Cyclic Oligomers Research Articles

An efficient cyclodepolymerization route for the chemical recycling of poly(ethylene adipate)

We present here a green cyclodepolymerization route for the chemical recycling of poly(ethylene adipate) to its cyclic oligomers based on ring–chain equilibria in solution.

Tribological properties of cyclic phenylene sulfide heat‐treated carbon fiber/polyphenylene sulfide composites

AbstractHigh‐performance self‐lubricating polyphenylene sulfide (PPS)/carbon fiber (CF) composites were obtained by treating the CF surface with heat‐treated cyclic phenylene sulfide oligomers (CPS). The influence of CPS treat conditions on the structure and properties such as mechanical and tribological performance of the composites were studied in detail. The results indicate that the PPS/CPS‐sized CF composites exhibit higher mechanical strength and better tribological performance than the PPS/original CF composites, especially under the condition of higher loads and speeds (300 N × 200 rpm and 200 N × 200 rpm). The performance enhancement is reasonably ascribed to the improved compatibility of the modified CF with the PPS matrix. Further structural analysis reveals that the modified CF treated at 300°C under N2(CF‐300N) has the most similar structure to the PPS matrix, which makes the comprehensive performances of PPS/CF‐300N composites superior to the products obtained under the other heat‐treatment conditions.

De novo design of obligate ABC-type heterotrimeric proteins

The de novo design of three protein chains that associate to form a heterotrimer (but not any of the possible two-chain heterodimers) and that can drive the assembly of higher-order branching structures is an important challenge for protein design. We designed helical heterotrimers with specificity conferred by buried hydrogen bond networks and large aromatic residues to enhance shape complementary packing. We obtained ten designs for which all three chains cooperatively assembled into heterotrimers with few or no other species present. Crystal structures of a helical bundle heterotrimer and extended versions, with helical repeat proteins fused to individual subunits, showed all three chains assembling in the designed orientation. We used these heterotrimers as building blocks to construct larger cyclic oligomers, which were structurally validated by electron microscopy. Our three-way junction designs provide new routes to complex protein nanostructures and enable the scaffolding of three distinct ligands for modulation of cell signaling.

Activation of Ge-H and Sn-H Bonds with N-Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene.

A study of the reactivity of several N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene (cAACMe ) with the group 14 hydrides GeH2 Mes2 and SnH2 Me2 (Me=CH3 , Mes=1,3,5-(CH3 )3 C6 H2 ) is presented. The reaction of GeH2 Mes2 with cAACMe led to the insertion of cAACMe into one Ge-H bond to give cAACMe H-GeHMes2 (1). If 1,3,4,5-tetramethyl-imidazolin-2-ylidene (Me2 ImMe ) was used as the carbene, NHC-mediated dehydrogenative coupling occurred, which led to the NHC-stabilized germylene Me2 ImMe ⋅GeMes2 (2). The reaction of SnH2 Me2 with cAACMe also afforded the insertion product cAACMe H-SnHMe2 (3), and reaction of two equivalents Me2 ImMe with SnH2 Me2 gave the NHC-stabilized stannylene Me2 ImMe ⋅SnMe2 (4). If the sterically more demanding NHCs Me2 ImMe , 1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene (iPr2 ImMe ) and 1,3-bis-(2,6-di-isopropylphenyl)-imidazolin-2-ylidene (Dipp2 Im) were employed, selective formation of cyclic oligomers (SnMe2 )n (5; n=5-8) in high yield was observed. These cyclic oligomers were also obtained from the controlled decomposition of cAACMe H-SnHMe2 (3).

Molecular simulations of liquid aliphatic carboxylic acids (C1-C6) using the 3D-RISM-KH molecular solvation theory

The liquid structures of short straight chain aliphatic carboxylic acids (C1-C6) and halogenated acetic acids (trifluoro and trichloro) are analyzed with molecular dynamics simulations, three-dimensional reference interaction site model, and density functional theory calculations. The neat acids are found to exist in multimeric ordered form consisting of both open chain and cyclic oligomers. Introduction of water breaks the hydrogen bonding networks between adjacent acetic acid molecules by inserting water as a bridging molecule. The electronic structure calculations confirm the formation of chain and ring type structures in the liquid state.

