Facile non‐lithographic route to highly aligned silica nanopatterns using unidirectionally aligned polystyrene‐block‐polydimethylsiloxane films

Thin films (monolayer and bilayer) of cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) were shear aligned by the swelling and deswelling of a crosslinked PDMS pad that was physically adhered to the film during solvent vapor annealing. The nanostructures formed by self‐assembly were exposed to ultraviolet‐ozone to partially oxidize the PDMS, followed by calcination in air at 500 °C. In this process, the PS segments were fully decomposed, while the PDMS yielded silica nanostructures. The highly aligned PDMS cylinders were thus deposited as silica nanolines on the silicon substrate. Using a bilayer film, the center‐to‐center distance of these features were effectively halved from 38 to 19 nm. Similarly, by sequential shear‐alignment of two distinct layers, a rhombic array of silica nanolines was fabricated. This methodology provides a facile route to fabricating complex topographically patterned nanostructures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1058–1064     

Controlled co‐solvent vapor annealing and the importance of quenching conditions in thin‐film block copolymer self‐assembly

A controlled co‐solvent vapor annealing system was designed and constructed to investigate the effects of solvent vapor activity during the rapid ambient quenching process on the morphology of a cylinder‐forming poly(styrene)‐b‐poly (ethylene oxide) (PS‐PEO) annealed in toluene and water vapor. A phase transformation from cylinders in the bulk to close‐packed spheres in swollen thin films occurred, which was reversed upon quenching with dry nitrogen. Quenching with humidified nitrogen preserved the spherical morphology but could significantly alter domain spacing and reduce long‐range order in the dried films under some circumstances. Specifically, long‐range order in the quenched films was found to decrease as the quenching humidity decreased from the humidity used during annealing, and the best long‐range order was obtained when the humidity remained consistent throughout both annealing and quenching. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1125–1130     

Alignment behaviour of the discotic nematic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene on polyimide and cetyltrimethylammonium bromide coated substrates

The orientational behaviour of the nematic discotic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene (C8OBT) on substrates coated with a polyimide or cetyltrimethylammonium bromide (CTAB) was investigated by polarizing optical microscopy. The averaged order parameters and directions of the triphenylene core and the carbonyl groups of C8OBT were evaluated by an infrared dichroic method. The discotic nematic (N_D) phase of C8OBT exhibits a homeotropic alignment on a polyimide film, a typical nematic schlieren texture on a glass substrate, and a tilted or planar homogeneous alignment on a CTAB-coated substrate. The order parameter of the triphenylene core is higher on a polyimide film (S = 0.6) than on a CTAB-coated substrate (S = 0.2), whereas that of the carbonyl groups remains roughly constant at 0.2 to 0.3 independent of the substrate for the N_D phase.     

Temperature induced structural evolution of a fluorene‐thiophene copolymer on rubbed surfaces

The thermal alignment of the liquid crystalline fluorene‐thiophene copolymer (F8T2) on rubbed polyimide surfaces is investigated by ex‐situ and in‐situ X‐ray scattering experiments. The ex‐situ characterization allows an assignment of the observed diffraction peaks to distances between polymer backbones (1.6 nm), distances between the flexible side groups of the polymer chains (0.43 nm), and intramolecular distances of adjacent ring units (0.5 nm). The in‐situ characterization allows a temperature dependent observation of the polymer chain alignment. A gradual alignment process of the polymer backbones is observed for temperatures up to 563 K. Decreasing temperature after the polymer chain alignment is accompanied by a glass transition of the side chains at 380 K. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:1599–1604, 2009     

Synthesis,characterization and liquid crystal‐aligning properties of new poly{3‐[4‐(n‐alkyloxy)phenyloxy]pyromellitimide}s

