Relaxation of liquid‐crystalline polymer fibers in polycarbonate–liquid‐crystalline polymer blend system

The relaxation of liquid‐crystalline polymer (LCP) fibers in the polycarbonate (PC)/LCP blend was examined under various conditions on a hot‐stage microscope. LC5000 is a thermotropic LCP consisting of 80/20 hydroxybenzoic acid and poly(terephthalate). The geometry of the fibers is not an important factor in the relaxation process. Fibers of different aspect ratios and lengths relaxed at the same rate and exhibited identical onset times. Increasing the temperature caused the fibers to relax faster, especially near the nematic‐transition temperature. The fibers relaxed almost immediately when subjected to a temperature of 285 °C. At 280 °C the fibers were stable for 43 min, whereas at 270 °C no noticeable relaxation was evident. Addition of compatibilizer stabilized the fibers by enhancing the interfacial adhesion between the fibers and the PC matrix. Consequently, LCP fibers in the compatibilized system relaxed at a much higher temperature (294 °C) as compared with the uncompatibilized system (275–280 °C). © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2307–2312, 2003     

Living cationic polymerization of dihydrofuran and its derivatives

Cationic polymerization of 2,3‐dihydrofuran (DHF) and its derivatives was examined using base‐stabilized initiating systems with various Lewis acids. Living cationic polymerization of DHF was achieved using Et_1.5AlCl_1.5 in toluene in the presence of THF at 0 °C, whereas it has been reported that only less controlled reactions occurred at 0 °C. Monomer‐addition experiments of DHF and the block copolymerization with isobutyl vinyl ether demonstrated the livingness of the DHF polymerization: the number–average molecular weight of the polymers shifted higher with low polydispersity as the polymerization proceeded after the monomer addition. Furthermore, this base‐stabilized cationic polymerization system allowed living polymerization of ethyl 1‐propenyl ether and 4,5‐dihydro‐2‐methylfuran at ?30 and ?78 °C, respectively. In the polymerization of 2,3‐benzofuran, the long‐lived growing species were produced at ?78 °C. The obtained polymers have higher glass transition temperatures compared to poly(acyclic alkyl vinyl ether)s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4495–4504, 2008     

Characterization of annealed isotactic polypropylene in the solid state by 2D time‐domain 1H NMR

Two‐dimensional time‐domain ¹H NMR was used to investigate annealed isotactic polypropylene in the solid phase. The spin–lattice relaxation in the laboratory frame and in the rotating frame were correlated with the shape of the free induction decay to identify and characterize relaxation components over the temperature range −120 to 120 °C. Several phase transitions were observed, and three distinct solid phases, with different chain mobilities, were detected. Two of these phases were identified as regions with different mobilities within the crystalline phase. The third phase was characterized by a high degree of isotropy in molecular motion. This phase, identified as the amorphous phase, appeared as the polymer was heated above a low‐temperature (−45 °C) phase transition. All transitions observed at higher temperatures occurred exclusively in this phase. About one‐third of the polymer chains reside between crystalline lamellae, whereas the majority form amorphous regions outside fibrils of multilamellar structure. Furthermore, the glass‐to‐rubber transition, occurring above −15 °C, consists of three stages. During the first stage, between −15 °C and 15 °C, regions with an increased segment mobility (labeled intermediate phase) appear gradually within the amorphous phase. At 15 °C, the intermediate phase consists of ∼10% of the polymer units, or one‐third of the polymer units constituting the amorphous phase. Between 15 °C and 25 °C, the intermediate phase increases rapidly to 18%. This is associated with the appearance of semiliquid and liquid regions, likely within the intermediate phase. Polymer chain segments (and possibly entire chains) involved in the liquidlike phases exhibit heterogeneous molecular motion with a correlation frequency higher than 10⁶ Hz. These two stages of glass‐to‐rubber transition occur within amorphous regions outside multilamellar structures. The third stage of the glass transition, appearing above 70 °C, is associated with the upper glass transition and occurs within the interlamellar amorphous phase. Finally, on a timescale of 100 ms or less, spin diffusion does not couple the amorphous regions outside fibrils with crystalline and amorphous regions within multilamellar fibrils. However, on a timescale of hundreds of milliseconds to seconds, all different regions within isotactic polypropylene are partially coupled. It is proposed that the relative magnitude of the crystalline magnetization, as observed in the T_1ρ experiment, is a good measure of polymer crystallinity. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2487–2506, 2000     

