Alkyl End Groups Research Articles

Heterocyclic group end-capped polyethylene glycol: Synthesis and used as corrosion inhibitors for mild steel in HCl medium

In this work, two categories of water-soluble polymeric corrosion inhibitors (CIs) are contributed. These CIs are composed by polyethylene glycol (PEG) middle segment and oleic imidazoline (or thiophene) end groups, respectively labeled as OIM-PEG-OIM and Th-PEG-Th. Two facile synthetic strategies involve epoxy-amino reaction and thiol-acrylate Michael addition were employed. Both Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy verified that a series of target products were successfully obtained. The solution transmittance measurements indicated that with the increase of the PEG segment length, the water solubility of CIs enhanced. And these obtained CIs exhibit somewhat surface activity and could reduce the solution surface tensions to a certain extent. The inhibition efficiencies of these CIs for mild steel in HCl medium were evaluated by weight loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). It was found that both OIM-PEG-OIM and Th-PEG-Th show an improved corrosion inhibition efficiency as compared to PEG. And as compared to heterocyclic compounds, introduction of PEG segment showed a negligible influence on their performances. Both CIs can form chemisorption on the metal surface, and the adsorption process follow Langmuir adsorption mechanism. OIM-PEG-OIM exhibit superior inhibition performance and stability as compared to Th-PEG-Th, which can be attributed to the fact that OIM-PEG-OIM bearing two long hydrophobic alkyl end groups. Scanning electron microscope (SEM) observations as well as atomic force microscopy (AFM) measurements also confirmed both OIM-PEG-OIM and Th-PEG-Th could serve as water-soluble CIs for mild steel.

Simultaneous Tuning of Alkyl Chains and End Groups in Non-fused Ring Electron Acceptors for Efficient and Stable Organic Solar Cells.

Fine-tuning the alkyl chains and end groups of non-fused ring electron acceptors (NFREAs) plays vital roles in the promotion of charge transfer (CT) and power conversion efficiency (PCE). In this work, we developed a series of A-D-A'-D-A-type NFREAs, which possess the same terminals (A), the cyclopentadithiophene unit (D), and the thieno[3,4-c]pyrrole-4,6-dione (A'). Despite the subtle difference in side chains and halogenated end groups, the six acceptors exhibit a considerable difference in the efficiency and device stability of the organic solar cells (OSCs). Among the molecules, chlorinated NFREAs show a broader light absorption than the fluorinated ones do. Compared with C8C8-4F (1-octylnonyl and fluorination) and C6C4-4Cl (2-butyloctyl and chlorination), C8C8-4Cl (1-octylnonyl and chlorination) exhibits a lower highest occupied molecular orbital level, higher electron mobility, and denser molecular packing. The OSCs based on PM6:C8C8-4Cl yield the best PCE of 14.11%, which is attributed to the faster charge transport, high miscibility, and preferable morphology. Moreover, the PM6:C8C8-4Cl devices retain 91.1% of the initial PCE after being placed in air with 67% relative humidity for 50 days. This work shows that the simultaneous optimization of side chains and end groups facilitates the CT and improves the stability in the OSCs, offering a novel view into the molecular design of A-D-A'-D-A-type NFREAs.

Removal of Trithiocarbonyl End Group of RAFT-Polymerized Poly(stearyl acrylate) and Effect of the End Group on Thermal and Structural Properties.

The effect of a long alkyl end group on the thermal and structural properties of RAFT (reversible addition-fragmentation chain transfer)-polymerized poly(stearyl acrylate) (PSA) was investigated. RAFT-polymerized PSA was prepared using 2-cyano-2-[(dodecylsulfanylthiocarbonyl) sulfanyl] propane (CDTP) with long alkyl group as a chain transfer agent and azobisisobutyronitrile (AIBN) as an initiator. The RAFT polymerization resulted in the polymerized structure having trithiocarbonyl (TTC) at one end and isobutyronitrile at the other end. RAFT-polymerized PSA was prepared with two different molecular weights. The TTC end group was replaced by isobutyronitrile using radical reaction with AIBN through optimization of the conditions, which resulted in isobutyronitrile at both ends. The effect of the end group on the thermal and structural properties was investigated using differential scanning calorimetry and X-ray diffraction, and the results indicated that the long alkyl group from TTC lowers the melting point and semi-crystalline structure in the case of low molecular weight PSA.

