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A series of uniaxially oriented polyimide (PI) films were fabricated via hot drawing at varying temperatures and draw ratios, and their orientation structure and thermal dimensional stability were investigated in detail. The infrared dichroism based on C = O symmetrical stretching was employed to effectively determine the orientation of chain segments. Other characteristic peaks, such as C = O asymmetric and C-N stretching, were highly sensitive to the geometric structure of chain segments, thereby providing a valuable means for comprehending their morphology. It has been observed that lower thermal expansion coefficient (CTE) can be achieved through low-temperature stretching, while high-temperature stretching is more effective in suppressing thermal shrinkage of the film. By quantitatively analyzing the orientation structure of infrared groups, the minimum structural unit highly associated with CTE was determined. These findings help to deepen our understanding of PI film performance and provide new ideas for studying thermal dimensional stability and draw processing. [ABSTRACT FROM AUTHOR]

Polyimides are a group of polymers with excellent thermal and mechanical properties. However, generally, they exhibit brown coloration due to charge transfer interactions between diamine donor and dianhydride acceptor moieties. In this study, semi-alicyclic polyimides derived from cyclohexane tetracarboxylic dianhydride and 4,4′-oxydianiline were prepared using a two-step method, where the imidization step proceeded via a chemical route. The effects of the catalyst type (quinoline, triethylamine, and 1,4-diazabicyclo(2.2.2)octane (DABCO)) and reaction temperature (120, 140, and 160 °C) on the imidization process were evaluated using infrared spectroscopy and nuclear magnetic resonance spectroscopy. The prepared polyimides' thermal, mechanical, and optical properties were compared with those synthesized via standard thermal imidization. Polyimide films possessing favorable mechanical properties, thermal stability, and good optical transparency were prepared via a simple preparation route based on chemical imidization using the triethylamine catalyst at the reaction temperature of 160 °C, which was shown to be a promising way for the PI preparation on an industrial scale. [ABSTRACT FROM AUTHOR]

Poly(amic acid) (PAA) is prepared by the reaction of dianhydride 4,4′-biphthalic anhydride and diamine bis[4-(3-aminophenoxy)phenyl]sulfone in N,N'-dimethylacetamide. Two types of fillers were dispersed in the as-synthesized PAA via a solution intercalation method; polyimide (PI) hybrid films were synthesized under various heat treatment conditions. Octylamine (C8) was introduced into graphene sheets (C8-GS) and bentonite (C8-BTN), which were then used as nanofillers in the PI hybrid films. The synthesized nanofillers were used in varying amounts of 0.25–1.00 wt% with respect to the matrix PI. The thermal and morphological properties and optical transparency of the hybrid films were investigated and compared for both C8-GS and C8-BTN at varying nanofiller content. The C8-BTN nanocomposite showed superior thermal properties, and optical transparency, and the filler was well dispersed in the PI matrix compared to the C8-GS nanocomposite. The thermal stability of the hybrid films improved upon the addition of small amounts of the nanofiller. However, beyond a certain critical filler concentration, the thermal stability declined. These results were verified through the dispersion of fillers via transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Black polymer films with high thermal stability are highly desired in flexible electrical and electronic fields. Conventional black polymer films based on high-temperature resistant polymers and black inorganic dyes are usually suffered from the poor electrical and tensile properties. In the current work, a series of intrinsically black polyimide (BPI) films with International Commission on Illumination (CIE) Lab optical parameters close to zero and high thermal stability have been designed and prepared. For this purpose, an electron-rich aromatic diamine, 4,4′-iminodianiline (NDA), was copolymerized with 1,4-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (sBPDA) to afford a series of poly(amic acid) (PAA) solutions, which were then thermally dehydrated to provide the final BPI films at elevated temperatures up to 400 °C in air. The molar fraction of NDA in the total diamine monomers was 0 for BPI-0 (sBPDA-PDA), 10% for BPI-1, 20% for BPI-2, 30% for BPI-3, 40% for BPI-4, 50% for BPI-5, and 100% for BPI-6. For comparison, two referenced polyimide (PI) films, including PI-ref1 and PI-ref2, were prepared according to a similar procedure. The former was derived from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) and the latter was from PMDA and NDA. The BPI films exhibited an increasing degree of blackness with the increasing contents of NDA units in the polymer films. For example, the BPI-6 (sBPDA-NDA) film exhibited the optical transmittance of 1.4% at a wavelength of 650 nm (T650), which was obviously lower than those of PI-ref1 (T650 = 74.6%) and PI-ref2 (T650 = 3.6%). In addition, the BPI-6 film showed the CIE Lab parameters of 0.39 for L*, 2.65 for a*, 0.66 for b*, and haze of 1.83, which was very close to the criterion of "pure blackness" for polymer films (L* = a* = b* = 0). At last, incorporation of the NDA units in the rigid-rod BPI-0 (BPDA-PDA) film slightly deteriorated the high-temperature dimensional stability of the derived BPI films. BPI-6 film showed a linear coefficient of thermal expansion (CTE) value of 34.8 × 10−6/K in the temperature range of 50 to 250 °C, which was higher than those of the BPI-0 (CTE = 12.3 × 10−6/K), PI-ref1 (CTE = 29.5 × 10−6/K), and PI-ref2 (CTE = 18.8 × 10−6/K) films. Nevertheless, the BPI films maintained good thermal stability with the 5% weight loss temperatures (T5%) higher than 590 °C, and the glass transition temperatures (Tg) higher than 340 °C. [ABSTRACT FROM AUTHOR]

