Ruptured conjugated polymer thin films formed during spin coating

The formation of ruptured poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenyl vinylene] (MEH–PPV) thin films coated from undried tetrahydrofuran (THF) solutions was investigated. Because of the incompatibility of water and MEH–PPV, the polymer films coated from THF/water solutions showed a ruptured film structure. In the photoluminescence (PL) spectra of the polymer thin films, the ruptured polymer films showed a redshifted emission in comparison with continuous polymer thin films. According to a comparison of the PL spectra of polymer solutions and films, MEH–PPV in THF showed a coil–cylinder transition during precipitation from solution. Because of the incompatibility of water and MEH–PPV, an increase in the water content could increase the ratio of polymer chains in the cylinder conformation, resulting in a redshifted emission for the films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 79–84, 2006     

Regiospecific design strategies for 3‐arylpolythiophenes with pendant stable radical groups

Carbon—carbon bond‐forming polymerization of 2‐bromo‐3‐(3′,5′‐di‐t‐butyl‐4′‐methoxyphenyl)‐thiophene yields poly[3‐(3′,5′‐di‐t‐butyl‐4′‐methoxyphenyl)‐2,5‐thienylene] with regiospecific connectivity and a degree of polymerization of about six. Lewis‐acid‐moderated‐cleavage of the methoxy groups on the pendant phenyl group yield the corresponding polyphenolic polymer, which is oxidized under solution conditions to yield the title polyradical. Poly[3‐(3′,5′‐di‐t‐butyl‐4′‐oxyphenyl)‐2,5‐thienylene] exhibits a strong, persistent electron spin resonance spectrum and a UV–visible spectrum consistent with formation of the pendant phenoxyl spin‐bearing units. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 779–788, 1999     

High‐performing random terpolymer‐based nonfullerene polymer solar cells fabricated using solvent additive‐free as‐cast blend films

Two new random terpolymers containing 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) as a donating unit, methyl‐3‐thiophenecarboxylate (3MT) as a weak accepting unit, and the more electron‐deficient benzo[c][1,2,5]thiadiazole (BTz) or 5,5′‐bis(2‐ethylhexyl)‐4H,4′H‐1,1′‐bithieno[3,4‐c]pyrrole‐4,4′,6,6′(5H,5′H)‐tetraone (BiTPD) unit as a third monomer (respectively yielding 3MTB and 3MTT ) were synthesized in order to achieve improved physical and optoelectronic properties relative to the 3MT‐Th copolymer bearing only BDT and 3MT. The UV–vis absorption spectra and optical bandgap energies of these terpolymers were broader and smaller than those of the 3MT‐Th copolymer. In thin films, the terpolymers displayed the face‐on polymer chain orientation, indicating that the BTz or BiTPD unit in the terpolymer backbones did not affect the molecular arrangement on the substrate. In comparison with 3MT‐Th ‐based polymer solar cells (PSCs) as control devices, the PSCs employing blend films of these terpolymers as the donor and 2,2′‐[[6,6,12,12‐Tetrakis(4‐hexylphenyl)‐6,12‐dihydrodithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,8‐diyl]bis[methylidyne(3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis[propanedinitrile] (ITIC) as the acceptor exhibited higher power conversion efficiencies (>8.0%) for the same device configuration. In addition, the 3MTB‐ and 3MTT‐ based PSC devices displayed excellent shelf‐life even after aging for over 1000 h. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1528–1535     

Photodegradation‐induced photoluminescence behaviors of π‐conjugated polymers upon the doping of organometallic triplet emitters