Optimizing the Charge Carrier and Light Management of Nonfullerene Acceptors for Efficient Organic Solar Cells with Small Nonradiative Energy Losses

The photovoltaic properties and energy losses of organic solar cells (OSCs) based on nonfullerene acceptors (NFAs) are highly dependent on their molecular structures and aggregation morphologies. Charge carrier and light managements are important to optimize NFA molecules. Herein, four NFAs with different alkyl substituents and end groups, named BTP‐C11‐N2F, BTP‐C9‐N2F, BTP‐C9‐IC4F, and BTP‐C9‐N4F, are designed and synthesized by side‐chain shortening, end‐acceptor π‐extension, and fluorination. As a result, a favorable morphology is achieved in BTP‐C9‐N4F‐based OSCs by using typical high bandgap polymer PM6 as a donor, and this system obtains the highest power conversion efficiency of 17.0% with a short circuit current (Jsc) of 26.3 mA cm−2, an open circuit current (Voc) of 0.85 V, and a fill factor (FF) of 75.7%. In addition, its light (Jsc) and charge carrier (Voc × FF) managements relative to the Shockley–Queisser limit are also increased. Extending the conjugation of the end groups increased the energy levels of NFAs and enabled an Eloss of 0.50 eV with a nonradiative recombination loss of as low as 0.20 eV in BTP‐C11‐N2F‐based OSCs. This work provides an efficient strategy to optimize the molecular structures of nonfullerene acceptors and further improve the properties of OSCs.

Controlled Synthesis of Polyphosphazenes with Chain-Capping Agents.

N-alkyl phosphoranimines were synthesized via the Staudinger reaction of four different alkyl azides with tris(2,2,2-trifluoroethyl) phosphite. N-adamantyl, N-benzyl, N-t-butyl, and N-trityl phosphoranimines were thoroughly characterized and evaluated as chain-capping compounds in the anionic polymerization of P-tris(2,2,2-trifluoroethoxy)-N-trimethylsilyl phosphoranimine monomer. All four compounds reacted with the active chain ends in a bulk polymerization, and the alkyl end groups were identified by 1H-NMR spectroscopy. These compounds effectively controlled the molecular weight of the resulting polyphosphazenes. The chain transfer constants for the monomer and N-benzyl phosphoranimine were determined using Mayo equation.

The Interaction of Glymes with Surfactant Micelles

AbstractThe critical micelle concentrations (CMC) values and counterion dissociation (α values) have been determined for a number of mixed micellar systems consisting of two typical ionic surfactants and glycol ethers (glymes) as cosurfactants, namely diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. Conductance experiments were used to determine the CMC and α values of the mixed micelles as a function of glyme concentration in the aqueous mixed solvent. Favorable interactions between sodium dodecyl sulfate micelles and glyme cosurfactants were deduced from the decreases in the CMC values and the large increase in the α values of these systems as a function of increasing glyme concentration in the mixed solvents. In contrast to the anionic surfactant/glyme systems, in general, there appeared to be little favorable interactions between the surfactant and glymes when micelles of the cationic surfactant dodecyltrimethylammonium bromide were formed in water/glyme solvent systems containing an increasing amount of the glymes. The interaction of glymes with the surfactant micelles was examined closely via 13C nuclear magnetic resonance (NMR) chemical shifts for both surfactant and glyme carbons; these chemical shifts changes were interpreted in terms of the distribution and the localization of the glymes in the aggregates. Finally, partition constants, determined from two‐dimensional diffusion‐oriented spectroscopy (2D‐DOSY) experiments, were used to calculate thermodynamic quantities of transfer of the glymes between the bulk phase and the self‐assembled aggregates. All these results are interpreted in terms of the key contributions that both the glyme ethoxylated groups and alkyl endgroups make to the hydrophobic interactions.

