End-group Modification Research Articles

Effect of end-groups on sulfobetaine homopolymers with the tunable upper critical solution temperature (UCST)

One-step syntheses of well-defined Poly(3-((2-(Methacryloyloxy) ethyl) (dimethyl) ammonio)-1-propanesulfonate) (PDMAPS) with a carboxylic acid end-functional reversible addition-fragmentation chain transfer (RAFT) agent and further end-group modification were described. The upper critical solution temperature (UCST) of homo-zwitterions can be precisely adjusted by the surrounding pH due to the presence of a carboxyl end-group. Meanwhile, after esterification of the carboxylic acid group by methyl, ethyl, hexyl, phenethyl alcohol, UCST of all resulted PDMAPS with ester terminated groups showed more significant increases. Dynamic light scattering (DLS), Zeta-potential and small-angle X-ray scattering (SAXS) results demonstrated that the ionization/protonation from the carboxylic end-group and hydrophobicity of ester groups contribute significantly to the tunability. This end-group modification technique provides an easy and economical way of synthesizing temperature-responsive homo-polyzwitterions with precise and controllable temperature range owing to the designability of RAFT polymerization, where the products are suitable for biomedical and environmental engineering applications.

Efficient Exciton Dissociation Enabled by the End Group Modification in Non-Fullerene Acceptors

For organic photovoltaic (OPV) cells, in order to overcome the larger Coulombic binding energy between holes and electrons, an extra driving force is required for efficient exciton dissociation. He...

Two‐Dimension Conjugated Acceptors Based on Benzodi(cyclopentadithiophene) Core with Thiophene‐Fused Ending Group for Efficient Polymer Solar Cells

The previously reported nonfullerene small molecule ITIC‐SF achieved via side chain tuning, promotes the power conversion efficiency of polymer solar cells (PSCs) with PBDB‐T‐SF as the donor from 10.1% and ITIC2 acceptors up to 12.2% for ITIC‐SF acceptors. To further this research, benzene end groups of molecules are herein substituted with thiophene rings, obtaining two new molecules BDTCH‐IC with alkylthio substituents, and BDTSF‐IC with alkylthio and fluorine substituents on their thiophene‐conjugated side chains. The absorption edges of BDTCH‐IC and BDTSF‐IC are red‐shifted to 824 and 793 nm, respectively. Strengthened molecular crystallinity, promoted charge extraction, and upgraded morphology endorse the advancement of photovoltaic performance of the small molecular acceptors. Using donor PM6, the two small molecule acceptors show good photovoltaic performance, although the highest occupied molecular orbit energy offsets are small between donor and acceptor materials. As a combination of side‐chain and end‐group engineering, the photovoltaic performance of the PSCs is increased to 13.1%, together with the best short‐circuit current (JSC) and fill factor reported thus far for this series of molecules. The results indicate that the modification of side chain and end groups is an effective way to improve the photovoltaic performance of small molecule acceptors.

Characterization of microstructures and reaction mechanisms of Tröger's base polymers of intrinsic microporosity.

Tröger's base polymers of intrinsic microporosity (PIMs) are receiving increasing attention for applications such as polymer molecular sieve membranes. Development of novel membrane materials requires microstructure analysis in order to overcome processing and applications challenges. This study aims to address these challenges and overcome some of the solubility/aggregation issues that hinder the analysis of these materials. A combination of matrix-assisted laser desorption/ionization mass spectrometry and collision-induced dissociation was used to examine the reaction products of unfunctionalized Tröger's base PIMs. Enhanced data mining, using ultrahigh-resolution mass spectrometry and statistical analysis, yielded a wealth of information on the molecular mass, chemical connectivity, and end groups of species generated during synthesis. Modifications of interest include N-methyl, N-methanimine, N-formyl, and N-methylol end-capping moieties, as well as incomplete backbone methanodiazocine rings with missing bridging methylene linkages. Most importantly, a general fragmentation mechanism, supported by computational modeling, was developed to assist in the rapid identification of main-chain and end-group modifications in Tröger's base PIMs. Unfunctionalized Tröger's base polymers were selected as a model system, to thoroughly study their end-group modification chemistry. This model system could then be used to gain insights into complex hydroxy-functional PIM materials.

Fluoropolymer Nanoparticles Prepared Using Trifluoropropene Telomer Based Fluorosurfactants.