The different effects on the photodegradation‐induced photoluminescence (PL) of π‐conjugated polymeric thin films upon the doping of Ir(III) containing triplet emitters in ambient conditions at room temperature were investigated. In this study, we prepared spin‐coated thin films using three different polymer matrices including poly(9‐vinylcarbazole) (PVK), poly[9,9‐bis(2‐ethylhexyl)fluorene‐2,7‐diyl] (PF2/6), and poly[2‐(5′‐cyano‐5′‐methyl‐hexyloxy)‐1,4‐phenylene] (CNPPP) derivatives doped with Ir(III) containing triplet emitters: Ir(III) bis[(4,6‐fluorophenyl)‐pyridinato‐N,C²′] picolinate (FIrpic), or Ir(III)fac‐tris(2‐phenylpyridine) (Ir(ppy)₃), or Ir(III)bis(2‐(2′‐benzothienyl) pyridinato‐N‐acetylacetonate) (Ir(btp)₂acac). Using the doped films, and their neat films, on quartz substrates, the UV‐Visible absorption (UV‐Vis) and PL spectra were recorded under continuous illumination with the excitation wavelengths at the absorption maxima of the corresponding matrix polymers. The dopant effects on the photodegradation‐induced PL were extracted from the kinetic data obtained from the doped films by subtracting the mutual degradation kinetics of their corresponding neat films. The obtained dopant effects show a strong correlation between the photo‐induced PL degradation and the exciton migration behaviors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2395–2403, 2008     

Self‐assembly of metallo‐supramolecular block copolymers in thin films

The self‐assembly of a metallo‐supramolecular PS‐[Ru]‐PEO block copolymer, where ‐[Ru]‐ is a bis‐2,2′:6′,2″‐terpyridine‐ruthenium(II) complex, in thin films was investigated. Metallo‐supramolecular copolymers exhibit a different behavior as compared to their covalent counterparts. The presence of the charged complex at the junction of the two blocks has a strong impact on the self‐assembly, effecting the orientation of the cylinders and ordering process. Poly(ethylene oxide) cylinders oriented normal to the film surface are obtained directly regardless of the experimental conditions over a wide range of thicknesses. Exposure to polar solvent vapors can be used to improve the lateral ordering of the cylindrical microdomains. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4719–4724, 2008     

Crown‐ether and azobenzene‐containing liquid crystalline polymers: An influence of macromolecular architecture on optical properties and photo‐orientation processes

A series of novel crown ether‐containing photochromic comb‐shaped liquid crystalline polyacrylates with different macromolecular structure of side groups were synthesized and investigated. Phase behavior, optical and photo‐optical properties of thin spin‐coated films of these polymers were studied. A special attention was paid to a comparative study of the photo‐orientation phenomena occurring in the polymer films under a polarized light action. It was shown that complex formation with the potassium ions results in the decrease in degree of the photoinduced order that can be used for the creation of new materials for sensor devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Azine bridge formation during the electrografting of acrylonitrile

We report the electrografting of polyacrylonitrile (PAN) films onto evaporated gold, silver, and copper substrates, and onto platinum foil. The FTIR spectra of the films are virtually identical to library spectra of PAN and show no evidence of the cyclization observed by some authors. Raman spectra of the same films, however, display a broad absorption band centered at ～1520 cm^?1 and a second band at 1096 cm^?1, which are neither present in spin‐coated films of commercially obtained PAN nor are they present in the FTIR spectra. These previously unreported Raman bands are dependent on a number of factors in the electrografting process; the working electrode metal, the monomer concentration, the solvent used, and the electrochemical protocol used for cleaning the working electrode. The relative intensity of the bands was found to be strongest in films grown on platinum and weakest in those grown on gold, and stronger in thin films (<50 nm) than in thick films (>100 nm). We suggest that these new spectral features are associated with azine‐linked polymer chains in a ladder‐like structure close to the electrode surface as a result of the predominantly isotactic brush‐like conformation of the polymer during the early stages of electrografting. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1685–1695, 2009     

Synthesis of poly(p‐phenylene vinylene)‐ and poly(phenylene ethynylene)‐based polymers containing p‐terphenyl in the main chain with alkoxyphenyl side groups

