Photoinitiators with functional groups. VI. Chemically bound sensitizers

Several benzophenone‐ and thioxanthone‐based photosensitizers (PSs) were covalently bonded to hydroxyalkylphenone‐ and aminoalkylphenone‐based photoinitiators (PIs) to enhance the rate of the excitation‐transfer effect due to the close vicinity of the PS to the PI. The properties of these new systems were investigated with UV spectroscopy and photo‐differential scanning calorimetry. Broadband irradiation experiments and selective excitation of the PS were carried out for the physical mixtures and covalently bonded PI/PS combinations to investigate the effect of excitation transfer. Selective excitation of the PS chromophore revealed that the energy transfer was significantly increased in covalently bonded initiators in comparison with the physical mixtures. This effect was most pronounced for the hydroxyalkylphenones that were sensitized by suitable benzophenone derivatives, especially at low PI concentrations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2285–2301, 2004     

Photoinitiators with double and triple bonds

In continuation of our research on new chromophores for photoinitiators (PIs) we investigated a series of double and triple bond containing PIs based on benzophenone (BP), thioxanthone, benzil (BZ), benzildimethylketal (BDK), and hydroxyalkylphenone. UV‐Vis spectroscopy revealed an absorption shifted up to 50 nm to the visible range of the spectrum. With steady state photolysis experiments, the rates of decomposition (R_d) were determined. Compared to the commercially available reference PIs the R_d of the new PIs were nearly identical. By quenching reactions with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), α‐cleavage was identified for Type I initiators. Generally, all new compounds are suitable as PI especially for longer wavelengths. Nevertheless it has to be noted that the PI concentration has to be selected carefully to achieve optimum reactivity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 289–301, 2008     

Synthesis of highly refractive and transparent polyimides derived from 4,4′‐thiobis[2″,6″‐dimethyl‐4″‐(p‐phenylenesulfanyl)aniline]

New sulfur‐containing aromatic diamines with methyl groups at the ortho position of amino groups have been developed to prepare highly refractive and transparent aromatic polyimides (PIs) in the visible region. All aromatic PIs derived from 4,4′‐thiobis[2″‐methyl‐4″‐(p‐phenylenesulfanyl)aniline ( 2 ), 4,4′‐thiobis[2,″6″‐dimethyl‐4″‐(p‐phenylenesulfanyl)aniline ( 5 ), and aromatic dianhydride, 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride ( 6 ) were prepared via a two‐step polycondensation. All PIs showed good thermal properties, such as 10% weight loss temperature in the range of 497–500 °C and glass transition temperatures above 196 °C. In addition, the PIs showed good optical properties, such as optical transparency above 75% at 450 nm with a 10‐μm film thickness, high refractive indices ranging from 1.7135 to 1.7301, and small in‐plane/out‐of‐plane birefringences between 0.0066 and 0.0076. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 656–662, 2010     

Synthesis of highly refractive polyimides derived from 3,6‐bis(4‐aminophenylenesulfanyl)pyridazine and 4,6‐bis(4‐aminophenylenesulfanyl)pyrimidine

A series of aromatic polyimides (PIs) containing pyridazine or pyrimidine in their main chains has been developed. All of the PIs were prepared from newly synthesized diamines, 3,6‐bis(4‐aminophenylenesulfanyl)pyridazine (APP), 4,6‐bis(4‐aminophenylenesulfanyl)pyrimidine (APPM) and aromatic dianhydrides, 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) and 4,4′‐oxydiphthalic anhydride (ODPA) via the conventional two‐step polycondensation. The PIs showed good thermal stability with 10% weight loss at temperatures above 450 °C and glass transition temperatures above 190 °C. Films with a 10‐μm thickness exhibited good optical transparency above 80% at 500 nm, high refractive indices ranging from 1.7218 to 1.7499, and low birefringence between 0.0066 and 0.0102. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4886–4984, 2009     