Polyimide thin films with high thermal stability and resistance will contribute to the development of flexible energy devices, which could be compatible with their high temperature fabrication process. Thus, we have prepared poly(amic acid) solutions with bisbenzimidazole and bisbenzoxazole based diamines and finally fabricated polyimide thin films. After comparing with commercial type polyimides, the polyimides containing bisbenzimidazole and bisbenzoxazole segments showed excellent thermal decomposition temperatures (of 581 and 584 °C, respectively), outstanding mechanical properties (with a tensile strength of 218 and 192 MPa, respectively), and relatively low water absorption percentages (of 0.68% and 0.63%, respectively). The superior properties should be ascribed to the rigid molecular chain skeleton, strong inter- and intra-molecular-chain forces, and hydrogen bonds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two series films were prepared using APBIA and TFMB as diamine, PMDA and ODPA as dianhydride, TAPOB as crosslinking agent. • The addition of TAPOB maked for the adverse effects caused by adding fluorinated groups and lowering imidization temperature. • The XTTOP5-0.15 film with suitable monomer ratios and imidization temperature showed excellent comprehensive performance. • In molecular simulation, TAPOB content of PBII model is controlled by a TAPOB connecting chains of different lengths. In order to solve the problem of high-water absorption and low transparency of benzimidazole polyimide (PBII) films, this study introduced fluorine-containing groups into the benzimidazole polyimide molecule chains, and a series of benzimidazole polyimide films with different fluorine-containing ratios were prepared. In addition, a micro-branched crosslinking structure was established by adding triamino compounds to the system, and the effect of the micro-branched crosslinking structure on the film properties was investigated. The research showed that adding a certain amount of fluorine-containing groups could effectively improve the optical properties and decrease water absorption of polyimide films while having a small effect on the heat resistance and thermal dimensional stability. The incorporation of a small amount of triamino compounds effectively compensated for the adverse effects on the mechanical properties, heat resistance, and thermal dimensional stability caused by the addition of fluorine-containing groups and lowering the imidization temperature. In addition, the water absorption could be further reduced by establishing a cross-linked structure. In this study, a new design idea was provided to achieve the balance of heat resistance, thermal dimensional stability, water absorption, transparency, and mechanical properties of benzimidazole polyimide films. [ABSTRACT FROM AUTHOR]

A new class of polyimides had been synthesized from a novel aromatic diamine, 2',7'-bis(4-aminophenoxy)-spiro(4,5-diazafluoren-9,9'-xanthene). Polyimides were prepared by two-stage polycondensation of diamine monomer with various aromatic dianhydride. These polymers showed good thermal stability, solubility and optical transparency. These polymers showed good thermal stability, solubility and optical transparency. Except 6a, all polyimides were dissolved in aprotic polar solvents at room temperature. The glass transition temperatures (Tg) of the poly(ether imide)s were determined to be 338–423 °C and 345–428 °C by dynamic mechanical thermal analyses (DMA) and differential scanning calorimeter (DSC), respectively. Decomposition temperature for 10% weight loss all of these poly(ether imide)s above 560 °C in both nitrogen and air atmospheres. Normalized transparencies in the visible region (400–780 nm) were recorded between 67% and 83%. The dielectric constants of polyimide film were recorded in the range of 2.56–3.12 at 1 KHz. [ABSTRACT FROM AUTHOR]