Effect of Alkyl Substituents on DPP‐based Small Molecules for Organic Solar Cells

Two diketopyrrolopyrrole (DPP)‐based π‐conjugated small molecules, DPP4T and α‐DPP4T, were synthesized to investigate the effect of alkyl end groups on the physical properties of the molecules. The flexible alkyl end groups resulted in lower phase‐transition temperatures and enhanced solubility of α‐DPP4T. The UV–vis absorption maxima (λmax) of films of both small molecules were blue‐shifted compared with those of solutions of the molecules. More importantly, a relatively larger shift in λmax between the solution and film states and an enhanced shoulder peak in the longer‐wavelength region were observed in the spectra of the α‐DPP4T film, indicating relatively greater intermolecular packing of α‐DPP4T molecules. The enhanced device performance (in particular, a higher short‐circuit current density and better external quantum efficiency profile) of the α‐DPP4T‐based device was explained by the improved film morphology and stronger intermolecular interactions of α‐DPP4T. After device optimization, a power conversion efficiency of 2.42% was achieved using α‐DPP4T.

Molecular Mass Affects the Phase Separation of Aqueous PEG-Polycation Block Copolymer.

Mechanisms of the phase separation and remixing of cationic PEG-containing block copolymers have been investigated in aqueous lithium triflate solutions. The polycation was poly(vinylbenzyl trimethylammonium triflate). We have previously reported on one such block copolymer, which upon cooling of a hot clear solution first underwent phase separation into a turbid colloid and, later, partially cleared again with further cooling. To better understand the balance of various interactions in the solutions/dispersions, a series of polymers with varying DP of the cationic block was synthesized. From one of the polymers, the alkyl end group (a fragment of the chain transfer agent) was removed. The length of the cationic block affected critically the behavior, but the hydrophobic end group had a minimal effect. Polymers with a short cationic block turn cloudy and partially clear again during a temperature decrease, whereas those with a long cationic block phase separate and slowly precipitate and remix only when heated. Phase separation takes place via particle formation, and we suggest different mechanisms for colloidal stabilization of particles composed of short or long chains.

Incorporation of Radicals during Ni(II)-Catalyzed Ethylene Insertion Polymerization

A possible involvement of radicals in catalytic insertion chain growth remains elusive, albeit it could account for thus far inconclusive experimental observations and enable yet unachieved synthetic reaction schemes. This work shows that radicals present, deliberately generated for this purpose, are incorporated as end groups in ethylene insertion polymerizations. Azo initiators (R-N = N-R′ with R = C(CH3)2COOMe, Ph, 3,5-F2C6H3) added to pressure reactor Ni(II)salicylaldiminato-catalyzed ethylene polymerizations afforded initiator-derived aryl or alkyl end groups, respectively, as revealed by in-depth NMR studies of the polymer formed. The observation of additional solvent- derived aryl end groups, originating from radical transfer to toluene, underlines that end groups are indeed formed from radicals. Evidence for incorporation as a chain-initiating as well as -terminating end group is discussed.

High‐Performance All‐Small‐Molecule Solar Cells Based on a New Type of Small Molecule Acceptors with Chlorinated End Groups

AbstractWhile a wide variety of nonfullerene acceptors are developed and perform well in combination with polymer donors, only a few nonfullerene acceptors can work well with small molecule donors. Here, all‐small‐molecule solar cells with high performance enabled by a new type of small molecule acceptors (F‐0Cl, F‐1Cl, and F‐2Cl), which contain linear alkyl side chains and end groups substituted with various number of chlorine atoms, are reported. End group chlorination leads to redshifted absorption, enhanced crystallinity, and high electron mobility. These properties make them competitive as electron acceptors for all‐small‐molecule solar devices. When combined with two popular small molecule donors DRTB‐T and DRCN5T, these nonfullerene acceptors offer power conversion efficiencies up to 10.76 and 9.89%, which are among the top efficiencies reported in all‐small‐molecule solar cells and indicate the great potential of all‐small‐molecule solar devices.