Photoinitiators with functional groups. V. New water‐soluble photoinitiators containing carbohydrate residues and copolymerizable derivatives thereof

The synthesis of new water‐soluble photoinitiators (PIs) based on hydroxyalkylphenones, benzophenones, and thioxanthones with carbohydrate residues such as glucose, cellobiose, and 1‐amino‐1‐deoxy‐D ‐glucitol (glucamine) is described. In addition, selected initiators were reacted with methacryloyl chloride to obtain copolymerizable initiators with improved migration stability. Results from photo differential scanning calorimetry and gel‐content measurements in commercially available water‐thinnable and emulsion‐type resins as well as 2‐hydroxyethyl acrylate are included. Glucose‐modified PIs gave the best results with respect to compatibility with the resin, reactivity, and gel content. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1504–1518, 2002     

1,5‐Diphenyl‐1,4‐diyn‐3‐one: A highly efficient photoinitiator

In a continuation of our research on new chromophores for photoinitiators (PIs), we investigated a triple‐bond‐containing benzophenone derivative. 1,5‐Diphenyl‐1,4‐pentadiyn‐3‐one ( 2 ) was prepared from phenylacetylene and ethyl formate by a one‐pot reaction. Differential scanning photocalorimetry experiments in lauryl acrylate of 2 showed surprisingly high activity for the double‐bond conversion and rate of polymerization at the lowest PI concentrations and even without any coinitiator. By the application of monomers with abstractable hydrogens, significant improvement in the photoreactivity was observed. Ultraviolet–visible spectroscopy revealed strong absorption up to 350 nm. Steady‐state photolysis experiments proved that the photochemistry of this compound was faster than that of benzophenone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 101–111, 2005     

High solubility,low‐dielectric constant,and optical transparency of novel polyimides derived from 3,3′,5,5′‐tetramethyl‐4,4′‐diaminodiphenyl‐4″‐isopropyltoluene

A series of novel polyimides (PIs) ( 3a–d ) were prepared from 3,3′,5,5′‐tetramethyl‐4,4′‐diaminodiphenyl‐4 ″ ‐isopropyltoluene ( 1 ) with four aromatic dianhydrides via a one‐step high temperature polycondensation procedure. The obtained PIs showed excellent solubility, with most of them dissoluble at a concentration of 10 wt % in amide polar solvents and chlorinated solvents. Their films were nearly colorless and exhibited high‐optical transparency, with the UV cutoff wavelength in the range of 328–353 nm and the transparency at 450 nm >80%. They also showed low‐dielectric constant (2.49–2.94 at 1 MHz) and low‐water absorptions (0.44–0.65%). Moreover, these PIs possessed high‐glass transition temperatures (T_g) beyond 327 °C and excellent thermal stability with 10% weight loss temperatures in the range of 530–555 °C in nitrogen atmosphere. In comparison with some fluorinated poly(ether imide)s derived from the trifluoromethyl‐substituted bis(ether amine)s, the resultant PIs 3a–d showed better solubility, lower cutoff wavelength, and higher T_g. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3309–3317, 2009     

Constitutionally isomeric alicyclic polyimides: Origin of siteselectivity in the reaction of unsymmetrical dianhydride and structure‐derived difference in physical properties

Two constitutionally isomeric alicyclic polyimides (PIs), head‐to‐head (HH) and random types, were successfully synthesized on the basis of a siteselective ring opening reaction of an unsymmetric spiroalicyclic dianhydride, rel‐[1R,5S,6R]‐3‐oxabicyclo[3,2,1]octane‐2,4‐dione‐6‐spiro‐3′‐(tetrahydrofuran‐2′,5′‐dione), with using several kinds of diamines only by changing reaction procedures. A model reaction study revealed that the origin of the siteselectivity in the reaction of the dianhydride was due to both the enhanced reactivity of six‐membered anhydride embedded in bicyclo[3.2.1] system and the reduced reactivity of five‐membered anhydride in the spiro[4.5] system. The HH‐PIs showed higher glass transition temperature and higher dielectric constant than those of random PIs. Specific gravity of the PI films showed that the differences in physical properties stem from different packing density of the two constitutionally isomeric PIs. This is the first example for constitutionally isomeric both amorphous polycondensates with different physical properties. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Partially bio‐based aromatic polyimides derived from 2,5‐furandicarboxylic acid with high thermal and mechanical properties