[Display omitted] • The transparent, flexible, semi-aliphatic CPI films were elaborately prepared. • CPI-55 film has excellent thermal stability and high transparency. • The outstanding dielectric and mechanical properties are given to CPI-55 film. • CPI-55 film has an excellent prospect for application in the display technology. A set of colorless polyimide (CPI) films with norbornene-aliphatic ring structures has here been prepared through polycondensation reactions by using cyclopentanone bis-spironorbornane tetracarboxylic dianhydride (CpODA), 4,4′-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 4,4′-diaminodiphenyl ether (ODA) monomers as raw materials. The transmissivities, dielectric properties and thermal stabilities of CPI films are optimized by adjusting the CpODA-to-6FDA molar ratios. Compared with the aromatic and aliphatic PI films, the thermal stabilities and transmissivities of CPI films are well balanced. Moreover, the CPI films possessed low dielectric constants and low dielectric losses. The thermal expansion coefficients, temperatures at a 5% weight loss and glass-transition temperatures are maintained at 31–41 ppm K−1, 461–484 °C and 348–362 °C, respectively. In addition, the transmittances (86–89%), dielectric constants (2.15–2.47) and dielectric losses (<0.023) are all prominent. In short, the CPI films have been shown to have a high potential for use in the display technology. [ABSTRACT FROM AUTHOR]

Intrinsic polyimides (PIs) with high glass transition temperature (T g), excellent thermal stability, and favorable mechanical properties have been in great demand in recent years with the rapid development of flexible displays. In this work, an interchain-interaction "strengthener" has been introduced to obtain PIs with improved thermal resistance and stability. Benzimidazole-based diamines imparting rigidity, conjugation, crosslinking, and especially hydrogen bonding have been incorporated into benzoxazole-polyimide. Frequency shifts in the IR bands spectra of C O and N H bonds were indicative of strong hydrogen bonding in benzimidazole-incorporating PIs, resulting in an increase in T g from 333 °C to 442 °C. Furthermore, because of more extensive hydrogen bonding, PIs containing bis-benzimidazole units exhibited much higher crystallinity and T g than those containing mono-benzimidazole units. The 5% weight loss temperature ( T d 5 ) was above 550 °C because of the rigidity of the conjugated structure and the tightly packed state of the polymer chains. T g and T d 5 of PIs annealed in air were higher than those of samples annealed in vacuo , whereas the opposite trend was seen in crystallinity and mechanical properties. Finally, we delineated the effects of intermolecular interaction strengthener and annealing atmosphere on the properties of PIs, which may be helpful for the future design of flexible PI substrates. Image 1 • Polyimide matrix with tensive hydrogen-bonding network was achieved by introducing benzimidazole-substituted diamines. • The T g of these polyimides was improved from 333 °C to 442 °C. • 5% Weight loss temperature of these polyimides was higher than 556 °C. • The polyimides cured in air exhibits higher thermal resistance and stability than those cured in vacuo. [ABSTRACT FROM AUTHOR]

Abstract Six polyimides, containing pyridine and spirocyclic units, were successfully synthesized by chemical imidization. Structure-dependent properties such as thermal decomposition temperatures and gas permeabilities of the high-performance polymers were explicitly investigated. Results showed that all polyimide films exhibited good solubility in common organic solvents and non-polar solvents such as chloroform and tetrahydrofuran. The polymers exhibited good thermal stability, all demonstrating thermal decomposition temperatures (T d10%) over 496 °C in nitrogen. Important from a commercial viewpoint, the permeability coefficients of these for the acidic gas CO 2 showed an increase over other tested gases by virtue of the basic group pyridine (C–N linkages) in their structures. Graphical abstract Image 1 Highlights • Polyimides exhibited good solubility, which is easily to cast into film and apply in practice. • Polymers exhibited good thermal stability which maintain their structural integrity below 450 °C. • The permeability coefficients of CO 2 increased significantly by introduction of the pyridine groups. • Demonstrated the importance of introducing the rigidity to the chains for improving gas separation performance. [ABSTRACT FROM AUTHOR]

To develop colorless and soluble polyimide films, a novel dianhydride containing 1,4:3,6-dianhydro-D-mannitol unit, 2,5-bis(3,4-dicarboxyphenoxy)-1,4:3,6-dianhydromannitol dianhydride (IMDA) was synthesized. And two series of polyimides were prepared via a two-step thermal imidization, PI−(1–4) were obtained from IMDA and four kinds of aromatic diamines while PI−(5–7) from IMDA and three kinds of semiaromatic diamines. All the polyimides were readily soluble in common polar solvents and could afford flexible, tough and colorless films with transparency up to 89% at 450 nm. Especially, polyimides simultaneously containing 1,4:3,6-dianhydrohexitol units in diamine and dianhydride exhibited comparable optical and soluble performance with the alicyclic fluorinated ones. Meanwhile, it was certified that 1,4:3,6-dianhydrohexitol fragment in dianhydride was more determinant in solubility and transmittance of polyimides than that in diamine. An overall investigation of these polyimides on thermal, mechanical, morphological, soluble, optical and dielectric properties was presented, and their structure-property relationships were discussed in detail. [ABSTRACT FROM AUTHOR]