Four new polypyromellitimides (MC_m‐PPIs and MC_m‐OPIs, m = 6, 8) that are singly substituted with a flexible n‐alkyloxy side branch at the pyromellitimide ring were prepared by the two‐step polycondensation of 3‐[4‐(n‐alkyloxy)phenyloxy]pyromellitic dianhydrides (MC_m‐PMDAs, m = 6, 8) with p‐phenylenediamine (PDA) and 4,4′‐oxydianiline (ODA), respectively. The dianhydride monomers were synthesized from durene via several reaction steps. Inherent viscosities of the precursor poly(amic acid)s ranged from 0.57 to 1.58 dl/g. After chemical structures of the polyimides had been characterized, their thermal properties, crystalline structures, and liquid crystal (LC) aligning abilities on their rubbed thin films were determined and discussed in comparison to the polypyromellitimides that are doubly substituted at the pyromellitimide ring with the same side branches. For all polymers thermogravimetric analysis (TGA) programs showed a typical two‐step degradation behavior with onset temperatures in the 430–455°C range. In X‐ray scattering studies all the samples were found to be amorphous, but the presence of a loosely developed layer structure could be confirmed, in which two main chains gather together to form a double‐strand backbone layer and n‐alkyl branches fill the space between the layers. On the rubbed surfaces of the polyimide thin films LCs uniformly aligned parallel to the rubbing direction with the pre‐tilt angles 5–7° in MC_m‐OPIs and 18–32° in MC_m‐PPIs. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and characterization of fluorene‐based oligomers and polymers incorporating N‐arylphenothiazine‐S,S‐dioxide units

A series of 3,7‐bis(9,9‐di‐n‐hexylfluoren‐2‐yl)‐N‐arylphenothiazine‐S,S‐dioxide trimers and (9,9‐di‐n‐octylfluorene‐2,7‐diyl‐co‐N‐arylphenothiazine‐S,S‐dioxide) co‐polymers, with varying ratios of phenothiazine‐S,S‐dioxide units, have been prepared in good yields by palladium‐catalyzed cross‐coupling reactions. The materials are deep blue emitters and show no solvatochromism or evidence for an intramolecular charge‐transfer state. The photoluminescence quantum yields of the trimers are ?_PL 15–30% in solution and 14–25% in films. The polymers demonstrated very high values in solution (?_PL 74–84%) and ?_PL values in films of 28–47%. The estimated HOMO energy levels are between ?5.64 and ?5.62 eV for the polymers with 15% incorporation of the phenothiazine‐S,S‐dioxide units. An analogous N‐arylphenothiazine co‐polymer shows significantly red shifted absorption and emission. Solution electrochemical data and density functional theory calculations are also presented. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

New photoluminescent conjugated polymers with 1,4‐dioxo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole (DPP) and 1,4‐phenylene units in the main chain

A series of π‐conjugated polymers and copolymers containing 1,4‐dioxo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole (also known as 2,5‐dihydro‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole‐1,4‐dione) (DPP) and 1,4‐phenylene units in the main chain is described. The polymers are synthesised using the palladium‐catalysed aryl‐aryl coupling reaction (Suzuki coupling) of 2,5‐dihexylbenzene‐1,4‐diboronic acid with 1,4‐dioxo‐2,5‐dihexyl‐3,6‐di(4‐bromophenyl)pyrrolo[3,4‐c]pyrrole and 1,4‐dibromo‐2,5‐dihexylbenzene in different molar ratios. Soluble hairy rod‐type polymers with molecular weights up to 21 000 are obtained. Polymer solutions in common organic solvents such as chloroform or xylene are of orange colour (λ_max = 488 nm) and show strong photoluminescence (λ_max = 544 nm). The photochemical stability is found to be higher than for corresponding saturated polymers containing isolated DPP units in the main chain. Good solubility and processability into thin films render the compounds suitable for electronic applications.     