Modification of alkyl group terminated hyperbranched polyester on paving epoxy asphalt

Epoxy asphalt is a kind of high performance asphalt material that has been widely used in steel deck pavement. However, because high modulus and low toughness also exist in thermosetting epoxy asphalt mixture at low temperature, crack would be initiated by innerstress caused by temperature change. Hyperbranched polyester (HBP) is a kind of toughness modifier with low viscosity and high reactivity for thermosetting materials. It can effectively improve the toughness of thermosetting epoxy asphalt. However, hydroxyl end groups of HBP would accelerate the reaction rate of epoxy asphalt and disturb the phase dispersion between resin phase and asphalt phase. Therefore, it is necessary to modify the hydroxyl end groups of HBP as inert alkyl end groups to avoid its rapid curing reaction with epoxy resin. And by this, the excellent effects of HBP, such as viscosity reduction, compatibility improvement and toughening on thermosetting materials can be obviously observed in the HBP modified epoxy asphalt. Adding different alkyl end groups modified HBP into epoxy asphalt, not only the viscosity of epoxy asphalt can be reduced, but also the toughness of cured epoxy asphalt can be improved significantly.

Brush Polymer of Donor-Accepter Dyads via Adduct Formation between Lewis Base Polymer Donor and All Carbon Lewis Acid Acceptor.

A synthetic method that taps into the facile Lewis base (LB)→Lewis acid (LA) adduct forming reaction between the semiconducting polymeric LB and all carbon LA C60 for the construction of covalently linked donor-acceptor dyads and brush polymer of dyads is reported. The polymeric LB is built on poly(3-hexylthiophene) (P3HT) macromers containing either an alkyl or vinyl imidazolium end group that can be readily converted into the N-heterocyclic carbene (NHC) LB site, while the brush polymer architecture is conveniently constructed via radical polymerization of the macromer P3HT with the vinyl imidazolium chain end. Simply mixing of such donor polymeric LB with C60 rapidly creates linked P3HT-C60 dyads and brush polymer of dyads in which C60 is covalently linked to the NHC junction connecting the vinyl polymer main chain and the brush P3HT side chains. Thermal behaviors, electronic absorption and emission properties of the resulting P3HT-C60 dyads and brush polymer of dyads have been investigated. The results show that a change of the topology of the P3HT-C60 dyad from linear to brush architecture enhances the crystallinity and Tm of the P3HT domain and, along with other findings, they indicate that the brush polymer architecture of donor-acceptor domains provides a promising approach to improve performances of polymer-based solar cells.

Synthesis of Poly(methylene-b-ε-caprolactone) and Poly(ε-caprolactone) with Linear Alkyl End Groups: Synthesis, Characterization, Phase Behavior, and Compatibilization Efficacy

Diblock copolymers of poly(methylene-b-e-caprolactone) (PM-b-PCL) were synthesized in two steps: (a) polyhomologation, to obtain, following oxidative cleavage of the carbon–boron (PM, block1), an α-hydroxyl-ω-methyl polymethylene (PMOH, CH3–[CH2]m–OH) and, following the transfer reaction to the ring-opening polymerization catalyst, (b) ring-opening polymerization (ROP) of e-caprolactone (CL) (PCL, block2). In addition, a series of homopolymers derived from poly(e-caprolactone) (PCL) oligoesters containing an end group of docosyl (CH3–[CH2]21– or C22; C22–PCL) were obtained as a model to compare their physical properties by DSC with those of PM-b-PCL. The oligomers derived from PM-b-PCL and C22–PCL were characterized by 1H and 13C NMR, AFM, DSC, GPC, and MALDI-TOF. PM-b-PCL and C22–PCL were evaluated as compatibilizers for PE/PCL polymer blends. Identification and analysis of optimized blocks of PM-b-PCL by POM and SEM showed improved mixing of PE/PCL blends.