• Properties of two types of CPI films under the photo-oxidation are investigated. • The yellowness index, thermal stability and mechanical properties are degraded. • The microstructure evolution of CPI films under the photo-oxidation are studied. • The content of the C O with the depth under the photo-oxidation is studied. • The relationship between properties and the microstructure has been revealed. Colorless transparent polyimide (CPI) films with high thermal stability, superior mechanical and dielectric properties are widely used in optoelectronic devices, in which the properties are degraded in service. In this work, the degradation in properties and molecular mechanisms of the CPI-L film with the trifluoromethyl group and CPI-T film with the alicyclic group under photo-oxidation are revealed. It is found that for CPI-L and CPI-T films after 168 h photo-oxidation, the mechanical properties and thermal stability are decreased, especially the yellowness index is increased by 740% and 530%, respectively. Consequently, the degradation of the CPI-L film is more severe than the CPI-T film after photo-oxidation. This is because that the transmission at 365 nm of CPI-L and CPI-T films before photo-oxidation is 51% and 64%, respectively. After photo-oxidation, the ether bond, imide ring and phenyl of both CPI films are broken, and the rearrangement of C N in the CPI-L film is observed. And eroded voids and/or microcracks caused by off-gassing appear at 120 h and 72 h, respectively. Furthermore, possible molecular mechanisms of CPI films during photo-oxidation are proposed, and the relationship between molecular mechanisms and properties degradation is elucidated. Moreover, the content of the C O is decreased with the increased depth of CPI-L and CPI-T films, indicating the enrichment of the C O on the surface. It is mainly because free radicals generated during photo-oxidation can combine with the atmospheric O 2. [ABSTRACT FROM AUTHOR]

A series of new organic polyimides were synthesized from 4-fluoro-4'4"-diaminotriphenylmethane and four different aromatic dianhydrides through a one-step, high-temperature, direct polycondensation in m-cresol at 180-200 °C, resulting in the formation of high-molecular-weight polyimides (inherent viscosities ∼ 1.0-1.3 dL/g). All the resulting polyimides exhibited good thermal stability with initial decomposition temperatures above 434 °C, glass-transition temperatures between 285 and 316 °C, and good solubility in polar aprotic solvents. Wide-angle X-ray scattering data indicated that the polyimides were amorphous. Dense membranes were prepared by solution casting and solvent evaporation to evaluate their gas transport properties (permeability, diffusivity, and solubility coefficients) toward pure hydrogen, helium, oxygen, nitrogen, methane, and carbon dioxide gases. In general, the gas permeability was increased as both the fractional free volume and d-spacing were also increased. A good combination of permeability and selectivity was promoted efficiently by the bulky hexafluoroisopropylidene and 4-fluoro-phenyl groups introduced into the polyimides. The results indicate that the gas transport properties of these films depend on both the structure of the anhydride moiety, which controls the intrinsic intramolecular rigidity, and the 4-fluoro-phenyl pendant group, which disrupts the intermolecular packing. [ABSTRACT FROM AUTHOR]

• A hierarchical "brick and plank" structure is fabricated by dopamine modified h -BN nanomaterials. • This special structure can be used to improve the performance of polyimide. • The modified PI films have quasi-isotropic thermal conductivity and high thermal stability. • The modified PI films have good flexibility and excellent electrical insulation. • The modified PI films show faster shape memory response time reducing 50 %. Currently, the application of polyimide (PI) based materials often demands mutual additional properties, such as high thermal conductivity, good flexibility, high thermal stability and low dielectric constant and loss, etc.. Herein, a well-aligned hierarchical "brick and plank" architecture by rational assembly of dopamine modified hexagonal boron nitride flakes and nanoparticles (PDA-BNF@BNNPs) which can effectively improve the thermal conductivity, thermal stability, electrical conductivity, dielectric properties and shape memory performance of pure PI. The alternating stacking of vertically arranged h -BNNPs and horizontally laid h -BNFs yield a quasi-isotropic thermal conductivity of PI films with a high through-plane thermal conductivity of 6.43 W/(mK) and an in-plane thermal conductivity of 11.85 W/(mK) because of the simultaneously vertical and horizontal phonon scattering enabled by the vertically arranged h -BNNPs and horizontally laid h -BNFs. Besides, this special structure also endues PI films high thermal stability of over 560 °C, prominent electrical resistance of over 1.40 × 10-13 Ω•cm, and low dielectric loss of less than 0.02 in the high frequency. Moreover, the PDA-BNF@BNNP/PI films exhibit excellent flexibility and shape memory performance with faster recovery response time reduced over 50 % comparing with that of pure PI film. These outstanding properties combining with the facile and scalable fabrication process make PDA-BNF@BNNP/PI films are very promising in diverse electronic device applications, especially in flexible electronic devices or circuits requiring additionally high thermal conductivity and low dielectric loss. [ABSTRACT FROM AUTHOR]

