Formation Of Cyclic Oligomers Research Articles

Unraveling The Impact of Isomerism on Enzymatic Polymerization of Furanic Polyesters

AbstractAs awareness of the environmental impact of fossil‐based polymers grows, the demand for biobased alternatives rises. In this context, combining eco‐friendly synthesis techniques with renewable resources is important to produce polymers efficiently and sustainably. Furandicarboxylic acid (FDCA) is one of the key building blocks for producing biobased polymers. However, most studies predominantly focus on 2,5‐FDCA, while FDCA encompasses other noteworthy isomers, namely, 2,4‐ and 3,4‐FDCA. The polymers derived from these two isomers have recently gained attention due to their promising properties. In this study, an environmentally friendly approach for producing biobased polyesters from 2,5‐, 2,4‐, and 3,4‐FDCA dimethyl ester isomers is proposed. The synthesis is conducted under greener conditions, utilizing Candida antarctica lipase B (CALB) enzyme as a biocatalyst. The performance of the enzyme is assessed, revealing CALB preference for polymerizing 2,5‐FDCA over 2,4‐ and 3,4‐FDCA dimethyl ester, which is elucidated by docking analysis. Moreover, CALB shows varying rates of cyclic oligomer formation for each isomer, favoring 2,5‐FDCA cyclization. The structure‐property relationship, encompassing the variation in isomeric structure, is evaluated through structural characterization, thermal analysis, and surface properties. This study primarily emphasized enzymatic polymerization and highlighted its versatility in accommodating different monomer isomeric substitutions.

Rhodium(I) PNN Pincer Complexes with Proton‐responsive Ligands: Synthesis, Characterisation, and Catalytic Dehydrocoupling of Amine Boranes

AbstractCoordination of a pyridine‐pyrazole‐based PNN(H) ligand to RhI produces a family of neutral (1) and cationic (2Cl) RhI complexes. Deprotonation of the parent Rh chloride complex with LiNiPr2 results in formation of a dinuclear LiCl bridged species 3 bearing a pyrazolate fragment. Complexes 1, 2Cl and 3 were tested as precatalyst for the dehydrocoupling of amine boranes. All complexes studied show activity for the formation of cyclic oligomers with N‐methylcyclotriborazane as the main product. Base activation of the neutral Rh chloride complex 1 produces catalyst systems that are significantly more active than the parent system, suggesting that dehydrohalogenation of the Rh chloride precatalyst 1 is one of the key steps for catalyst formation.

Effects of cross-linking degree and steric hindrance on the thermal degradation behavior of novel hybrid zirconium-silicone resin

Although silicone resins are commonly seen as popular candidates for heat-resistant applications, the severe weight loss at the temperature from 400 to 800 °C remains a challenge. Herein, we reported a strategy to enhance the thermal resistance by introducing Zr into the main chain. Molecular simulation shows the Zr atoms led to the formation of high energy Zr–O bonds and increased the cross-linking degree which in turn suppressed the formation of cyclic oligomers, the results was further supported by TG-IR. The degradation activation energy was increased from 75.26 (ZAS0) to 88.67 kJ/mol (ZAS5) for the major degradation stage. The degradation kinetics study shows the degradation of ZAS5 followed the cylindrical symmetrical three-dimensional diffusion mechanism (n = 1.5). This work could provide a systemic experimental and theoretical foundation for thermal properties enhancement through metal atoms incorporation.

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).

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.

Advanced analytical, chemometric, and genomic tools to identify polymer degradation products and potential microbial consumers in wastewater environments