Design of pyridyl-modified amphiphilic polymeric ligands: Towards better passivation of water-soluble colloidal quantum dots for improved optical performance

HypothesisAn effective surface passivation is crucial to obtain quantum dots (QDs) with good photoluminescence response. Whereas the encapsulation of QDs inside amphiphilic polymers provides colloidal stability, a decrease in the quantum yield (QY) is observed. Pyridyl motifs are known to bind strongly to the ZnS on core/shell QD and increase the structure rigidity. Hence, the incorporation of pyridyl groups into the polymer could make it more compact in order to improve the optical behavior of the QDs. ExperimentsPyridyl-modified amphiphilic polymeric ligands were synthesized based on a poly(isobutylene-alt-maleic anhydride) backbone with pyridyl and alkyl end-groups as anchoring groups. The proportion of both ligands was optimized. The resulting QDs were characterized using complementary techniques such as absorption spectroscopy, static and time-resolved photoluminescence spectroscopy, transmission electron microscopy, and dynamic light scattering. FindingsCoating with the designed polymer maintains the high QY of the QDs after being transferred to water and provides them colloidal stability under relevant biological conditions (i.e. wide range of pH and ionic strength, biological buffers and stability over time). The significant improvements of such ligand may be attributed to the synergistic effect of two anchoring groups (pyridyl and alkyl groups) which establish different types of interaction with the QD.

Dendrons with urea/malonamide linkages for gate insulators of n-channel organic thin film transistors

A series of urea/malonamide dendritic molecules were prepared as gate insulators for organic thin film transistors (OTFTs). This series of molecules with different degrees of branching possess peripheral stearyl groups are dendrons generation 0.5 (G0.5), generation 1 (G1), generation 1.5 (G1.5), generation 2 (G2) and generation 2.5 (G2.5). In addition, two types of tetracarboxylic diimide derivatives, i.e. perylene diimide (PDI) and naphthalene diimide (NDI) with two different chain lengths of fluorinated alkyl end groups were prepared as semiconductors for OTFTs such as NDI-C4F7, NDI-C7F9, PDI-C4F7 and PDI-C7F9. The n-channel types of OTFTs were fabricated by spin-coating the gate insulators on Si/SiO2 substrates, and then depositing the semiconducting layers in vacuum without heating the substrate. Silver was used as contact electrodes for source and drain. The performance of OTFTs with dendrons as gate insulators were better than that of OTFTs modified by octadecyltrichlorosilane (ODTS). Moreover, the threshold voltages (Vths) of OTFTs shifted from positive voltage to negative voltage as the device was incorporated with higher generation of dendrons. This is because of different dielectric constants or surface energies between the interface of gate insulator and semiconducting layer. Among all samples in this study, the n-channel OTFT comprising PDI-C4F7 and G1.5 exhibited the best performance. In addition, an enhanced electron mobility and Ion/Ioff ratio measured under ambient condition were 4.71×10−4cm2V−1s−1 and 7.7×103, respectively. Apart from that, the influence of semiconducting molecular packing order on dendron gate insulator layers was investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM). Furthermore, pentacene-based p-channel OTFTs with G1.5 gate insulator also exhibited the highest performance. These OTFTs achieved 0.1cm2V−1s−1 and 6.3×104 for mobility (μ) and Ion/Ioff ratio, respectively.

Sequence Effects in Conjugated Donor-Acceptor Trimers and Polymers.

To investigate the sequence effect on donor-acceptor conjugated oligomers and polymers, the trimeric isomers PBP and BPP, comprising dialkoxy phenylene vinylene (P), benzothiadiazole vinylene (B), and alkyl endgroups with terminal olefins, are synthesized. Sequence effects are evident in the optical/electrochemical properties and thermal properties. Absorption maxima for PBP and BPP differ by 41 nm and the electrochemical band gaps by 0.1 V. The molar emission intensity is five times greater in PBP than BPP. Both trimers are crystalline and the melting points differ by 17 °C. The PBP and BPP trimers are used as macromonomers in an acyclic diene metathesis polymerization to give PolyPBP and PolyBPP. The optical and electrochemical properties are similar to those of their trimer precursors-sequence effects are still evident. These results suggest that sequence is a tunable variable for electronic materials and that the polymerization of oligomeric sequences is a useful approach to introducing sequence into polymers.

