Preparation and Properties of Cyano-Containing Polyimide Films Based on 2,6-Bis(4-aminophenoxy)- benzonitrile

Polyimide-Derived Supramolecular Systems Containing Various Amounts of Azochromophore for Optical Storage Uses

The progress of digital technologies demands more speed and larger storage capacity. Optical storage systems have the advantage of being cheap, fast and capacious. This article explores the potential use of polyimide-based films as a recording medium for optical storage devices. The materials were designed through a host-guest approach that involves a cyano-containing polyimide precursor and an azochromophore combined in the following ratios: 1:0.25, 1:0.5, 1:0.75 and 1:1. After thermal treatment up to 200 °C, polyimide systems were formed with supramolecular structures constructed via hydrogen bonding as shown by molecular modeling and FTIR at around 3350 cm^-1. The aspects arising from the variation of the azo-dye content in the polyimide samples and their impact on the vitrification temperature, colorimetric features, refractive index, band gap, non-linear optical susceptibility and birefringence were investigated for the first time. The thermal analysis indicated a slight decrease in the vitrification temperature from 190.84 °C for the sample without azo dye to 163.91 °C for the film containing the highest leading of azo dye. The morphology images revealed the occurrence of periodic structures in azo-derived materials exposed to a UV laser, which is accentuated by the addition of more azo dye molecules. Optical tests allowed observation of the increase in the dominant wavelength, refractivity and optical conductivity of the samples, produced by the incorporation of azochromophore and laser irradiation. The photo-generated birefringence increased from 0.014 (sample with 1:0.25) to 0.036 (sample with 1:1), which in combination with the created regular topography pattern, is essential for the use of these materials as recording media in optical storage applications.

Low-Tg polyimides containing multiple ether linkages and cyano pendants

Some multi-ether linked polyimides (PIs) derived from two diamine monomers containing various amount of cyano groups are synthesized by a typical two-step polymerization. Meanwhile, the PIs with similar chemical structure but without cyano groups are prepared as counterparts for comparison purposes. The obtained PIs exhibit low glass transition temperature values of 211–258°C, which are associated with their multi-ether chemical structure. Furthermore, these PIs have high thermal stability, and the temperatures at 10% weight loss are in the range of 524–616°C under nitrogen atmosphere. It is found that the introduction of cyano groups would have a great influence on the properties of the PIs. The tensile strength and Young’s modulus of one cyano-containing PI reach 121 MPa and 1.4 GPa, respectively, which are much higher than those cyano-free ones. In addition, the cyano-containing PIs exhibit different behaviors of dielectricity and solubility in comparison with the corresponding cyano-free counterparts.

Synthesis and properties of the novel polyimides containing cyano and biphenyl moieties

A series of cyano-functionalized polyimides (CN-PIs) were prepared and derived from a novel diamine monomer having cyano and biphenyl groups. Meanwhile, another series of PIs without cyano groups (H-PIs) were prepared as counterparts for comparison purposes. Both series of PIs exhibited good solvent resistance, good thermal stability, remarkable film-forming ability, and excellent tensile properties. The Tg values of CN-PIs were 260–330°C, which were 10–17°C higher than the corresponding –CN free H-PIs. The CN-PIs exhibited no obvious decomposition below 470°C, and their 5% weight loss temperatures were above 568°C under nitrogen atmosphere. All the CN-PI films had high tensile strength and Young’s moduli, which were related to their rigid backbones and strong interactions between molecular chains. Due to their higher molar polarization, CN-PIs expressed the higher dielectric constants (3.29–3.69 at 1 MHz) in comparison with the corresponding H-PIs. CN-PIs exhibited the improved transparency, and both CN-PIs and H-PIs had better transparency than commercial Kapton® film. Introducing –CN groups could have an effect on the coefficient of thermal expansion and peel strength of the PIs. The peel strength of the PI, which was derived from cyano-functionalized diamine monomer and 4,4′-oxydiphthalic anhydride, could even reach 1.10 N mm-1, suggesting its strong interaction to copper matrix and potential use in flexible circuit board.

Synthesis and properties of cyano group–containing polyimides with high peel strength

In order to investigate the effect of cyano groups (–CN) on the properties of the polymers, two series of polyimides (PIs) based on a –CN-containing diamine monomer and a diamine monomer without –CN group were synthesized and characterized, respectively. After studying the structure–property relationships of these polymers, it was found that some properties could be greatly improved with the incorporation of –CN groups. Firstly, the tensile test showed that the –CN-containing polymeric films had higher tensile strength and Young’s moduli. The tensile strength and the Young’s modulus of 4,4′-(hexafluoroisopropylidene) diphthalic with –CN groups anhydride reached 154.1 MPa and 1.66 GPa, respectively. Secondly, thermogravimetric analysis results revealed that the –CN-containing polymers (CN-PI polymers) had good thermal stability and exhibited no decomposition below 470°C under nitrogen atmosphere. Thirdly, the dielectric constants of the CN-PI polymers were in the range of 3.67–3.84 at 10 MHz, which had an increase of 0.5 in comparison with the corresponding PIs without –CN groups. Fourthly, the CN-PI polymers had higher peel strength to copper foils. The peel strength of 4,4′-biphenyltetracarboxylic dianhydride-containing –CN groups could reach 1.28 N mm−1, suggesting its strong interaction to copper matrix and the potential use in flexibility circuit board. Finally, all the films showed better optical transparency compared with DuPont’s Kapton® film.

