Low Molecular Weight Oligomers Research Articles

Pharmaceutical strategies against amyloidosis: old and new drugs in targeting a "protein misfolding disease".

The group of diseases caused by abnormalities of the process of protein folding and unfolding is rapidly growing and includes diseases caused by loss of function as well as diseases caused by gain of function of misfolded proteins. Amyloidoses are caused by gain of function of certain proteins that lose their native structure and self-assemble into toxic insoluble, extracellular fibrils. This process requires the contribution of multiple factors of which only a few are established, namely the conformational modification of the amyloidogenic protein, protein's post-translational modifications and the co-deposition of glycosaminoglicans and of serum amyloid P component. In parallel with the exponential growth of biochemical data regarding the key events of the fibrillogenic process, several reports have shown that small molecules, through the interaction with either the amyloidogenic proteins or with the common constituents, can modify the kinetics of formation of amyloid fibrils or can facilitate amyloid reabsorption. These small molecules can be classified on the basis of their protein target and mechanism of action, according to the following properties. 1) molecules that stabilize the amyloidogenic protein precursor 2) molecules that prevent fibrillogenesis by acting on partially folded intermediates of the folding process as well as on low molecular weight oligomers populating the initial phase of fibril formation 3) molecules that interact with mature amyloid fibrils and weaken their structural stability 4) molecules that displace fundamental co-factors of the amyloid deposits like glycosaminoglycans and serum amyloid P component and favor the dissolution of the fibrillar aggregate.

Enzyme-Catalyzed Ring-Opening Polymerization of ε-Caprolactone in Supercritical Carbon Dioxide

We report the ring-opening polymerization reaction of e-caprolactone in supercritical carbon dioxide (scCO2) using an enzyme catalyst, Lipase B from Candida antarctica supported on macroporous beads (Novozym-435). Ring-opening polymerization of lactones is more commonly performed in organic solvents or in bulk using a Lewis acid catalyst. Recently there has been much interest in the replacement of such catalysts by enzymes. We demonstrate that the enzymatic route is viable in scCO2, yielding poly(e-caprolactone) (Mn = 12 000−37 000 g mol-1) with molecular weights very similar to those obtained from the same enzyme catalysts in organic solvents, but with lower polydispersities (typical PDI = 1.4−1.6) and higher yields of polymer product (typically 95−98%). In the same process the unique “gaslike” mass transfer properties of scCO2 can also be exploited to remove quantitatively any unconverted monomer and low molecular weight oligomers by scCO2 extraction. It is also shown that the enzyme catalyst can be cle...

Synthesis and characterization of low molecular weight oligomers of soluble polyaniline by electrospray ionization mass spectrometry

Mass spectrometry (MS) has not been utilized extensively for its ability to analyze the structure of polyaniline. This has been a result of polyaniline not being directly soluble in MS-“friendly” solvents. Here, low molecular weight oligomers of polyaniline are synthesized, using a modified room temperature synthesis of polyaniline, that are soluble in solvents that are better suited to electrospray MS analysis. Oligomers up to the 9-mer are identified from the mass spectra. Importantly, several different types of polyaniline oligomers that differ from one another based on their end groups were distinguished in the mass spectra. The use of tandem mass spectrometry (MS/MS) enabled identification of these various end groups.

Laser stereolithography and supercritical fluid processing for custom-designed implant fabrication.

This paper describes the laser photopolymerization of a liquid mixture of polyfunctional acrylic monomers, photoinitiator and hydroxyapatite (HA). Pure polymeric and composite materials of specific shape and structure were fabricated by laser stereolithography based on images derived from three-dimensional (3D) computer modeling. The polymeric objects then were treated with supercritical carbon dioxide to remove potentially toxic residues (monomers, low molecular weight oligomers, etc.) and to provide interconnective microporosity. Finally, samples were implanted into white rats (diastolic epiphysis of femoral bone) to study living tissue response and processes of osteointegration and osteoinduction. It was shown that incorporation of HA into the composite implant structure encouraged periosteal as well as endosteal osteogenesis and improved their osteointegrative characteristics in particular. Supercritical carbon dioxide treatment significantly enhanced the biocompatibility of the materials, increasing the area of direct contact of the implant surface with regenerated bone tissue.