Two novel bio‐based diamines are synthesized through introduction of renewable 2,5‐furandicarboxylic acid (2,5‐FDCA), and the corresponding aromatic polyimides (PIs) are then prepared by these diamines with commercially available aromatic dianhydrides via two‐step polycondensation. The partially bio‐based PIs possess high glass transition temperatures (T_gs) in the range from 266 to 364 °C, high thermal stability of 5% weight loss temperatures (T_5%s) over 420 °C in nitrogen and outstanding mechanical properties with tensile strengths of 79–138 MPa, tensile moduli of 2.5–5.4 GPa, and elongations at break of 3.0–12.3%. Some colorless PI films (PI‐1‐b and PI‐1‐c) with the transmittances at 450 nm over 85% are prepared. The overall properties of 2,5‐FDCA‐based PIs are comparable with petroleum‐based PI derived from isophthalic acid, displaying the potential for development of innovative bio‐based materials. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1058–1066     

Comparative study on polyimides from isomeric 3,3′‐, 3,4′‐, and 4,4′‐linked bis(thioether anhydride)s

Three isomeric bis(thioether anhydride) monomers, 4,4′‐bis(2,3‐dicarboxyphenylthio) diphenyl ketone dianhydride (3,3′‐PTPKDA), 4,4′‐bis(3,4‐dicarboxyphenylthio) diphenyl ketone dianhydride (4,4′‐PTPKDA), and 4‐(2,3‐dicarboxyphenylthio)‐4′‐(3,4‐dicarboxyphenylthio) diphenyl ketone dianhydride (3,4′‐PTPKDA), were prepared through multistep reactions. Their structures were determined via Fourier transform infrared, NMR, and elemental analysis. Three series of polyimides (PIs) were prepared from the obtained isomeric dianhydrides and aromatic diamines in N‐methyl‐2‐pyrrolidone (NMP) via the conventional two‐step method. The PIs showed excellent solubility in common organic solvents such as chloroform, N,N‐dimethylacetamide, and NMP. Their glass‐transition temperatures decreased according to the order of PIs on the basis of 3,3′‐PTPKDA, 3,4′‐PTPKDA, and 4,4′‐PTPKDA. The 5% weight loss temperatures (T_5%) of all PIs in nitrogen were observed at 504–519 °C. The rheological properties of isomeric PI resins based on 3,3′‐PTPKDA/4,4′‐oxydianiline/phthalic anhydride showed lower complex viscosity and better melt stability compared with the corresponding isomers from 4,4′‐ and 3,4′‐PTPKDA. In addition, the PI films based on three isomeric dianhydrides and 2,2′‐bis(trifluoromethyl)benzidine had a low moisture absorption of 0.27–0.35%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of polyethylene and polypropylene containing fluorene units in the side chain

Copolymerizations of ethylene or propylene and allyl monomers containing 9‐fluorenyl group, diallyl‐di‐9‐fluorenylsilane (DAFS), 9,9‐diallylfluorene (DAF), and 9‐allylfluorene (AF), were investigated with various zirconocene catalysts using methylaluminoxane as a cocatalyst. The bridged zirconocene catalysts, especially a syndioselective catalyst, showed a higher reactivity for all the comonomers than the nonbridged catalysts. DAFS was mainly incorporated into the polymer chain via cyclization insertion, whereas DAF was copolymerized via both 1,2‐ and cyclization insertions. Cyclization selectivity, ratio of cyclized insertion unit, of DAF in the copolymerization with propylene was higher than that in the copolymerization with ethylene. Copolymerization with AF yielded low‐molecular weight copolymer because of frequent chain transfer reaction. Optical properties of the propylene based‐copolymers were investigated by UV‐vis and photoluminescence spectroscopy, and absorption‐ and emission‐derived from fluorenyl groups were detected in the copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3542–3552, 2010     

