Guiyang Li

Synthetic control of network topology and pore structure in microporous polyimides based on triangular triphenylbenzene and triphenylamine units

Four new polyimide networks were prepared via a one-step polycondensation method by using tris(4-aminophenyl)amine and 1,3,5-tris(4-aminophenyl)benzene to react with pyromellitic dianhydride (PMDA) and naphthalene-1,4,5,8- tetracarboxylic dianhydride (NTDA), respectively. It was found that the topological structures and pore morphologies of the networks were tightly related to the geometrical shape of the net nodes, the molecular volume of the connecting struts, the reactivity of the monomers as well as the polymerization conditions. The results revealed that the reactions between triangular triamines and rod-like PMDA tended to form six-membered ring units, which were then extended to yield polyimide crosslinking networks, reflected by the complete disappearance of the endgroup signals in the FTIR and 13C CP MAS spectra, the significantly high thermal stability, large accessible surface area (818 cm2 g−1) and narrow pore size distribution centered at 4–8 A. On the contrary, the low reactivity and steric bulky naphthyl group of the NTDA monomer led to the generation of branched or hyperbranched oligomers, which were further mutually crosslinked at a high temperature to produce the polyimde networks. In this way, a small amount of unreacted groups unavoidably remained, and the polymers exhibited a heterogeneous topological architecture, a broad pore size distribution and a low surface area of only 232 cm2 g−1. The influences of synthetic control and monomer structures on the pore morphologies and properties are investigated.

The directing effect of linking units on building microporous architecture in tetraphenyladmantane-based poly(Schiff base) networks

Tetraphenyladamantane-based porous poly(Schiff base)s with BET surface area (>1000 m(2) g(-1)), CO2 uptake (15 wt%, 273 K/1 bar) and H2 uptake (1.26 wt%, 77 K/1 bar) were synthesized. The structure-directing effect of isomers of phenyl diamines on building porous architecture was investigated.

Micro- and mesoporous poly(Schiff-base)s constructed from different building blocks and their adsorption behaviors towards organic vapors and CO2 gas

Four porous poly(Schiff-base)s, PSN-DA, PSN-TAPB, PSN-TAPA and PSN-TAPM, are synthesized via one-pot condensation from 1,3,5,7-tetrakis(4-formylphenyl)adamantane with rod-like m-phenyldiamine, triangular 1,3,5-tris(4-aminophenyl)benzene and tris(4-aminophenyl)amine as well as tetrahedral tetrakis(4-aminophenyl)methane, respectively. It is found that the variation of the geometrical shape of the building blocks significantly alters the surface areas, pore sizes and distributions of the resultant porous polymers and thereby remarkably influences their adsorption behaviors towards organic vapors and CO2 gas. PSN-DA, PSN-TAPB and PSN-TAPA are microporous materials with pore sizes of 0.72, 0.95 and 1.04 nm, whereas PSN-TAPM is a micro- and mesoporous material with the major pores centered at 0.86 and 2.62 nm, respectively. Their BET surface areas are in the range from 419 to 1045 m2 g−1. At P/Po = 0.9 and 298 K, PSN-DA possesses high uptakes for both aromatic vapor (benzene, 86.1 wt%) and aliphatic vapor (cyclohexane, 77.9 wt%). In addition, the adsorption and desorption isotherms of CO2 gas in the four porous polymers are reversible – a characteristic which is convenient for the regeneration of CO2 adsorbents. Their adsorption capacities of CO2 are up to 15.0 wt% (273 K/1 bar) with the ideal selectivities of CO2/N2 and CO2/CH4 up to 71 and 14, respectively. showing potential applications in the removal of toxic organic vapors and capture of CO2 from air.

Microporous polyimides with functional groups for the adsorption of carbon dioxide and organic vapors

Highly cross-linked microporous polyimide networks using (hexafluoroisopropylidene)diphenyl, benzophenone and biphenyl as linking struts and tetraphenylmethane and tetraphenyladamantane as net nodes were synthesized under well controlled polymerization conditions. The resultant polyimides show initial decomposition temperatures over 500 °C and BET surface areas up to 781 m2 g−1 with quite uniform pore sizes at around 0.5 nm. It is found that the presence of a high density of trifluoromethyls gives rise to a simultaneously larger CO2 uptake (13.5 wt%, 273 K/1 bar) and CO2/N2 selectivity (53.5, IAST method), while the introduction of benzophenone groups enhances the interaction between the CO2 molecules and polymer skeleton, thereby leading to a high heat of adsorption (33.3 kJ mol−1) and selectivities of CO2/N2 (59.2) and CO2/CH4 (15.8). The polyimides exhibit large adsorption capacities for organic vapors such as benzene (104.9 wt%) and cyclohexane (60.2 wt%) at 298 K and P/Po = 0.8. In addition, the low-surface-energy trifluoromethyls significantly decrease the water uptake in the fluorinated polyimide compared to the non-fluorinated samples. The improved hydrophobicity is advantageous for the practical application of porous adsorbents in CO2 capture from flue gas and natural gas.

Starburst dendrimers consisting of triphenylamine core and 9-phenylcarbazole-based dendrons: synthesis and properties.

Novel dendrimers consisting of a triphenylamine core and 1st to 3rd generations of 9-phenylcarbazole-based dendrons were synthesized by Suzuki coupling reaction through convergent approach. Their structures were confirmed by two-dimensional correlated H-H COSY and C-H HSQC NMR spectra, MALDI-TOF MS and elemental analysis. The dendrimers exhibit excellent thermal stability with 5% weight loss temperatures over 540 °C. The computer modeling reveals that the dendrons in dendrimers greatly twisted with the generation, leading to the dendrimers decreased crystalline ability. Of interest is the observation that, for an identical dendrimer, the solid film displays the similar UV absorption and luminescence emission profiles to the solution sample, indicating that, after evaporation of solvent, the rigid dendrimer can well maintain its conformational morphology and the aggregation or stacking of the chromophoric groups is significantly inhibited. All the dendrimers can emit intense fluorescence with narrow full width at half maximum (FWHM) around 46-50 nm. Moreover, with the incremental generation, the quantum efficiencies remarkably increase from 64 to 95%, suggesting that the highly contorted and bulky dendrons effectively decrease energy wastage and non-radiative decay. The synergistic effect of electron-donating triphenylamine core and 9-phenylcarbazole-based dendrons results in the HOMO energy level of -5.36 eV for the 3rd-generation dendrimer, very close to the work function of the ITO/PEDOT electrode (-5.2 eV), which characteristic is very advantageous for the hole injection and transport materials.

Dendrimers with tetraphenylsilane core and 9-phenylcarbazole-based dendrons: synthesis, photophysics, and electrochemical behavior

Three generations of novel dendrimers (G1, G2 and G3) with a tetraphenylsilane core and 9-phenylcarbazole-based dendrons have been successfully synthesized. These dendrimers possess excellent thermal stability with 5% weight-loss temperatures in the range of 574 to 622 °C. Compared to the lower generation of dendrimer, G3 exhibits a high glass transition at 271 °C, indicating that the high content of 9-phenylcarbazole results in a dendrimer with significantly enhanced rigidity. The contorted dendrons effectively inhibit the aggregation of conjugative chromophore groups, leading to a fluorescence quantum yield of up to 99.1%. Moreover, all the dendrimers have high energy band gaps, a characteristic which is especially desirable for host materials in the fabrication of organic light-emitting devices.