The worldwide growth in the production of plastics and lack of appropriate waste management has led to unsustainable environmental pollution of global concern. Hence, determining the key drivers characterizing the degradation of polymers in water is a rising topic. Here we propose a workflow based on advanced high throughput data analysis and processing tools aiming at the characterization of (a) the degradation products of polymers exposed to an aquatic environment, and (b) the taxonomical composition of the potential microbial consumers' consortia. To test this approach, polycaprolactonediol (PCLD) polymer probes were exposed to different wastewater environments (influent, aerobic, and anaerobic denitrifying reactors) in four different wastewater treatment plants (WWTPs). Probes were extracted and analyzed by non-target liquid chromatography-high resolution mass spectrometry (LC-HRMS) and the acquired data were processed using advanced chemometric tools (Regions of Interest-Multivariate Curve Resolution-Alternate Least Squares, ROIMCR-ALS). Up to 26 components explaining ca. 69% of the variance were resolved, and 20 of these were further identified. Degradation was dominated by two processes: (a) hydrolysis of the ester groups present in PCLD and (b) formation of cyclic polycaprolactone oligomers. These transformation pathways occurred regardless of what were the WWTPs and the treatment stages, varying only the respective concentrations of the formed by-products. The composition of the microbial communities attached to the polymer and free-living in the surrounding water was characterized by 16S rDNA amplicon sequencing analysis. The two communities showed taxonomic differences and were unique in each WWTP treatment stage. Polymer-attached communities were tentatively proposed as potential consumers.

Theoretical Investigation on the Oligomerization of Methylglyoxal and Glyoxal in Aqueous Atmospheric Aerosol Particles

Secondary organic aerosol (SOA) is the main component of atmospheric particulate matter with wide implications for air quality, human health, and climate change. However, the formation mechanism of SOA has not been fully understood. Methylglyoxal (MGLY) and glyoxal (GLY) are ubiquitous dicarbonyls in the atmosphere and have been considered as important precursors for SOA formation, especially through the oligomerization in the atmospheric aqueous phase. In this paper, the oligomer formation mechanism through the self-oligomerization of MGLY and GLY, and especially their cross-reactions in the atmospheric aqueous phase were investigated by density functional theory (DFT) calculations. Carbenium ions play a key role in the oligomerization, and all of the reactions take place barrierless under acidic conditions. First-generation oligomers (dimers) lead to the formation of chain and cyclic (including five- and six-membered) oligomers, among which five-membered cyclic oligomers are the dominant products. The products identified and described by the energetics of their formation pathways are discussed in view of available experimental findings from the literature. Many of the products were actually measured and assigned. In addition, the diffusion rate constants (kD) of the nucleophilic addition were determined to estimate the formation rate of oligomers in the aqueous phase, and the calculated kD’s are in the range of 1.20–1.31 × 1010 L mol–1 s–1. All of these findings will help us to gain a better understanding of the oligomerization of the dicarbonyl compounds in the atmospheric aqueous aerosol particles, and thus to provide a scientific support toward controlling and reducing SOA formation.

Design of novel optically active oligomers consist of units similar to BODIPY molecules

In this study, based on new designed and reported molecules with chemical formula of C13H13B2N, novel electrically and optically active oligomers with different size were suggested. It was shown that the suggested structures have no imaginary frequency and have high negative values of the cohesive energies which show feasibility of their formation. Additionally, increasing the numbers of unit in oligomers created the narrower values of Eg. Similar results were obtained in calculating the optical properties of oligomers using two different methods. Considerable improvements in optical properties of oligomers were observed by increasing numbers of units in their structures. The feasibility of formation of cyclic oligomers with 8 units was studied, and it was shown that formation of this structure is possible which has considerable optical properties. A noteworthy result is that the circular oligomer comprised 8 units has cup-like structure which is very attractive.

An Improved PO3G Model–Accounting for Cyclic Oligomers

AbstractA comprehensive model is developed for polycondensation of 1,3‐propanediol in a batch reactor. The model accounts for formation, consumption, and evaporation of cyclic oligomers. Measurements of species and end‐group concentrations in the reactor and collected condensate are used to estimate 36 kinetic and mass‐transfer parameters. The model and parameter estimates provide good fits to cyclic‐oligomer data obtained using four different levels of super‐acid catalyst. Predictions from the model reveal that end‐biting reactions are important for formation of cyclic oligomers during early stages of each batch‐reactor run, whereas back‐biting reactions become important at longer reaction times. Simulation results reveal that ring‐opening polyaddition reactions contribute significantly to growth of polymer chains at long reaction times.

