Counterpart Polymers Research Articles

Preparation of Dye Semiconductors via Coupling Polymerization Catalyzed by Two Catalysts and Application to Transistor.

Organic dye semiconductors have received increasing attention as the next generation of semiconductors, and one of their potential applications is as a core component of organic transistors. In this study, two novel diketopyrrolopyrrole (DPP) dye core-based materials were designed and separately prepared using Stille coupling reactions under different palladium catalyst conditions. The molecular weights and elemental compositions were tested to demonstrate that both catalysts could be used to successfully prepare materials of this structure, with the main differences being the weight-average molecular weight and the dispersion index. PDPP-2Py-2Tz I with a longer conjugation length exhibited better thermodynamic stability than the counterpart polymer PDPP-2Py-2Tz II. The intrinsic optical properties of the polymers were relatively similar, while the electrochemical tests showed small differences in their energy levels. The polymers obtained with different catalysts displayed similar and moderate electron mobility in transistor devices, while PDPP-2Py-2Tz I possessed a higher switching ratio. Our study provides a comparison of such dye materials under different catalytic conditions and also demonstrates the great potential of dye materials for optoelectronic applications.

Depolymerised lignin oil: A promising building block towards thermoplasticity in polyurethanes

The use of lignin as building block in the preparation of lignin-based thermoplastics has been a great challenge for the scientific community. Indeed, both the heterogeneous branched structure and the high hydroxyl functionality of lignin favours crosslinking reactions leading to the formation of thermosetting chemical structures. Some attempts have been made to circumvent these limitations, although the approaches required labour-intensive and time-consuming modifications of lignin and used only a relatively low amount in the materials. To tackle this problem, the present work employs lignin hydrogenolysis oil (LHO) which contains a low hydroxyl functionality oligomeric fraction suitable for the synthesis of thermoplastic polyurethanes (TPUs) via a two-step polymerization process. A series of TPUs were synthesized to investigate the impact of lignin content as well as soft segment molar mass on the chemical and thermo-mechanical properties of the materials. The study demonstrates that the use of high lignin content (38–46 wt. %) and high molar mass of the polyol (polypropylene glycol, PPG, Mn=4 kg mol−1) enhanced the mechanical properties of the obtained TPUs compared to counterpart polymers synthesized with lower molar mass of PPG. Additionally, LHO-based TPUs were applied as hot-melt adhesives for wood and their bonding strengths were evaluated by single lap shear tests. The lap shear adhesiveness was found to increase with increasing LHO concentration and decreasing molar mass of PPG. The developed methodology could lead to the preparation of robust thermoplastic lignin-based polyurethanes with a wide range of desired properties.

Effects of replacing carbamate with alkyl side chains on the properties and temperature sensing performance of hemi-isoindigo-based polymers