Study on long fiber–reinforced thermoplastic composites prepared by in situ solid‐state polycondensation

AbstractLong glass fiber–reinforced thermoplastic composites were prepared by a new process, in situ solid‐state polycondensation (INSITU SSP). In this process reinforcing continuous fibers were impregnated by the oligomer of PET melt, and then the impregnated continuous fibers were cut to a desired length (designated prepreg); finally, the prepreg was in situ polymerized in the solid state to form the high molecular weight matrix. SEM, FTIR spectra, short‐beam shear stress test, flexural strength test, impact strength test, and the intrinsic viscosity measurement were used to investigate the wetting and interfacial adhesion, the mechanical properties of the composite, and the molecular weight of matrix resin in the composite. The results showed that the molecular weight of PET in the matrix resin and mechanical properties could be adjusted by controlling the SSP time and that the high level of interfacial adhesion between reinforcing fibers and matrix resin could be achieved by this novel INSITU SSP process, which are attributed to the good wetting of reinforcing fibers with low molecular weight oligomer melt as the impregnation fluid, the in situ formation of chemical grafting of oligomer chains onto the reinforcing fiber surface, and the in situ formation of the high molecular weight PET chains in the interphase regions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3959–3965, 2004

The Development of Ultra-cool Melt Adhesives for Mounting Resin-Coated (RC) Photographic Papers.

ABSTRACTThe development of an adhesive that is a hybrid between a pressure sensitive adhesive and a heat seal adhesive is described. The goal of this project, which is a joint collaboration between the Museum of Modern Art and the Polymer Research Institute, is to develop a preservation quality adhesive for application to RC print photographs. RC prints are clad in polyethylene, a low surface energy (LSE) polymer that requires special consideration when devising an adhesive to adhere to it. In arriving at a formula for this purpose research has focused on a combination of hydrocarbon-based polymers and low molecular weight oligomers. In addition, this work addresses other aspects such as activation conditions and joint design, factors critical to developing an adhesive that has the potential to satisfy the stringent criteria of a material acceptable to conservation applications.

Self-Assembly of a Charge-Neutral Molecular Square

Complexation of cadmium(II) by the ditopic (bis-tridentate) thiocarbazone ligand 1,5-bis(6-methyl-2-pyridyl- methylene)thiocarbonohydrazide, H2L1, results in the self-assembly of a charge-neutral 2 × 2 molecular grid, [Cd4(L1)4], comprising four metals and four ligands in an interlocked cyclic array. The solid-state structure of this tetramer has been established by X-ray crystallography and in solution by 1H NMR spectroscopy. The presence of lower molecular weight oligomers was identified by both NMR and ESI-MS.

Nucleation-elongation polymerization under imbalanced stoichiometry.

As a result of the helical structure of the polymeric product, the folding-driven polymerization of oligo(m-phenyleneethynylene) imines in solution should inherently show nucleation-elongation in chain growth. Here, we present evidence for this behavior based on results of polymerizations conducted under conditions of imbalanced stoichiometry. Because the polymerization proceeds via imine metathesis between a pair of bifunctional monomers of types A-A and B-B, the molar ratio of the polymerizing functional groups can be arbitrarily varied. Alternatively, stoichiometry can be controlled by the addition of a monofunctional oligomer. Similar results were obtained in both cases whereby the molecular weight distribution was significantly different from that expected for classical step-growth polymerizations. At equilibrium, high molecular weight polymers were observed to coexist with the monomer in excess. Thermodynamic equilibrium was established by showing that the same distribution was reached starting either from a monomer mixture or from high polymers to which one monomer was added. These results are in great contrast to the low molecular weight oligomers that were produced when the reaction was conducted by melt condensation of bifunctional aldehyde and amine monomers, a polymerization that apparently proceeds without the nucleation event. An equilibrium model that captures the features of nucleation-elongation under conditions of imbalanced stoichiometry qualitatively supports the monomer-polymer distribution observed experimentally.