Polycondensation Kinetics: 2. Time-Dependent29Si NMR Spectra of Poly-Dimethyldimethoxysilane

The polycondensation of dimethyldimethoxysilane has been studied by 29Si NMR to high degrees of conversion at pH 2.8. The relative concentrations of nonbonded Si atoms (D0) and bound by one (D1) and two (D2) Si–O–Si bonds have been determined from the integrated intensities of the multiplets assigned to them. The measurement results have been considered in terms of the kinetic scheme proposed in the first paper. It has been found that the D0(t), D1(t), and D2(t) curves coincide with those measured for the ratio of the constants of competing processes of aggregation and addition of monomers k ≈ 0.15. The time-dependent molecular mass distributions have been determined with allowance for chain termination during the formation of cyclic and entangled oligomers.

Understanding the water droplet initiated discharges on gamma irradiated silicone rubber insulation

Corona inception voltage (CIV) due to water droplet on gamma‐irradiated silicone rubber indicates that its value reduces with increase of conductivity and with number of droplet in the electrode gap along the axis of the electrode. Increase in dosage of gamma irradiation to silicone rubber reduces the CIV. The UHF signal generated during corona inception due to water droplet has frequency bandwidth in the range of 0.3–1.2 GHz. The discharges occur in the phase range of 30°–130° in the positive half cycle and about 210°–270° in the negative half cycle. The water droplet shape gets altered on application of voltage. Surface charge accumulation studies indicate characteristic change with gamma irradiated specimen. In the presence of water droplet, the charge decay occurs rapidly with a single droplet and with three droplets. Thermal analysis of gamma radiation dosed samples reveals the destabilization of silicone material and the formation of higher order cyclic siloxane oligomers and oxygenated organics, which are expected to act as potential charge trapping sites. POLYM. ENG. SCI., 59:182–191, 2019. © 2018 Society of Plastics Engineers

Synthesis of polyenaminones by acid-catalysed amino–enaminone ‘click’ polymerisation

A mild amino–enaminone ‘click’ polymerisation method for the preparation of polyenaminones by transamination of α,α′-bis-enaminocyclopentanones with diamines was developed. A series of 12 representative polymers were synthesised by acid-catalysed transamination of two bis-enaminones with six primary 1,2-, 1,3-, and 1,4-diamines. The method allows for combinatorial preparation of structurally diverse polyenaminones from easily available diamines and bis-enaminones. The reaction mechanism was studied by NMR and MS. It involves formation of open-chain and cyclic oligomers, which then undergo a step-wise polymerisation to furnish the title polymers with high average molecular weight (Mw > 5.0 × 104 Da) and with spherical and porous microstructure. The obtained polymers were insoluble in most organic solvents, stable in diluted acids and bases, while degradable in concentrated hydrochloric acid at room temperature. They were thermally stable up to 200 °C and exhibited film-forming and UV–vis-shielding properties.

Acid-activated bentonite (Maghnite- $$\hbox {H}^{+})$$ H + ) as a novel catalyst for the polymerization of decamethylcyclopentasiloxane

In this study, we propose Maghnite-\(\hbox {H}^{+}\), as an ecological, cost-effective and easily renewable catalyst, for the polymerization of decamethylcyclopentasiloxane (D5). The Maghnite is a clay consisting primarily of smectite minerals (montmorillonite group), which can be activated/reactivated through a simple process, by replacing interlayer cations by protons. Linear polymers with higher molecular mass and narrower molecular mass distribution (MMD) can be obtained with less cyclic by-products, using Maghnite-\(\hbox {H}^{+}\). The reaction was investigated in bulk, taking into account the effect of time, temperature and amount of catalyst on the monomer conversion and MMD. When the yield rises to 96%, the MMD is broadened, suggesting the formation of cyclic oligomers and/or crosslinking bonds, this was confirmed experimentally by infra-red spectroscopy, proton nuclear magnetic resonance (\(^{1}\hbox {H}\) NMR) and \(^{13}\hbox {C}\) NMR analyses. The kinetics have been also studied; the reaction is first order in the monomer. The proposed reaction mechanism shows clearly the role of Maghnite-\(\hbox {H}^{+}\) for D5 polymerization.

