Preparative GPC Research Articles

The effect of residual palladium on the performance of organic electrochemical transistors

Organic electrochemical transistors are a promising technology for bioelectronic devices, with applications in neuromorphic computing and healthcare. The active component enabling an organic electrochemical transistor is the organic mixed ionic-electronic conductor whose optimization is critical for realizing high-performing devices. In this study, the influence of purity and molecular weight is examined for a p-type polythiophene and an n-type naphthalene diimide-based polymer in improving the performance and safety of organic electrochemical transistors. Our preparative GPC purification reduced the Pd content in the polymers and improved their organic electrochemical transistor mobility by ~60% and 80% for the p- and n-type materials, respectively. These findings demonstrate the paramount importance of removing residual Pd, which was concluded to be more critical than optimization of a polymer’s molecular weight, to improve organic electrochemical transistor performance and that there is readily available improvement in performance and stability of many of the reported organic mixed ionic-electronic conductors.

Application of Polysaccharide-Based Chiral High-Performance Liquid Chromatography Columns for the Separation of Regio-, E/Z-, and Enantio-Isomeric Mixtures of Allylic Compounds.

Daicel Chiralpak IA, IB, and IC, which are the polysaccharide-based chiral stationary phase (CSP) columns for high-performance liquid chromatography (HPLC), were applied in the separation of the non-enantiomeric isomeric mixtures obtained by the various allylation reactions and were highly effective in separating the regio- and (E)/(Z)-isomers in the allylation products. Due to the close structural similarity of the isomeric allylic compounds in the reaction mixtures, separations of the isomers are laborious and could not be accomplished by the conventional methods such as silica gel column chromatography, silica gel HPLC, preparative GPC, distillation, and so forth. This study has shown potential advantages of using the polysaccharide-based CSP columns in the separation of not only enantiomeric but also non-enantiomeric isomeric mixtures.

Hybrid polymers bearing oligo-l-lysine(carboxybenzyl)s: synthesis and investigations of secondary structure.

Hybrid polymers of peptides resembling (partially) folded protein structures are promising materials in biomedicine, especially in view of folding-interactions between different segments. In this study polymers bearing repetitive peptidic folding elements, composed of N-terminus functionalized bis-ω-ene-functional oligo-l-lysine(carboxybenzyl(Z))s (Lysn) with repeating units (n) of 3, 6, 12, 24 and 30 were successfully synthesized to study their secondary structure introduced by conformational interactions between their chains. The pre-polymers of ADMET, narrowly dispersed Lysns, were obtained by ring opening polymerization (ROP) of N-carboxyanhydride (NCA) initiated with 11-amino-undecene, following N-terminus functionalization with 10-undecenoyl chloride. The resulting Lysns were subsequently polymerized via ADMET polymerization by using Grubbs’ first generation (G1) catalyst in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) generating the ADMET polymers (A-[Lysn]m) (m = 2–12) with molecular weights ranging from 3 to 28 kDa, displaying polydispersity (Đ) values in the range of 1.5–3.2. After chemical analyses of Lysns and A-[Lysn]ms by 1H-NMR, GPC and MALDI-ToF MS, secondary structural investigations were probed by CD spectroscopy and IR spectroscopy in 2,2,2-trifluoroethanol (TFE). In order to study A-[Lysn]ms with defined molecular weights and low polydispersity values (Đ = 1.03–1.48), the ADMET polymers A-[Lysn=3]m=3 and A-[Lysn=24]m=4 were fractionated by preparative GPC, and subsequently analysed by 1H-NMR, analytical GPC, MALDI-ToF MS and CD spectroscopy. We can demonstrate the influence of chain length of the generated polymers on the formation of secondary structures by comparing Lysns with varying n values to the ADMET-polymers with the help of spectroscopic techniques such as CD and FTIR-spectroscopy in a helicogenic solvent.