Late-Transition-Metal Complexes with Bisazaferrocene Ligands for Ethylene Oligomerization

Herein we report the synthesis, characterization, and ethylene polymerization properties of novel C2-symmetric and unsymmetric bisazaferrocene complexes with late-transition-metal Ni(II) and Pd(II). In the designed complexes, the two sp2-hybridized nitrogen atoms in the azaferrocene rings coordinate to the transition metals with the azaferrocene architecture presenting pentamethyl or pentaphenyl cyclopentadiene (Cp* or Cp°) rings above and below the coordination plane for the purpose of preventing the associative chain transfer processes of ethylene from the axial faces. The Ni(II) and Pd(II) complexes were prepared and characterized by mass spectrometry (MS), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Upon activation with methylaluminoxane (MAO), the bisazaferrocene complexes with NiBr2 (2a) and PdCl2 (2b) showed very low activities toward ethylene polymerization. Well-defined preactivated bisazaferrocene-Pd(II) complexes (5 and 6) exhibited relatively high thermal stability for ethylene oligomerization: for example, complex 5 remains active in ethylene oligomerization at temperatures up to 120 °C. They have moderate activities in ethylene polymerizations to form relatively low molecular weight oligomers. The polyethylene oligomers formed have branching densities ranging from 20 to 60 branches/1000 carbons. To overcome the difficulty encountered in the synthesis of complex 6, a novel route was developed to make Pd(Me)Cl complexes with various dinitrogen ligands by in situ ligand substitution reaction. Finally, to gain mechanistic insight into the low reactivity of the bisazaferrocene-PdII complexes (5 and 6) as compared to their α-diimine counterparts, kinetic studies were undertaken to measure the energetic barriers for the first methyl migration and subsequent ethylene consumption. It was found that the insertion barriers (ΔG⧧) for both the first methyl migration and subsequent ethylene insertion for complex 5 were about 2−3 kcal/mol higher than the values for the α-diimine counterparts, which corresponds to a 2-order difference in the rate of polymerization. Variable-temperature experiments further revealed that the higher ethylene insertion barrier for the bisazaferrocene-Pd(II) complexes arises from both higher activation enthalpy (ΔH⧧) and smaller activation entropy (ΔS⧧).

Acid and base catalyzed ring-opening polymerization of 2,2,4,4,6,6-hexamethyl-8,8-diphenylcyclotetrasiloxane

Triflic acid and P 4- t-Bu superbase both catalyze the ring-opening polymerization (ROP) of 2,2,4,4,6,6-hexamethyl-8,8-diphenylcyclotetrasiloxane ( I) to yield a mixture of linear copoly(dimethylsiloxane/diphenylsiloxane) (3:1 mole ratio), low molecular weight oligomer and cyclic siloxanes. The molecular weight distribution, microstructure and thermal properties of the copolymers have been determined. The composition of the low molecular weight fractions have been analyzed. Triflic acid catalyzed ROP of I yields a copolymer whose microstructure can be accounted for by chemoselective ring opening of a single silyloxonium ion intermediate. In addition, 40% of I is recovered. On the other hand, P 4- t-Bu superbase catalyzed ROP of I yields a copolymer whose microstructure is random. The low molecular weight fraction, in this case, is made up of oligomer and a number of cyclotetra-, cyclopenta- and cyclohexasiloxanes.

Effects of gamma- and electron-beam irradiation on semi-rigid amorphous polyethylene terephthalate copolymers

Two semi-rigid amorphous polyethylene terephthalate copolymer materials (in both sheet and powder forms) containing 3% 1,4-cyclohexane dimethanol (CHDM) and 31% CHDM were irradiated at 5, 25 and 50 kGy at ambient temperature with a 60Co radiator or an electron-beam accelerator. After irradiation, volatiles were determined using static headspace sampling with capillary gas chromatography and mass selective detection or flame ionization detection (HS/GC/MSD or FID). Non-volatiles were extracted with 10% aqueous ethanol and 100% n-heptane food-simulating solvents, maintained at 40°C for up to 10 days. The non-volatiles in the materials and those migrating into the food-simulating solvents were determined by high-performance liquid chromatography (HPLC) with ultraviolet and/or photodiode array detection. The results obtained from the HS/GC/MSD suggest that no new chemicals were detected by either gamma- or e-beam irradiation when compared with non-irradiated specimens. The major volatiles in the copolymers were acetaldehyde and 2-methyl-1,3-dioxolane. The concentrations of acetaldehyde increased from 1.24–1.96 mg kg-1 to 1.94–3.65, 3.52–7.23 and 5.45–15.37 mg kg-1 after exposure to 5, 25 and 50 kGy doses, respectively. The concentrations of 2-methyl-1,3-dioxolane decreased from 2.49–5.26 mg kg-1 to 2.07–3.13, 1.33–2.14 and 0.64–2.24 mg kg-1 after exposure to 5, 25 and 50 kGy doses, respectively. The results of analysis of the copolymers for non-volatiles show that irradiation did not produce any new detectable non-volatile chemicals. A 5 kGy dose had no detectable effect on either copolymer. The 25 and 50 kGy doses had slightly different effects with respect to gamma- and e-beam irradiation on low MW oligomers. However, these increased doses did not significantly affect migration. The concentration of most low molecular weight oligomers migrating into 10% ethanol and 100% heptane was ⩽2 ng g-1 of each oligomer for both copolymers. The cyclic trimer migrating from the 3% CHDM copolymer was approximately 4 ng g-1; it was 3 ng g-1 for the 31% CHDM copolymer. The overall results suggest that irradiation significantly increased levels of acetaldehyde but had no effect on non-volatile compounds migrating into food simulants.