Synthesis of Cyclic Oligomers of 4,4′′-Diethynyl-4′,5′-dioctyl-o-terphenyl Using Eglington Coupling Reaction: Formation of Large Cyclic Oligomers as Major Products under Standard Conditions

Abstract Dimer 2, trimer 3, hexamer 6, octamer 8, and decamer 10 of 4,4′′-diethynyl-4′,5′-dioctyl-o-terphenyl 1 were synthesized by using copper(II) acetate-mediated Eglington coupling reaction of 1 in pyridine or pyridine–methanol. Although dimer 2 and trimer 3 were formed as major products under high dilution conditions, large oligomers such as hexamer 6, octamer 8, and decamer 10 were obtained in moderate total yield under standard Eglington conditions. The MALDI-TOF MS and GPC behavior of large oligomers exhibit the formation of giant macrocycles 3 nm diameter and 2–4 nm long in one-pot procedure.

Self-Accelerating Click Reaction in Step Polymerization

A self-accelerating double-strain-promoted azide–alkyne cycloaddition reaction (DSPAAC) was used in the step polymerization for the first time. This produced a novel stoichiometric imbalance-promoted homogeneous step polymerization method using sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD) and various bis-azide compounds (N3-R-N3) as respective monomers. Because of the self-accelerating property of DSPAAC reaction, the novel step polymerization method could prepare high molecular weight polymers under stoichiometry imbalance condition with excess molar amounts of DIBOD to N3-R-N3. Based on the click property of DSPAAC reaction, the novel step polymerization could be efficiently performed in very mild reaction conditions such as in air at room temperature without requiring any metal catalyst or chemical stimulus. Under the present polymerization condition, the preparation of high molecular weight polymers from this novel method was accompanied by the formation of cyclic oligomers with a weight content a...

Cooperative Activation of Isocyanates by Al-N-Based Active Lewis Pairs and the Generation of a C5 Chain by Simultaneous Formation of Two C-C Bonds.

The active Al/N Lewis pair, (Me3 C)2 Al-C(SiMe3 )=C(H)-N(CHMe-CH2 )2 CH2 (2), reacted with isocyanates to afford a fascinating variety of products. One equivalent of Ph-N=C=O yielded by the release of H-C≡C-SiMe3 an urea-type ligand which coordinated the Al atom in a chelating manner (4). Dipp-N=C=O gave a similar product, but the bulky substituent hindered the approach of the N-aryl group to Al. A situation similar to that of frustrated Lewis pairs resulted in the coordination of the alkyne to the Al and N atoms (6) by C-H bond activation. Dual insertion was observed upon treatment of 2 with two equivalents of isocyanates (8 to 11). The preferred formation of cyclic oligomers is prevented by the specific cooperative properties of the Lewis pair. A metal-free dimeric isocyanate (13) was formed by hydrolysis. Replacement of the CMe3 groups in 2 by less bulky isobutyl groups (7) afforded the insertion of two isocyanate molecules into the Al-vinyl bonds without alkyne elimination. The resulting highly functionalised compound had a chain formed by two isocyanates and the organic backbone of the Lewis pair. Me3 C-N=C=O and 2 afforded a unique compound (14) in which an isocyanate ligand connects two molecules of 2 by the release of dimethylpiperidine. The combination of a C1 building block and two C2 groups gave an unsaturated branched C5 moiety by the simultaneous formation of two C-C bonds. The molecular structure showed an interaction between an Al atom and a C-C π-bond.

Thermal degradation behavior of Copoly(propylene carbonate ε-caprolactone) investigated using TG/FTIR and Py-GC/MS methodologies

Thermal degradation behaviors of copoly(propylene carbonate ε-caprolactone)s (PPCCLs) with different ε-caprolactone (CL) contents were studied at various pyrolysis temperatures by the combination of thermogravimetric analysis/Fourier transform infrared spectrometry (TG/FTIR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) techniques. TGA curves of the copolymers clearly show two stages. The experimental results indicate that the increase of CL content in PPCCL chain leads to an increase of both first and second stage maximum decomposition temperature. The dominant degradation pathway is a backbiting ester interchange reaction involving OH chain ends of PPCCLs, resulting in the formation of cyclic oligomers. In addition, at a relative higher pyrolysis temperature, besides the major products propylene carbonate and caprolactone, some diol and long chain chemicals with ester group were also detected, showing a main intramolecular transesterification accompanied with chain scission decomposition mechanism.