Previously, we developed several carbamate side chain-substituted hemi-isoindigo (HID)-based π-conjugated polymers, which demonstrated excellent sensitivity and stability as the sensing layers in chemiresistive temperature sensors. This work investigated the effects of the side chains on the HID units by changing the carbamate to alkyl side chains. Specifically, a series of 2-ethylhexyl-substituted HID polymers, poly(3-((3'',4'-bis(dodecyloxy)-[2,2':5',2''-terthiophen]-5-yl)methylene)-1-(2-ethylhexyl)indolin-2-one-6,5”-diyl) (PTAB), poly(3-((3'',4'-bis(dodecyloxy)-3,4-dimethoxy-[2,2':5',2''-terthiophen]-5-yl) methylene)-1-(2-ethylhexyl)indolin-2-one-6,5”-diyl) (PMAB), and poly(3-((7-(3,3'-bis(dodecyloxy)-[2,2'-bithiophen]-5-yl)-2,3-dihydrothieno[3,4-b] [1,4]dioxin-5-yl)methylene)-1-(2-ethylhexyl)indolin-2-one-6,5”-diyl) (PEAB) were synthesized, and their properties and temperature sensing performance were compared with their counterpart carbamate-substituted HID polymers, poly(2-ethylhexyl-3-((3'',4'-bis(dodecyloxy)-[2,2':5',2''-terthiophen]-5-yl)methylene)-2-oxoindoline-1-carboxylate-6,5”-diyl) (PTEB), poly(2-ethylhexyl-3-((3'',4'-bis(dodecyloxy)-3,4-dimethoxy-[2,2':5',2''-terthiophen]-5-yl)methylene)-2-oxoindoline-1-carboxylate-6,5”-diyl) (PMEB), and poly(2-ethylhexyl-3-((7-(3,3'-bis(dodecyloxy)-[2,2'-bithiophen]-5-yl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)methylene)-2-oxoindoline-1-carboxylate-6,5”-diyl) (PEEB), and their thermally annealed products, poly(3-((3'',4'-bis(dodecyloxy)-[2,2':5',2''-terthiophen]-5-yl)methylene)indolin-2-one-6,5”-diyl) (PTNB), poly(3-((3'',4'-bis(dodecyloxy)-3,4-dimethoxy-[2,2':5',2''-terthiophen]-5-yl)methylene)indolin-2-one-6,5”-diyl) (PMNB), and poly(3-((7-(3,3'-bis(dodecyloxy)-[2,2'-bithiophen]-5-yl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)methylene)indolin-2-one-6,5”-diyl) (PENB). The highest occupied molecular orbital energy (E HOMO) level and crystallinity of PEAB are very similar compared to PEEB. Chemiresistor devices with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) (PEAB:F4TCNQ) fabricated on flexible plastic substrates exhibited a high temperature coefficient of resistance (TCR) of −1.09% °C−1, although the value is lower than that (−1.92% °C−1) of the device based on PENB:F4TCNQ. The device based on PEAB:F4TCNQ also showed excellent stability with no performance degradation over 1 month, which is similar to the device based on PENB:F4TCNQ. On the other hand, PTAB and PMAB showed significantly higher E HOMO levels and crystallinity compared to their counterpart polymers. Sensors based on PTAB:F4TCNQ and PMAB:F4TCNQ showed TCR values of −1.02% °C−1 and −1.15% °C−1, respectively, which are lower than their corresponding annealed carbamate-substituted HID polymers. PTAB has a much lower E HOMO level (−4.95 eV) than that of PTNB (−4.69 eV) and is more crystalline than the latter, which should lead to poorer stability of the doped complex PTAB:F4TCNQ. Surprisingly, PTAB:F4TCNQ showed much better long-term stability than PTNB:F4TCNQ. It was considered that the hydrophobic alkyl side chains in PTAB can help prevent the interaction of water in the air with the PTAB:F4TCNQ complex, thereby stabilizing the complex. This study provided new insights into the design principles of conjugated polymers for printed and flexible temperature sensors.

Adenine-functionalized conjugated polymer as an efficient photocatalyst for hydrogen evolution from water

Conjugated polymers have emerged as a promising class of organic photocatalysts for photocatalytic hydrogen evolution from water splitting due to their adjustable chemical structures and electronic properties. However, developing highly efficient organic polymer photocatalysts with high photocatalytic activity for hydrogen evolution remains a significant challenge. Herein, we present an efficient approach to enhance the photocatalytic performance of linear conjugated polymers by modifying the surface chemistry via introducing a hydrophilic adenine group into the side chain. The adenine unit with five nitrogen atoms could enhance the interaction between the surface of polymer photocatalyst and water molecules through the formation of hydrogen bonding, which improves the hydrophilicity and dispersity of the resulting polymer photocatalyst in the photocatalytic reaction solution. In addition, the strong electron-donating ability of adenine group with plentiful nitrogen atoms could promote the separation of light-induced electrons and holes. As a result, the adenine-functionalized conjugated polymer PF6A-DBTO2 shows a high photocatalytic activity with a hydrogen evolution rate (HER) of 25.21 mmol g−1 h−1 under UV-Vis light irradiation, which is much higher than that of its counterpart polymer PF6-DBTO2 without the adenine group (6.53 mmol g−1 h−1). More importantly, PF6A-DBTO2 without addition of a Pt co-catalyst also exhibits an impressive HER of 21.93 mmol g−1 h−1 under visible light (λ > 420 nm). This work highlights that it is an efficient strategy to improve the photocatalytic activity of conjugated polymer photocatalysts by the modification of surface chemistry.

