Oligomer Chain Research Articles

Chemical Reactions and Their Kinetics of atactic-Polyacrylonitrile As Revealed by Solid-State 13C NMR

Inter- and intramolecular chemical reactions and their kinetics for 13C-labeled atactic-polyacrylonitrile (aPAN) powder heat-treated at 220–290 °C under air and vacuum were investigated by various solid-state nuclear magnetic resonance (ssNMR) techniques. By applying 13C direct polarization magic angle spinning (DPMAS) as well as through-bond and through-space double quantum/single quantum ssNMR techniques, it was concluded that aPAN heat-treated under air at 290 °C for 300 min adopted the ladder formation, namely, conjugated six-membered aromatic rings with partially cross-linked and oxidized rings and polyene components. In contrast, aPAN heat-treated under vacuum at the same condition thermally decomposed into oligomeric chains that were mainly composed of isolated aromatic rings connected by alkyl segments. Furthermore, early stages of the chemical reactions were investigated by 13C cross-polarization (CP) and DPMAS spectra. The latter provided quantitative information regarding the kinetics of the chemical reactions. As a result, it was shown that chemical reactions under oxygen occurred homogeneously with a higher activation energy (Ea) of 122 ± 3 kJ/mol compared to that of vacuum at 47 ± 2 kJ/mol. By comparing both chemical structures and kinetics under two different conditions, the chemical reaction mechanisms of aPAN will be discussed in detail.

A multi-scale method for modeling degradation of bioresorbable polyesters

The original work in this paper is a multi-scale method (including micro scale, mesoscopic scale, macro scale and their coupling) for modeling degradation of bioresorbable polyesters and provides understanding to the process of degradation of biodegradable polymers. The result denotes the solution is reliable. As we know, there have no papers recently to implement three scales modeling and its coupling. There is a two-scale model of amorphous polyester degradation described by Han and Pan (Acta Biomaterialia 2011), our model accounts for effects of re-crystallization to explain the degradation process from three scales and takes into account of copolymers. From our model, the molecular weight distribution with time, chain number with time, degree of crystallinity with time, the evolution of polymer inner shape, weight loss with time (which is found from calculation that both oligomer diffusion and small molecules solution work to the weight loss) can be obtained from the calculation of the three scale model.

Enzymatic Synthesis of a Bio-Based Copolyester from Poly(butylene succinate) and Poly((R)-3-hydroxybutyrate): Study of Reaction Parameters on the Transesterification Rate.

The enzyme-catalyzed synthesis of fully biobased poly(3-hydroxybutyrate-co-butylene succinate) (poly(HB-co-BS)) copolyesters is reported for the first time. Different Candida antarctica lipase B (CALB)-catalyzed copolyesters were produced in solution, via a one-step or a two-step process from 1,4-butanediol, diethyl succinate, and synthesized telechelic hydroxylated poly(3-hydroxybutyrate) oligomers (PHB-diol). The influence of the ester/hydroxyl functionality ratio, catalyst amount, PHB-diol oligomer chain length, hydroxybutyrate (HB) and butylene succinate (BS) contents, and the nature of the solvent were investigated. The two-step process allowed the synthesis of copolyesters of high molar masses (Mn up to 18 000 g/mol), compared to the one-step process (Mn ∼ 8000 g/mol), without thermal degradation. The highest molar masses were obtained with diphenyl ether as solvent, compared with dibenzyl ether or anisole. During the two-step process, the transesterification rate between the HB and BS segments (i) increased with increasing amount of catalyst and decreasing molar mass of the PHB-diol oligomer, (ii) decreased when anisole was used as the solvent, and (iii) was not influenced by the HB/BS ratio. Tendencies toward block or random macromolecular architectures were observed as a function of the reaction time, the PHB-diol oligomer chain length, and the chosen solvent. Immobilized CALB-catalyzed copolyesters were thermally stable up to 200 °C. The crystalline structure of the poly(HB-co-BS) copolyesters depended on the HB/BS ratio and the average sequence length of the segments. The crystalline content, Tm and Tc decreased with increasing HB content and the randomness of the copolymer structure.