Influence of the molecular weight in P3HT block on fully conjugated block copolymers

All-conjugated donor-acceptor block copolymers (BCP) were synthesized in a one-pot reaction by a Stille coupling polycondensation through a terminal functional polymer copolymerization process. Mono bromo end-functionalized P3HT samples with various molecular weights (P3HT-Br, Mn: 5, 9, and 26 kg/mol) were copolymerized with AA (N,Nʹ-Bis(2-decyl-1-tetradecyl)-2,6-dibromonaphthalene-1,4,5,8-tetracarboxylic acid bisimide, NDI) and BB (5,5′-bis(trimethylstannyl)-2,2′-bithiophene) type monomers. Further purification by preparative GPC removed excess P3HT to yield block copolymers of low polydispersities with different donor and acceptor block chain lengths. The block copolymers were characterized by 1H-NMR and UV–vis absorption and FTIR spectroscopy. The optical properties, film morphologies, and optoelectronic properties of the block copolymer were strongly influenced by the donor and acceptor block chain lengths. Furthermore, the fully conjugated D-A block copolymer films exhibited fine structures, smooth film morphologies, and better OPV performance than those features of P3HT/PNDIT2 polymer blends. In polymer solar cells based on the various block copolymer as active layers, the device power convention efficiency was improved by maintaining the acceptor block content at 40–50 kg/mol and increasing the P3HT chain from 5 to 26 kg/mol.

TEMPO-oxidized O-acetyl galactoglucomannan oligomers: isolation and comprehensive structural elucidation

Hemicelluloses, the second most abundant polysaccharides right after cellulose, represent complex biopolymers whose structural features are not yet fully understood. Hence, the applicability of functionalized hemicellulose derivatives is still limited. Thus, the development of practical methods to reveal their structure is essential. Anionic, carboxylated GGM was prepared as the substrate, and their corresponding oligomers have been isolated and fully characterized for the first time in the present work. In order to accomplish this, each step has been optimized sequentially. Oxidized GGM was enzymatically digested, and the corresponding oligomers were isolated by preparative GPC. A toolset of wet chemistry and instrumental methods was used to characterize the isolated compounds in detail. Moreover, quantitative 13C-NMR combined with MALDI was demonstrated to deliver accurate analytical data compared to standard but time-consuming wet chemistry methods. The developed toolset is expected to be applicable to other plant polysaccharides and their derivatives as well.

Orthogonal solubility in fully conjugated donor-acceptor block copolymers: Compatibilizers for polymer/fullerene bulk-heterojunction solar cells

Donor-acceptor (D-A) type fully conjugated block copolymer systems have been rarely reported due to the challenges in synthetic approaches to prepare well-defined low-polydispersity products. In this work, fully conjugated block copolymers are synthesized in a one-pot reaction through Stille coupling polycondensation, by utilizing the end-functional polymer copolymerization method. End-functional P3HT are copolymerized with AA (2,7-dibromo-9-(heptadecan-9-yl)-9H-carbazole) and BB (4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole, TBT) type monomers, respectively. The orthogonal solubility between the very soluble P3HT donor and the insoluble PCDTBT acceptor block improves the purity of block copolymers as well as distinct nano-scale phase-separation compared with other reports on miscibility of donor and acceptor polymer block. Further purification via preparative GPC is carried out to remove the excess of unreacted P3HT and free PCDTBT as well as to achieve low polydispersity of block copolymers. The chemical structure of the P3HT-b-PCDTBT block copolymers are verified via 1H-NMR, and further confirmed by FTIR spectra. The block copolymer shows broad absorption and moderate optical band gap of 1.8 eV. Furthermore, the fully conjugated block copolymer films exhibit significant fine structures, much smoother film morphology compared to P3HT/PCDTBT polymer blends. By adding a small amount of block copolymer P3HT-b-PCDTBT as a compatibilizer into the bulk-heterojunction of P3HT:PC61BM blends, polymer solar cells with an 8% increase of short circuit current (J sc and 10% increase of power conversion efficiency (PCE) are achieved owing to the improvement of the active-layer film morphology. To the best of our knowledge, this is the first report on donor-acceptor type fully conjugated block copolymer as an effective ternary additive in polymer: fullerene bulk heterojunction solar cells.

Fully conjugated block copolymers for single-component solar cells: synthesis, purification, and characterization

All-polymer solar cells using the preparative GPC separated block copolymer P3HT-b-PBIT2 as a simple active layer show a power conversion efficiency of 1.0%.

