Low Molecular Weight Oligomers Research Articles

Adiponectin isoform distribution in women—relationship to female sex steroids and insulin sensitivity

Little is known about the associations between adiponectin and its oligomeric isoforms with female sex steroids, and the relevance of these relationships to insulin sensitivity in women. In a cross-sectional study of 32 healthy women (12 premenopausal, 10 postmenopausal, and 10 early pregnant), we investigated the correlations of total adiponectin and the high–, medium–, and low–molecular weight oligomers (HMW, MMW, and LMW, respectively) with estrogen, progesterone, adiposity, and insulin resistance. Fat mass and serum concentrations of estradiol, progesterone, insulin, glucose, and total and isoform adiponectin were measured. The homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Serum concentrations of total and HMW adiponectin were highest in postmenopausal women and lowest in pregnant women. Concentrations of the MMW and LMW isoforms were not significantly different between the 3 groups. Total adiponectin, HMW adiponectin, and MMW adiponectin were negatively associated with estradiol and progesterone; but no associations between the LMW isoform and female sex steroids were observed. Fat mass and HOMA-IR were highest in pregnant women and lowest in premenopausal women. The HOMA-IR was positively associated with fat mass, estradiol, and progesterone, and negatively associated with total, HMW, and MMW adiponectin. Multivariate stepwise regression analysis revealed that fat mass explained 34% of the variance in HOMA-IR and that total and isoform adiponectin contributed an additional 10% to 15%. In the multivariate linear regression analysis, there were significant interactions of estradiol and progesterone with adiponectin or fat mass in the associations with HOMA-IR. In conclusion, there are strong negative associations of serum adiponectin and some of its isoforms with estradiol and progesterone. Female sex steroids are likely to affect insulin sensitivity through modulation of adiponectin and body fat.

Single-domain antibodies recognize selectively small oligomeric forms of amyloid β, prevent Aβ-induced neurotoxicity and inhibit fibril formation

Neurotoxic oligomers of amyloid β (Aβ) peptide have been incriminated in the pathogenesis of Alzheimer’s disease. Further exploration of this issue has been hampered to this date by the fact that all previously described anti-Aβ antibodies are unable to discriminate between the different conformations of the peptide (oligomers, protofibrils and fibrils). Here, we describe the generation of novel camelid single-chain binding domains (VHHs) that recognizes specifically low molecular-weight (MW) oligomers. Three VHH specific for Aβ were obtained from an immunized alpaca phage display library. Two were able to recognize selectively intraneuronal Aβ oligomers; furthermore, one of them, V31-1, prevented Aβ-induced neurotoxicity and inhibited fibril formation. This study confirms that VHHs may recognize non-conventional epitopes and illustrates their potential for the immunodiagnostic of diseases due to protein accumulation.

Preparation and characterization of asymmetric planar supported bilayers composed of poly(bis-sorbylphosphatidylcholine) on n-octadecyltrichlorosilane SAMs