Starting from the pyrylium salt and following a facile synthetic route, we synthesized and polymerized 4,4″‐diiodo‐2′,6′‐di[4‐(2′‐ethylhexyl)oxy]phenyl‐p‐terphenyl with p‐divinylbenzene or p‐diethynylbenzene. The resulting polymers had moderate molecular weights, were amorphous, and dissolved in tetrahydrofuran and chloroform, with glass‐transition temperatures of 120–131 °C. The polymers behaved as violet‐blue‐emitting materials with photoluminescence maxima around 420 and 450 nm in solution and in thin films, respectively. They possessed well‐defined chromophores resulting from steric interactions in the polymer chain. The photoluminescence quantum yields were up to 0.29. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2591–2600, 2002     

Synthesis and optical properties of an azoaromatic,chromophore‐functionalized,oligomeric polyelectrolyte

A main‐chain, azoaromatic, chromophore‐functionalized polyelectrolyte with an oligomeric molecular weight was synthesized by the reaction of 4,4′‐azobispyridine and 1,6‐dibromohexane. The polyelectrolyte was designed to contain ionic groups to impart electrostatic self‐assembly with polyanion and azoaromatic groups for photoprocessability. The polymer solution exhibited a solvatochromic effect, having different absorption maxima in water (294 nm) and N,N‐dimethylformamide (400 nm). By a change in the counteranions of the bispyridinium groups, the solubility of the polymer could be controlled, and this made it possible to fabricate electrostatic assembled films or spin‐cast films for further applications. The direct photofabrication of laser‐induced interference patterns on polymer surfaces with large surface modulation was also investigated with an argon ion laser. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1196–1201, 2003     

A new terpyridine tethered polythiophene: Electrosynthesis and characterization

A novel polythiophene bearing a pendant terpyridine moiety has been synthesized by electrochemical polymerization of a new thiophene monomer, namely 4′‐(2,2′:5′,2″‐terthien‐3′‐ethynyl)‐2,2′:6′,2″‐terpyridine (TAT). The insertion of a conjugated ethynyl spacer between the terthiophene and the terpyridine fragments provides for an effective extension of the delocalization of electrons within the structural unit and the polymer as a whole. The synthesis and characterization of the relevant monomer, the electrosynthesis of the corresponding polymer and its electrochemical, UV–visible spectroelectrochemical and IR characterization are described. Finally, a comparison between the electrochemical, spectroscopic, and spectroelectrochemical properties of PTAT and the analogue, saturated‐spacer PTTT (TTT = 4′‐[(2,2′:5′,2″‐terthien‐3′‐yl)methoxy]‐2,2′:6′,2″‐terpyridine) polymer is discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of multiple adduct fullerenes on charge generation and transport in photovoltaic blends with poly(3‐hexylthiophene‐2,5‐diyl)

The effect of replacing [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) by its multiadduct analogs (bis‐PCBM and tris‐PCBM) in bulk heterojunction organic solar cells with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) is studied in terms of blend film microstructure, photophysics, electron transport properties, and device performance. Although the power conversion efficiency of the blend with bis‐PCBM is similar to the blend with PCBM, the performance of the devices with tris‐PCBM is considerably lower as a result of small photocurrent. Despite the lower electron affinity of the fullerene multiadducts, μs‐ms transient absorption measurements show that the charge generation efficiency is similar for all three fullerenes. The annealed blend films with multiadducts show a lower degree of fullerene aggregation and lower P3HT crystallinity than the annealed blend films with PCBM. We conclude that the reduction in performance is due largely to poorer electron transport in the blend films from higher adducts, due to the poorer fullerene network formation as well as the slower electron transport within the fullerene phase, confirmed here by field effect transistor measurements. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Effects of the oriented mesophase on the cold crystallization of syndiotactic polystyrene and its blend with poly(2,6‐dimethyl‐1,4‐phenylene oxide)