Engineering of Energy Levels for Fully Conjugated D‐A Block CopolymersviaTuning the Ratios of Donor P3HT and Acceptor PNDIT

AbstractFully conjugated donor‐acceptor (D‐A) block copolymers, P3HT‐b‐PNDIT, containing p‐type poly(3‐hexylthiophene) (P3HT) and n‐type poly(naphthalene bismide) (PNDIT) segments are synthesized in a one‐pot reaction via Stille coupling polycondensation. Various D‐A block copolymers with low polydispersities (1.42–1.56) are obtained through further separation via preparative GPC. The structural and molecular features of block copolymers are verified by1H NMR, FTIR spectra, UV‐Vis absorption, differential scanning calorimetry (DSC) and cyclic voltammetry (CV). It is found that optical and electrochemical properties of D‐A block copolymers are strongly dependent on the combination ratio of the donor P3HT and acceptor PNDIT segment. By reducing the acceptor block lengths, the highest occupied molecular orbital (HOMO) energy levels of D‐A block copolymers sequentially rise, leading to the sequential decrease of energy gaps. To the best of our knowledge, this is the first report on engineering the energy levels of fully conjugated D‐A block copolymers by tuning donor and acceptor chain lengths. More?over, compared to D/A polymer blends, the all‐conjugated D‐A block copolymer films show significant fine structures and much smoother film morphologies.

Power conversion efficiency enhancement in diketopyrrolopyrrole based solar cells through polymer fractionation

Fractionation of a DPP copolymer by preparative GPC and device optimisation affords significant organic solar sell performance enhancement.

Synthesis, Purification, and Characterization of Well-Defined All-Conjugated Diblock Copolymers PF8TBT-b-P3HT

We present the synthesis, purification, and characterization of all-conjugated block copolymers comprising poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (PF8TBT) and poly(3-hexylthiophene) (P3HT). Suzuki step-growth polycondensation is used for the synthesis of PF8TBT, which is subsequently terminated via the addition of narrow-distributed, monobrominated P3HT-Br. Purification via preparative GPC is carried out to reduce polydispersity and to remove excess P3HT. Wavelength-dependent GPC and careful NMR end group analysis, assisted by model compounds, reveal pure diblock copolymers of PF8TBT-b-P3HT. Insight into structure formation is given by temperature-dependent UV–vis absorption, DSC, and X-ray scattering. These indicate that PF8TBT-b-P3HT does not microphase-separate within the investigated range of composition and molecular weight. The critical role of introducing sufficient dissimilarity between the segments in all-conjugated block copolymers...

Efficient access to multi‐arm star block copolymers by a combination of ATRP and RAFT‐HDA click chemistry

A study was conducted to provide an access route to diene-functionalized polymers through atom transfer radical polymerization (ATRP) and their utilization in the reversible addition-fragmentation chain transfer (RAFT)-hetero-Diels-Alder (HDA) protocol, which opened the possibilities of controlled radical polymerization (CRP) techniques to access complex architectures. 1,8-Diazabicyclo[5.4.0]undec-7-ene, trans,trans-2,4-hexadiene-1-ol, succinic anhydride, N,N-iisopropylethylamine, zinc chloride, and 1,10-azobis(cyclohexanecarbonitrile) were used for the study as received. Preparative GPC analysis was also carried out with CHCl3 as the solvent at a flow rate of 10 mL min-1 at room temperature. It was observed that the bromine end groups from the ATRP mechanism provided a synthetic handle for post-polymerization modifications. It was concluded that the RAFT-HDA conjugation approach was suitable for the tailor-made synthesis of complex macromolecular architectures.

Adsorption Kinetics of Amphiphilic Diblock Copolymers: From Kinetically Frozen Colloids to Macrosurfactants