Synthesis and characterization of novel fluorinated aromatic polyimides derived from 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,5‐ditrifluoromethylphenyl)‐2,2,2‐trifluoroethane and various aromatic dianhydrides

A novel fluorinated aromatic diamine, 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,5‐ditrifluoromethylphenyl)‐2,2,2‐trifluoroethane (9FMA), was synthesized by the coupling reaction of 3′,5′‐ditrifluoromethyl‐2,2,2‐trifluoroacetophenone with 2,6‐dimethylaniline under the catalysis of 2,6‐dimethylaniline hydrochloride. A series of fluorinated aromatic polyimides were synthesized from 9FMA and various aromatic dianhydrides, including pyromellitic dianhydride, 3,3′4,4′‐biphenyl tetracarboxylic dianhydride, 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), and 4,4′‐hexafluoroisopropylidene diphthalic anhydride, via a high‐temperature, one‐stage imidization process. The inherent viscosities of the polyimides ranged from 0.37 to 0.74 dL/g. All the polyimides were quickly soluble in many low‐boiling‐point organic solvents such as tetrahydrofuran, chloroform, and acetone as well as some polar organic solvents such as N‐methyl‐2‐pyrrolidinone, N,N′‐dimethylacetamide, and N,N′‐dimethylformamide. Freestanding fluorinated polyimide films could be prepared and exhibited good thermal stability with glass‐transition temperatures of 298–334 °C and outstanding mechanical properties with tensile strengths of 69–102 MPa and elongations at break of 3.3–9.9%. Moreover, the polyimide films possessed low dielectric constants of 2.70–3.09 and low moisture absorption (<0.58%). The films also exhibited good optical transparency with a cutoff wavelength of 303–351 nm. One polyimide (9FMA/BTDA) also exhibited an intrinsic negative photosensitivity, and a fine pattern could be obtained with a resolution of 5 μm after exposure at the i‐line (365‐nm) wavelength. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2665–2674, 2006     

Thermotropic liquid‐crystalline polyesters of 4,4′‐biphenol and phenyl‐substituted 4,4′‐biphenols with 4,4′‐oxybisbenzoic acid

A series of thermotropic polyesters, derived from 4,4′‐biphenol (BP), 3‐phenyl‐4,4′‐biphenol (MPBP), and 3,3′‐bis(phenyl)‐4,4′‐biphenol (DPBP), 4,4′‐oxybisbenzoic acid (4,4′‐OBBA), and other aromatic dicarboxylic acids as comonomers, were prepared by melt polycondensation and were characterized for their thermotropic liquid‐crystalline (LC) properties with a variety of experimental techniques. The homopolymer of BP with 4,4′‐OBBA and its copolymers with either 50 mol % terephthalic acid or 2,6‐naphthalenedicarboxylic acid had relatively high values of the crystal‐to‐nematic transition (448–460 °C), above which each of them formed a nematic LC phase. In contrast, the homopolymers of MPBP and DPBP had low fusion temperatures and low isotropization temperatures and formed nematic melts above the fusion temperatures. Each of these two polymers also exhibited two glass‐transition temperatures, which were associated with vitrified noncrystalline (amorphous) regions and vitrified LC domains, as obtained directly from melt polycondensation. As expected, they had higher glass‐transition temperatures (176–211 °C) than other LC polyesters and had excellent thermal stability (516–567 °C). The fluorescence properties of the homopolymer of DPBP with 4,4′‐OBBA, which was soluble in common organic solvents such as chloroform and tetrahydrofuran, were also included in this study. For example, it had an absorption spectrum (λ_max = 259 and 292 nm), an excitation spectrum (λ_ex = 258 and 292 nm with monitoring at 350 nm), and an emission spectrum (λ_em = 378 nm with excitation at 330 nm) in chloroform. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 141–155, 2002     

Spontaneous formation of hierarchical proton‐conductive structures in sulfonated poly(p‐phenylene terephthalamide) copolymer films