The effects of molecular orientation on the crystallization and polymorphic behaviors of syndiotactic polystyrene (sPS) and sPS/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) blends were studied with wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry. The oriented amorphous films of sPS and sPS/PPO blends were crystallized under constraint at crystallization temperatures ranging from 140 to 240°C. The degree of crystallinity was lower in the cold‐crystallized oriented film than in the cold‐crystallized isotropic film. This was in contrast to the case of the cold crystallization of other polymers such as poly(ethylene terephthalate) and isotactic polystyrene, in which the molecular orientation induced crystallization and accelerated crystal growth. It was thought that the oriented mesophase was obtained in drawn films of sPS and that the crystallization of sPS was suppressed in that phase. The WAXD measurements showed that the crystal phase was more ordered in an sPS/PPO blend than in pure sPS under the same annealing conditions. The crystalline order recovered in the cold‐crystallized sPS/PPO blends in comparison with the cold‐crystallized pure sPS because of the decrease in the mesophase content. The crystal forms depended on the crystallization temperature, blend composition, and molecular orientation. Only the α′‐crystalline form was obtained in cold‐crystallized pure sPS, regardless of molecular orientation, whereas α′, α″, and β′ forms coexisted in the cold‐crystallized sPS/PPO blends prepared at higher crystallization temperatures (200–240°C). The β′‐form content was much lower in the oriented sPS/PPO blend than in the isotropic blend sample at the same temperature and composition. It was concluded that the oriented mesophase suppressed the crystallization of the stable β′ form more than that of the metastable α′ and α″ forms during the cold crystallization of sPS/PPO blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1665–1675, 2003     

Thin films of PS/PS‐b‐pnipam and ps/pnipam polymer blends with tunable wettability

We developed thin films of blends of polystyrene (PS) with the thermoresponsive polymer poly(N‐isopropylacrylamide) (PNIPAM) (PS/PNIPAM) and its diblock copolymer polystyrene‐b‐poly(N‐isopropylacrylamide) (PS/PS‐b‐PNIPAM) in different blend ratios, and we study their surface morphology and thermoresponsive wetting behavior. The blends of PS/PNIPAM and PS/PS‐b‐PNIPAM are spin‐casted on flat silicon surfaces with various drying conditions. The surface morphology of the films depends on the blend ratio and the drying conditions. The PS/PS‐b‐PNIPAM films do not show an increase in their water contact angles with temperature, as it is expected by the presence of the PNIPAM block. All PS/PNIPAM films show an increase in the water contact angle above the lower critical solution temperature of PNIPAM, which depends on the ratio of PNIPAM in the blend and is insensitive to the drying conditions of the films. The difference between the wetting behavior of PS/PS‐b‐PNIPAM and PS/PNIPAM films is due to the arrangement of the PNIPAM chains in the film. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 670–679     

Synthesis and characterization of color‐stable electroluminescent polymers: Poly(dinaphtho[1,2‐a:1′,2′‐g]‐s‐indacene)s

Two new stepladder conjugated polymers, that is, poly(7,7,15,15‐tetraoctyldinaphtho[1,2‐a:1′,2′‐g]‐s‐indacene) (PONSI) and poly(7,7,15,15‐tetra(4‐octylphenyl)dinaphtho[1,2‐a:1′,2′‐g]‐s‐indacene) (PANSI) with alkyl and aryl substituents, respectively, have been synthesized and characterized. In comparison with poly(indenofluorene)s, both polymers have extended conjugation at the direction perpendicular to the polymer backbone because of the introduction of naphthalene moieties. The emission color of the polymers in film state is strongly dependent on the substituents. While PONSI emits at a maximum of 463 nm, PANSI with the same backbone but aryl substituents displays dramatically redshifted emission with a maximum at 494 nm. Both polymers show stable photoluminescence spectra while annealing at 200 °C in inert atmosphere. The PONSI‐based devices with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al turn on at 3.7 V, and emit at a maximum of 461 nm with the CIE coordinates of (0.19, 0.26), a maximum luminance efficiency of 1.40 cd/A, and a maximum brightness of 2036 cd/m² at 13 V. Meanwhile, the emission color of the devices is independent of driving voltage and keeps unchanged during the continuous operation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4866–4878, 2008     