Chemisorption and thermally induced transformations of polydimethylsiloxane on the surface of nanoscale silica and ceria/silica

Compositions of polydimethylsiloxane (PDMS) polymer with nanosized silica and ceria/silica were prepared. The influence of these nano-fillers on the thermal stability and degradation mechanism of silicone polymer was investigated using Thermogravimetric Analysis (TGA) and Temperature Programmed Desorption Mass Spectrometry (TPD MS). The results showed that thermal decomposition of pure and adsorbed PDMS differs significantly. The three main stages of the PDMS thermal transformations in the adsorbed state were determined to be: 1) chemisorption of PDMS chains involving the terminal trimethylsilyl groups of the polymer and silanol groups of the silica surface; 2) formation and desorption of cyclic oligomers; 3) high temperature radical degradation of the polymer accompanied by the formation of methane and ethylene. The kinetic parameters of the corresponding reactions were calculated from the TPD MS data. It was found that nanoparticles of cerium dioxide strongly influence the degradation pattern, lower the decomposition temperature and catalyze the formation of methane.

Thermal degradation of poly(lactide-co-propylene carbonate) measured by TG/FTIR and Py-GC/MS

Thermal degradation behaviors of poly(lactide-co-propylene carbonate)s (PLAPCs) with different PC contents were studied at various pyrolysis temperatures by the combination of thermo gravimetric analysis/Fourier transform infrared spectrometry (TG/FTIR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) techniques. The activation energies of thermal degradation are calculated by Kissinger method. The experimental results indicate that increasing PC content in PLAPC chain lead to a decrease of maximum decomposition temperature. The activation energy of degradation increases with increasing PC content. The dominant degradation pathway is a backbiting ester interchange reaction involving OH chain ends of PLAPCs, resulting in the formation of cyclic oligomers. In addition, at a relative higher pyrolysis temperature, besides the major products propylene carbonate and lactide, small amounts of propenoic acid and acetaldehyde were also detected, showing a main intramolecular trans-esterification accompanied with chain scission decomposition mechanism.

Supramolecular polymers with tunable topologies via hierarchical coordination-driven self-assembly and hydrogen bonding interfaces

A powerful strategy to obtain complex supramolecular materials is the bottom-up construction of noncovalently bound materials by hierarchical self-assembly. This assembly process involves stepwise, uniform increases to the architectural complexity of a substrate, starting from discrete precursors and growing in dimensionality through controlled reactivity to a final product. Herein, two orthogonal processes are exploited: coordination-driven self-assembly and hydrogen bonding. The former relies on the predictable formation of metal-ligand bonds wherein the directionalities of the rigid precursors used determines the structural outcome. The latter uses 2-ureido-4-pyrimidinone interfaces that are structurally robust by virtue of the quadruple hydrogen bonding that can occur between subunits. By combining these two processes into a single system, it is possible to generate hierarchical materials that preserve the attractive tunability associated with discrete supramolecular coordination complexes. For instance, the synthesis of a one-dimensional chain comprising linked metalla-rhomboids is readily adapted to a 2D cross-linked hexagonal network by simply selecting a different metal acceptor precursor as an assembly component. The specific interactions between subunits, in this case platinum(II)-pyridyl bonds and the quadruple H-bonding of ureidopyrimidinone, are unchanged, establishing a unique strategy to obtain supramolecular polymers with marked topological differences with minimal synthetic redesign. In addition, the structural rigidity imposed by the inclusion of the platinum metallacycles serves to minimize the formation of cyclic oligomers, increasing the efficacy of formation and improving the properties of the resultant materials. Furthermore, this study taps the potential of organoplatinum(II) metallacycles in materials science.