Many-body analysis and spectroscopic characterization of diazene oligomers: A theoretical study

The present study reports the many-body analysis and spectroscopic characterization of linear and cyclic diazene oligomers in gas and water solvent states. The oligomers of diazene from monomer to pentamer have been considered for the study. The spectroscopic studies such as geometrical parameters, infrared spectra, electronic absorption spectra, and natural transition orbitals (NTOs) were reported. Many-body analysis techniques have been implemented to study the interactions among the diazene oligomers. These calculations have been performed using exchange and correlation functional (B3LYP) and 6–311++G (d,p) basis set. The geometrical parameters and infrared modes of monomer diazene in the gas state are well-matched with the available experimental determinations at this level of theory. A significant change in vibrational modes of linear and cyclic diazene oligomers has been observed in the gas phase-to-water solvent state. The time-dependent density functional theory (TD-DFT) has been used to calculate the electronic absorption spectra of diazene oligomers. The Wavelength of electronic transitions, oscillator strength, and HOMO to LUMO gap has been reported. Many-body analysis shows that two-, three-, four-, and five-body energies have a remarkable contribution to the binding energy in addition to relaxation energies. All these calculations have been performed using Gaussian 16 program package.

Thiol‐ene emulsion step polymerization in a photochemical stirred tank reactor: Molecular weight, cyclization, and fragmentation

AbstractUnlike many step polymerizations, the polymerization of bifunctional thiol and alkene monomers can be carried in emulsion to prepare a range of sulfur‐containing polymer particles differing markedly from conventional emulsion chain polymers. This study examines how the change of polymerization mechanism affects polymer molecular weight, structure and composition. A 2,2′‐dimercaptodiethyl sulfide/diallyl phthalate emulsion is photopolymerized in a photochemical stirred‐tank reactor equipped with Light‐emitting diodes (LEDs) to yield a 30% solids content latex with a high weight‐average molecular weight (100 kDa) and a broad molecular weight distribution (Đ = 8.5). Intramolecular cyclization occurs during polymerization by the addition of a thiyl radical to the unsaturated end group of the same molecule. Irreversible ring‐closure takes place to produce “dead” cyclic oligomers in the early stage of the reaction, whereas chain‐growth continues at high conversion. Consequently, the particles are composed of high molecular weight linear chains and a fraction of stable oligomer cycles, showing a broad and bimodal molecular weight distribution. The linear poly(thioether) chains include occasionally disulfide units due to thiyl radical recombination. The reversibility of disulfide bonds causes a decrease of molecular weight during storage. The addition of radical inhibitor to the latex stops fragmentation of SS bonds.

Oligomers in polybutylene terephthalate for food contact—strategies on identification, quantification, and risk assessment

Oligomers are a significant group of migrating substances from food contact materials made of polyesters like polybutylene terephthalate (PBT). Twenty-three cyclic and linear oligomers with different end groups including olefin-terminated oligomers, which are associated with thermal stress of the material, were tentatively identified in PBT extracts by high-performance liquid chromatography with mass spectrometry and diode array detection. Quantification approaches based on chromophore concentration, relative response factors, and overall oligomer determination after hydrolysis to the monomer terephthalic acid were employed. An exhaustive extraction of thirteen PBT samples yielded an overall oligomer content of 1.87–6.10 mg/g material (sum of individual oligomers < 1,000 Da) with a predominant content of cyclic over linear oligomers. Migration experiments were performed according to Regulation (EU) No. 10/2011 using the official food simulants as well as cows’ milk. A total of 218 µg cyclic oligomers/L milk were detected in the third migrate relevant for risk assessment of repeated-use articles under hot-fill conditions (70 °C, 2 h). The official food simulant for milk, 50% ethanol, was found to overestimate the actual migration into milk by a factor of four. Frying conditions using sunflower oil as the food simulant (200 °C, 10 min) resulted in a migration of 7.5 mg cyclic oligomers/kg oil. The exposure to migrating oligomers is critical in some scenarios when evaluated by the threshold of toxicological concern concept; however, the toxicological evaluation poses a challenge due to the possible hydrolysis of cyclic oligomers in the human gastrointestinal tract. Our experiments display the need for a toxicological evaluation of PBT oligomers because the migration of cyclic oligomers is expected to exceed the current in silico–based thresholds under foreseeable conditions of use.