Effect of processing conditions and catalyst type on the thermal oxidative degradation mechanisms and melt stability of metallocene and Ziegler‐catalyzed ethylene‐1‐hexene copolymers

AbstractPolyolefins have traditionally been polymerized via the heterogeneous Ziegler Natta (Z‐N) catalysts since their discovery in the 1950s, but the later developments of the homogeneous single site metallocene/methylaluminoxane (MAO) catalysts have opened the possibility for the synthesis of polyolefin polymers and copolymers (commercialized in the 1990s) with highly defined microstructure and great degree of control of their molecular architecture resulting in some unique beneficial properties compared to their Z‐N counterparts. The main aim of the work reported here was to examine critically the effects of the processing conditions during multipass extrusions on the molecular and rheological characteristics of metallocene‐catalyzed linear low density polyethylene and a Ziegler‐Natta‐based counterpart polymer and on the thermoxidative (in the melt) stability of their melts and their stabilization. Both polymers examined here were based on ethylene‐1‐hexene copolymers and produced by the same manufacturer with similar density and melt index (MI) values. The melt stability and rheological properties of the polymers were determined from melt flow and capillary rheometric measurements. The molecular characteristics were investigated using GPC for molecular weight determination, 13C‐NMR for short chain branching, 1H‐NMR and FTIR for the type and concentration of unsaturation groups, FTIR for carbonyl‐containing compounds and chemical analysis for hydroperoxide determination. The processibility of the two polymers was compared through examination of different processing conditions (die temperatures 210–285°C, screw speeds 50–200 rpm) used for a multipass extrusion process. Further, the effects of the processing conditions on the melt thermoxidation of the differently catalyzed LLDPE polymers were investigated. The results demonstrated that both the catalyst type and the processing conditions have a great effect on both the rheological and the themoxidative behavior of the polymers as well as on the balance between the competing oxidative reactions taking place in the polymer melt, for example, chain scission and crosslinking reactions. The results obtained for the different multipass extrusion conditions of the two polymers have illustrated clearly that the degradation mechanisms during their melt processing are substantially different. The melt degradation route of the Ziegler‐catalyzed polymer was shown to be dominated by chain scission reactions under all the processing conditions examined, and more so at the higher shear rates and temperatures. By contrast, the evidence clearly showed that the metallocene‐catalyzed polymer gave rise to crosslinking reactions that predominated even under the more severe processing conditions, that is, higher temperatures and shear rates.

Toward High‐Performance Dihydrophenazine‐Based Conjugated Microporous Polymer Cathodes for Dual‐Ion Batteries through Donor–Acceptor Structural Design

AbstractRecent studies have demonstrated that dihydrophenazine (Pz) with high redox‐reversibility and high theoretical capacity is an attractive building block to construct p‐type polymer cathodes for dual‐ion batteries. However, most reported Pz‐based polymer cathodes to date still suffer from low redox activity, slow kinetics, and short cycling life. Herein, a donor–acceptor (D–A) Pz‐based conjugated microporous polymer (TzPz) cathode is constructed by integrating the electron‐donating Pz unit and the electron‐withdrawing 2,4,6‐triphenyl‐1,3,5‐triazine (Tz) unit into a polymer chain. The D–A type structure enhances the polymer conjugation degree and decreases the band gap of TzPz, facilitating electron transportation along the polymer skeletons. Therefore the TzPz cathode for dual‐ion battery shows a high reversible capacity of 192 mAh g−1 at 0.2 A g−1 with excellent rate performance (108 mAh g−1 at 30 A g−1), which is much higher than that of its counterpart polymer BzPz produced from 1,3,5‐triphenylbenzene (Bz) and Pz (148 and 44 mAh g−1 at 0.2 and 10 A g−1, respectively). More importantly, the TzPz cathode also shows a long and stable cyclability of more than 10 000 cycles. These results demonstrate that the D–A structural design is an efficient strategy for developing high‐performance polymer cathodes for dual‐ion batteries.