Synthesis and properties of new organo‐soluble and strictly alternating aromatic poly(ester‐imide)s from 3,3‐bis[4‐(trimellitimidophenoxy)phenyl]phthalide and bisphenols

A series of new strictly alternating aromatic poly(ester‐imide)s having inherent viscosities of 0.20–0.98 dL/g was synthesized by the diphenylchlorophosphate (DPCP) activated direct polycondensation of the preformed imide ring‐containing diacid, 3,3‐bis[4‐(trimellitimidophenoxy)phenyl]phthalide (I), with various bisphenols in a medium consisting of pyridine and lithium chloride. The diimide–diacid I was prepared from the condensation of 3,3‐bis[4‐(4‐aminophenoxy)phenyl]phthalide and trimellitic anhydride. Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents such as N‐methyl‐2‐pyrrolidone (NMP) and N,N‐dimethylacetamide (DMAc). Transparent and flexible films of these polymers could be cast from their DMAc solutions. The cast films had tensile strengths ranging 66–105 MPa, elongations at break from 7–10%, and initial moduli from 1.9–2.4 GPa. The glass‐transition temperatures of these polymers were recorded between 208–275 °C. All polymers showed no significant weight loss below 400 °C in the air or in nitrogen, and the decomposition temperatures at 10% weight loss all occurred above 460 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1090–1099, 2000     

From toroidal to rod‐like nanostructure,a mechanism study for the reversible morphological control on amphiphilic triblock copolymer micelles

Mechanism of the morphological changes between toroidal and rod‐like nanostructures of P4VP‐b‐PS‐b‐P4VP amphiphilic triblock copolymer micelles has been investigated in aqueous solution. This transition is proved to be highly reversible and tunable upon changing temperature. The toroidal structure, evolving from fibers at 20 °C, can transform to rod‐like morphology as the temperature either gradually or directly increases to 80 °C, and vice versa. However, the transition mechanisms are quite different in different temperature‐changing processes. The structure and thickness of the micelles are dependent on the specific temperature, whereas the transition mechanism is related to the method of the temperature change. These morphological changes are considered as a result from the interaction parameter between the solvent and the copolymer blocks, especially the hydrophobic block. Our research complements the external control over the reversible morphological transition of block copolymer micelles without changing the composition of the system or introducing additional influencing factors. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1450–1457     

Polybenzimidazoles tethered with N‐phenyl 1,2,4‐triazole units as polymer electrolytes for fuel cells

Polybenzimidazole (PBI) polymers tethered with N‐phenyl 1,2,4‐triazole (NPT) groups were prepared from a newly synthesized aromatic diacid, 3′‐(4‐phenyl‐4H‐1,2,4‐triazole‐3,5‐diyl) dibenzoic acid (PTDBA). The obtained polymers show superior thermal and chemical stability and good solubility in many aprotic solvents. The inherent viscosities of all polymers were around 1 dL/g. They exhibit high thermal stability with initial decomposition temperature ranging from 515 to 530 °C, high glass transition temperature ranging from 375 to 410 °C, and good mechanical properties with tensile stress in the range of 66–98 MPa and modulus 1897–2600 MPa. XRD analysis indicates that these polymers are amorphous in nature. Physicochemical properties such as water and phosphoric acid‐uptake, oxidative stability, and proton conductivity of membranes of these polymers have also been determined. The proton conductivity ranged from 4.7 × 10^?3 to 1.8 × 10^?2 S cm^?1 at 175 °C in dry conditions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2289–2303, 2009     

Synthesis,thermal, rheological characteristics,and enzymatic degradation of aliphatic polyesters with lignin‐based aromatic pendant groups