New polyimide (PI) films containing zeolite L and/or silica, having a thickness of tens of micrometers, were prepared using a PI matrix with pendant carboxylic groups. The influence of various ratios of inorganic filler on thermal stability, dielectric behavior, and gas transport properties of the films was studied with respect to their structure. The surface morphology was investigated by scanning electron microscopy. The films were flexible, tough, and showed good thermal properties with a glass transition temperature in the range of 187–218°C. The dielectric spectroscopy revealed γ and β subglass transitions having the corresponding relaxation activation energy in the range of 44.7–51.4 kJ mol−1 and 65.1–121.6 kJ mol−1, respectively. At temperatures above 200°C, a conductivity relaxation process was evidenced. Gas permeation tests using small molecules (O2, N2 and CO2), at 6 atm and 30°C, indicated that the PI films containing higher amount of zeolite showed the highest permeability for all gases. [ABSTRACT FROM AUTHOR]

Homopolyimides are prepared by 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as dianhydride monomer and several diamine monomers. The copolyimides are prepared with 4,4′-oxydianiline as an amine monomer， 3,3′,4,4′-oxydiphthalic anhydride as an anhydride monomer with the addition of 4,4′-(ethyne-1,2-diyl)diphthalic anhydride as another anhydride monomer. The structure of polyimides is characterized by Fourier transform infrared spectroscopy and X-ray diffraction. Thermogravimetric analysis, thermomechanical analysis and thermo-oxidative degradation kinetics analysis are used to investigate the properties of polyimides. The homopolyimide show the best thermal stability in both nitrogen and air atmosphere by 4,4′-oxydianiline and 4,4′-(ethyne-1,2-diyl)diphthalic anhydride. The results also indicate that the thermally cross-linkable copolyimide films not only enhance the thermal stability behaviors of polyimide by controlling the addition of dianhydride, but also improve substantially the upper limit temperature of thermal aging by undergoing chemical cross-linking reaction of the diphenylethynylene structures and providing multifarious naphthalene ring groups and biphenyl structures. Diphenylacetylene crosslinking merging to the long-chain of polyimide is a useful conversion for enhancing the thermal stability and the thermal degradation stability of aromatic polymers. [Display omitted] • Multi polyimides containing the diphenylethynylene structures were researched. • Studying on thermal aging and thermal properties of diphenylethynylene copolyimide. • Heat treatment can greatly improve the thermal properties of as-prepared polyimide. • Excellent thermal property (The upper limit aging temperature > 360 °C; T g > 300 °C). [ABSTRACT FROM AUTHOR]