Two partially sulfonated copolymers of poly(p‐phenylene terephthalamide) were studied; the sulfonated diamine to nonsulfonated diamine ratios were x = 1 and x = 2. Polymer solutions in water demonstrated lyotropic liquid‐crystalline behavior, with the critical concentration for nematic phase formation being around 0.7 wt %. Films of these copolymers could be considered for fuel‐cell applications. The in‐plane proton conductivities were of the order of 10^?3 to 10^?2 S cm^?1 between 20 and 90 °C. Increasing the sulfonation level resulted in a more conductive material. Spontaneous alignment of the polymer occurred during film formation, as revealed by X‐ray diffraction. Scattering along the polymer backbone was observed perpendicular to the film, implying that the polymer chains were homeotropically aligned with respect to the film. The average degree of alignment was determined to be 0.66 and 0.77 for x = 1 and x = 2, respectively. Evidence of secondary layering within the plane of the film was seen in SEM images. These layers could provide a pathway for proton conduction to occur within the plane of the film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 666–676, 2007     

Synthesis,characterization, photo‐induced alignment,and surface orientation of poly(9,9‐dioctylfluorene‐alt‐azobenzene)s

Three types of bi‐functionalized copolymers ( P1FAz , P2FAz , and P3FAz ) with different numbers of fluorene units and an azobenzene unit were synthesized and characterized using UV–vis and polarized absorption spectroanalysis. The trans‐cis photoisomerization was conformed under 400 nm light irradiation for all copolymers in chloroform. However, in the film state, only the trans‐cis photoisomerization occurred by mono‐fluorene attached copolymer poly[(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl)‐alt‐4,4′‐azobenzene)] ( P1FAz ). Photo‐induced alignment was achieved using the P1FAz film after irradiation with linear polarized 400 nm light and subsequent annealing at 60 °C. Surface orientation of a spin‐coating film of poly(9,9‐didodecylfluorene) ( F12 ) was achieved using the photo‐induced alignment layer of the P1FAz film after annealing at 90 °C. The photo‐induced alignment layer of P1FAz has potential application to the surface orientation technique for appropriate polymers, which will be useful for the fabrication of optoelectronics devices. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Single‐Step Sulfo‐Selenization Method to Synthesize Cu2ZnSn(SySe1−y)4 Absorbers from Metallic Stack Precursors

Pentenary Cu₂ZnSn(S_ySe_1?y)₄ (kesterite) photovoltaic absorbers are synthesized by a one‐step annealing process from copper‐poor and zinc‐rich precursor metallic stacks prepared by direct‐current magnetron sputtering deposition. Depending on the chalcogen source—mixtures of sulfur and selenium powders, or selenium disulfide—as well as the annealing temperature and pressure, this simple methodology permits the tuning of the absorber composition from sulfur‐rich to selenium‐rich in one single annealing process. The impact of the thermal treatment variables on chalcogenide incorporation is investigated. The effect of the S/(S+Se) compositional ratio on the structural and morphological properties of the as‐grown films, and the optoelectronic parameters of solar cells fabricated using these absorber films is studied. Using this single‐step sulfo‐selenization method, pentenary kesterite‐based devices with conversion efficiencies up to 4.4 % are obtained.     

Dewetting behavior of Langmuir−Blodgett films of polystyrene‐b‐poly(methyl methacrylate) induced by solvent vapor annealing

In order to explore the degree of contact between hydrophilic blocks and the substrate, the dewetting behavior of Langmuir–Blodgett (LB) films of polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) induced by PMMA‐selective acetone vapor were investigated by atomic force microscopy (AFM) for the first time. With the annealing of acetone vapor, the LB films of PS‐b‐PMMA undergo the swelling and coalescing of aggregates, the formation of bicontinuous patterns, the formation of droplets, and the periodic increase and decrease of droplets. The emergence of the bicontinuous patterns indicates that the dewetting occurs via the spinodal dewetting mechanism. The periodic droplet evolution is a novel phenomenon observed for the first time and quite different from the single droplet evolution of spin‐coated films, which is probably due to the degree of contact between PMMA blocks and the substrate in the LB films being larger than that in the latter. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 825–830     

Effect of annealing on the structure and properties of poly(vinylidene fluoride) β‐form films