Energy Transport in PEG Oligomers: Contributions of Different Optical Bands

The transport of high-frequency vibrational energy in linear oligomer chains can be fast and efficient if specific conditions which permit ballistic transport are satisfied. These conditions include high delocalization and slow dephasing rate of chain states. We present new experimental results probing the energy transport in linear polyethylene glycol (PEG) oligomers of 0, 4, 8, and 12 PEG units terminated with IR-active end groups, N3 and succinimide ester. The energy transport was initiated by vibrational excitation of one of the end groups and the energy arrival to another end group was detected using dual-frequency, two-dimensional infrared spectroscopy. In addition to end-group to end-group energy transport dynamics, the end-group-to-chain-state and chain-state-to-chain-state waiting-time dynamics are reported. The results show that despite rather short lifetimes for several IR-active chain states, the end-to-end energy transport occurs with a constant and rather high speed of 5.5 A/ps, regardless o...

Characterization of Aniline Tetramer by MALDI TOF Mass Spectrometry upon Oxidative and Reductive Cycling.

By combining electrochemical experiments with mass spectrometric analysis, it is found that using short chain oligomers to improve the cycling stability of conducting polymers in supercapacitors is still problematic. Cycling tests via cyclic voltammetry over a potential window of 0 to 1.0 V or 0 to 1.2 V in a two-electrode device configuration resulted in solid-state electropolymerization and chain scission. Electropolymerization of the aniline tetramer to generate long chain oligomers is shown to be possible despite the suggested decrease in reactivity and increase in intermediate stability with longer oligomers. Because aniline oligomers are more stable towards reductive cycling when compared to oxidative cycling, future conducting polymer/oligomer-based pseudocapacitors should consider using an asymmetric electrode configuration.

Fused Helicene Chains: Towards Twisted Graphene Nanoribbons.

By taking advantage of an unexpected regioselectivity of intramolecular Scholl reactions on pentaphenylene compounds that favors distorted [5]helicenes over their flat counterparts, a new synthetic approach to twisted graphene nanoribbons has been designed based on side-fused di-tert-butyl-[5]helicene fragments. Syntheses of both small monomers and dimers have been achieved and their structures have been studied. An iterative synthetic strategy has been developed for the formation of longer flexible precursors, which relies on the step-by-step elongation of mono-functionalized oligomeric chains. The flexible trimer and tetramer have, thus, been synthesized and submitted to intramolecular Scholl reactions, which revealed important purification and characterization issues.

Investigating the effect of multi-functional chain extenders on PLA/PEG copolymer properties

Biodegradable copolymers polylactic acid-co-poly ethylene glycol (PLA-co-PEG) were synthesized at a specific volume ratio (PLA/PEG) (80/20) using direct melt polycondensation without solvent. The effects of an oligomeric chain extender (CE) on the mechanical, molecular weight, thermal stability, and degradation were evaluated. The copolymers were tailored by introducing classes of CE contents (0.25, 0.5, 0.075, 1.0, 1.25, and 1.5wt%) (styrene- glycidyl acrylate copolymer). Apparently, the mechanical properties of copolymers were enhanced in the presence of CE. A long chain branch structure has led to a slight improvement of tensile strength to reach 70MPa at CE 1.25%, compared with 60MPa for neat PLA. A significant increase of 17% was observed for the elongation at break of copolymers after addition of CE 1.25%. In addition, the impact strength increased to 7.9KJ/m2 in the ranges of CE 1–1.25%. Melt flow index dramatically reduces with the addition of CE contents. Gas Permeation Chromatography (GPC) showed that the addition of CE 1.25% has resulted in increasing the PLA molecular weight to 132.569kDa with a broad molecular weight distribution, MWD (2.066), and bimodal distribution. Differential Scanning Calorimetric (DSC) results revealed that the chain extension process improved glass transition temperature (Tg) 62°C, melting temperature (Tm) 161°C, and crystallinity (X%) 34.9% as a result of CE 1.25%. Thermal gravimetric analyses (TGA) results indicated that the CEs have a positive effect on the enhancement of thermal stability. Moreover, Scanning Electron Microscopic (SEM) showed that the compatibility and interfacial adhesion between the PLA and PEG chains were enhanced in the existence of the CE contents. The weight loss of the copolymer during 30days of degradation time was 28%, while the weight loss of CE 1.5% was only 3% during the same time interval.