Aggregation Tuning with Heavily Fluorinated Donor Polymer for Efficient Organic Solar Cells

The fluorination/sulfofication-induced effect in the photovoltaic polymer solar cells (PSCs) needs to be paid much attention. In this work, a new donor polymer PBDB-PS2F was synthesized by heavily fluorinated and decorated S atom on the side chain of benzo[1,2-b:4,5-b']dithiophene (BDT) unit to explore the internal combined effect of F&S on the photoelectric performance. It was found that the heavy fluorination on the side chain could make PBDB-PS2F achieve a low highest occupied molecule orbital (HOMO) energy level of -5.72 eV and weaken the torsion of the main chain and effectively increase the intermolecular π-π* transition. Encouragingly, compared with the counterpart polymer PBDB-PS without the fluorination, PBDB-PS2F exhibited a much intense aggregation at room temperature but showed a tendency of reduced aggregation at high temperatures. This feature gives excellent solution processability and uniform morphology in the active layer of a PBDB-PS2F-based device, enabling an outstanding photovoltaic performance with the power conversion efficiency (PCE) of 13.56% (VOC = 0.90 V, JSC = 21.53 mA/cm2, FF = 69.68%). Compared with that of the counterpart polymer PBDB-PS with no heavy fluorination, the VOC of PBDB-PS2F increased by 15.4% and the PCE increased by 30.9%. Thus, the heavy-fluorination-induced effect to construct photovoltaic polymers could be used to improve the performance of polymer solar cells.

More Interaction Sites and Enhanced Fluorescence for Highly Sensitive Fluorescence Detection of Methamphetamine Vapor via Sidechain Terminal Functionalization of Conjugated Polymers

AbstractA strategy of sidechain terminal functionalization was proposed to further improve the sensitivity of MA vapor detection. In this work, three fluorescent conjugated polymers (CPs) were synthesized by introducing NHBoc group at the end of the side chains and characterized by GPC, 1H NMR, FT‐IR and 19F NMR. The test results show that the introduction of the NHBoc group reduces the effect of aggregation‐caused quenching (ACQ), thereby improving the fluorescence intensity and fluorescence quantum efficiency of CPs. Secondly, it increases the interaction sites for MA capture and expands the scope of the interaction, thereby increasing the contact probability and interaction between the CPs and MA. Thirdly, the morphology of the CPs has also changed, especially the polymer containing 5‐fluoro‐2,1,3‐benzothiadiazole (1F‐2NHBoc‐CP), whose film has a network‐crosslinked porous structure, which is conducive to the enrichment and penetration of N‐methylphenethylamine (MPEA, a simulant of MA) vapor at low concentration. All these effects contribute to efficient fluorescence quenching, so the 1F‐2NHBoc‐CP can achieve more than 74% fluorescence quenching within 30 s. Taking fluorescence quenching to 1% as the detection limit, MPEA vapor with an actual concentration of 41 ppt can be detected, and its sensitivity is increased by about 25 folds relative to the NHBoc‐free counterpart polymer. Furthermore, it showed a linear correlation with MPEA vapor in the range of 41 ppt to 16 ppm, which spanned five orders of magnitude. This strategy will find a great potential in developing highly sensitive fluorescent probe for dangerous chemical vapor detection.

Influence of Backbone Regioregularity on High-Mobility Conjugated Polymers Based on Alkylated Dithienylacrylonitrile.