Folding-Driven Reversible Polymerization of Oligo(m-phenylene ethynylene) Imines: Solvent and Starter Sequence Studies

Bis(imino) end-functionalized oligo(m-phenylene ethynylene)s were equilibrated in a closed system under conditions that promote reversible imine metathesis. The metathesis reaction joins two oligomers and produces a small molecule byproduct. In polar solvents, equilibration gave high molecular weight polymers while equilibration in chloroform produced only low molecular weight oligomers. This polymerization is hypothesized to be driven by the free energy gained from the folding of the long polymer chains directed by the noncovalent, intramolecular aromatic stacking and solvophobic interactions. This polymerization was also conducted in a series of solvents in which m-phenylene ethynylene oligomers have previously shown varied, intermediate folding stabilities. These experiments revealed a good correlation of the product molecular weight with the stability of the m-phenylene ethynylene helix. The equilibrium state of the metathesis reaction was also demonstrated to depend on the chain length of the starter...

Pyrolysis mass spectrometric analysis of poly(pyrrole-g-(2-( N-pyrrolyl)ethylvinylether)

Preparation of block and graft copolymers of conducting polymers with insulating polymers with good mechanical properties have been attempted in order to improve their mechanical properties. Yet, complete structural characterization is still limited due to the insolubility of the polymer samples. In this work, direct insertion pyrolysis mass spectrometry technique had been applied for structural and thermal characterization of a polymer prepared by electrochemical polymerization of pyrrole on a poly(2-( N-pyrrolyl)ethylvinylether) (PPEVE) precoated anode. For this purpose, pyrolysis analyses of polypyrrole (PPY), PPEVE and polypyrrole/poly(2-( N-pyrrolyl)ethylvinylether) graft copolymer (PPY/PPEVE), were performed. The extent of dissociation during the ionization in the mass spectrometer was investigated by repeating the experiments at different electron energies. Single ion current temperature profiles of characteristic fragments evolved during the pyrolysis of each component of the copolymer was compared with those of the corresponding fragments evolved from the copolymer, PPY/PPEVE. Experimental results confirmed that the growth of pyrrole takes place through the pyrrole moieties of PPEVE. The observed increase in the relative intensities of the monomer, and low molecular weight oligomer peaks of pyrrole in the pyrolysis mass spectra of the copolymer, was attributed to a decrease in the extent of network structure, which is common for the electrochemically synthesized PPYs.

A Kinetic Analysis of the Mechanism of β-Amyloid Induced G Protein Activation

β-Amyloid (Aβ) is the primary protein component of senile plaques found in Alzheimer's disease. In an aggregated (amyloid fibril, protofibril, or low molecular weight oligomer) state, Aβ has been consistently shown to be toxic to neurons, but the molecular mechanism of this toxicity is poorly understood. We have previously shown that Aβ activates a G i/o protein, and that inhibition of this specific G protein activation attenuated Aβ-induced cell toxicity. In the present study, we use a kinetic analysis to examine the mechanism of Aβ-induced G protein activation. Using synthetic Aβ(1–40) and phospholipid vesicles containing purified G 0α subunits, we examined the relationship between Aβ concentration, G 0α subunit concentration, GTP concentration and rate of GTP hydrolysis experimentally. We found that at low concentrations of Aβ (less than 10 μM), Aβ increased the rate of GTP hydrolysis over the rate of hydrolysis in the absence of peptide, however, at high concentrations of Aβ, significantly decreased rates of GTP hydrolysis were observed. We postulated several molecular level mechanisms for the observed rate behavior, from those mechanisms derived rate equations, and then tested the mechanisms against our experimental rate data. Based on our results, we identified a plausible mechanism for Aβ-induced G protein activation which is consistent with available experimental data. This work demonstrates the utility of an engineering approach to examining steps in the mechanism of Aβ-induced cell toxicity and could provide insight into our understanding of the mechanism of Alzheimer's disease.