We investigated the spontaneous adsorption properties of charged amphiphilic diblock copolymers on hydrophobic surfaces and explained the transition of behavior from depleting frozen colloids (that do not adsorb at all) to fast adsorbing macrosurfactants when the hydrophobicity of the nonsoluble block is reduced. Three copolymer families have been used with the same hydrophilic block poly(acrylic acid), a weak acid whose ionization alpha can be varied by changing the pH. The hydrophobic blocks polystyrene, PS, poly(n-butyl acrylate), PBA, and poly(diethylene glycol ethyl ether acrylate), PDEGA, have interfacial tensions with water gammacore/solvent, respectively, of 32, 20, and 3 mN/m. We were mainly interested in the regime of high ionization alpha > 0.3, where PAA chains have no affinity for hydrophobic surfaces, and we verified experimentally that micelles do not adsorb directly. With the three copolymer families we show that the adsorption kinetics at an early stage is driven by the self-assembly properties in bulk solution: adsorption is hampered for PS-b-PAA (physically/kinetically frozen micelles in solution), controlled by unimer extraction for PBA-b-PAA (nonequilibrium micelles in solution with very low CMC < 10-4 wt %), and controlled by unimer diffusion and electrostatic repulsion for PDEGA-b-PAA (micelles at equilibrium in solution with high CMC is approximately 1-5 wt %). This explains the power law dependences of adsorption with concentration as C-1 for PBA-b-PAA and C-2 for PDEGA-b-PAA. It is finally the interfacial tension with water of the nonsoluble block and not its glass transition that is the main control of bulk solution self-assembly and consequently of the adsorption kinetics properties of amphiphilic diblocks. We also proved by preparative GPC that the fraction of non-self-assembling diblock chains, which exists in all highly hydrophobic amphiphilic diblock systems, plays a negligible role in the adsorption properties. Finally, we investigated the intrinsic thermodynamic affinity between amphiphilic diblocks and hydrophobic surfaces. We show quantitatively that this affinity depends dominantly on the interfacial energies between the hydrophobic block, the surface, and water: diblocks with strongly hydrophobic nonsoluble blocks (PS, PBA) have a low affinity for weakly hydrophobic surfaces, and oppositely, diblocks with weakly hydrophobic nonsoluble block (PDEGA) have a universal affinity for hydrophobic surfaces (like small-molecule surfactants but for different physical reasons). Finally, we showed via surface rheology that when adsorption occurs anchoring is strong and irreversible for very hydrophobic diblocks (PBA-b-PAA) and weaker and (partially) reversible for less hydrophobic diblocks (PDEGA-b-PAA).

A Set of Homologous Hetarylenediyne Macrocycles by Oxidative Acetylene-Acetylene Coupling

The synthesis of a set of bipyridine-containing macrocycles by oxidative acetylene-acetylene dimerization is described. The cycles are separated by preparative GPC, and the smallest homologue is analyzed by single-crystal X-ray diffraction, which shows a layered structure with channels that are partially filled with parts of the flexible chains of adjacent macrocycles. The cyclic trimer has a D3h symmetry and is a possible candidate for the formation of metal organic supramolecular assemblies on surfaces.

Structure Representation of Asphaltene GPC Fractions Derived from Kuwaiti Residual Oils

Two asphaltenes obtained from a residual oil before and after hydrotreatment were subjected to preparative GPC. Selected GPC fractions were analyzed by NMR and XRD to derive structural parameters to investigate whether there is a relationship between the molecular size of the asphaltene fraction and its structural features. Under the GPC experimental conditions (∼5 wt % THF solution), some eluting species are aggregates rather than monomeric molecules. Nevertheless, a correlation between the molecular size of the GPC fraction and its structure was found. The higher the molecular weight (MW), the more aromatic and condensed is the fraction. Moreover, the asphaltene fractions with the highest MW of both residues, before and after hydrotreating, show very similar structural features. This fact suggests that during hydrotreatment the low MW asphaltenes are converted to distillates, whereas the higher MW fractions (>6000 Da) stay unaltered and can cause severe coking in the downstream processes because of the ...

Polydisperse composition of mixed monolayer-protected, spin-labeled Au nanoparticles.

Using EPR spectroscopy and spin-labeled ligands, we have studied product distribution in the ligand exchange reactions of Au nanoparticles. When the incoming ligand was used in excess, the exchanged nanoparticles had uniform composition of the organic shell. Preparative GPC was employed to fractionate these materials according to the diameter of the Au core, as confirmed by TEM, UV, and EPR measurements. When the exchange reaction was carried out with less than a stoichiometric amount of the incoming ligand, nanoparticles with polydisperse composition of the organic shell were formed. This was established by the EPR analysis of the exchange reaction mixtures following their GPC fractionation. The GPC separation of these mixtures is controlled by both Au core size and shell composition.

High Yield Synthesis, Separation and Structural Characterization of New [n+n]-Polyazamacrocycles

t-Bu- and isopropyl-substituted aromatic dialdehydes (la-c) and diamines (2a-f) were used to synthesize a series of imine macrocycles (3a-m). The highly selective cyclization reaction resulted either in a [2+2] stoechiometry or in a mixture of different [n+n] cycles, depending on the diamine building block. For some defined macrocycles (3b, 3d, 3e) the structure was elucidated by single crystal X-Ray diffraction that revealed a column-like arrangement of the macrocycles in the solid state. Mixtures of macrocycles were investigated with a combination of MALDI-Tof and analytical GPC which brought significant improvements in the determination of the exact size distribution. Isolated higher homologues of polyimine cycles were made available by preparative GPC for the first time. The possibility to reduce the imine macrocycles quantitatively to their corresponding amine analogues was demonstrated exemplary by the reduction of two pyridine containing cycles (4a-b).