Planar supported lipid bilayers (PSLBs) have been widely studied as biomembrane models and biosensor scaffolds. For technological applications, a major limitation of PSLBs composed of fluid lipids is that the bilayer structure is readily disrupted when exposed to chemical, mechanical, and thermal stresses. A number of asymmetric supported bilayer structures, such as the hybrid bilayer membrane (HBM) and the tethered bilayer lipid membrane (tBLM), have been created as an alternative to symmetric PSLBs. In both HBMs and tBLMs, the inner monolayer is covalently attached to the substrate while the outer monolayer is typically composed of a fluid lipid. Here we address if cross-linking polymerization of the lipids in the outer monolayer of an asymmetric supported bilayer can achieve the high degree of stability observed previously for symmetric PSLBs in which both monolayers are cross-linked [E.E. Ross, L.J. Rozanski, T. Spratt, S.C. Liu, D.F. O'Brien, S.S. Saavedra, Langmuir 19 (2003) 1752]. To explore this issue, HBMs composed of an outer monolayer of a cross-linkable lipid, bis-sorbylphosphatidylcholine (bis-SorbPC), and an inner SAM were prepared and characterized. Several experimental conditions were varied: vesicle fusion time, polymerization method, and polymerization time and temperature. Under most conditions, bis-SorbPC cross-linking stabilized the HBM such that its bilayer structure was largely preserved after drying; however these films invariably contained sub-micron scale defects that exposed the hydrophobic core of the HBM. The defects appear to be caused by desorption of low molecular weight oligomers when the film is removed from water, rinsed, and dried. In contrast, poly(bis-SorbPC) PSLBs prepared under similar conditions by Ross et al. were nearly defect free. This comparison shows that formation of a cross-linked network in the outer leaflet of an asymmetric supported bilayer is insufficient to prevent lipid desorption; inter-leaflet covalent linking appears to be necessary to create supported poly(lipid) assemblies that are impervious to repeated drying and rehydration. The difference in stability is attributed to inter-leaflet cross-linking between monolayers which can form in symmetric bis-SorbPC PSLBs.

A Soluble Oligomer of Tau Associated with Fiber Formation Analyzed by NMR

Alzheimer's disease (AD) is characterized by the intracellular accumulation of the neurofibrillary tangles comprised mainly of the microtubule-associated protein, tau. A critical aspect of understanding tangle formation is to understand the transition of soluble monomeric tau into mature fibrils by characterizing the structure of intermediates along the aggregation pathway. We have carried out multidimensional NMR studies on a C-terminal fragment of human tau (tau (187)) to gain structural insight into the aggregation process. To specifically monitor intermolecular interaction between tau molecules in solution, we combined (15)N- and (14)N-labeled tau, the latter of which was modified with a paramagnetic nitroxide spin label (MTSL). Paramagnetic relaxation enhancement (PRE) of (15)N-tau by interaction with MTSL- (14)N-tau allowed identification of low molecular weight oligomers of tau (187) that formed in response to heparin-induced aggregation. Two regions, VQIINK (280) and VQIVYK (311), were exclusively broadened by MTSL located at varied positions in the tau molecule. We propose that soluble oligomers of tau (187) are generated via intermolecular interactions at these motifs triggered by heparin addition. However, the associated line broadening at these motifs cannot be due to interaction between tau (187) and heparin directly. Instead, these specific interactions necessarily occur between tau molecules and are intermolecular in nature. Our data support the idea that VQIINK (280) and VQIVYK (311) are the major, if not sole, critical regions that directly mediate intermolecular contact between tau molecules during the early phases of aggregation.

The Role of Allylanisole in Metallocene-Catalyzed Propylene Polymerization and Synthesis of End-Capped Oligomers

Propylene was copolymerized with allylanisole (AA) using Me2Si(Ind)2ZrCl2 and Et(Ind)2ZrCl2, and the methylaluminoxane MAO cocatalyst at 70 °C and a cocatalyst to catalyst (Al:Zr) molar ratio of 1 000. It was fed at 8.5 bar(g). The weight-average molecular weight, , for both metallocenes decreased as the AA feed concentration increased. Therefore, allylanisole acted as an in situ chain transfer agent. The chain transfer constants, ktr/kp, of AA for Et(Ind)2ZrCl2 and Me2Si(Ind)2ZrCl2 turned out to be 0.33 and 0.40, respectively. The characterization of the resulting products by 1H NMR demonstrated that AA end-capped the isotactic poly(propylene) chains which showed to be low molecular weight oligomers; 4.96 × 103 ≤ ≤ 9.80 × 103. An appropriate chain transfer mechanism for AA has been proposed.

Characterisation of polyurethane networks based on vegetable derived polyol

A polyurethane (PU) network based on vegetable derived polyol has been characterised and compared to a synthetic based network. Fracture mechanics studies showed the lowest tear strength for the vegetable networks, which decreased as molecular weight of the vegetable based polyol increased. Swelling studies were carried out to determine the molecular weight between crosslinks and polymer networks made from wholly synthetic polyols were shown to have higher molecular weight between crosslinks. Moreover, vegetable networks showed higher solubles' content. Sol-fractions were analysed by several techniques. It was found that vegetable networks based sol-fraction was mainly its correspondent raw polyol while low molecular weight oligomers were detected for the most part in synthetic networks based sol-fraction.