Iterative synthesis, structures, and properties of acyclic and cyclic acridone oligomers

AbstractAcyclic and cyclic acridone‐2,7‐diyl oligomers were synthesized by an iterative procedure from 10‐mesitylacridone as heteroatom containing π‐conjugated compounds. The oligomeric chain was elongated by a combination of regioselective bromination, borylation, Ni(0)‐mediated homocoupling, and Suzuki‐Miyaura coupling up to acyclic hexamer. Subsequently, the cyclic hexamer was synthesized by the bromination and intramolecular coupling of the acyclic hexamer. The DFT calculations revealed that the acyclic oligomers preferred to take extended structures with anti conformations, whereas the cyclic hexamer took a macrocyclic structure with syn conformations. The UV/Vis and fluorescence spectra of the series of oligomers were measured, and the effects of the chain length and the cyclization are discussed in terms of π‐conjugation.

Synthesis of Linear and Cyclic Discrete Oligomers with Defined Sequences via Efficient Anionic Coupling Reaction

We hereby report a new strategy to prepare sequence-defined discrete oligomers with uniform molecular weight through carbanionic addition and coupling reactions using specific monomers possessing 1,1-diphenylethylene (DPE) and tert-butyldimethylsilyloxy (TBS) moieties. The strategy allows the molecular weight growth by iterative attaching of the sec-butyllithium (s-BuLi) activated monomer or dimer unit to the halomethyl end-group, released from deprotection of TBS, of the proceeding oligomer starting from a dichloromethyl core. A series of linear discrete oligomers with alternating and ABCD/ACBD sequences are synthesized. These linear sequence-defined oligomers are subsequently modified with double vinyl groups and cyclized through ring-closing metathesis (RCM) reaction into corresponding sequence-defined macrocycles. The molecular structures of the linear and cyclic oligomers are analyzed by using size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). The features of the present approach are the presynthesized monomers or dimers with specific functionalities, the efficient carbanionic reactions, as well as the easy separation of the products due to the increasing difference between the molecular weights of the monomer/dimer and the products. More interestingly, sequence and topology effects were observed on Förster resonance energy transfer (FRET) measurements using naphthalene (donor) and pyrene (acceptor) functionalized linear and cyclic ABCD/ACBD oligomers having identical molecular weights and compositions for the two sequences.

Effect of oligo(ethylene glycol) length on properties of poly(oligoethylene glycol terephthalate)s and their cyclic oligomers

We present here the effect of oligo(ethylene glycol) (OEG) segmental length on properties of cyclic oligo(oligoethylene glycol terephthalate)s (COEGTs) and their corresponding polymer counterparts, poly(oligoethylene glycol terephthalate)s (POEGTs). COEGT monomers were synthesized from terephthaloyl chloride with corresponding diethylene glycol, triethylene glycol, and tetraethylene glycol under pseudo-high-dilution conditions. As those large ring cyclic monomers are hard to be polymerized via traditional ring-opening polymerization, a cascade polycondensation-coupling ring-opening polymerization method is utilized to obtain high molecular weight POEGTs. The cascade polymerization mechanism is confirmed by the kinetics study. The structures of COEGTs and POEGTs were well characterized and their properties were studied to reveal the structure-property relationship. With the increment of OEG length in repeating units, the chain flexibility of POEGT and COEGTs is enhanced. As a result, the melting temperatures of COEGTs and glass transition temperatures of POEGTs decrease. On the other hand, the thermal degradation temperature of POEGTs and COEGTs increases due to the enhanced ether fraction and reduced ring strain. Solid-state polymer electrolytes based on POEGTs was prepared by blending with lithium bis(trifluoromethanesulfonyl)imide. The measured ionic conductivity increased with the OEG length in POEGT repeating units. Our results revealed the effect of OEG length on the structure-property relationship in cyclic oligo(ether ester)s and copoly(ether ester)s, providing a facile way to tune their properties.

Tuning the electrochemical activity of Li–Se batteries by redox mediator additives

A lithium–selenium (Li–Se) battery is considered as a promising next-generation energy storage system due to its ultrahigh volumetric energy density. However, the capacity attenuation due to the dissolution and shuttle effect of polyselenides is urgent to be addressed. Herein, 1,4-benzenedithiol (1,4-BDT) and benzeneselenol (PhSeH) are proposed as redox mediator additives in the electrolyte. They both change the multi-step reaction of Se and accelerate the redox kinetics, thus suppressing the shuttle effect of polyselenides and improving the cycling stability and rate performance. The Li–Se cell with 1,4-BDT exhibits steady 450 cycles at 1 C with capacity decay only 0.058% per cycle. Differently, the Li–Se cell with PhSeH features fast kinetics, which shows 91.4% capacity retention after 450 cycles at a high rate of 5 C. Due to the difference of molecular structures between 1,4-BDT and PhSeH, the cyclic oligomers formed in the Li–Se cell with 1,4-BDT diminish the solubility of polyselenides enhancing the cycling stability, while the chain-like diphenyl selenides generated in the Li–Se cell with PhSeH promote kinetics performance through a single-phase reaction. This work provides an effective redox regulation strategy that will stimulate interest in exploration of organic mediators for rechargeable batteries.