A fluorosurfactant based on 3,3,3-trifluoropropene (TFP) telomer was synthesized as an environmentally friendly alternative to perfluorooctanoic acid (PFOA) using TFP and 2-iodoperfluoropropane ((CF3)2CF-I) as starting materials. TFP telomerization was initiated by addition of di-tert-butylperoxide in the presence of (CF3)2CF-I as a chain transfer agent. The surfactant was obtained by modification of the iodine end-group on the TFP telomer to form an allylic functionality followed by the addition of thioglycolic acid via a thiol-ene reaction. The resulting fluorosurfactant exhibited a lower critical micellar concentration (CMC = 0.87 g·L-1) than that of PFOA (CMC = 3.0 g·L-1). This surfactant was used to prepare fluoropolymer nanoparticles by solvent evaporation from a solution composed of the surfacant and poly[2-(perfluorobutyl)ethyl methacrylate]. The oil-in-water emulsion was initially formed due to the adsorption of the surfactant molecules at the oil/water interface and subsequently converted into a nanoparticle suspension after solvent evaporation. Because of the strong hydrophobic interactions between the fluorinated surfactant tail and fluoropolymer, the obtained nanoparticle suspension was quite stable against water dialysis.

End-Group Chemistry and Junction Chemistry in Polymer Science: Past, Present, and Future

The current goal in functional polymeric material research is the preparation of polymers with high-fidelity nanoscale self-assembled structures and advanced functionality. Thus, recent research efforts have focused on linking chemistry for the development of tailor-made polymers with desired properties. The design of α- or ω-functionalized telechelic polymers with strongly associative interactions is connected to their unique supramolecular self-assembly behavior in homopolymers and blends. In addition, the end-group modification of block copolymers has shown to alter the polymer morphology radically, resulting in unprecedented property changes arising from confinement effects. This is fascinating because the content of terminal moieties is small compared to that of macromolecular polymer backbones. As an emerging theme in polymer designs and end-group chemistry, the controlled synthesis of polymers with complex architectures and functional linkages has been performed extensively in the past few decades....

Study on the adsorption mechanism of benzoylurea insecticides onto modified hyperbranched polysilicon materials.

Several hyperbranched polysilicon (HBPS) materials with different end group modifications were designed and synthesized and the structures were characterized. The modified HBPS polymers were applied to the adsorption of benzoylurea insecticides (BUs). The binding mode and binding energy between the HBPS and BUs were quantified and the results of an adsorption kinetics study and an adsorption thermodynamics experiment were verified by calculation and mutual verification. The adsorption mechanism of BUs onto HBPS was also discussed. The theoretical results show that the most effective way to combine the adsorbent and BUs is via hydrogen bonding when the end group is an amino group. Moreover, the most effective combination when the end group is β-cyclodextrin is the interaction of the BUs with the interior of the cavity to form a host–guest coating. The theoretical results of other end group-modified HBPS materials were also obtained and verified by adsorption experiments. In this work, an experimental method for obtaining the binding mode by theoretical calculations and then verifying it according to adsorption experiments was established.

Squaraine-based AIEgens for reversible mechanochromism, sensitive and selective hypochlorite detection and photostable far-red fluorescence cell imaging

Squaraines have been successfully designed to exhibit AIE properties based on TPE-functionalized diarylamine derivatives. The modification of end-groups can endow the derived dyes with different optical properties for different applications.

An Efficient Ring-Closure Method for Preparing Well-Defined Cyclic Polynorbornenes.

An efficient bimolecular ring-closure method is developed to prepare the well-defined cyclic polynorbornenes by combining the living ring-opening metathesis polymerization (ROMP) with the self-accelerating double strain-promoted azide-alkyne cycloaddition (DSPAAC) reaction. In this method, ROMP is used to synthesize the well-defined linear polynorbornenes with both azide terminals by virtue of a N-hydroxysuccinimide-ester-functionalized Grubbs initiator following the modification of polymer end groups. DSPAAC click reaction is then used to ring-close the linear polymer precursors and prepare the corresponding well-defined cyclic polynorbornenes using the sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD) as small linkers. The self-accelerating DSPAAC ring-closing reaction facilitates this method to efficiently prepare pure cyclic polynorbornenes in the presence of a molar excess of DIBOD small linkers to the linear polynorbornene precursors. This is the first report to prepare well-defined polynorbornenes with cyclic topology based on the ring-closure strategy for cyclic polymers.