Electron Transfer Studies on Conjugated Ferrocenyl-Containing Oligomers

1,2-Divinylferrocene (1) and 1,2-diformylferrocene (3) have been converted to ferrocenyl-containing oligomers in good yields using ADMET (acyclic diene metathesis) and HWE (Horner–Wadsworth–Emmons) reaction protocols. The resulting oligomers showed a high uniformity (low dispersity values); however, the poor solubility limits the chain growth and led to low average molecular weights. Within electrochemical measurements (CV) the conjugated materials showed reversible behavior that was stable during multicyclic experiments. Coupled electrochemical and spectroscopic studies confirmed electron transfer interactions between the ferrocenyl units through the oligomeric chains.

Step‐growth thiol–thiol photopolymerization as radiation curing technology

ABSTRACTThis report introduces a novel UV‐curing technology based on thiol–thiol coupling for polydisulfide network formation. Beginning with a model tris(3‐mercaptopropionate) trithiol monomer and xanthone propionic acid‐protected guanidine as photobase generator, a comprehensive characterization based on spectroscopic techniques supports the reaction of thiols into disulfides without side reactions. The best experimental conditions are described as regards to film thickness, irradiance, emission wavelength, and atmosphere composition. The results shed light on a step‐growth photopolymerization mechanism involving two steps: first, the formation of thiyl radicals by thiolate air oxidation or/and thiol photolysis, and second, their recombination into disulfide. By varying thiol functionality and structure, oligomer chain length and monomer/oligomer ratio, the network architecture can be finely tuned. The molecular mobility of the polydisulfide network is crucial to high thiol conversion rates and yields as revealed by 1H T2 NMR relaxation measurements. Ultimately, spatial control enables the formation of a photopatterned poly(disulfide) film, used as next‐generation high refractive index photoresist. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 117–128.

Ultrafast exciton migration in an HJ-aggregate: Potential surfaces and quantum dynamics

Quantum dynamical and electronic structure calculations are combined to investigate the mechanism of exciton migration in an oligothiophene HJ aggregate, i.e., a combination of oligomer chains (J-type aggregates) and stacked aggregates of such chains (H-type aggregates). To this end, a Frenkel exciton model is parametrized by a recently introduced procedure [Binder et al., J. Chem. Phys. 141, 014101 (2014)] which uses oligomer excited-state calculations to perform an exact, point-wise mapping of coupled potential energy surfaces to an effective Frenkel model. Based upon this parametrization, the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method is employed to investigate ultrafast dynamics of exciton transfer in a small, asymmetric HJ aggregate model composed of 30 sites and 30 active modes. For a partially delocalized initial condition, it is shown that a torsional defect confines the trapped initial exciton, and planarization induces an ultrafast resonant transition between an HJ-aggregated segment and a covalently bound “dangling chain” end. This model is a minimal realization of experimentally investigated mixed systems exhibiting ultrafast exciton transfer between aggregated, highly planarized chains and neighboring disordered segments.

Fluorescent oligo(N‐phenylmaleimide)s via aerobic radical telomerization initiated by benzylic hydrocarbons: Catalytic effect of CoII/N‐hydroxyphthalimide pair

ABSTRACTRadical oligomerization of N‐phenylmaleimide (NPMI) was performed in benzylic hydrocarbons as the solvent. The thermally induced oligomerization occurred only above 130 °C, with the initiation attributed to autoxidation of benzylic hydrocarbons as well as formation and dissociation of charge‐transfer complexes between benzylic hydrocarbons and maleimides. The end‐group analysis on oligo(N‐ethylmaleimide) prepared under similar conditions confirmed that the chain transfer to benzylic hydrocarbons was the primary fashion in forming oligomeric chains, and radical telomerization underlaid the oligomerization with benzylic hydrocarbons as both the solvent, the initiator and the telogen. CoII/N‐hydroxyphthalimide (NHPI) pairs could catalyze the telomerization at 110 °C. In such a catalytic process, CoII‐based oxidative complexes oxidized benzylic hydrocarbons and NHPI into benzylic radicals and phthalimide N‐oxyl (PINO), and benzylic hydrocarbons underwent hydrogen atom transfer (HAT) to PINO. Oligo(NPMI)s were formed via HAT with benzylic hydrocarbons and NHPI. These oligo(NPMI)s exhibited fluorescent properties with excitation at 270–350 nm and 400–550 nm and emission at 530–750 nm. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3846–3857

Analysis of the electronic, IR, and 1H NMR spectra of conjugated oligomers based on 4,4'-triphenylamine vinylene