High Tg and high organosolubility of novel unsymmetric polyimides

A series of new polyimides (PIs) containing di‐tert‐butyl side groups were synthesized via a polycondensation of 1‐(4‐aminophenoxy)‐4‐(4‐amino‐2‐methylphenyl)‐2,6‐di‐tert‐butylbenzene ( 3 ) with various aromatic tetracarboxylic dianhydrides. The novel unsymmetric PIs exhibited a low dielectric constants (2.78–3.02), low moisture absorption (0.53–1.35%), excellent solubility, and high glass transition temperature (308–450 °C). The PI derived from the new diamine and the very rigid naphthalene‐1,4,5,8‐tetracarboxylic dianhydride (NTDA) was soluble in N‐methyl‐2‐pyrrolidone, chloroform, m‐cresol, and cyclohexanone. The unsymmetric di‐tert‐butyl pendent groups significantly enhance the rotational barrier of the polymer chains; thus these PIs had high T_gs. The ¹H NMR spectrum of the diamine 3 revealed that the protons of 4‐aminophenoxy moiety are not chemical shift equivalent. This is because the steric hindrance of the bulky di‐tert‐butyl groups prevents the benzene ring of 4‐aminophenoxy moiety from rotating freely. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2443–2452, 2009     

Synthesis,characterization, and emulsion polymerization of polymerizable coumarin derivatives

We describe the synthesis of a new polymerizable coumarin derivative, [6‐(β‐acryloxyethoxy)‐7‐isopropoxy‐4‐methyl coumarin ( 3 )], whose UV absorption spectrum significantly overlaps the emission spectrum of 9‐alkyl phenanthrene chromophore. This dye can serve several purposes in latex films. It can be a tracer for fluorescence microscopy experiments, or it can act as a donor or acceptor dye in nonradiative energy transfer experiments. Here we emphasize its role as an energy transfer acceptor in experiments with phenanthrene as the corresponding donor. Coumarin‐labeled poly(butyl methacrylate) latex dispersions could be synthesized by conventional batch emulsion polymerization with complete monomer conversion, complete dye incorporation, and uniform dye distribution. Attempts to extend this reaction to poly(vinyl acetate) copolymers failed because the dye inhibited monomer conversion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3479–3489, 2004     

Selective localization of organoclay and effects on the morphology and mechanical properties of LDPE/PA11 blends with distributed and co‐continuous morphology

A study was made on the effect of small amounts of organically modified clay on the morphology and mechanical properties of blends of low‐density polyethylene and polyamide 11 at different compositions. The influence of the filler on the blend morphology was investigated using wide angle X‐ray diffractometry, scanning and transmission electron microscopy and selective extraction experiments. The filler was found to locate predominantly in the more hydrophilic polyamide phase. Although such uneven distribution does not have a significant effect on the onset of phase co‐continuity of the polymer components, it brings about a drastic refinement of the microstructure for the blends both with droplets/matrix and co‐continuous morphologies. In addition to the expected reinforcing action of the filler, the resulting fine microstructure plays an important role in enhancing the mechanical properties of the blends. This is essentially because of a good quality of stress transfer across the interface between the constituents, which also seems to benefit for a good interfacial adhesion promoted by the filler. Our results provide the experimental evidence for the capabilities of nanoparticles added to multiphase polymer systems to act selectively as a reinforcing agent for specific domains of the material and as a medium able to assist the refinement of the polymer phases during mixing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 600–609, 2010     