Self-assembly of stimuli-responsive block copolymers in aqueous solutions: an overview

The review reports an aqueous solution behavior of commercially available and easy-to-use polymers, i.e., Pluronics®- and PNIPAM-based block copolymers. Both the polymers are stimuli responsive in nature. The present review covers the different aspects of aggregation behavior of Pluronics®- and PNIPAM-based block copolymeric micelles. Here, a comparison of physical properties such as EO–PO block, CP, CMC and CMT is made. Such physical parameters can be modulated with ease by the presence of external stimuli, viz. electrolytes, organic additives such as alcohols, phenols, amides and acids, different types of surfactants and water-soluble polymers, and also by modification of end groups of Pluronics®. But in this review, our main focus is to study the addition of salts and non-electrolytes on the aggregation behavior of Pluronics®. With the help of above parameters, users can get idea about the stability, partition coefficient, solubilization capacity, etc. In analogy with Pluronics®, PNIPAM is also a thermo-responsive polymer with ~ 32 °C lower critical solution temperature (LCST). However, the LCST is independent of the degree of polymerization, i.e., molecular weight of homopolymer. However, the LCST can be tuned in the presence of external stimulus. PNIPAM-based di-block copolymers form various morphologies in different environments. An inverted morphology by double-hydrophilic-block copolymers is also possible. According to US and British Pharmacopoeia, some of the Pluronics® and PNIPAM are recognized as pharmaceutical excipients. Therefore, they have been extensively used for various pharmaceutical formulations. The other applications of these polymers are tissue engineering, bioseparation devices, active membranes, biosensors, rheological modifier, lithium batteries, etc.

End-group functionalization of poly(2-oxazoline)s using methyl bromoacetate as initiator followed by direct amidation

Poly(2-alkyl/aryl-2-oxazoline)s (PAOx) are an alluring class of polymers for many applications due to the broad chemical diversity that is accessible for these polymers by simply changing the initiator, terminating agent and the monomer(s) used in their synthesis. Additional functionalities (that are not compatible with the cationic ring-opening polymerization) can be introduced to the polymers via orthogonal post-polymerization modifications. In this work, we expand this chemical diversity and demonstrate an easy and straightforward way to introduce a wide variety of functional end-groups to the PAOx, by making use of methyl bromoacetate (MeBrAc) as a functional initiator. A kinetic study for the polymerization of 2-ethyl-2-oxazoline (EtOx) in acetonitrile (CH3CN) at 140 °C revealed relatively slow initiation and slower polymerization than the commonly used initiator, methyl tosylate (MeOTs). Nonetheless, well-defined polymers could be obtained with MeBrAc as initiator, yielding polymers with near-quantitative methyl ester end-group functionality. Next, the post-polymerization modification of the methyl ester end-group with different amines was explored by introducing a range of functionalities, i.e. hydroxyl, amino, allyl and propargyl end-groups. The lower critical solution temperature (LCST) behavior of the resulting poly(2-ethyl-2-oxazoline)s was found to vary substantially in function of the end-group introduced, whereby the hydroxyl group resulted in a large reduction of the cloud point transition temperature of poly(2-ethyl-2-oxazoline), ascribed to hydrogen bonding with the polymer amide groups. In conclusion, this paper describes an easy and fast modular approach for the preparation of end-group functionalized PAOx.

Well-defined poly(ether sulfone)-b-polylactide: synthesis and microphase separation behavior

We investigated the microphase separation behavior of well-defined poly(arylene ether sulfone)-b-polylactide (PES-b-PLA) diblock copolymers. PES was synthesized by the nucleophilic aromatic substitution polymerization of 4-fluoro-4′-hydroxydiphenyl sulfone potassium salt in the presence of an allyl-functionalized initiator, which follows a chain growth condensation polymerization mechanism. A hydroxyl group installed via a thiol-ene reaction was utilized as the initiating site for the ring opening polymerization of d,l-lactide, producing the target polymer. The polymers were further purified by preparative size-exclusion chromatography and analyzed by small-angle X-ray scattering with temperature variations from room temperature to 150 °C. The PES block was glassy in the employed temperature range, but the PLA chains provided sufficient mobility for ordering of the block copolymer when PES was the minor fraction. An order-disorder transition (ODT) with changing temperature could not be located because PLA was not stable above 170 °C. From the degree of polymerization values of the polymers near the ODT, the Flory–Huggins interaction parameter, χ, could be roughly estimated as 0.12 at 150 °C. This high χ value suggests that engineering plastic-containing block copolymers could be useful in advanced lithographic and filtration applications. Well-defined poly(arylene ether sulfone)-b-polylactides (PES-b-PLAs) were successfully synthesized and their microphase separation behavior was investigated. PES was obtained via chain growth condensation polymerization, and subsequent end group modification followed by ring opening polymerization of d,l-lactide produced the diblock copolymers. By small-angle X-ray scattering experiments in bulk, the formation of ordered morphologies including spherical, cylindrical, gyroidal, and lamellar was observed. An effective interaction parameter at 150 °C was roughly estimated as 0.12 for the first time in engineering plastic-containing block copolymers.