We designed and synthesized two donor-acceptor type conjugated polymers, the regioirregular polymer RI-PDPP-CNTVT-6 and its regioregular counterpart RR-PDPP-CNTVT-6, based on diketopyrrolopyrrole (DPP) and alkylated dithienylacrylonitrile (CNTVT) units. Among them, the 2-decyltetradecyl side chain on the DPP acceptor unit and the hexyl side chain on the CNTVT donor unit were used to ensure enough solubility for them. The backbone regioregularity was used to tune electronic structures and carrier transport of the conjugated system. The two conjugated polymers were characterized for their thermal, photophysical, electrochemical, and solution-processable properties, thin-film microstructures, and morphologies. The top-gate bottom-contact configuration organic field-effect transistor (OFET) devices based on these two conjugated polymers showed excellent ambipolar performances. Remarkably, the regioirregular polymer RI-PDPP-CNTVT-6 exhibited higher charge-carrier mobilities than the regioregular counterpart polymer RR-PDPP-CNTVT-6 did, as their highest hole/electron mobilities (μhmax/μemax) were 1.48/1.27 and 0.48/0.052 cm2 V-1 s-1, respectively. Moreover, the influence of backbone regioregularity on its thermal stability, electrochemical and photophysical properties, solution processability, and charge-carrier mobility was intensively studied. Our results afforded a promising pathway toward the development of excellent ambipolar OFETs with high performance, good solution processability, and thermal stability.

The regulation of π-bridge of indacenodithiophene-based donor-π-acceptor conjugated polymers toward efficient polymer solar cells

The instinct feature of π-bridges of donor-π-acceptor (D-π-A) conjugated polymers plays a critical role in tailoring the polymer basic properties as well as the photovoltaic performance. In this work, we designed two new D-π-A polymers PSeBDDIDT and PTzBDDIDT based on donor unit indacenodithiophene (IDT), acceptor unit benzo[1,2-c:4,5-c’]dithiophene-4,8-dione (BDD) with varying π-conjugated bridges of selenophene and thiazole units. Compared to the counterpart polymer PThBDDIDT with thiophene π-bridge, polymers PSeBDDIDT and PTzBDDIDT exhibited enhanced intermolecular interactions, expanded absorption range and better molecular planarity arising from the suppressed steric hindrance between the respective bridge and the adjacent BDD moiety. Conventional polymer solar cells were fabricated with PC71BM as the acceptor. The results witness a greatly improved efficiency for PSeBDDIDT based solar cell compared to PThBDDIDT based counterpart device (7.04%). As a result, the champion PCE of 8.65% was recorded with VOC of 0.899 V, JSC of 16.04 mA cm−2 and FF of 0.60. It is worth highlighting that this is the highest efficiency among all IDT-based polymeric donors reported till now. As a contrast, the devices fabricated from PTzBDDIDT demonstrated a low efficiency of 2.75%, with increased VOC of 0.968 V, JSC of 8.12 mA cm−2 and FF of 0.35. The inferior photocurrent and fill factor of PTzBDDIDT based device was in accord with the poor exciton dissociation probability (38%) and low hole and electron charge transport inside the polymer solar cell. In conclusion, this work demonstrates a state of the art IDT-based polymeric donor with selenophene π-bridge and the importance of rational regulation of π-bridges on polymer properties and photovoltaic efficiency of polymer solar cells.

Aggregation of Cationic Amphiphilic Block and Random Copoly(vinyl ether)s with Antimicrobial Activity.

In this study, we investigated the aggregation behaviors of amphiphilic poly(vinyl ether)s with antimicrobial activity. We synthesized a di-block poly(vinyl ether), B3826, composed of cationic primary amine and hydrophobic isobutyl (iBu) side chains, which previously showed antimicrobial activity against Escherichia coli. B3826 showed similar uptake behaviors as those for a hydrophobic fluorescent dye, 1,6-diphenyl-1,3,5-hexatriene, to counterpart polymers including homopolymer H44 and random copolymer R4025, indicating that the iBu block does not form strong hydrophobic domains. The cryo-TEM observations also indicated that the polymer aggregate of B3826 appears to have low-density polymer chains without any defined microscopic structures. We speculate that B3826 formed large aggregates by liquid-liquid separation due to the weak association of polymer chains. The fluorescence microscopy images showed that B3826 bonds to E. coli cell surfaces, and these bacterial cells were stained by propidium iodide, indicating that the cell membranes were significantly damaged. The results suggest that block copolymers may provide a new platform to design and develop antimicrobial materials that can utilize assembled structures and properties.