Simultaneous monitoring of peptide aggregate distributions, structure, and kinetics using amide hydrogen exchange: Application to Aβ(1‐40) fibrillogenesis

Increasing evidence indicates that soluble aggregates of amyloid beta protein (Abeta) are neurotoxic. However, difficulty in isolating these unstable, dynamic species impedes studies of Abeta and other aggregating peptides and proteins. In this study, hydrogen-deuterium exchange (HX) detected by mass spectrometry (MS) was used to measure Abeta(1-40) aggregate distributions without purification or modification that might alter the aggregate structure or distribution. Different peaks in the mass spectra were assigned to monomer, low molecular weight oligomer, intermediate, and fibril based on HX labeling behavior and complementary assays. After 1 h labeling, the intermediates incorporated approximately ten more deuterons relative to fibrils, indicating a more solvent exposed structure of such intermediates. HX-MS also showed that the intermediate species dissociated much more slowly to monomer than did the very low molecular weight oligomers that were formed at very early times in Abeta aggregation. Atomic force microscopy (AFM) measurements revealed the intermediates were roughly spherical with relatively homogenous diameters of 30-50 nm. Quantitative analysis of the HX mass spectra showed that the amount of intermediate species was correlated with Abeta toxicity patterns reported in a previous study under the same conditions. This study also demonstrates the potential of the HX-MS approach to characterizing complex, multi-component oligomer distributions of aggregating peptides and proteins.

The trans-10, cis-12 isomer of conjugated linoleic acid decreases adiponectin assembly by PPARγ-dependent and PPARγ-independent mechanisms

The adipocyte-derived secretory protein adiponectin functions as an insulin-sensitizing agent. In plasma, adiponectin exists as low, medium, and high molecular weight oligomers. Treatment with trans-10, cis-12 conjugated linoleic acid (t-10, c-12 CLA) reduces levels of adiponectin as well as triglyceride (TG) in mice and adipocyte cell culture models. The aim of this study was to determine whether the effects of t-10, c-12 CLA on adiponectin and TG are mediated through modulation of the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma). 3T3-L1 cells were treated either during or after differentiation into adipocytes with 100 microM t-10, c-12 CLA with or without 10 microM troglitazone, a PPARgamma agonist, or 1 microM GW9662, a PPARgamma antagonist, and adiponectin and TG levels were analyzed. Treatment with t-10, c-12 CLA reduced TG as well as cellular and secreted adiponectin levels and impaired the assembly of adiponectin oligomers. These changes were accompanied by decreases in PPARgamma mass. Troglitazone was able to reverse the t-10, c-12 CLA-mediated decrease in TG levels and restore the assembly of adiponectin oligomers but was unable to restore adiponectin synthesis. Conversely, treatment with GW9662 decreased TG mass and impaired adiponectin oligomer assembly but did not decrease total adiponectin mass. In a reporter assay, t-10, c-12 CLA appeared to be a partial PPARgamma agonist and prevented the stimulation of reporter activity by troglitazone. Therefore, the t-10, c-12 CLA isomer appears to alter adipocyte adiponectin metabolism through PPARgamma-dependent and PPARgamma-independent mechanisms.