A versatile method for cyclic polymers from conjugated and unconjugated vinyl monomers

ABSTRACTA versatile method was introduced to prepare cyclic polymers from both conjugated and unconjugated vinyl monomers. It was developed on the combination of the RAFT polymerization and the self‐accelerating double strain‐promoted azide‐alkyne click (DSPAAC) reaction. In this approach, a switchable chain transfer agent 1 was designed to have hydroxyl terminals and a functional pyridinyl group. The protonation and deprotonation of pyridinyl group endowed the chain transfer agent 1 with a switchable control capability to RAFT polymerization of both conjugated and unconjugated vinyl monomers. Based on this, RAFT polymerization and the following hydroxyl end group modification were used to prepare various azide‐terminated linear polymers including polystyrene, poly(N‐vinylcarbazole), and polystyrene‐block‐poly(N‐vinylcarbazole). Using sym‐dibenzo‐1,5‐cyclooctadiene‐3,7‐diyne (DBA) as small linkers, the corresponding cyclic polymers were then prepared via the DSPAAC reaction between DBA and azide terminals of the linear precursors. Due to the self‐accelerating property of DSPAAC reaction, this bimolecular ring‐closing reaction could efficiently produce the pure cyclic polymers using excess molar amounts of DBA to linear polymer precursors. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1811–1820

Fabrication of Polymer Micelles with Zwitterionic Shell and Biodegradable Core for Reductively Responsive Release of Doxorubicin.

To achieve a high stability in physiological environment and rapid intracellular drug release, a biodegradable zwitterionic triblock copolymer with a disulfide-linked poly-ε-caprolactone and polycarboxybetaine methacrylate (PCBMA-SS-PCL-SS-PCBMA) was prepared for micellar carrier to delivery doxorubicin (DOX) into tumor cells. PCBMA-SS-PCL-SS-PCBMA was obtained by following steps: i) introducing disulfide bonds through end-group modification of PCL diol with cystamine dihydrochloride; ii) preparing PCL-RAFT macromolecular chain transfer agent by EDC/NHS chemistry; iii) RAFT polymerization of zwitterionic monomer. Self-assembling from PCBMA-SS-PCL-SS-PCBMA, polymeric micelles had many advantages, such as ultra-low protein absorption in serum and obvious reduction-responsiveness in the presence of DTT. Furthermore, DOX-loaded micelles exhibited high stability upon centrifugation and lyophilization, a fast intracellular drug release and enhanced drug efficacy due to GSH-triggered PCBMA shell shedding and micellar reassembling. Thus, the polymeric micelles integrated several functions and properties could be prospectively utilized as valuable nanocarriers in cancer chemotherapeutics.

Synthesis and characterization of novel ABA type poly(Ester-ether) triblock copolymers

Oligomers of poly(3-hydroxypropionate) (P3HP) were synthesized via hydrogen transfer polymerization of acrylic acid. Olefinic end-group of the oligomers were modified through epoxidation and bromination to obtain activated oligomers with epoxy and bromide end-groups, respectively. Terminally hydroxyl oligomeric poly(ethylene glycol) (PEG-1450) was also converted to sodium alkoxide of PEG-1450 through reaction with sodium hydride. Novel ABA type P3HP-b-PEG-b-P3HP triblock copolymers were successfully obtained through simple nucleophilic addition reactions between alkoxy and epoxy/alkyl bromide. Water uptake measurements of the triblock copolymers were calculated. Characterization of the modified oligomers and the triblock copolymers was performed by using FT-IR, 1H-NMR and MALDI-MS analyses. Thermal transitions and degradation features of the copolymers were investigated by using DSC and TGA methods. Spectroscopic and thermal analyses revealed that both end-group modifications and coupling reactions were successfully achieved.

Efficient Polymer Solar Cells Having High Open-Circuit Voltage and Low Energy Loss Enabled by a Main-Chain Twisted Small Molecular Acceptor

A new main-chain twisted small molecular acceptor with nonhalogenated end groups (i-IEICO) is designed and synthesized. In contrast to its planar analogue IECIO, i-IEICO possesses an obviously twisted backbone, leading to significant hypsochromic shift in film absorption, slight enhancement in solution extinction coefficient, and significantly elevated molecular energy level. Benefited from these features, i-IEICO is matched well with two wide band gap polymer donor materials (J52 and PBDB-T) both in absorption spectra and molecular energy levels. Relative to the planar-molecule IEICO-based devices, the open-circuit voltage ( VOC), short-circuit current density, and fill factor of the i-IEICO-based devices are simultaneously improved, giving rising to a 10.48% (with J52) and 8.79% (with PBDB-T) power conversion efficiency, respectively. Moreover, J52:i-IEICO device exhibits a high VOC of 0.96 V accompanied by a small energy loss of 0.64 eV, which can be further improved to 1.01 V and 0.59 eV for the PBDB-T-based device. The obtained VOC of i-IEICO-based devices are among one of the highest values of either J52 or PBDB-T-based binary devices, suggesting the effectiveness of main-chain twisted strategy coupled with end-group modification to achieve highly efficient nonfullerene acceptors with low energy loss and high VOC.