Polyethylene containing aliphatic ring and aromatic ring defects in the main chain: Synthesis via ADMET and comparisons of thermal properties and crystalline structure

Three polyethylene containing different non-planar aliphatic ring ether units (1,4-cyclohexylenedioxy, 4,4′-bicyclohexylenedioxy and 4,4′-isopropylidenedicyclohexylenedioxy) were synthesized via acyclic diene metathesis polymerization (ADMET) and subsequent hydrogenation. They were compared with their counterpart polymers containing aromatic ring defects in aspects of chain structural, thermal properties and crystalline structure by investigations with 1H NMR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). Regardless of the trans/cis isomers of cyclohexane moieties in these polymers, the results demonstrated that polyethylene containing non-planar aliphatic ring units showed decreased thermal stability as compared with the corresponding PE containing aromatic ring defects. Moreover, study on crystallization behaviors indicated that in contrast to their aromatic counterparts, introduction of the non-planar aliphatic defects perturbed the corresponding crystal structure more intensively, and larger space is needed to include these defects in the solid phase. As a result, their WAXD reflections shifted to lower scattering angles that correspond to increased d-spacing, and the polymers exhibited lower melting points. SAXS results proved that non-planar aliphatic ring defects result in increased dimension of amorphous region. Calculated by melting points and enthalpy, these polymers had smaller crystalline lamella thickness and lower crystallinity than their aromatic counterparts.

Highly Crystalline Low Band Gap Polymer Based on Thieno[3,4-c]pyrrole-4,6-dione for High-Performance Polymer Solar Cells with a >400 nm Thick Active Layer.

Two thieno[3,4-c]pyrrole-4,6-dione (TPD)-based copolymers combined with 2,2'-bithiophene (BT) or (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TV) have been designed and synthesized to investigate the effect of the introduction of a vinylene group in the polymer backbone on the optical, electrochemical, and photovoltaic properties of the polymers. Although both polymers have shown similar optical band gaps and frontier energy levels, regardless of the introduction of vinylene bridge, the introduction of a π-extended vinylene group in the polymer backbone substantially enhances the charge transport characteristics of the resulting polymer due to its strong tendency to self-assemble and thus to enhance the crystallinity. An analysis on charge recombination in the active layer of a solar cell device indicates that the outstanding charge transport (μ = 1.90 cm(2)·V(-1)·s(-1)) of PTVTPD with a vinylene group effectively suppresses the bimolecular recombination, leading to a high power conversion efficiency (PCE) up to 7.16%, which is 20% higher than that (5.98%) of the counterpart polymer without a vinylene group (PBTTPD). More importantly, PTVTPD-based devices do not show a large variation of photovoltaic performance with the active layer thickness; that is, the PCE remains at 6% as the active layer thickness increases up to 450 nm, demonstrating that the PTVTPD-based solar cell is very compatible with industrial processing.

Synthesis and photovoltaic properties of an alternating polymer based on benzo[1,2-b:4,5-b′]dithiophene and fluorine substituted 4,7-dithiophene-2-yl-2,1,3-benzothiadiazole

An alternating polymer (PBDTFC10DBT) with benzo[1,2-b:4,5-b′]dithiophene (BDT) as electron-rich unit and 4,7-bis(4-decylthiophen-2-yl)-5-fluorine-2,1,3-benzothiadiazole (FC10DBT) as electron-withdrawing unit was synthesized and characterized. PBDTFC10DBT showed similar absorption property with that of the counterpart polymer without fluorine atom (PBDTC10DBT). However, the low-lying highest occupied molecular orbit (HOMO) energy level of PBDTFC10DBT was −5.42eV, about 0.22eV deeper than that of PBDTC10DBT. In order to study the photovoltaic properties of the materials, polymer solar cells (PSCs) were fabricated with PBDTFC10DBT as donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as acceptor. The power conversion efficiency (PCE) of PSC was 1.19% with a high open circuit voltage (Voc) of 0.62V for an optimized PBDTFC10DBT:PC61BM ratio of 1:4, in comparison with that of PBDTC10DBT-based device (PCE of 0.99% with Voc of 0.53V). This study indicated that fluorine substituted 4,7-dithiophene-2-yl-2,1,3-benzothia-diazole based copolymers would be promising material for the application in polymer solar cells.