IVIVC of Octreotide in PLGA-Glucose Microsphere Formulation, Sandostatin® LAR.

In vitro-in vivo correlation (IVIVC) analysis reveals a relationship between in vitro release and in vivo pharmacokinetic response of the drug of interest. Sandostatin LAR Depot (SLD) for endocrine tumors and acromegaly is a sustained-release formulation of octreotide, a cyclic oligomer of 8 amino acids, which prolongs therapeutic efficacy and enhances medication compliance of octreotide. Since the efficacy of SLD is dependent on the pharmacokinetic characteristics of octreotide released from a biodegradable matrix polymer, poly(lactide-co-glycolide)-glucose, of SLD, the IVIVC of SLD is critical for predicting an in vivo behavior of the octreotide. In this study, in vitro release of octreotide from SLD was investigated using the release test media each containing 0.02% or 0.5% surfactant and having different pH values of 7.4 and 5.5. In vivo pharmacokinetic profiles of SLD were determined by LC-MS/MS analysis of the systemic blood concentration of octreotide after the SLD injection to rodents. In IVIVC analysis, the Weibull model was adopted as a drug release model for biodegradable microsphere formulation. The IVIVC analyses revealed the in vitro release test condition of SLD with the highest IVIV correlation coefficient. By applying the in vitro release data to the model derived from the IVIVC analysis, pharmacokinetic parameters of SLD could be predicted with the prediction error of ± 10 ~ 15%. IVIVC analysis and pharmacokinetic prediction model of SLD in our study can be an efficient tool for the development of long-acting pharmaceutical dosage forms.

Theoretical studies on donor–acceptor based macrocycles for organic solar cell applications

We have designed a series of new conjugated donor–acceptor-based macrocyclic molecules using state-of-the-art computational methods. An alternating array of donors and acceptor moieties in these macrocycle molecules are considered to tune the electronic and optical properties. The geometrical, electronic, and optical properties of newly designed macrocyclic molecules are fully explored using various DFT methods. Five conjugated macrocycles of different sizes are designed considering various donor and acceptor units. The selected donor and acceptors, viz., thiophene (PT), benzodithiophene (BDT), dithienobenzodithiophene (DTBDT), diketopyrrolopyrrole (DPP), and benzothiazole (BT), are frequently found in high performing conjugated polymer for different organic electronic applications. To fully assess the potential of these designed macrocyclic derivatives, analyses of frontier molecular orbital energies, excited state energies, energy difference between singlet–triplet states, exciton binding energies, rate constants related to charge transfer at the donor–acceptor interfaces, and electron mobilities have been carried out. We found significant structural and electronic properties changes between cyclic compounds and their linear counterparts. Overall, the cyclic conjugated D–A macrocycles’ promising electronic and optical properties suggest that these molecules can be used to replace linear polymer molecules with cyclic conjugated oligomers.

Migration and Chemical Characterization of Cyclic Oligomers from Polyester Fiber in Waterless Dyeing System

Migration and Chemical Characterization of Cyclic Oligomers from Polyester Fiber in Waterless Dyeing System

A Supramolecular Strategy for the Synthesis of Cyclic Oligomers and Polymers by Ring Expansion.

Ring-opening metathesis polymerization (ROMP) of strained macrocycles is a key method to prepare diverse polymers. However, lack of ring strain in most macrocycles is an impediment to polymerization. In this paper, the polymerization/oligomerization of unstrained macrocycles was achieved using a supramolecular approach, leading selectively to cyclic products. Diphenyl thiourea and other guest molecules were used as additives to the ROMP reaction of unstrained macrocycles. An intermediate host-guest complex leads to the stabilization of the open form of the macrocycle after treatment with Grubbs catalysts, thereby favoring polymerization by inhibiting the ring-closing reaction back to the monomer. This proof-of-concept enables ring-expansion polymerization of unstrained macrocycles leading to cyclic polymers with molecular weights up to 6700 Da.