Stability of proteins encapsulated in injectable and biodegradable poly(lactide- co-glycolide)-glucose millicylinders

Purpose To characterize protein stability in poly(lactide- co-glycolide) 50/50-glucose star (PLGA-Glu) injectable millicylinders and to compare results with linear PLGA 50/50. Methods Bovine serum albumin (BSA), a model protein, was encapsulated in PLGA-Glu and linear PLGA millicylinders by solvent-extrusion and incubated under physiological conditions. Important system properties were characterized, including: polymer molecular weight distribution, soluble acidic residues, polymer morphology, polymer water uptake, microclimate pH, protein content and release, and protein aggregation. The polymer microclimate late in the release incubation was simulated and protein recovery was analyzed by UV 280, size exclusion chromatography, amino acid analysis, and a modified Bradford assay. Results PLGA-Glu contained higher levels of low molecular weight oligomers, more rapidly biodegraded, and exhibited a lower microclimate pH than the linear 50/50 PLGA, which is the most acidic type in the PLGA family. BSA, when encapsulated in PLGA-Glu millicylinders, underwent extensive noncovalent insoluble aggregation over 2 weeks in vitro release, which was almost completely inhibited upon co-encapsulation of Mg(OH) 2. However, by 5 weeks release for base-containing formulations, although insoluble aggregation was still suppressed, the soluble fraction of protein in the polymer was unrecoverable by the modified Bradford assay. Polymer microclimate simulations with extensive protein analysis strongly suggested that the low recovery was mostly caused by base-catalyzed hydrolysis of the oligomeric fraction of BSA. Conclusions In PLGA-Glu, the acidic microclimate was similarly responsible for insoluble aggregation of encapsulated BSA. BSA aggregation was inhibited in millicylinders by co-incorporation into the polymer an insoluble base, but over a shorter release interval than linear PLGA likely because of a more acidic microclimate in the star polymer.

Polymerization of 1,3-Dienes with Functional Groups. 4.

Anionic polymerization of N,N-diethyl-2-methylene-3-butenamide (DEA), which is a 1,3-butadiene derivative containing a diethylamide function, was carried out in tetrahydrofurane (THF) under various conditions. When DEA was polymerized in THF at −78°C using potassium naphthalenide (K-Naph) or diphenylmethylpotassium (DPMK) as an initiator, a polymer of predictable molecular weight with a narrow molecular weight distribution was obtained. However, the rate of polymerization was extremely slow to reach 80% conversion after 720 h. When the polymerization temperature was raised to 20°C, a low molecular weight oligomer with a broad molecular weight distribution was obtained because of a chain transfer reaction. On the other hand, no such side reaction occurred even at 20°C, when polymerization was carried out in the presence of LiCl. Also, the chain transfer reaction did not occur in lithium naphthalenide (Li-Naph) initiated polymerization. The microstructure of the polymer prepared using a potassium counter cation was a 1 : 1 mixture of 1,4-E and 1,2- structures. In the case of Li-Naph or DPMK/LiCl systems, the microstructure was a complicated mixture of 1,4-E, 1,4-Z, and 1,2-structures.

Synthesis, Characterization, and Evaluation of Amine‐Terminated Cycloaliphatic‐Substituted Polysiloxanes

AbstractCyclopentyl‐ and cyclohexyl‐substituted polysiloxanes terminated with amino groups were prepared. Initially, the cycloalkene and dichlorosilane were reacted at high pressure (approx. 250 psi) and high temperature (120 °C) to yield the cycloaliphatic dichlorosilane in a two‐step process. Both the mono‐ and disubstituted chlorosilane monomers underwent an oligomerization to produce cyclic oligomers of low molecular weight (≈2 000 g · mol−1). Amine‐terminated polysiloxanes were produced via a base‐catalyzed ring‐opening polymerization of the cyclic oligomers with 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane to yield low molecular weight polysiloxanes (≈9 000 g · mol−1, amine equivalent weight = ≈4 300 g · equiv.−1). The polysiloxanes were characterized by 1H and 29Si NMR, and Fourier transform‐infrared spectroscopy (FT‐IR). The amine‐terminated polysiloxane was mixed with a cycloaliphatic epoxy‐functionalized cycloaliphatic polysiloxane in order to produce crosslinked epoxy–amine films. The mechanical and physical properties of the film were evaluated and afford a glass transition of the material was 29.5 ± 0.7 °C for the cyclopentyl‐substituted polysiloxane and 38.6 ± 0.7 °C for the cyclohexyl‐substituted polysiloxane. Evaluation of pull‐off adhesion indicated that 0.5 MPa of normal force was required to remove the epoxy/amine film from an aluminum substrate.magnified image