Oligomer-Rich Fraction from Polydisperse Sample of Poly(bis(β-phenoxyethoxy)phosphazene)

Poly[bis(β-phenoxyethoxy)phosphazene] [PBPEP] had been shown in our previous paper to be a very useful polymer for investigating the crystallization mechanism of polymers, as the crystallization rate of PBPEP is extraordinarily small when isothermally crystallized from the melt. The crystallization of the low molecular weight oligomers of PBPEP was first studied in comparison to the high molecular weight polymers. The oligomer-rich fraction was obtained by fractionation of the as-polymerized sample, which had a broad molecular weight distribution. The fractions thus obtained were characterized by solution viscometry and size exclusion chromatography. The melting temperature and the growth rate of the spherulite from the melt were investigated by differential scanning calorimetry and optical microscopy. The growth rate was one or two orders of magnitude smaller in the oligomer-rich fraction than in the other high molecular weight fractions. A collapsed spherulite appeared in the oligomer-rich fraction at high crystallization temperatures. It is speculated that in the oligomer-rich fraction there is an excess free energy due to defects in the crystal phase. This defect is considerably larger in the oligomer-rich fraction than in the other fractions because a large quantity of short length chains is present.

Biocatalytic Polymerization of p-Cresol: An in-Situ NMR Approach To Understand the Coupling Mechanism

The nature of the initial coupling mechanism in the enzymatic polymerization of p-cresol was investigated by in-situ 1H NMR spectroscopy in an aqueous−organic media. Two types of in-situ experiments were performed, in which the course of polymerization was monitored with (i) incremental additions of H2O2 to the reaction mixture in the NMR tube at a regular interval and (ii) a function of reaction time after a known amount of addition of H2O2. These experiments were used to understand the coupling mechanism at the very early stage of reaction and during the course of polymerization reaction. In the early stage of the polymerization, the reaction mixture contains monomer as a dominant fraction and a small concentration of low molecular weight oligomers such as dimer, trimers, etc. The analysis of the reaction mixture by 1D and 2D in-situ NMR methods suggests the ortho−ortho C−C coupling as the dominant coupling mechanism during the initial stage of the polymerization. The quantitative NMR analysis indicates...

Polycarbonate networks. Part 2. Cure study and determination of mechanical, adhesive, and crystallization properties

Vinylphenylcarbonate terminated oligocarbonates were thermally cured into insoluble three-dimensional networks. The cure reaction of the functional oligomers with varied molecular weights was studied under different reaction temperatures and cure times. The K 1c fracture toughness was determined for the cured samples and the values obtained show that the polycarbonate networks retain some of the toughness of linear thermoplastic polycarbonate. Dynamic mechanical analysis was performed on the uncured, partially cured, and fully cured samples and a shift in glass transition temperature ( T g) to higher values was observed with extent of cure. The low temperature secondary relaxation peaks were observed to broaden toward higher values with extent of cure. Tensile measurements of cured samples demonstrated an increase in tensile strengths for the cured materials relative to low molecular weight oligomers, but with no change in modulus, while the tensile elongations of the cured samples showed an improvement over oligomers. The crystallizability of the cured materials was examined and it was determined that a significant improvement in solvent resistance to crystallization was obtained over that of linear polycarbonate. The materials also show potential as structural adhesives.