The relatively poor atomic-oxygen (AO) resistance of the standard polyimide (PI) films greatly limits the wide applications in low earth orbit (LEO) environments. The introduction of polyhedral oligomeric silsesquioxane (POSS) units into the molecular structures of the PI films has been proven to be an effective procedure for enhancing the AO resistance of the PI films. In the current work, a series of POSS-substituted poly (pyromellitic anhydride-4,4′-oxydianiline) (PMDA-ODA) films (POSS-PI) with different POSS contents were synthesized via a POSS-containing diamine, N-[(heptaisobutyl-POSS)propyl]-3,5-diaminobenzamide (DABA-POSS). Subsequently, the effects of the molecular structures on the thermal, tensile, optical, and especially the AO-erosion behaviors of the POSS-PI films were investigated. The incorporation of the latent POSS substituents decreased the thermal stability and the high-temperature dimensional stability of the pristine PI-0 (PMDA-ODA) film. For instance, the PI-30 film with the DABA-POSS content of 30 wt% in the film exhibited a 5% weight loss temperature (T5%) of 512 °C and a coefficient of linear thermal expansion (CTE) of 54.6 × 10−6/K in the temperature range of 50–250 °C, respectively, which were all inferior to those of the PI-0 film (T5% = 574 °C; CTE = 28.9 × 10−6/K). In addition, the tensile properties of the POSS-containing PI films were also deteriorated, to some extent, due to the incorporation of the DABA-POSS components. The tensile strength (TS) of the POSS-PI films decreased with the order of PI-0 > PI-10 > PI-15 > PI-20 > PI-25 > PI-30, and so did the tensile modulus (TM) and the elongations at break (Eb). PI-30 showed the TS, TM, and Eb values of 75.0 MPa, 1.55 GPa, and 16.1%, respectively, which were all lower than those of the PI-0 film (TS = 131.0 MPa, TM = 1.88 GPa, Eb = 73.2%). Nevertheless, the incorporation of POSS components obviously increased the AO resistance of the PI films. All of the POSS-PI films survived from the AO exposure with the total fluence of 2.16 × 1021 atoms/cm2, while PI-0 was totally eroded under the same circumstance. The PI-30 film showed an AO erosion yield (Es) of 1.1 × 10−25 cm3/atom, which was approximately 3.67% of the PI-0 film (Es = 3.0 × 10−24 cm3/atom). Inert silica or silicate passivation layers were detected on the surface of the POSS-PI films after AO exposure, which efficiently prevented the further erosion of the under-layer materials. [ABSTRACT FROM AUTHOR]

Shape memory polyimides (SMPIs) have gained considerable attention as smart deformation materials for their excellent properties. However, the relationship between shape memory performance and polyimide structure have hardly mentioned. Hence, three shape memory polyimides were manufactured with different structure monomers. Pyridine-contained polyimide (PI-1) and trifluoromethyl-contained polyimide (PI-3) were investigated by experimentally and molecular simulations on the physical properties and shape memory behaviors comparing with the benzene-structured polyimide (PI-2). Results showed that all polyimide films exhibited good thermal properties (T g DMA>258 °C). All PIs possessed great shape memory performances and stabilities. It was found that the introduction of pyridine group (PI-1) will restrict the tensile strain in dual-shape memory process of 155% but enhance the R f and R r of 99.7% and 93.7%, comparing with PI-2 of 256%, 99.8% and 89.2%, respective. Moreover, PI-3 with the presence of trifluoromethyl group can marked improve the elongation strain of 313%, in the meanwhile kindly reduce the R r of 88.4%. Additionally, fractional free volume and storage modulus under high temperature provided simultaneous support for different shape memory performances. The current research may have specified a new way for the production and usage of the smart materials in practice. Image 1 • Polyimides exhibited good thermal stability, which can apply in high temperature condition. • Polyimides based on different chain structures processed various shape memory effects. • Demonstrated the importance of structure-shape memory properties especially strain and shape memory recovery rate. [ABSTRACT FROM AUTHOR]

In this study, we developed a series of highly stable UV absorbers for polymers which require lengthy high temperature processes, such as polyimide (PI). Three types of linear dimeric hydroxyphenyl benzotriazole derivatives were synthesized by linking monomers with different linker moieties (phenyl, disulfide, biphenyl). The arrangement between the monomers was affected by the type of linker moiety introduced in the dimeric hydroxyphenyl benzotriazole derivatives. As a result, the intermolecular interactions changed resulting in changes in thermal stability and solubility. These results revealed that dimeric hydroxyphenyl benzotriazole derivatives had remarkable stability compared to the monomer. Especially, a novel dimeric UV absorber with phenyl linker (PBT) exhibited excellent stability suitable for high temperature processes. Image 1 • Novel linear dimeric hydroxyphenyl benzotriazole derivatives were synthesized and used as UV absorber for polyimide film. • Synthesized dimeric UV absorbers showed higher thermal stability than monomer due to increased intermolecular interactions. • A novel compound PBT exhibited excellent thermal stability in transparent polyimide film. [ABSTRACT FROM AUTHOR]