In Vitro and In Vivo Neurotoxicity of Prion Protein Oligomers

The mechanisms underlying prion-linked neurodegeneration remain to be elucidated, despite several recent advances in this field. Herein, we show that soluble, low molecular weight oligomers of the full-length prion protein (PrP), which possess characteristics of PrP to PrPsc conversion intermediates such as partial protease resistance, are neurotoxic in vitro on primary cultures of neurons and in vivo after subcortical stereotaxic injection. Monomeric PrP was not toxic. Insoluble, fibrillar forms of PrP exhibited no toxicity in vitro and were less toxic than their oligomeric counterparts in vivo. The toxicity was independent of PrP expression in the neurons both in vitro and in vivo for the PrP oligomers and in vivo for the PrP fibrils. Rescue experiments with antibodies showed that the exposure of the hydrophobic stretch of PrP at the oligomeric surface was necessary for toxicity. This study identifies toxic PrP species in vivo. It shows that PrP-induced neurodegeneration shares common mechanisms with other brain amyloidoses like Alzheimer disease and opens new avenues for neuroprotective intervention strategies of prion diseases targeting PrP oligomers.

Conversion of non-fibrillar β-sheet oligomers into amyloid fibrils in Alzheimer’s disease amyloid peptide aggregation

Aβ(1–40) is one of the main components of the fibrils found in amyloid plaques, a hallmark of brains affected by Alzheimer’s disease. It is known that prior to the formation of amyloid fibrils in which the peptide adopts a well-ordered intermolecular β-sheet structure, peptide monomers associate forming low and high molecular weight oligomers. These oligomers have been previously described in electron microscopy, AFM, and exclusion chromatography studies. Their specific secondary structures however, have not yet been well established. A major problem when comparing aggregation and secondary structure determinations in concentration-dependent processes such as amyloid aggregation is the different concentration range required in each type of experiment. In the present study we used the dye Thioflavin T (ThT), Fourier-transform infrared spectroscopy, and electron microscopy in order to structurally characterize the different aggregated species which form during the Aβ(1–40) fibril formation process. A unique sample containing 90 μM peptide was used. The results show that oligomeric species which form during the lag phase of the aggregation kinetics are a mixture of unordered, helical, and intermolecular non-fibrillar β-structures. The number of oligomers and the amount of non-fibrillar β-structures grows throughout the lag phase and during the elongation phase these non-fibrillar β-structures are transformed into fibrillar (amyloid) β-structures, formed by association of high molecular weight intermediates.

Effects of hydrogen in ethylene polymerization and oligomerization with magnesium chloride‐supported bis(imino)pyridyl iron catalysts

AbstractThe effects of hydrogen in ethylene polymerization and oligomerization with different bis(imino)pyridyl iron(II) complexes immobilized on supports of type MgCl2/AlEtn(OEt)3–n have been investigated. Hydrogen has a significant activating effect on polymerization catalysts containing relatively bulky bis(imino)pyridyl ligands, but this is not the case in ethylene oligomerization with a catalyst containing relatively little steric bulk in the ligand. It was found that the presence of hydrogen in the latter system led to decreased activity and an overall increase rather than a decrease in product molecular weight, indicating deactivation of active species producing low molecular weight polymer and oligomer. Decreased formation of vinyl‐terminated oligomers in the presence of hydrogen can therefore contribute to the activating effect of hydrogen in ethylene polymerization with immobilized iron catalysts, if it is assumed that hydrogen activation is related to chain transfer after a 2,1‐insertion of a vinyl‐terminated oligomer into the growing polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4054–4061, 2007

Globular and full-length forms of adiponectin mediate specific changes in glucose and fatty acid uptake and metabolism in cardiomyocytes