Oriented poly(vinylidene fluoride) (PVDF) films consisting of β crystals were prepared by the solid‐state coextrusion (SC) of a gel film near the melting temperature (T_m) and by conventional cold tensile drawing (TD) of a melt‐quenched film. These films were annealed over the temperature range of 75–190 °C (below and above the static T_m) while the sample length was kept constant or constant loads were applied. After annealing with the sample length kept constant, the dynamic Young's modulus markedly decreased because of the relaxation of oriented amorphous chains, as shown by infrared spectroscopy. In contrast, annealing under a constant load improved the chain orientation in both the crystalline and amorphous regions, resulting in an increase in the modulus from an initial 10.5 to 14.3 GPa for the SC and from an initial 3.3 to 4.8 GPa for the TD. The SC, annealed at 190 °C with a constant load corresponding to an initial tension of 200 MPa, exhibited an extreme crystalline‐chain orientation of 0.998 and a modulus of 14.3 GPa, among the highest values ever reported for PVDF. Although the remanent polarization (P_r) of the TD increased slightly from the initial 62 to 68 mC/m², P_r of the SC stayed constant at 100 mC/m² independently of the annealing conditions. This suggests that the P_r value of 100 mC/m² approached the equilibrium value for this PVDF sample containing 3.5 mol % structural defects. Therefore, although the modulus and P_r of the TD increased slightly with annealing, the maximum values achieved by annealing were markedly lower than those of the SC and annealed SC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1701–1712, 2003     

Synthesis and characterization of novel fluorinated polyimides derived from 4,4′‐[2,2,2‐trifluoro‐1‐(3‐trifluoromethylphenyl)ethylidene]diphthalic anhydride and aromatic diamines

A novel fluorinated aromatic dianhydride, 4,4′‐[2,2,2‐trifluoro‐1‐(3‐trifluoromethyl‐phenyl)ethylidene]diphthalic anhydride (TFDA) was synthesized by coupling of 3′‐trifluoromethyl‐2,2,2‐trifluoroacetophenone with o‐xylene under the catalysis of trifluoromethanesulfonic acid, followed by oxidation of KMnO₄ and dehydration. A series of fluorinated aromatic polyimides derived from the novel fluorinated aromatic dianhydride TFDA with various aromatic diamines, such as p‐phenylenediamine (p‐PDA), 4,4′‐oxydianiline (ODA), 1,4‐bis(4‐aminophenoxy)benzene (p‐APB), 1,3‐bis(4‐amino‐phenoxy)benzene (m‐APB), 4‐(4‐aminophenoxy)‐3‐trifluoromethylphenylamine (3FODA) and 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene (6FAPB), were prepared by polycondensation procedure. All the fluorinated polyimides were soluble in many polar organic solvents such as NMP, DMAc, DMF, and m‐cresol, as well as some of low boiling point organic solvents such as CHCl₃, THF, and acetone. Homogeneous and stable polyimide solutions with solid content as high as 35–40 wt % could be achieved, which were prepared by strong and flexible polyimide films or coatings. The polymer films have good thermal stability with the glass transition temperature of 232–322 °C, the temperature at 5% weight loss of 500–530 °C in nitrogen, and have outstanding mechanical properties with the tensile strengths of 80.5–133.2 MPa as well as elongations at breakage of 7.1–12.6%. It was also found that the polyimide films derived from TFDA and fluorinated aromatic diamines possess low dielectric constants of 2.75–3.02, a low dissipation factor in the range of 1.27–4.50 × 10^?3, and low moisture absorptions <1.3%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4143–4152, 2004     

An in situ GISAXS study of selective solvent vapor annealing in thin block copolymer films: Symmetry breaking of in-plane sphere order upon deswelling