Peptization mechanism of aluminum phosphate sol

Aluminum phosphate sol attracts more and more attention due to its excellent particle size and bonding properties. The structure, morphology and Zeta potential of aluminum phosphate sol during the peptizing process were investigated with NMR, FTIR, Raman, TEM and DLS. The results show that the pseudo boehmite particles were fragmentated, dissolved, and then peptized under the electrostatic repulsion of H+. The peptization process presents three stages: the fragmentation-polymerization stage, the reaction stage, and the stabilization stage. The particle diameter of the stable aluminum phosphate sol ranged from 30 to 50 nm, and the particles with varying sizes were interconnected to form a “hand-in-hand” cyclic system. Meanwhile, the dehydration condensation reaction between H3PO4 and pseudo boehmite was occurring continuously. When 2.1 ≤ n(P)/n(Al) < 3, the proportion of QP01, QP10 and QP11 polymers in the system increased to 25–27 %, the degree of polymerization was deepened, and some cyclic oligomers and polymers appeared. Additionally, the crystal water concentration was increased and the peptization solubility was enhanced.

Structure elucidation and toxicological evaluation of cyclic Polyethersulfone oligomers present in extracts of membrane filters

Polyethersulfone (PES) is a widely used polymer in consumer and technical products. An important application is PES membranes used in the biopharmaceutical industry for sterilizing-grade filtration and for filtration of food and beverages. For both uses, detailed information about migrating compounds that can be extracted from the polymeric material into a liquid must be gathered. In the pharmaceutical industry, comprehensive extractables studies are required for contact materials, and the data is used in the qualification of the process equipment. PES is generated via polycondensation, which forms cyclic oligomers as a by-product of the reaction. However, no structural information is available for these cyclic oligomers so far. In this publication, we present the analytical determination of PES cyclic oligomers. Their presence in extracts of PES membrane filters is confirmed. The structure of the PES cyclic trimer is elucidated by X-ray and NMR investigation, obtained as crystals from the sublimation of the PES raw material. A strategy is shown to assess the toxicity of such cyclic oligomers and to derive a permitted daily exposure (PDE). The data will reduce the levels of unknowns in extractables and leachables screenings and supports the risk assessment of PES sterile filters.

Thermal degradation of various types of polylactides research. The effect of reduced graphite oxide on the composition of the PLA4042D pyrolysis products

This study was aimed to investigate the effect of reduced graphene oxide (rGO) on the pyrolysis of polylactide composites (PLA4042D/rGO) prepared in solution. GC-MS analysis of PLA4042D/rGO pyrolysis products showed that introduction of rGO into the composition with PLA leads to a significant change in the ratio of main degradation products. A sharp decrease of five-membered dioxolanones accompanied by a growth in the content of lactides and cyclic oligomeric lactides was observed in PLA4042D/rGO pyrolysis products as compared with pristine PLA. DSC studies of PLA4042D crystallization in the melt showed that the adsorption of PLA macromolecules on rGO surface can cause the decrease in their segmental mobility. Apparently, a decrease in the segmental mobility of PLA chains hinders the formation of dioxolanones via the intramolecular nonradical ester interchange reaction. At the same time, the role of intermolecular reactions with the formation of cyclic oligomers of lactides increases.

Synthesis and application of poly methyl indole-4-carboxylate with blue light blocking properties

Blue light hazards have garnered increasing attention owing to the popularity of displays. Although melanin on the retina acts as a blue light barrier, overexposure to blue light increases the risk of visual damage. A class of methyl indole-n-carboxylate oligomers (O-MInC, n = 3, 4, 5, 6, and 7) was synthesized through solid-phase oxidative polymerization. Based on the experimental characterizations, including time-of-flight mass spectrometry, infrared spectroscopy, and density functional theory calculations of the average local ionization energy, we proposed a mechanism for the oxidative polymerization of methyl indole-4-carboxylate (MI4C). Methyl indole-4-carboxylate oligomer (O-MI4C) is composed of cyclic oligomers containing large conjugated structures that are generated by the repetition of electron deprivation, radical coupling, and dehydrogenation reactions. O-MI4C exhibits the best blue light absorption among its allotropes substituted at different positions with a cut-off absorption wavelength of 530 nm. Finally, O-MI4C was added to polymethylmethacrylate (PMMA) and Columbia resin 39 (CR-39) flakes through in situ polymerization to investigate the behavior of blue light blocking. The PMMA/O-MI4C (0.01 wt%) and CR-39/O-MI4C (0.02 wt%) can block 25% and 35% of blue light; however, they have no significant effect on green and orange lights.