Our aim was to investigate the regulation of glucose and fatty acid metabolism in cardiomyocytes by the globular (gAd) and full-length (fAd) forms of adiponectin. We produced fAd (consisting of high, medium and low molecular weight oligomers) in a mammalian expression system and gAd in bacteria. These were used to treat primary neonatal rat cardiomyocytes (up to 48 h), and we employed 3H- or 14C-labeled substrates to monitor glucose uptake and subsequent metabolism via oxidation, glycogen synthesis or lactate production and fatty acid uptake and oxidation. Enzymatic assay for acetyl CoA carboxylase activity was employed, and protein phosphorylation and expression was determined by immunoblotting cell lysates. The role of adiponectin receptor (AdipoR) isoforms was determined via siRNA-mediated knockdown. There was an initial (1 h) increase in glucose uptake and oxidation in response to gAd or fAd. Fatty acid uptake was stimulated by gAd or fAd, and by 24 h a decrease in acetyl CoA carboxylase activity and elevated fatty acid oxidation were observed. After 48 h increased fatty acid oxidation correlated with decreased glucose oxidation and pyruvate dehydrogenase activity, while glycogen synthesis and lactate production increased. Both gAd and fAd elicited phosphorylation of AMP kinase, insulin receptor substrate-1, Akt and glycogen synthase kinase-3beta. Knockdown of AdipoR1 or AdipoR2 attenuated the effect of both gAd and fAd on fatty acid uptake and oxidation. Only AdipoR1 knockdown prevented the ability of gAd (1 h) to increase glucose uptake and oxidation; however, reducing either AdipoR1 or AdipoR2 expression attenuated the long-term (24 h) effects of gAd. These results clearly demonstrate that gAd and fAd mediate distinct and time-dependent effects on cardiomyocyte energy metabolism via AdipoR1 and AdipoR2.

In Vitro Degradation of Poly(lactic‐co2‐glycolic) Acid Random Copolymers

AbstractWe have investigated the in vitro degradation of poly(lactic‐co‐glycolic) acid copolymer with a lactic to glycolic ratio of 65/35. The degradation studies were performed on solvent‐cast films of controlled thickness and shape. The samples were then incubated at 37 °C in phosphate buffered saline solution. The degradation was followed using potentiometry, light microscopy, gravimetry, gel permeation chromatography and differential scanning calorimetry. Water was found to diffuse inside the film as soon as the sample was placed in the degradation media. Wrinkles formed on the upper layer while degradation took place via chain scission in the bulk of the film. After 10 days, this led to the creation of a vesicle where liquid low molecular weight oligomers were trapped inside a thin film of high molecular weight polymer. This thin film acted as a membrane allowing only low molecular weight compounds to diffuse out of the film.

Candida antarctica Lipase B-Catalyzed Synthesis of Poly(butylene succinate): Shorter Chain Building Blocks Also Work

Lipase catalysis was successfully employed to synthesize high molecular weight poly(butylene succinate) (PBS). Attempts to copolymerize succinic acid with 1,4-butanediol were unsuccessful due to phase separation of the reactants. To circumvent this problem, monophasic reaction mixtures were prepared from diethyl succinate and 1,4-butanediol. The reactions were studied in bulk as well as in solution. Of the organic solvents evaluated, diphenyl ether was preferred, giving higher molecular weight products. After 24 h in diphenyl ether, polymerizations at 60, 70, 80, and 90 degrees C yielded PBS with M(n) of 2000, 4000, 8000, and 7000, respectively. Further increase in reaction time to 72 h resulted in little or no further increase in M(n). However, increasing the reaction time produced PBS with extraordinarily low M(w)/M(n) due to the diffusion and reaction between low-molecular weight oligomers and chains that occurs at a greater frequency than interchain transesterification. Time-course studies and visual observation of polymerizations at 80 degrees C revealed PBS precipitates at 5 to 10 h, limiting the growth of chains. To maintain a monophasic reaction mixture, the polymerization temperature was increased from 80 to 95 degrees C after 21 h. The result was an increase in the PBS molecular weight to M(w) = 38 000 (M(w)/M(n) = 1.39). This work paves the way for the synthesis of PBS macromers and polymers that contain variable quantities of monomers with chemically sensitive moieties (e.g., silicone, epoxy, vinyl). Furthermore, this study established the feasibility of using lipase catalysis to prepare polyesters from alpha,omega-linear aliphatic diethyl ester/diol monomers with less than six carbons.