This research aims to produce lignin‐based biodegradable polyesters with improved thermal quality. A series of aliphatic polyesters with lignin‐based aromatic side groups were synthesized by conventional melt‐polycondensation. Decent molecular weight (21–64 kg mol^?1) was achieved for the polymerizations. The molecular structures and thermal and mechanical properties of the obtained polyesters were characterized. As a result, the obtained polyesters are all amorphous, and their glass‐transition temperature (T_g) depends on the size of the pendant aromatic group (31–51 °C). Furthermore, according to the TGA results, the thermal decomposition temperatures of the polyesters are all above 390 °C, which make them superior compared with commercial biodegradable polyesters like polylactic acid or polyhydroxyalkanoates. Finally, rheological characteristics and enzymatic degradation of the obtained polyesters were also measured. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2314–2323     

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3‐bis[4‐(4′‐aminophenoxyl) cumyl] benzene

The double melting behavior of a thermotropic liquid crystalline polyimide was studied by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS). This liquid crystalline polyimide exhibited a normal melting peak around 278 °C and transformed into a smectic A phase. The smectic A phase changed to nematic phase upon heating to 298 °C, then became isotropic melt around 345 °C. The samples annealed or isothermally crystallized at lower temperature showed double melting endotherms during heating scan. The annealing‐induced melting endotherm was highly dependent on annealing conditions, whereas the normal melting endotherm was almost not influenced by annealing when the annealing temperature was low. Various possibilities for the lower melting endotherm are discussed. The equilibrium melting points of both melting peaks were extrapolated to be 283.2 °C. Combined analytical results showed that the double melting peaks were from the melting of the two types of crystallites generated from two crystallization processes: a slow and a fast one. Fast crystallization may start from the well‐aligned liquid crystal domains, whereas the slow one may be from the fringed or amorphous regions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3018–3031, 2000     

Synthesis,photoluminescence, and electrochromic properties of wholly aromatic polyamides bearing naphthylamine chromophores

A series of novel polyamides with pendent naphthylamine units having inherent viscosities of 0.15–1.02 dL/g were prepared via direct phosphorylation polycondensation from various diamines and a naphthylamine‐based aromatic dicarboxylic acid, 1‐[N,N‐di(4‐carboxyphenyl)amino]naphthalene. These amorphous polyamides were readily soluble in various organic solvents and could be cast into transparent and tough films. The aromatic polyamides had useful levels of thermal stability associated with high glass‐transition temperatures (268–355 °C), 10% weight loss temperatures in excess of 480 °C, and char yields at 800 °C in nitrogen higher than 60%. These polymers showed maximum ultraviolet–visible absorption at 350–358 nm and exhibited fluorescence emission maxima around 435–458 nm in N‐methyl‐2‐pyrrolidinone solutions with fluorescence quantum yields ranging from 0.4 to 15.0%. The hole‐transporting and electrochromic properties were examined with electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium tin oxide coated glass substrate exhibited one oxidative redox couple around 1.08–1.16 V (oxidation onset potential) versus Ag/AgCl in an acetonitrile solution and revealed good stability of the electrochromic characteristics, with a color change from colorless to green at applied potentials ranging from 0 to 1.6 V. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6094–6102, 2006     

Synthesis and properties of aromatic polyamides based on a benzonorbornane bis(ether carboxylic acid)

A set of new aromatic polyamides containing ether and benzonorbornane units were synthesized by the direct phosphorylation polycondensation of 3,6‐bis(4‐carboxyphenoxy)benzonorbornane with various aromatic diamines. The polymers were produced in high yields and moderate to high inherent viscosities (0.64–1.70 dL/g). The polyamides derived from rigid diamines such as p‐phenylenediamine and benzidine were semicrystalline and insoluble in organic solvents. The other polyamides were amorphous and organosoluble and afforded flexible and tough films via solution casting. These films exhibited good mechanical properties, with tensile strengths of 95–101 MPa, elongations at break of 13–25%, and initial moduli of 1.97–2.33 GPa. The amorphous polyamides showed glass‐transition temperatures between 176 and 212 °C (by differential scanning calorimetry) and softening temperatures between 194 and 213 °C (by thermomechanical analysis). Most of the polymers did not show significant weight loss before 450 °C in nitrogen or in air. Some properties of these polyamides were also compared with those of homologous counterparts without the pendent norbornane groups. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 947–957, 2002     