Thin films of asymmetric poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymers are studied by means of in situ grazing-incidence small-angle X-ray scattering (GISAXS) during solvent vapor annealing in tetrahydrofuran, a solvent selective for the PS majority block of the copolymer. Upon swelling, PS-b-P4VP block copolymers form hexagonal arrays of spherical P4VP microdomains in a PS matrix in films 7–9 layers thick. Deswelling the films induces a transition from hexagonal to face-centered orthorhombic (fco) symmetry, which is stable only at ∼7 layers of spherical microdomains. Dry films show co-existing hexagonal and orthorhombic symmetries when the solvent is removed slowly, whereas instantaneous solvent removal suppresses the fco structure, resulting in films with only hexagonal structure. The in-plane order of microdomains is significantly deteriorated in dry films independent of the solvent removal rate.Spherical block copolymer microdomains are known to undergo a transition from hexagonal to orthorhombic packing in isothermally annealed thin films when the number of sphere layers is increased from 4 to 5. In this paper, in situ GISAXS experiments reveal that a similar transition occurs during solvent vapor annealing in a selective solvent. Interestingly, the transition from hexagonal to orthorhombic packing of spheres occurs as solvent is removed from a thin block copolymer film. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 331–338     

Highly organosoluble and flexible polyimides with color lightness and transparency based on 2,2‐bis[4‐(2‐trifluoromethyl‐4‐aminophenoxy)‐3,5‐dimethylphenyl]propane

A new diamine containing isopropylidene, methyl substituted arylene ether, and trifluoromethyl groups, 2,2‐bis[4‐(2‐trifluoromethyl‐4‐aminophenoxy)‐3,5‐dimethylphenyl]propane (BTADP), was synthesized and used in preparation of a series of polyimides by direct polycondensation with various aromatic tetracarboxylic dianhydrides in N, N‐dimethylacetamide (DMAc). All polymers derived from diamine (BTADP) with trifluoromethyl substituents were highly organosoluble in the solvents, like N‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethylacetamide, N,N‐dimethylformamide (DMF), pyridine, chloroform, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dichloromethane, cyclohexanone, and γ‐butyrolactone at room temperature or upon heating at 70 °C. Inherent viscosities of the polyimides were found to range between 0.58 and 0.97 dL·g^?1. These polyimides had glass transition temperatures between 256 and 307 °C, and their 10% mass loss temperatures ranged from 440 to 462 °C and 421 to 443 °C under nitrogen and air, respectively. These polyimides had low dielectric constants in the range of 2.84–3.09. All the polyimides could be cast into films from DMAc solutions and were thermally converted into color lightness, optically transparent, flexible, and tough polyimides. The polyimide films had a tensile strength in the range of 83–97 MPa and a tensile modulus in the range of 2.0–2.2 GPa. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5766–5774, 2004     

Annealing effect on performance and morphology of photovoltaic devices based on poly(3‐hexylthiophene)‐b‐poly(ethylene oxide)

Novel block copolymers, poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) (P3HT‐b‐PEO) were synthesized via Suzuki coupling reaction of P3HT and PEO homopolymers. The copolymers were characterized by NMR, gel permeation chromatography, differential scanning calorimeter, and UV–vis measurements. A series of devices based on the block copolymers with a fullerene derivative were evaluated after thermal or solvent annealing. The device using P3HT‐b‐PEO showed higher efficiency than using P3HT blend after thermal annealing. Phase‐separated structures in the thin films of block copolymer blends were investigated by atomic force microscopy to clarify the relationship between morphologies constructed by annealing and the device performance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Evolution in surface morphology during rapid microwave annealing of PS‐b‐PMMA thin films

Microwave annealing enables rapid (60 s) ordering and orientation of block copolymer films. The developed morphology in polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) thin films depends on details of the heating rate that is controlled by microwave output energy as well as the sample location in the microwave. Over a wide heating rate (1.1–2.7 °C/s), perpendicular orientation of the cylindrical mesostructure at the surface is >50% after 60 s, but goes through a maximum at 1.8 °C/s leading to approximately 97% perpendicular cylinders at the surface. The propagation of this perpendicular surface morphology through the film thickness is also dependent upon the microwave annealing conditions. The surface structure evolves with the microwave annealing time from imperfect ordering to perpendicular cylinders to parallel cylinders as the annealing time increases. This work demonstrates the importance of controlling the heating rate during microwave annealing, which will be critical for optimizing microwave conditions for directed self‐assembly. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1499–1506