Synthesis and characterization of high nitrile content polyimides as dielectric films for electrical energy storage

Three new isomeric diamines containing three, oxy‐linked benzonitriles (3BCN), one of which is asymmetric (meta, para, or m, p), are synthesized in a 3‐step sequence. Polycondensation of these diamines and four common dianhydrides (6FDA, OPDA, BTDA, and PMDA) in N,N‐dimethylacetamide via poly(amic acid) precursors and thermal curing at temperatures up to 300 °C lead to three series of tough, creasable polyimide (PI) films (tensile moduli = 1.63 ? 2.86 GPa). Among these PIs, two PMDA‐based PIs possess relatively high crystallinity and two OPDA‐based PIs, low crystallinity, whereas all 6FDA‐ and BTDA‐based PIs, and m,m‐3BCN‐OPDA‐PI are amorphous, readily soluble in common polar aprotic solvents. Thermally stable and having high T_g (216 ? 341 °C), these PIs lose 5% weight around 493–503 °C in air and 463–492 °C in nitrogen. Dielectric properties have been evaluated by broadband dielectric spectroscopy (BDS) and electric displacement‐electric‐field (D‐E) loop measurements. D‐E loop results show an increase in high temperature permittivity (at 190 °C/1 kHz) from 2.9 (for parent PI CP2 with no nitrile group) to as high as 4.9 for these PIs, while keeping their dielectric loss relatively low. Thus, an increase in dipole moment density by the presence of three neighboring CN per repeat unit can increase the overall permittivity, which could be further enhanced by sub‐T_g mobility of para‐phenylene linkages (BDS results). Published 2014. J. Polym. Sci., Part A: Polym. Chem. 2014 J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 422–436     

Synthesis and properties of poly(amic acid)s and polyimides based on 2,2′,6,6′‐biphenyltetracarboxylic dianhydride

Poly(amic acid)s (PAAs) having the high solution stability and transmittance at 365 nm for photosensitive polyimides have been developed. PAAs with a twisted conformation in the main chains were prepared from 2,2′,6,6′‐biphenyltetracarboxylic dianhydride (2,2′,6,6′‐BPDA) and aromatic diamines. Imidization of PAAs was achieved by chemical treatment using trifluoroacetic anhydride. Among them, the PAA derived from 2,2′,6,6′‐BPDA and 4,4′‐(1,3‐phenylenedioxy)dianiline was converted to the polyimide by thermal treatment. The heating at 300 °C under nitrogen did not complete thermal imidization of PAAs having glass‐transition temperatures (T_g)s higher than 300 °C to the corresponding PIs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6385–6393, 2006     

Synthesis and characterization of hyperbranched polyimides with good organosolubility and thermal properties based on a new triamine and conventional dianhydrides

A triamine monomer, 1,3,5‐tris(4‐aminophenoxy)benzene (TAPOB), was synthesized from phloroglucinol and 4‐chloronitrobenzene, and it was successfully polymerized into soluble hyperbranched polyimides (HB PIs) with commercially available dianhydrides: 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA), and 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA). Different monomer addition methods and different monomer molar ratios resulted in HB PIs with amino or anhydride end groups. From ¹H NMR spectra, the degrees of branching of the amino‐terminated polymers were estimated to be 0.65, 0.62, and 0.67 for 6FDA–TAPOB, ODPA–TAPOB, and BTDA–TAPOB, respectively. All polymers showed good thermal properties with 10% weight‐loss temperatures (T₁₀'s) above 505 °C and glass‐transition temperatures (T_g's) of 208–282 °C for various dianhydrides. The anhydride‐terminated HB PIs showed lower T₁₀ and T_g values than their amino‐terminated counterparts. The chemical conversion of the terminal amino or anhydride groups of the 6FDA‐based polyimides into an aromatic imido structure improved their thermal stability, decreased their T_g, and improved their solubility. The HB PIs had moderate molecular weights with broad distributions. The 6FDA‐based HB PIs exhibited good solubility even in common low‐boiling‐point solvents such as chloroform, tetrahydrofuran, and acetone. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3804–3814, 2002     