Structure development and physical properties achieved in the drawing and/or annealing of PEN fibers

As‐spun poly(ethylene‐2,6‐naphthalate) (PEN) fibers (i.e., precursors) prepared from high molecular weight polymer were drawn and/or annealed under various conditions. Structure and property variations taking place during the treatment process were followed via wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering, differential scanning calorimetry (DSC), and mechanical testing. Both the WAXS and DSC measurements of the cold‐drawn samples stretched from a low‐speed‐spun amorphous fiber indicate that strain‐induced crystallization can occur at a temperature below the glass‐transition temperature and that the resultant crystal is in the α‐form modification. In contrast, when the same precursor was subjected to constrained annealing, its amorphous characteristics remained unchanged even though the annealing was performed at 200 °C. These results may imply that the application of stretching stress is more important than elevated temperatures in producing α‐form crystallization. The crystalline structure of the hot‐drawn samples depends significantly on the morphology of the precursor fibers. When the precursor was wound at a very low speed and in a predominantly amorphous state, hot drawing induced the formation of crystals that were apparently pure α‐form modification. For the β‐form crystallized precursors wound at higher speeds, a partial crystalline transition from the β form to the α form was observed during the hot drawing. In contrast with the mechanical properties of the as‐spun fibers, those of the hot‐drawn products are not improved remarkably because the draw ratio is extremely limited for most as‐spun fibers in which an oriented crystalline structure has already formed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1424–1435, 2000     

Synthesis and characterization of thermally stable,high‐modulus polyimides containing benzimidazole moieties

A series of novel benzimidazole‐containing aromatic polyimides were prepared from synthesized 5,4′‐diamino‐2‐phenyl benzimidazole (DAPBI), and commercial dianhydrides by the conventional two‐step polymerization. The obtained films were amorphous and could afford flexible, transparent, and tough films with excellent thermal and mechanical properties. They showed high levels of tension strength of up to 234 MPa, modulus of up to 5.6 GPa without any stretching. According to thermal stability measurements, the glass‐transition temperatures of the polymers were observed between 329 and 425 °C. The 5% weight‐loss temperatures of most polyimides were above 600 °C in nitrogen. Excellent properties of these polyimides were proved to be attributed to the rigid‐rod structure and hydrogen bond of intermacromolecular. SAXS and SEM results showed self‐molecular orientation caused the formation of rod‐like extended conformations. It was demonstrated that high degree of supramolecular order led to the increase of thermal stability and mechanical properties of the polyimide films. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2024–2031, 2009     

Synthesis and properties of soluble,fluorescent polyesters and polyethers with substituted m‐terphenyl segments in the main chain

A new series of rigid polyesters and semiflexible polyethers were synthesized from 4,4″‐dihydroxy‐5′‐phenyl or anthracenyl‐m‐terphenyl. The polymers were characterized by viscometry, Fourier transform infrared, NMR, X‐ray, differential scanning calorimetry, thermomechanical analysis, thermogravimetric analysis, ultraviolet–visible, and luminescence spectroscopy. The polyesters were amorphous, whereas some of the polyethers showed a low degree of crystallinity. All the polymers displayed an enhanced solubility even in 1,1,2,2‐tetrachloroethane and tetrahydrofuran. The glass‐transition temperatures were 123–146 °C for the polyesters and 45–117 °C for the polyethers. The polymers were stable up to 213–340 °C and afforded anaerobic char yields of 36–62% at 800 °C. Their optical properties were investigated both in solution and in the solid state. They showed ultraviolet fluorescence, violet‐blue fluorescence, or both with emission maxima at 333–487 nm. The polymers with anthracenyl pendent groups exhibited higher fluorescence quantum yields and emission maxima redshifted compared with the corresponding polymers with phenyl pendent groups. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2381–2391, 2000     