The cationic oligomerization of p-aminostyrene 1. Trifluoroacetic acid-catalyzed polyaddition

It was found that p-aminostyrene (PAS) was easily oligomerized by CF3COOH (TFA) in CCl4 to give a low molecular weight oligomer 4 including phenylene, ethylidene and secondary amine groups in the backbone, i.e., the isomer of poly-p-aminostyrene 5. The NMR and IR spectra of the product are quite different from those of polymer 5 produced by 2,2'-azobisisobutyronitrile (AIBN) in toluene. The dimer D and trimer T were separated from the reaction solution through the preparative GPC. The reaction seems to proceed stepwisely to give D in the initial stage and finally the near pentameric oligomer 4 at the end of the reaction.

Miscibility and crystallization kinetics for the blend of isotactic polypropylene/ethylene-propylene random copolymer

Miscibility for blends of isotactic polypropylene (PP) and ethylene-D4-propylene random copolymer (EPR)s, which were prepared by copolymerization of propylene and 19 mol% (D-EPR19) and 47 mol% (D-EPR47) of perdeuterated ethylene with metallocene catalyst and then fractionated with a preparative GPC, have been investigated by SANS at various temperatures in the melt. SANS results indicate that most of PP/D-EPR blends are in homogeneous one-phase state in the melt and Flory–Huggins interaction parameter ( χ) analyzed by random phase approximation are approximately 5.0×10 −3 and less than 1.0×10 −3 for the blends of PP/D-EPR47 and PP/D-EPR19, respectively. Isothermal spherulite growth rate ( G) for the blends was also measured by optical microscope at various temperatures and the depression of G was observed.

Chemical synthesis of an amylose-like polysaccharide by polymerization of partially benzylated phenyl 1-thio- β-maltooctaoside derived from γ-cyclodextrin

An amylose-like α-(1,4)-glucan was synthesized by polycondensation and subsequent deprotection of a partially benzylated phenyl 1-thio- β-maltooctaoside having a sole hydroxyl group at the non-reducing end. The key octasaccharide monomer 6 was prepared by means of a single-site acetolytic reaction of fully acetylated γ-cyclodextrin and several subsequent chemical manipulations at its reducing and non-reducing ends. On activation with methyl triflate, the polycondensation of 6 was found to proceed in diethyl ether through intermolecular glycosidation. The molecular weight of the product obtained by preparative GPC on Sephadex LH-60 was 10 000–18 000. Removal of the O-benzyl groups under Birch reaction gave α-(1,4)-glucan, the stereoregularity of which was confirmed by 1H and 13C NMR spectroscopy.

Measurement of Diffusion Coefficients of Oligomeric Penetrants in Rubbery Polymer Matrixes

The diffusion coefficients of oligomeric radicals in monomer-polymer systems have a major influence on properties such as polymerization rates and molecular weight distributions. The present work reports the results of an extensive set of studies of diffusion coefficients of rubbery ternary systems comprising polymer, diluent, and oligomer, determined by pulsed-field-gradient NMR, at 25 and 40 degrees C. Oligomers of methyl methacrylate (MMA) and of butyl methacrylate (BMA) were synthesized by using a catalytic cobalt chain transfer agent to produce macromonomers with a terminal double bond. Where necessary, these were fractionated by preparative GPC to obtain samples ranging from dimeric to decameric; typical polydispersities were 1.08. Pulsed-field gradient NMR is facilitated by being able to monitor the proton NMR of the CH2 hydrogens on the double bond. Matrixes used were high molecular weight polyMMA and polyBMA, the weight fraction of polymer (w(p)) being varied by adding appropriate amounts of diluent (the saturated equivalents of MMA and BMA, viz., methyl isobutyrate and butyl isobutyrate). Above c* (the concentration at which chains start to overlap), all data for diffusion coefficients Di of an oligomer of degree of polymerization i could be fitted with acceptable accuracy by D-1(w(p))/D-i(w(p)) = i(0.664+2.02wp), for both BMA and MMA oligomers in both MMA and BMA matrixes; the same relation also fits earlier data on styrene oligomers in polystyrene. If more accurate scaling parameters are obtained experimentally for smaller oligomers, these can be used to predict data for higher oligomers with even better reliability. For MMA monomer in pMMA, where free-volume parameters are available, the predicted dependences of monomer diffusion coefficient on w(p) and temperature are in accord with experiment.