A new aromatic diamine bearing ether and pendant 9(10H)-anthrone groups, 10,10-bis[4-(4-aminophenoxy)phenyl]-9(10H)-anthrone was reacted with various aromatic dianhydrides to yield the corresponding cardo polyimides via the poly(amic acid) (PAA) precursors and thermal or chemical imidization. The PAAs were produced with moderate to high inherent viscosities of 0.91–1.53 dL/g. All the PAAs could be cast from DMAc solution and thermally converted into transparent, flexible and tough polyimide films with tensile strength of 79.6–115.2 MPa, tensile modulus of 1.97–2.48 GPa, and elongation at break of 10.8–21.7%. These polyimides were predominantly amorphous, and displayed excellent thermal stability with glass-transition temperature of 290–359 °C, 10% weight loss temperature of 522–566 °C, and the residue of 59–65% at 800 °C in nitrogen. Most of the polyimides obtained by chemical cyclodehydration procedure were found to be soluble in NMP, DMF and mcresol at room temperature. [ABSTRACT FROM AUTHOR]

Low coefficient of thermal expansion (CTE) in the range of 40–400 °C is a crucial factor for polyimide (PI) films serving as the flexible substrate for display devices. The introduction of hydrogen bonds (H-bonds) is an effective method to obtain high Tg and low in-plane CTE below polyimide (PI) film. However, these H-bonds commonly exhibit low thermal stability and would be ruptured at high temperature (>300 °C), which leads to a remarkable increase of CTE. Herein, we report a strategy to improve thermal stability of H-bonds at the high temperature via intermolecular crosslinking. For neat PI, its in-situ FTIR results confirm severe dissociation of H-bonds above 300 °C, While after the crosslinking reaction, the content of strong H-bonds at 400 °C is 110% higher than that of neat PI, which indicates this intermolecular crosslinking restrains dissociation of H-bonds. Correspondingly, CTE values of crosslinked PI films at 300oC–400 °C are sharply decreased from 33.8 ppm/K to 6.0 ppm/K. Moreover, decrease of in-plane orientation accompanying lower CTEs in crosslinked PI deviates from common rule reported in linear PIs, implying the important roles of H-bonds and crosslinking. More over, the contribution of H-bonds and crosslink to the decrease of CTE are performed by Pearson correlation analysis and the results indicate that the decrease of CTE in crosslinked PIs at low temperatures is completely attributed to confinement effect of crosslinking, but contribution of stable H-bonds becomes more prominent above 300 °C. Consequently, the obtained PI films exhibit ultra low CTE (1.9 ppm/K) at the range of 40oC–400 °C, along with high Tg (>450 °C) exhibiting great potential for flexible-display substrates. Schematic diagram of effect of chemical crosslinking and hydrogen bonding interactions on dimensional stability is presented here. At low temperature (40–300 °C), hydrogen bonding dissociation is not so dramatic and group vibration is inhibited to some degree. Thus, CTE of PI-0 is very low (2.9 ppm/K) in this temperature range. At high temperature, dissociation of most of hydrogen bonds weakens interchain interaction and consequently intensifies group vibration and dimensional expansion, leading to high CTEs (33.8 ppm/K). Introducing a small portion of crosslinking sites, confinement of covalent bond suppresses group vibration and consequently inhibits extension of distance between hydrogen bonding donors and accepters at high temperature, leading to the enhancement of stability of hydrogen bonding. Those stable hydrogen bonds further promote dimensional stability especially at high temperature, leading to significant decrease of CTE of PI-DCX-0.35 from 33.8 ppm/K to 6.0 ppm/K in the range of 300oC–400 °C. Image 1 • Stability of H-bonds in PI films at high temperature is obviously enhanced via confinement effect of chemical crosslinking. • It was verified that, in heating procession, s-H-bonds are weakened, which induces vibration of benzimidazole ring and imide ring. • It was verified by Pearson correlation analysisthat contribution of stable H-bonds on decrease of CTE becomes prominent only above 300 °C. [ABSTRACT FROM AUTHOR]