Achieving Balanced Charge Transport and Favorable Blend Morphology in Non-Fullerene Solar Cells via Acceptor End Group Modification

Generally, the electron-withdrawing substitution on the end-capping group of the acceptor–donor–acceptor type small-molecule acceptor (SMA) narrows the optical bandgap, and the electron-donating group lifts the lowest unoccupied molecular orbital (LUMO) energy level of nonfullerene SMA, which increase the short-circuit current density (JSC) and open circuit voltage (VOC) of the organic solar cells (OSCs), respectively; however, their synergistic effect on the properties of SMA has remained elusive. Here, we first report a new end-capping group (EG), namely, 5-fluoro-6-methyl-3-dicycanovinylindan-1-one (CFDCI), that concurrently possesses an electron-withdrawing fluorine substitute and an electron-donating methyl group. A prototype SMA (namely, ITCF) based on CFDCI and its two control counterparts were prepared to fully understand the structure–property relationship that the new EG exerts on the resultant SMA. The ITCF demonstrated a moderately crystalline morphology in pristine film and more balanced char...

Probing membrane asymmetry of ABC polymersomes

We report the sensitivity of the membrane asymmetry of ABC (PEO-b-PCL-b-PMOXA) polymersomes towards the end-group modification of a shorter C block. While a non-modified ABC polymer formed polymersomes with the A block outside and the C block inside, a mixture of ABC and ABC-biotin formed polymersomes with the C block outside.

End group modification of polyethylene glycol (PEG): A novel method to mitigate the supercooling of PEG as phase change material

Polyethylene glycol (PEG) is a kind of phase change material with high phase change enthalpy and good compatibility with the environment. However, there is relatively large supercooling for PEG, limiting their practical applications. To reduce their supercooling degree, herein we use three different small molecules (acryloyl chloride, acetyl chloride, and thionyl chloride) to modify PEG and study the effects of different end group modification on their phase change properties. Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (1H-NMR) spectroscopy are used to confirm the molecular structure of the PEG with different molecular weights and functionalities after chemical modification. Crystal structures of the PEG before and after the modification are verified by X-ray diffractometry (XRD) method and show no change. Differential scanning calorimetry (DSC) results show that the end group modification is quite effective for mitigating the supercooling of PEG with double -OH end groups but not effective for PEG with mono -OH end group. The mechanism for the change of supercooling behavior is proposed. The costs of different modification methods are estimated and compared.

Surface Modifications of Ti2 CO2 for Obtaining High Hydrogen Evolution Reaction Activity and Conductivity: A Computational Approach.

The identification of hydrogen evolution reaction (HER) catalysts with high conductivity and high activity is the top priority in the development of renewable energy. Oxygen-terminated Ti2 C (Ti2 CO2 ), as one of the typical MXenes, shows good HER Gibbs free energy (ΔGH ) at low hydrogen coverage, whereas the large band gap of approximately 1.0 eV limits its conductivity capability. By doping phosphor (P) or sulfur (S) to partially substitute the surficial O, the average free energy (ΔGHa ) at various hydrogen coverages has been draggd to approach zero, and the conductivity is also significantly improved by narrowing the band gap to lower than 0.3 eV. Partial charge analysis indicates that doping P or S on the surface induces the diffusion of electrons on oxygen from O 2px to O 2pz , resulting in O 2pz reaction with H 1s. The facial overlapping of H 1s with O 2pz will strengthen the binding strength, hence lowering ΔGH . The energy shift toward Fermi level of Ti 3d after P or S doping contributes to the reduced band gap and high conductivity. Surficial O or P vacancies are created to evaluate the vacancy effect on HER performance, which not only improves ΔGHa and conductivity but also leads to a low reaction barrier of H2 O splitting (<0.2 eV). The armchair nanoribbon (ANR) displays improved HER activity by P-doping at 50% ratio. Our research shows that modification of end-group in MXenes can effectively improve HER catalytic activity and conductivity, which is expected to promote their potential applications in electrocatalysis and energy conversion.