Soluble dithienothiophene polymers: Effect of link pattern

Soluble conjugated polymers based on 3,5‐didecanyldithieno[3,2‐b:2′,3′‐d]thiophene—single‐bond ( 1 ), double‐bond ( 2 ), and triple‐bond linked ( 3 )—were synthesized by palladium(0)‐catalyzed Stille coupling reaction and oxidation polymerization. The thermal, absorption, emission, and electrochemical properties of these polymers were examined; the effect of the link pattern was studied. All polymers exhibit decomposition temperatures over 295 °C and glass‐transition temperatures in the range of 137–202 °C. The absorption spectra of 1 , 2 , and 3 in thin films exhibit absorption maxima at 381, 584, and 444 nm, respectively. Polymer 1 exhibits intense green emission located at 510 nm in film, whereas polymers 2 and 3 are nonemissive both in solution and in film due to H‐aggregate. Cyclic voltammograms of polymers 1 , 2 , and 3 display irreversible oxidation waves with onset oxidation potentials at 1.73, 0.78, and 1.03 V versus Ag⁺/Ag, respectively. Theory calculation on model compounds suggests that the dihedral angle decreases in the order of 1 > 3 > 2 . On reducing the dihedral angle, the polymer exhibits a longer absorption maximum, a smaller bandgap, a less oxidizing potential and fluorescence quench, due to more coplanar and more π‐electron delocalized backbone structure. Polymer solar cells were fabricated based on the blend of polymer 2 and methanofullerene [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM). The power conversion efficiency of 0.45% was achieved under AM 1.5, 100 mW cm^?2 using polymer 2 :PCBM (1:2, w/w) as active layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2843–2852, 2009     

Full color light‐emitting electrospun nanofibers prepared from PFO/MEH‐PPV/PMMA ternary blends

In this study, luminescence electrospun (ES) nanofibers based on ternary blends of poly(9,9‐dioctylfluoreny‐2,7‐diyl) (PFO)/poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV)/poly(methyl methacrylate) (PMMA) were prepared from chloroform solutions using a single capillary spinneret. Effects of PFO/MEH‐PPV ratio on the morphology and photophysical properties were studied while the PMMA weight percentage was fixed at 90 wt %. The morphologies of the prepared ES fibers were characterized by FE‐SEM and fluorescence microscopy. The obtained fibers had diameters around a few hundred nm and pore sizes in the range of 30–35 nm. The emission colors of the PFO/MEH‐PPV/PMMA blend ES fibers changed from blue, white, yellowish‐green, greenish‐yellow, orange, to yellow, as the MEH‐PPV composition increased. In contrast, the emission colors of the corresponding spin‐coated films were blue, orange, pink‐red, red, and deep‐red. Based on the values of solubility parameters, the PFO and MEH‐PPV are miscible to each other and trapped in the PMMA matrix. Hence, energy transfer between these two polymers is possible. The smaller aggregated domains in the ES fiber compared to those of spin‐coated films possibly reduce the efficiency of energy transfer, leading to different emission colors. Also, the prepared ES fibers had higher photoluminescence efficiencies than those of the spin‐coated films. Pure white light‐emitting fibers prepared from the PFO/MEH‐PPV/PMMA blend ratio of 9.5/0.5/90 had the Commission Internationale de L'Eclairage (CIE) coordinate of (0.33, 0.31). Our results showed that different color light‐emitting ES fibers were produced through optimizing the composition of semiconducting polymer in the transparent polymer matrix. This type of ES fibers could have potential applications as new light sources or sensory materials for smart textiles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 463–470, 2009     

Morphology and Performance of Poly(2-methoxy-5-(20-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV)∶(6,6)-Phenyl-C61-butyric Acid Methyl Ester (PCBM) Based Polymer Solar Cells