Pursuit of reinitiation efficiency of resonance‐stabilized monomeric allyl radical generated via “degradative monomer chain transfer” in allyl polymerization

For a deeper understanding of allyl polymerization mechanism, the reinitiation efficiency of resonance‐stabilized monomeric allyl radical was pursued because in allyl polymerization it is commonly conceived that the monomeric allyl radical generated via the allylic hydrogen abstraction of growing polymer radical from monomer, i.e., “degradative monomer chain transfer,” has much less tendency to initiate a new polymer chain and, therefore, this monomer chain transfer is essentially a termination reaction. Based on the renewed allyl polymerization mechanism in our preceding article, the monomer chain transfer constant in the polymerization of allyl benzoate was estimated to be 2.7 × 10^?2 at 80 °C under the polymerization condition, where the coupling termination reaction of growing polymer radical with allyl radical was negligible and, concurrently, the reinitiation reaction of allyl radical was enhanced significantly. The reinitiation efficiencies of monomeric allyl radical were pursued by the dead‐end polymerizations of allyl benzoate at 80, 105, and 130 °C using a small amount of initiators; they increased remarkably with raised temperature. Thus, the enhanced reinitiation reactivity of allyl radical at an elevated temperature could bias the well‐known degradative monomer chain transfer characteristic of allyl polymerization toward the chain transfer in common vinyl polymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Photoluminescent energy transfer from poly(phenyleneethynylene)s to near‐infrared emitting fluorophores

Photoluminescent energy transfer was investigated in conjugated polymer‐fluorophore blended thin films. A pentiptycene‐containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near‐infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near‐infrared region on a completely dark background, offer substantial possibilities for designing highly sensitive turn‐on sensors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3382–3391, 2010     

Synthesis and properties of novel polyimides derived from 2,2′,3,3′‐benzophenonetetracarboxylic dianhydride

A new synthetic route to 2,2′,3,3′‐BTDA (where BTDA is benzophenonetetracarboxylic dianhydride), an isomer of 2,3′,3′,4′‐BTDA and 3,3′,4,4′‐BTDA, is described. Single‐crystal X‐ray diffraction analysis of 2,2′,3,3′‐BTDA has shown that this dianhydride has a bent and noncoplanar structure. The polymerizations of 2,2′,3,3′‐BTDA with 4,4′‐oxydianiline (ODA) and 4,4′‐bis(4‐aminophenoxy)benzene (TPEQ) have been investigated with a conventional two‐step process. A trend of cyclic oligomers forming in the reaction of 2,2′,3,3′‐BTDA and ODA has been found and characterized with IR, NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, and elemental analyses. Films based on 2,2′,3,3′‐BTDA/TPEQ can only be obtained from corresponding polyimide (PI) solutions prepared by chemical imidization because those from their polyamic acids by thermal imidization are brittle. PIs from 2,2′,3,3′‐BTDA have lower inherent viscosities and worse thermal and mechanical properties than the corresponding 2,3′,3′,4′‐BTDA‐ and 3,3′,4,4′‐BTDA‐based PIs. PIs from 2,2′,3,3′‐BTDA and 2,3′,3′,4′‐BTDA are amorphous, whereas those from 3,3′,4,4′‐BTDA have some crystallinity, according to wide‐angle X‐ray diffraction. Furthermore, PIs from 2,2′,3,3′‐BTDA have better solubility, higher glass‐transition temperatures, and higher melt viscosity than those from 2,3′,3′,4′‐BTDA and 3,3′,4,4′‐BTDA. Model compounds have been prepared to explain the order of the glass‐transition temperatures found in the isomeric PI series. The isomer effects on the PI properties are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2130–2144, 2004