Structure and properties of avian small heat shock protein with molecular weight 25 kDa

The primary structure of chicken small heat shock protein (sHsp) with apparent molecular weight 25 kDa was refined and it was shown that this protein has conservative primary structure 74RALSRQLSSG 83 at Ser77 and Ser81, which are potential sites of phosphorylation. Recombinant wild-type chicken Hsp25, its three mutants, 1D (S15D), 2D (S77D+S81D) and 3D (S15D+S77D+S81D), as well as delR mutant with the primary structure 74RALS-ELSSG 82 at potential sites of phosphorylation were expressed and purified. It has been shown that the avian tissues contain three forms of Hsp25 having p I values similar to that of the wild-type protein, 1D and 2D mutants that presumably correspond to nonphosphorylated, mono- and di-phosphorylated forms of Hsp25. Recombinant wild-type protein, its 1D mutant and Hsp25, isolated from chicken gizzard, form stable high molecular weight oligomeric complexes. The delR, 2D and 3D mutants tend to dissociate and exist in the form of a mixture of high and low molecular weight oligomers. Point mutations mimicking phoshorylation decrease chaperone activity of Hsp25 measured by reduction of dithiothreitol induced aggregation of α-lactalbumin, but increase the chaperone activity of Hsp25 measured by heat induced aggregation of alcohol dehydrogenase. It is concluded that avian Hsp25 has a more stable quaternary structure than its mammalian counterparts and mutations mimicking phosphorylation differently affect chaperone activity of avian Hsp25, depending on the nature of target protein and the way of denaturing.

Preparation of Nano-Particles of Poly(phenylsilsesquioxane)s by Emulsion Polycondensation of Phenylsilanetriol Formed in Aqueous Solution

Spherical nano-particles of Poly(phenylsilsesquioxane) (PPSQ) were prepared by emulsion polymerization of phenylsilanetriol (PST) that had been formed in aqueous solution after hydrolysis of trichlorophenylsilane (TCP). The average size of the resultant particles was controlled from 30 nm to 110 nm in diameter by changing the amount of the emulsifier added to the solution. The PPSQ forming the particles was low molecular weight oligomer, consisting of silanol groups that can be utilized as functional groups for further chemical modification.

Thermal latency of novel chelating borate catalysts as latent catalysts for epoxy–phenolic resins

AbstractNovel quaternary ammonium bis(2‐oxybenzoyloxy)borate salts (1a–1c) or quaternary ammonium bis(1,2‐benzenedioxy)borate salts (2a and 2b) with tetra‐n‐butylammonium (TBA+), tetra‐n‐octylammonium (TOA+), or bis(triphenylphosphoranylidene)ammonium (PNP+) cations were synthesized as latent catalysts of epoxy/phenol–novolac resins by the complexation between boric acid and salicylic acid or catechol, followed by neutralization with quaternary ammonium hydroxide. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with 1a–1c in diglyme at 150 °C for 6 h proceeded up to 85–96% conversions and gave polymers with number‐average molecular weights of 4180–10,500, whereas the polyaddition at 80 °C for 6 h gave less than 8% conversions. However, the polyaddition with 2a containing TBA+ cation proceeded to only a 32% conversion at 150 °C for 6 h in diglyme and to a 64% conversion even at 180 °C for 6 h in triglyme and only gave low molecular weight oligomers, and no reaction proceeded in the polyaddition at 80 °C. However, polyaddition with 2b containing PNP+ cation proceeded up to a 96% conversion at 150 °C for 6 h in diglyme and gave a higher molecular weight polymer with a number‐average molecular weight of 8050, whereas the polyaddition at 80 °C for 6 h gave only a 5% conversion. The catalytic activity of ammonium borates 1a–1c and 2a and 2b depended on the borate anion structure: 1a and 1c with bis(2‐oxybenzoyloxy)borate anion revealed higher activity than 2a and 2b with bis(1,2‐benzenedioxy)borate anion, respectively. In comparison with tetra‐n‐butylammonium bromide (TBAB) as a conventional ammonium salt or tetra‐n‐butylammonium tetrakis(benzoyloxy)borate (TBA‐TBB), 1a–1c and 2b revealed better thermal latency. The catalytic activity of ammonium borates also depended on the bulkiness of the ammonium cation, and the order of activity was 1c (PNP+) > 1b (TOA+) ≧ 1a (TBA+) and 2b (PNP+) > 2a (TBA+). The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts 1a–1c and 2a and 2b in bulk at 40 °C was much better than that with TBAB and TBA‐TBB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2702–2716, 2002