Semi-alicyclic colorless and transparent polyimide (CPI) films usually suffer from the high linear coefficients of thermal expansion (CTEs) due to the intrinsic thermo-sensitive alicyclic segments in the polymers. A series of semi-alicyclic CPI films containing rigid-rod amide moieties were successfully prepared in the current work in order to reduce the CTEs of the CPI films while maintaining their original optical transparency and solution-processability. For this purpose, two alicyclic dianhydrides, hydrogenated pyromellitic anhydride (HPMDA, I), and hydrogenated 3,3',4,4'-biphenyltetracarboxylic dianhydride (HBPDA, II) were polymerized with two amide-bridged aromatic diamines, 2-methyl-4,4'-diaminobenzanilide (MeDABA, a) and 2-chloro-4,4'-diaminobenzanilide (ClDABA, b) respectively to afford four CPI resins. The derived CPI resins were all soluble in polar aprotic solvents, including N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). Flexible and tough CPI films were successfully prepared by casing the PI solutions onto glass substrates followed by thermally cured at elevated temperatures from 80 °C to 250 °C. The MeDABA derived PI-Ia (HPMDA-MeDABA) and PI-IIa (HBPDA-MeDABA) exhibited superior optical transparency compared to those derived from ClDABA (PI-Ib and PI-IIb). PI-Ia and PI-IIa showed the optical transmittances of 82.3% and 85.8% at the wavelength of 400 nm with a thickness around 25 μm, respectively. Introduction of rigid-rod amide moiety endowed the HPMDA-PI films good thermal stability at elevated temperatures with the CTE values of 33.4 × 10−6/K for PI-Ia and 27.7 × 10−6/K for PI-Ib in the temperature range of 50–250 °C. Comparatively, the HBPDA-PI films exhibited much higher CTE values. In addition, the HPMDA-PI films exhibited good thermal stability with the 5% weight loss temperatures (T5%) higher than 430 °C and glass transition temperatures (Tg) in the range of 349–351 °C. [ABSTRACT FROM AUTHOR]

As one of the youngest graphene derivative, fluorinated graphene (FG) with excellent mechanical strength and lubricity was incorporated into polyimide polymer (PI) to strengthen the comprehensive performance of nanocomposite. This article gives a detailed characterization to investigate the tribological behaviors of PI/FG nanocomposite films under different friction conditions including both of dry sliding and seawater lubrication. Firstly, the chloroform-treated FG was proved to be stably dispersed in the PI matrix. Subsequently, mechanical properties, thermal stability and tribological properties of PI/FG nanocomposite films were greatly improved. Finally, analysis of the reasons for the significant improvement in wear resistance from the viewpoint of thermal, mechanical properties and the evolution of friction products. Meanwhile, the transfer of FG from polymer matrix to frictional duality was revealed during tribological testing. The above results suggest the potential application of FG in the field of reinforcing polymer friction properties. [ABSTRACT FROM AUTHOR]

A series of intrinsically black polyimide (PI) films have been designed and synthesized by the copolymerization of pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA) and 4,4′-diaminodiphenylamine (NDA) via a two-step polycondensation procedure, followed by the high temperature imidization reaction of the poly(amic acid) (PAA) intermediates. Incorporation of the electron-rich NDA diamine apparently enhanced the formation of charge transfer complex (CTC) between the electron-donating diamine units and the electron-accepting dianhydride moiety; thus greatly absorbing the visible light and endowing the derived PI films deep colors. PI-5 with the 100% molar ratio of NDA in the diamines exhibited a cutoff wavelength value of 555 nm, which was 127 nm higher than that of PI-1 without NDA component. The PI films were nearly totally opaque at the wavelength of 500 nm when the molar ratio of NDA exceeded 80% in the diamines. PI-5 showed International Commission on Illumination (CIE) lab color parameters of 23.36 for L*, 46.43 for a*, and 40.26 for b*, indicating the essentially black plus red color instead of the yellow plus blue color for PI-1 film (L* = 89.93, a* = −11.09, and b* = 84.23). In addition, introduction of NDA into the copolymer films increased the high temperature dimensional stability of the films. PI-5 exhibited a glass transition temperature (Tg) and coefficient of thermal expansion (CTE) of 431.6 °C and 18.8 × 10−6 /K, respectively, which were superior to those of the PI-1 film (Tg = 418.8 °C, CTE = 29.5 × 10−6 /K). At last, incorporation of NDA components somewhat decreased the tensile properties and thermal decomposition temperatures of the PI films. [ABSTRACT FROM AUTHOR]

Optically transparent polyimides with excellent thermal stability and shape memory effect have potential applications in optoelectronic devices and aerospace industries. A series of optically transparent shape memory polyimide hybrid films are synthesized from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis-(trifluoromethyl)biphenyl-4,4′-diamine (TFMB) with various polyhedral oligomeric silsesquioxane (POSS) contents and then subjected to thermal imidization. The hybrid films show good optical transparency (>80% at 400 nm and >95% at 500 nm) with cutoff wavelengths ranging from 318 to 336 nm. Following the incorporation of the inorganic POSS structure, the hybrid films exhibit excellent thermal stability with glass transition temperature (Tg) ranging from 351 to 372 °C. The hybrid films possess the highest Tg compared with the previously-reported shape memory polymers. These findings show that POSS is successfully utilized to develop transparent polyimides with excellent thermal stability and shape memory effect. [ABSTRACT FROM AUTHOR]