Two types of conjugated oligomers based on 4,4'-triphenylamine vinylene have been synthesized and characterized by the methods of IR, UV–visible, and 1H NMR spectroscopy. The corresponding spectra have also been simulated theoretically at the density functional theory level with application of the B3LYP and BMK hybrid exchange-correlation functionals. A comparative analysis of the experimental and theoretical spectra of polymers and oligomers has revealed regularities of the manifestation of spectral signals depending on the conjugation chain length and the presence of a substituent in the triphenylamine core. It has been established, in particular, that the absolute intensity of IR bands satisfies a linear dependence with increase in the degree of polymerization; however, no frequency shift is observed at the same time. The position of the main peak in electron absorption spectra demonstrates the bathochromic shift with an increase in the oligomeric chain length due to the narrowing of the energy gap between the boundary molecular orbitals. Based on the theoretical estimation of the hydrogen atoms chemical shifts, the signals of various protons types in the strongly broadened experimental 1H NMR spectra of the bis-(4-iodine phenyl)-phenylamine and N,N-bis-(4-iodine phenyl)-4'-(phenylethynyl)-phenylamine polymerization products have also been identified.

Modulated crystal structure of InMo4O6

The (3 + 1)-dimensional modulated crystal structure of the metal-rich cluster compound InMo4O6 was solved and refined from single-crystal data in the superspace group P4/mbm(00γ)00ss [q = 0, 0, 0.1536 (4); a = 9.6664 (9), c = 2.8645 (3) Å; R1(all) = 0.046, wR(all) = 0.076]. The crystal structure is closely related to the NaMo4O6 structure type. It is built from rods of Mo6 clusters condensed via trans edges. These form channels parallel to [001], in which In6 and In7 oligomers alternate. Weak diffuse planes parallel to (001)* interconnect the satellite reflections; they occur due to two-dimensional rod disorder of the In oligomer chains.

Hydrogen Bonding in a Reversible Comb Polymer Architecture: A Microscopic and Macroscopic Investigation

In this work, an investigation of the hydrogen-bonding mechanism in a transiently branched comb-like polymer system in the melt is reported. The system under investigation consists of a polybutylene oxide (PBO)-based backbone, randomly functionalized with thymine (thy) groups, in combination with shorter PBO graft chains, end-functionalized with diaminotriazine (DAT) groups. The functional groups are able to associate through hydrogen bonding. The heterocomplementary association of these groups leads to the formation of a transiently branched comb-like polymer system. Since recently virtually exclusive heterocomplementary association could be observed in the supramolecular association of telechelically modified oligomeric PEG chains, here we aim to extend the supramolecular assembly mechanism toward branched structures. The present work combines small angle neutron scattering (SANS) experiments on a selectively labeled system with macroscopic dynamics measured in linear rheology response. The association ...

New α-diimine nickel complexes—Synthesis and catalysis of alkene oligomerization reactions

Three α-diimine complexes of NiII of the general formula {2,3-bis[N,N-(aryl)imino]butane}NiBr2 with aryl groups 2,3,5,6-F4-C6H, 2-CF3-C6H4 and 2,4-(CH3)2-C6H3 were synthesized and used as catalyst precursors in oligomerization reactions of ethylene and propylene. Oligomerization catalysts were produced by activating the complexes with AlEt2Cl, Al2Et3Cl3, and with combinations of these compounds and PPh3. The catalysts convert ethylene into low molecular-weight materials (liquids and waxes) with oligomer chains containing 15–20mol.% of methyl branches and 4–6mol.% of ethyl branches, which are apparently produced in “chain-walking” reactions of active centers along oligomer chains. Oligomerization of propylene yields a variety of light products, mostly dimers, which are formed in primary and secondary insertion reactions of propylene into Ni–H and Ni–C bonds in active centers. Reaction schemes of oligomer formation are discussed.

Aramid–multiwalled carbon nanotube nanocomposites: effect of compatibilization through oligomer wrapping of the nanotubes

AbstractAramid–multiwalled carbon nanotube (MWCNT) nanocomposites with different CNT loadings were prepared by the solution‐blending technique. Aramid oligomeric chains having reactive amine end‐groups were covalently grafted and wrapped over the surface of acid‐functionalized MWCNTs. The presence of functional groups and surface modification of MWCNTs were studied using Raman, Fourier transform infrared and X‐ray photoelectron spectroscopic and transmission/scanning electron microscopic techniques. Addition of these MWCNTs resulted in a homogeneous dispersion throughout the aramid matrix. Dynamic mechanical thermal analysis showed an increase in the storage modulus and the glass transition temperature involved with α‐relaxations on CNT loading. The coefficient of thermal expansion (CTE) of aramid was reduced on loading with such CNTs. Strong interfacial interactions of the matrix with the surface‐modified CNTs reduced the stress‐transfer problem in the composite material and resulted in higher modulus of 4.26 GPa and a glass transition temperature of 338.5 °C, whereas the CTE was reduced to 101.8 ppm °C−1 on addition of only 2.5 wt% CNTs in the aramid matrix. © 2016 Society of Chemical Industry