Synthesis and Characterization of Aryl Ethynyl Terminated Liquid Crystalline Oligomers and Their Cured Polymers

In this paper the synthesis and characterization of two series wholly aromatic, main-chain, reactive liquid crystalline oligomers is reported. Phenylethynyl end-capped oligomers, based on 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), were successfully synthesized using standard high-temperature melt-condensation techniques. Melt processable oligomers, with M n = 1000, 5000, 9000, and 13 000 g mol -1 , and oligomers with HBA or HNA concentrations as high as 95 mol % were prepared. All oligomers showed well-defined, homogeneous, nematic melt behavior over a broad temperature range. The phenylethynyl end-capped oligomers could be cured at 370 °C and formed films with excellent mechanical and thermal properties, and without losing the nematic order. Low molecular weight oligomers, i.e. M n 5000 g mol -1 , polymerize predominantly via chain extension chemistry. The fully cured nematic polymers exhibit glass-transition temperatures (Tg) up to 203 °C, as determined by DMTA measurements, and thermal stabilities (5 wt % loss) up to 500 °C in both air and nitrogen atmosphere. The cured 1000 and 5000 g mol -1 oligomers, with 95 mol % HBA or HNA compositions, show significant improvements in storage modulus at elevated temperatures as compared to their high-molecular weight counterparts. Rheology experiments showed that these reactive nematic oligomers are melt-stable for at least 30 min at 300 °C and exhibit complex melt viscosities |η*| as low as 1 Pa·s at 100 rad·s -1 . In all examples no loss of mesophase could be observed during chain extension or cross-linking, which indicates that phenylethynyl cross-link chemistry is completely compatible with mesophase formation.

Thermal Reaction of Cinnamate Oligomers and Their Effect on the Orientational Stability of Liquid Crystals

Cinnamate groups are well-known for a dimerization reaction upon exposure to ultraviolet irradiation and a thermal reaction after being heated. In this study, to verify the thermal reaction of the cinnamate group in detail, we investigated the thermal crosslinking of cinnamate oligomers. The thermal reaction of cinnamate oligomers of low molecular weight is induced more readily by thermal energy compared with that of cinnamate polymers. This reaction is attributed to a radical reaction involving the carbon-carbon double bond in the cinnamate group. The orientation of the liquid crystal depended on the length of the spacers in the cinnamate oligomers.

Synthesis and characterization of poly(arylene ether ketone) (co)polymers containing sulfonate groups

Poly(arylene ether ketone)s containing sulfonate groups were synthesized by aromatic nucleophilic polycondensation of 4,4′-difluorobenzophenone (DFK), sodium 2,5-dihydroxybenzensulfonate (SHQ) and bisphenols. Only low-molecular weight oligomer was obtained when hydroquinone (HQ) was employed as comonomer, while copolymerization of DFK, SHQ, and phenolphthalein (PL) proceeded quantitatively to high-molecular weight (reduced viscosities above 0.68 dL/g) in dimethylsulfoxide at 175 °C in presence of anhydrous potassium carbonate. The sulfonated polymers were soluble in dipolar aprotic solvents, such as N, N-dimethylactamide and N-methyl-2-pyrrolidinone. Tough membranes cast from N, N-dimethylformamide solution with SHQ/DFK mole ratios ≤65:35 were obtained. Both glass transition temperatures and hydrophilicity of the copolymers increased with the content of sodium sulfonate groups. The materials are candidates as new polymeric electrolytes for proton exchange membranes.