Highly Soluble Benzo[ghi]perylenetriimide Derivatives: Stable and Air-Insensitive Electron Acceptors for Artificial Photosynthesis

A series of new benzo[ghi]perylenetriimide (BPTI) derivatives has been synthesized and characterized. These remarkably soluble BPTI derivatives show strong optical absorption in the range of λ=300-500 nm and have a high triplet-state energy of 1.67 eV. A cyanophenyl substituent renders BPTI such a strong electron acceptor (Ered =-0.11 V vs. the normal hydrogen electrode) that electron-trapping reactions with O2 and H2 O do not occur. The BPTI radical anion on a fluorine-doped tin oxide|TiO2 electrode is persistent up to tens of seconds (t1/2 =39 s) in air-saturated buffer solution. As a result of favorable packing, theoretical electron mobilities (10(-2) ∼10(-1) cm(2) V(-1) s(-1)) are high and similar to the experimental values observed for perylene diimide and C60 derivatives. Our studies show the potential of the cyanophenyl-modified BPTI compounds as electron acceptors in devices for artificial photosynthesis in water splitting that are also very promising nonfullerene electron-transport materials for organic solar cells.

Novel and processable polyimides with a N-benzonitrile side chain: thermal, mechanical and gas separation properties

A series of organo-soluble and thermally stable polyimides with N-benzonitrile side group were synthesized from a new diamine monomer, 3-(bis(4-aminophenyl)amino)benzonitrile with different aromatic dianhydrides via thermal or chemical imidization.

Thermal, mechanical and optical transport properties of nanocomposite materials based on triethoxysilane-terminated polyimide and TiO2 nanoparticles

Novel polyimide/TiO₂ nanocomposites with good mechanical, optical and thermal properties were prepared by the incorporation of TiO₂ nanoparticles into silane terminated polyimide.

Preparation, characterization and gas separation properties of nanocomposite materials based on novel silane functionalizing polyimide bearing pendent naphthyl units and ZnO nanoparticles

Nanocomposites of polyimide with silane end group and ZnO nanoparticles with good thermal and mechanical properties were prepared and were used for gas separation.

Pushing the Envelope of the Intrinsic Limitation of Organic Solar Cells

The photogeneration of Frenkel-type excitons, instead of pairs of free charges, is one of the main drawbacks of organic photovoltaics, when compared with the inorganic counterpart. The strong Coulomb interaction of charge carriers of opposite sign in organic materials is responsible for the complexity of the process of generation of unbound charges, affecting the photogenerated current and still not clearly understood, as well as for the free energy loss of electrons resulting in a diminished open circuit voltage. Despite this practical limitation, record power conversion efficiencies approaching 10% are currently reported for lab-scale single-junction structures made of low-bandgap electron-donating conjugated small molecules or polymers blended with electron-accepting fullerene derivatives. To go beyond, a deep understanding of charge generation dynamics, highly system dependent, is necessary for the definition of the rules for the design of high-performance organic materials for the photovoltaic application and possibly the reduction of exciton binding energy, through the increase of the dielectric constant, which definitively would overcome the practical constraints to high efficiency organic solar cells.

Study of Aromatic Polyimides Containing Cyano Groups

Aromatic polyimides containing cyano groups have been synthesized by solution polycondensation reaction of an aromatic diamine having cyano and ether groups, with various aromatic dianhydrides containing flexible groups such as carbonyl and hexafluoroisopropylidene. The properties of these polyimides were compared with those of related polymers based on rigid aromatic dianhydrides, such as biphenyltetracarboxylic and pyromellitic dianhydride, and the same cyano containing diamine. The polymers were easily soluble in polar organic solvents, such as N-methylpyrrolidinone, N, N-dimethylacetamide and N, N-dimethylformamide and exhibited remarkable film forming ability, except for polyimide derived from pyromellitic dianhydride. They showed high thermal stability, with initial decomposition temperature being above 400 °C and glass transition temperature in the range of 210—260 °C. Conformational rigidity parameters of these polymers have been calculated by Monte Carlo method with allowance for hindered rotation. Several physical properties such as solubility and glass transition temperature are discussed in relation to the structure of the polymers and rigidity of their chains. The calculation of parameters of conformational rigidity showed that the glass transition temperature values (220—230 °C) increase with the increase of the rigidity. The polymers based on pyromellitic dianhydride form a separate group having the glass transition temperature values above 250 °C.