Structure development of polyamide‐66 fibers during drawing and their microstructure characterization

Structure development during drawing was studied for three sets of polyamide‐66 (PA66) fibers with density, optical microscopy, wide‐angle X‐ray diffraction, and Fourier transform infrared spectroscopy. The crystallinity, estimated by density measurements, remained virtually constant with increasing draw ratios, indicating that stress‐induced crystallization did not occur for the PA66 fibers drawn at room temperature, but there was a rapid transformation from a hedrite morphology to a fibrillar one. The absence of stress‐induced crystallization differed from the behavior of polyamide‐6, and this was attributed to the stronger hydrogen bonding between polyamide chains and the higher glass‐transition temperature of PA66. Polarized infrared spectroscopy was used to measure the transition‐moment angles of the vibrations at 936 and 906 cm^?1, which were found to be 48 and 60°, respectively. The crystalline orientation was estimated from the band at 936 cm^?1, and the increase with an increasing draw ratio was in close quantitative agreement with X‐ray diffraction data; this showed that infrared spectroscopy could be used reliably to measure the crystalline orientation of PA66 fibers. Because we were unable to obtain the transition‐moment angle of the amorphous bands, the amorphous orientation was obtained with Stein's equation. The amorphous orientation developed more slowly than the crystalline orientation, which is typical behavior for flexible‐chain polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1940–1948, 2002     

Crystallization and morphology of polymerized cyclic butylene terephthalate

The crystallization behavior and morphology of polymerized cyclic butylene terephthalate (pCBT) were investigated by thermal differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The spherulite growth rate was analyzed based on the Hoffman and Lauritzen theory to better understand the crystallization behavior. We found four typical morphologic features of pCBT corresponding to the crystallization temperature spectrum: usual negative spherulite, unusual spherulite, mixed birefringence spherulite coexisting with boundary crystals, and highly disordered spherulitic crystallites. The Avrami crystallization kinetics confirmed the occurrence of combined heterogeneous nucleation accompanied by a change in the spherulitic shape of pCBT, which also agreed with the PLM results. The equilibrium melting temperature and glass transition temperature of pCBT were 257.8 °C and 41.1 °C, respectively. A regime II–III transition occurred at 200.9 °C, which was 10 °C lower than that reported for poly(butylene terephthalate) (PBT). Coinciding with and attributed to the regime transition, the boundary crystal disappeared at temperatures above 200 °C and the morphology changed from the mixed type to highly disordered spherulitic crystallites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1127–1134, 2010     

Synthesis and properties of soluble aromatic polyamides derived from 2,2′‐bis(4‐carboxyphenoxy)‐9,9′‐spirobifluorene

The synthesis of a new bis(ether carboxylic acid), 2,2′‐bis(4‐carboxyphenoxy)‐9,9′‐spirobifluorene, in which two orthogonally arranged carboxyphenoxyfluorene entities are connected through an sp³ carbon atom (the spiro center), is reported. The direct phosphorylation polycondensation of this diacid monomer with various aromatic diamines yields aromatic polyamides containing 9,9′‐spirobifluorene moieties in the main chain. The presence of the spiro segment restricts the close packing of the polymer chains and decreases interchain interactions, resulting in amorphous polyamides with enhanced solubility, and high glass‐transition temperatures and good thermal stability are maintained through controlled segmental mobility. The glass‐transition temperatures of these polyamides are in the range of 234–306 °C, with 10% weight losses occurring at temperatures above 530 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1160–1166, 2003     

Effects of electron irradiation on poly(vinylidene fluoride–trifluoroethylene) copolymers studied by solid‐state nuclear magnetic resonance spectroscopy