Synthesis, characterization, and transistor applications of new linear small molecules: Naphthyl-ethynyl-anthracene-based small molecules containing different alkyl end group

A novel small molecule consisting of triple bond-bridged naphthalene-anthracene core was synthesized with either a pentyl or decyl end group. The linear and planar shape of naphthalene-anthracene core allowed herringbone packing pattern with enhanced conjugation length and close molecular packing structure. The film morphology of naphthalene-anthracene based small molecules was also affected by the pentyl and decyl groups. The pentyl substituted molecule exhibited more unified and ordered packing patterns than did the decyl substituted example, which showed at least two polymorphs. The p-type semiconducting properties of the two new molecules were characterized by organic field-effect transistor measurements. In annealed devices at 80 °C, the field-effect mobility of pentyl analogue was 0.045 cm2/(V∙s), which was about 3 times higher than the decyl substituted compound.

A Comparison of Three Different Biodegradable Aliphatic Oligoesters (PGA, PLLA, and PCL) with Similar Linear Alkyl End Groups by DSC and SAXS

The biodegradable aliphatic oligoesters polyglycolide (PGA), poly(L-lactide) (PLLA), and poly(ϵ-caprolactone) (PCL) with similar number-average molecular weight Mn values but different linear alkyl end groups [CH3−[CH2−CH2]m−CH2−] were compared in terms of their physical properties, parameters such as melting temperature (Tm), crystallinity (xi), long period (L), and lamella thickness (D). They were analyzed by DSC and SAXS. The effect of a longer and nonpolar alkyl end group such as docosyl [CH3−[CH2−CH2]10−CH2−] on the long period (L) was more evident for PCL because it was the most nonpolar species in the family of oligoesters analyzed.

Synthesis and characterisation of rubbing-resistant polyimides with naphthalimide side-chain for liquid-crystal alignment layers

A novel diamine with a side-chain containing naphthalimide ring and non-polar alkyl end group, N-octyl-4-(3,5-dinitrobenzoyl)-amido-1,8-naphthalimide (N8), was synthesised and its chemical structure was confirmed by FTIR (fourier transform infrared) spectroscopy and nuclear magnetic resonance spectroscopy (1H-NMR). Then, a new family of polyimides (PIs) containing naphthalimide unit in the side-chains has been successfully synthesised by reaction of 4,4′-oxydiphthalic anhydride (ODPA) and 3,3′-dimethyl-4,4′-methylenediamine (DMMDA) with the novel functional diamine N8. The obtained polymers showed excellent solubility in a broad range of solvents, including tetrahydrofuran. Thermal properties of polymers were good enough to permit the use of these PIs on liquid-crystal displays (LCDs) applications. Alignment films obtained by casting offered outstanding rubbing-resistant ability, meanwhile kept the pretilt angle high above 89°. The PI seems to be prospective materials for alignment layers in LCDs.

Polyoxazoline adsorption on silica nanoparticles mediated by host–guest interactions

The objective of this work is to develop an original method of polyoxazoline brush generation based on supramolecular chemistry onto silica nanoparticles. A first layer is realized by adsorption of a polymer bearing β-cyclodextrin units (PβCD). This allows the anchoring of a second layer made of alkyl end-capped poly(2-methyl-2-oxazoline) (POXZ–C n ) via host–guest interactions between the alkyl end groups and the β-cyclodextrin units. The characteristics of the surface layers were studied by dynamic light scattering. A first study of PβCD adsorption allowed to define the conditions of homogeneous PβCD coverage onto the silica surfaces. Then the adsorption of the second polymer onto the PβCD coated nanoparticles was studied as a function of the POXZ–C n solution concentration. Brush layers with chains in extended conformation could be obtained above a critical POXZ–C n concentration. The large thickness sensitivity to the feeding POXZ–C n concentrations allowed to show that the POXZ–C n grafting ratio can be controlled by the POXZ–C n concentrations. In a limited concentration range, the nature of the anchoring end-group (C 12 or C 18) does not influence the shape of the POXZ layer.