From N-vinylpyrrolidone anions to modified paraffin-like oligomers via double alkylation with 1,8-dibromooctane: access to covalent networks and oligomeric amines for dye attachment.

The double alkylation of N-vinylpyrrolidone (N-VP) with 1,8-dibromooctane yields paraffin-like oligomeric chains bearing polymerizable vinyl moieties. These oligomers were radically crosslinked in bulk with N-VP as co-monomer yielding swellable polymer disks. The vinylic side groups of the N-VP oligomers allow thiol–ene click reactions with 2-aminoethanethiol hydrochloride to obtain reactive amino-functionalized oligomers. Further modification of the free amino groups with 1,4-difluoro-9,10-anthraquinone (DFA) yields red-colored oligomeric anthraquinone dyes. The final reaction of DFA-substituted N-VP oligomers with Jeffamine® M 600 leads to blue-colored and branched oligomers with poly(ethylene glycol) side chains.

Model problems in depolymerization kinetics of chain oligomers: 2. Random chain scission

Kinetic equations related to the model of random chain scission (RCS) in the initial oligomer and intermediates (radicals and biradicals) have been solved, and the time dependence of concentrations, the average chain length, and its variance have been found. Despite of the difference in the sequence of formation between the intermediates (sequential reduction of chain length in the model of successive detachment of terminal monomer units and the preferential buildup of short chains in the RCS model), the changes in the average chain length in the two models are similar; i.e., they coincide with an appropriate change of the time scale. In the absence of bimolecular recombination, both the models are ergodic and nonmixing, a property that is due to the equidistant nature of the eigenvalue spectrum. Recombination leads to mixing and transition to equilibrium depolymerization. The change of the mode is determined by the ratio between the bond rupture, recombination, and evaporation rates.

Complexes of gold(I) with a chiral diphosphine and bis(pyridine) ligands: Isomeric macrocycles and a polymer

The self-assembly of [Au2(μ-(±)binap)X2], which have weakly coordinated anions X−=trifluoroacetate, triflate or nitrate, with bis(amidopyridyl) ligands (NN) has given three different macrocyclic complexes of general formula [Au4(μ-(±)binap)2(μ-NN)2]X4, an open complex [Au2(μ-(±)binap)(κ1-NN)2]X2, and a polymer [{Au2(μ-(±)binap)(μ-NN)}n]X2n. Macrocycles with both homochiral (RR/SS) and heterochiral (RS/SR) combinations of the two binap ligands in the cations [Au4(μ-binap)2(μ-NN)2]4+ have been structurally characterized. The polymeric complex has the syndiotactic (heterochiral) architecture. The donor ability of the anion X− is shown to affect both the degree of self-assembly in solution, through competition with the bis(amidopyridyl) ligand for coordination to gold(I), and the conformation of the bis(amidopyridyl) ligand in the products, through hydrogen bonding effects. In solution, there is a rapid equilibrium between cyclic and open chain oligomers, as determined by ESI-MS and NMR studies.

Mercury Sulfide Dimorphism in Thioarsenate Glasses.

Crystalline mercury sulfide exists in two drastically different polymorphic forms in different domains of the P,T-diagram: red chain-like insulator α-HgS, stable below 344 °C, and black tetrahedral narrow-band semiconductor β-HgS, stable at higher temperatures. Using pulsed neutron and high-energy X-ray diffraction, we show that these two mercury bonding patterns are present simultaneously in mercury thioarsenate glasses HgS-As2S3. The population and interconnectivity of chain-like and tetrahedral dimorphous forms determine both the structural features and fundamental glass properties (thermal, electronic, etc.). DFT simulations of mercury species and RMC modeling of high-resolution diffraction data provide additional details on local Hg environment and connectivity implying the (HgS2/2)m oligomeric chains (1 ≤ m ≤ 6) are acting as a network former while the HgS4/4-related mixed agglomerated units behave as a modifier.