The effects of electron irradiation on the molecular chemical structure, conformation, mobility, and phase transition of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer have been investigated with variable‐temperature, solid‐state ¹⁹F nuclear magnetic resonance (NMR). It has been found that electron irradiation converts all‐trans conformations of both VDF‐rich and TrFE‐containing segments into dynamically mixed trans–gauche conformations accompanied by a simultaneous ferroelectric‐to‐paraelectric (or amorphous) transition. The variable‐temperature ¹⁹F magic‐angle‐spinning spectra results show that the paraelectric phase melts at much lower temperatures in irradiated films than in an unirradiated sample. Moreover, ¹⁹F NMR relaxation data (spin–lattice relaxation times in both the laboratory and rotating frames) reveal that electron irradiation enhances the molecular motion in paraelectric regions, whereas the molecular motion in a high‐temperature amorphous melt (>100 °C) is more constrained in irradiated films. Besides these physical changes, electron irradiation also induces the formation of several CF₃ groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1714–1724, 2006     

Synthesis and properties of aromatic polyimides derived from 2,2,′3,3′‐biphenyltetracarboxylic dianhydride

2,2,′3,3′‐Biphenyltetracarboxylic dianhydride (2,2,′3,3′‐BPDA) was prepared by a coupling reaction of dimethyl 3‐iodophthalate. The X‐ray single‐crystal structure determination showed that this dianhydride had a bent and noncopolanar structure, presenting a striking contrast to its isomer, 3,3,′4,4′‐BPDA. This dianhydride was reacted with aromatic diamines in a polar aprotic solvent such as N,N‐dimethylacetamide (DMAc) to form polyamic acid intermediates, which imidized chemically to polyimides with inherent viscosities of 0.34–0.55 dL/g, depending on the diamine used. The polyimides from 2,2,′3,3′‐BPDA exhibited a good solubility and were dissolved in polar aprotic solvents and polychlorocarbons. These polyimides have high glass transition temperatures above 283°C. Thermogravimetric analyses indicated that these polyimides were fairly stable up to 500°C, and the 5% weight loss temperatures were recorded in the range of 534–583°C in nitrogen atmosphere and 537–561°C in air atmosphere. All polyimides were amorphous according to X‐ray determination. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1425–1433, 1999     

Thermal transition of a wholly aromatic thermotropic liquid crystalline copolyester

A copolyester was prepared from p-hydroxybenzoic acid (HBA), 2,6-naphthalene dicaboxylic acid (NDA), and hydroquinone (HQ). Thermal transition behavior and the crystal structure of this copolyester were investigated by using polarized light microscopy (PLM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD) after annealing at solid-phase polymerization conditions. A glass transition or newly ordered structure in the 270–290°C range was observed on annealing at 260°C, which increased with annealing time, attributed to mobility and reactive rearrangement in amorphous regions. Broad and unclear WAXD profiles and multimelting behaviors were found on annealing at 280°C, and explained by hexagonal and orthorhombic lattice formation and transformation. A large increase in melting temperature was observed only on annealing at a temperature (320°C) near the crystal–nematic transition, suggesting annealing temperatures near the melting point are required for sufficient mobility to afford crystalline rearrangement via transesterification. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3763–3769, 1999     

Synthesis and properties of new hydroxyl‐pendant aromatic polyimides derived from trimethylsilylated 4,4′‐diamino‐3,3′‐dihydroxybiphenyl and aromatic tetracarboxylic dianhydrides

New phenolic hydroxyl‐pendant aromatic polyimides were synthesized with the N‐silylated diamine method in two steps: the ring‐opening polyaddition of tetrakis(trimethylsilyl)‐substituted 4,4′‐diamino‐3,3′‐dihydroxybiphenyl to various aromatic tetracarboxylic dianhydrides, giving trimethylsiloxy‐pendant poly(amic acid) trimethylsilyl esters, and thermal imidization. The hydroxyl‐bearing polyimides were amorphous but insoluble in organic solvents. They had glass‐transition temperatures greater than 370 °C and temperatures of 10% weight loss greater than 415 °C in nitrogen. The hydroxyl‐pendant polypyromellitimide film had a high tensile strength and a high modulus of 310 MPa and 10 GPa, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1790–1795, 2002