Polymer solar cells were fabricated based on composite films of poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV):fullerene derivative (6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) with weight blend ratio of 1:3, 1:4 and 1:5, spin‐coated from chloroform (CF), chlorobenzene (CB), and o‐dichlorobenzene (ODCB) solutions, respectively. Photoinduced current and power conversion efficiency (PCE) of the devices show a dependence on the solvents. The solar cells have the highest PCE at 1:5 blend ratio. Transmission electron microscopy (TEM) morphology reveals that there are some voids in MEH‐PPV:PCBM films. The void number decreases with the solvent from CF to CB and ODCB. We found the voids are located at the bottom of the films through electron tomography technique by TEM and film bottom‐side morphology study by atomic force microscopy. The charge carrier transport efficiency and collection efficiency should decrease greatly due to the voids, and the more voids the film has, the more degree the efficiencies decrease. PCE of the solar cell prepared from CF is lower than that of the solar cells prepared from CB and ODCB. The void phenomenon of MEH‐PPV:PCBM based solar cell and method to investigate the void position provide an experimental evidence and research mentality to fabricate polymer solar cell with high performance.     

Photoreactive main‐chain liquid‐crystalline polyesters: Synthesis,characterization, and photochemistry

Three series of semiflexible and rigid main‐chain polyesters containing photoreactive mesogenic units derived from p‐phenylenediacrylic acid (PDA) and cinnamic acid have been synthesized by high‐temperature polycondensation. The thermal and mesomorphic properties of the polymers have been determined. The photochemical behavior of polymer P‐[1]‐T, which contains a PDA unit, has been studied both in solution and in films. In solution, [2+2] photocycloaddition, E/Z photoisomerization, and photo‐Fries rearrangement can take place. In contrast, the dominant process in spin‐coated films is the [2+2] photocycloaddition reaction, which causes crosslinking of the polymer. In films, the photochemistry and induction of anisotropy are strongly influenced by the aggregation of the PDA phenylester unit. A dichroism of about 0.2 has been induced in films by irradiation with linearly polarized UV light, and thus the capability of these films to induce optical anisotropy and align liquid crystals has been demonstrated. Liquid‐crystalline cells have been made with polarized irradiated films of P‐[1]‐T as aligning layers. A commercial liquid‐crystalline mixture has been used for this study, and a similar liquid‐crystalline order determined by polarized Fourier transform infrared to a commercial cell with rubbed polyimide as an aligning layer has been detected. Because of crosslinking of the irradiated P‐[1]‐T photoaligning layer, the photoinduced anisotropy is stable at high temperatures, and the liquid‐crystalline molecules are insoluble in the irradiated polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4907–4921, 2005     

Improvement of thermoplasticity for s‐BPDA/PDA by copolymerization and blend with novel asymmetric BPDA‐based polyimides

Asymmetric biphenyl type polyimides (PI) derived from 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA) and p‐phenylenediamine (PDA) or 4,4′‐oxydianiline (ODA) show higher T_gs, and much better thermoplasticity than the corresponding isomeric PIs from symmetric 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA). In addition, a‐BPDA‐derived PIs are completely amorphous owing to their bent chain structures and highly distorted conformations, whereas the PIs from s‐BPDA are semicrystalline. a‐BPDA‐derived PIs possessing these properties or the a‐BPDA monomer were used as a flexible blend component or a comonomer to improve the insufficient thermoplasticity of semirigid s‐BPDA/PDA homo polymer. The blends composed of s‐BPDA/PDA (80%) with a‐BPDA‐derived PIs (20%), as well as the s‐BPDA/PDA‐based copolymer containing 20% a‐BPDA, showed a certain extent of thermoplasticity above the T_gs without causing a decrease in T_g. In addition, these blends and copolymer provided comparatively low thermal expansion coefficient (ca. 18 ppm). The improved film properties for the blends are related to good blend miscibility. On the other hand, when s‐BPDA/ODA was used as a flexible matrix polymer instead of a‐BPDA‐derived PIs, the 80/20 blend film annealed at 400°C exhibited no prominent softening at the T_g. This result arises from annealing‐induced crystallization of the flexible s‐BPDA/ODA component. Thus, these results revealed that a‐BPDA‐derived PIs are promising candidates as matrix polymers for semirigid s‐BPDA/PDA for the present purpose. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2499–2511, 1999