular sieve membranes by mixing silicon from macro-phase separation to molecule doping

Good gas separation performance and anti-aging ability are important for the applications of carbon molecular sieve membrane (CMSM). In this work, silicon atoms in the form of siloxane-Cl are introduced into 6FDA-DABA type polyimide (PI) precursor membrane, and benzimidazoles (BI) is copolymerized into PI to effectively improve the compatibility between PI and siloxane-Cl. By varying the content of siloxane-Cl, the composite membrane changes from macro-phase separation to molecule level miscibility, which leads to the formation of silicon-rich interface layer and silicon molecule doping after high temperature pyrolysis, respectively. The residual silicon content in CMSM could be as high as 1 wt%. The high content silicon doped CMSM exhibits much improved H2 permeability retention degree (3617 Barrer of H2 permeability, 62% higher) and H2/CH4 selectivity (138, 51% higher) as compared to control CMSM after 45 days of physical aging. This work proves that the incorporation of silicon in CMSMs in proper forms could significantly improve their molecular sieving and anti-aging performances; a higher content of residual silicon and molecule level doping are highly desired. The heteroatom doping is expected to pave a new way for finely tuning the micro-structures of CMSMs and improving gas separation performances.

Polyimide precursor/functionalized carbon nanotubes: molecular modeling and physical properties theoretical evaluation

This article explains the influence of –OH, –COOH, and –NH2 functional groups, bounded to carbon nanotubes, on the interactions occurring in composites having as matrix a polyimide precursor. The molecular modeling is used to visually reveal the optimized conformation of the polyimide precursor structural unit, carbon nanotubes with or without functional groups and corresponding composites where hydrogen bonding interactions is formed. Also, based on molecular modeling, quantitative structure activity relationship parameters and binding energies are calculated, indicating that the interaction energy between the matrix and the filler is greater as the functional group polarizability is higher. The theoretically estimated electrical conductivity of the composites increases by the addition of the filler and it is the highest for the ones containing carbon nanotubes functionalized with –OH. The theoretical analysis of the thermal conductivity of the composites reveals a better heat conduction for the same mentioned filler, being increased during the temperature rise. This kind of study is necessary to predict certain properties of the composites before synthesis, thus avoiding the wasting of raw compounds.