Synthesis and photovoltaic properties of an alternating polymer based fluorene and fluorine substituted quinoxaline derivatives

An alternating polymer (PFOFTQx) with 9,9-dioctylfluorene (FO) as electron-rich unit and fluorine substituted quinoxaline (FTQx) as electron-withdrawing unit was synthesized and characterized. PFOFTQx showed similar absorption property with that of the counterpart polymer without fluorine atom (synthesized APFO-15). However, the low-lying highest occupied molecular orbit (HOMO) energy level of PFOFTQx was −5.37eV, about 0.07eV smaller than that of synthesized APFO-15. In order to study the photovoltaic properties of the materials, polymer solar cells (PSCs) were fabricated with PFOFTQx as donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as acceptor. The power conversion efficiency (PCE) of PSC was 1.77% with a high open-circuit voltage (Voc) of 0.90V for an optimized PFOFTQx:PC61BM weight ratio of 1:5, in comparison with that of synthesized APFO-15-based device (PCE of 1.60% with Voc of 0.77V). This study indicated that fluorine substituted quinoxaline-based polymers would be promising material with a higher Voc for the application in polymer solar cells.

Atom Transfer Radical Polymerization Preparation and Photophysical Properties of Polypyridylruthenium Derivatized Polystyrenes

A ruthenium containing polymer featuring a short carbonyl-amino-methylene linker has been prepared by atom transfer radical polymerization (ATRP). The polymer was derived from ATRP of the N-hydroxysuccinimide (NHS) derivative of p-vinylbenzoic acid, followed by an amide coupling reaction of the NHS-polystyrene with Ru(II) complexes derivatized with aminomethyl groups (i.e., [Ru(bpy)2(CH3-bpy-CH2NH2)](2+) where bpy is 2,2'-bipyridine, and CH3-bpy-CH2NH2 is 4-methyl-4'-aminomethyl-2,2'-bipyridine). The Ru-functionalized polymer structure was confirmed by using nuclear magnetic resonance and infrared spectroscopy, and the results suggest that a high loading ratio of polypyridylruthenium chromophores on the polystyrene backbone was achieved. The photophysical properties of the polymer were characterized in solution and in rigid ethylene glycol glasses. In solution, emission quantum yield and lifetime studies reveal that the polymer's metal-to-ligand charge transfer (MLCT) excited states are quenched relative to a model Ru complex chromophore. In rigid media, the MLCT-ground state band gap and lifetime are both increased relative to solution with time-resolved emission measurements revealing fast energy transfer hopping within the polymer. Molecular dynamics studies of the polymer synthesized here as well as similar model systems with various spatial arrangements of the pendant Ru complex chromophores suggest that the carbonyl-amino-methylene linker probed in our target polymer provides shorter Ru-Ru nearest-neighbor distances leading to an increased Ru*-Ru energy hopping rate, compared to those with longer linkers in counterpart polymers.

Biodegradable alanine and phenylalanine alkyl ester polyphosphazenes as potential ligament and tendon tissue scaffolds

New polyphosphazenes were designed, synthesized, and characterized to determine their potential as scaffolds for ligament and tendon tissue engineering. The carboxylic acid moiety of the amino acids L-alanine and L-phenylalanine were protected with alkyl esters with increasing chain length from 5 to 8 carbon atoms. This combined the hydrolytic sensitivity of the amino acid ester polyphosphazenes with the elastomeric characteristics induced by the long chain alkoxy polyphosphazenes. Test side group substitution reactions were performed on the cyclic small molecule model, hexachlorocyclotriphosphazene (NPCl2)3, to determine if steric hindrance would inhibit the degree of chlorine replacement by the amino acid ester units. Counterpart polymers were then synthesized by replacement of the chlorine atoms in poly(dichlorophosphazene) (NPCl2)n by the same amino acid esters. The glass transition temperatures of the polymers decreased with increasing alkyl ester chain length, ranging from 11.6 to −24.2 °C. Polymer hydrolysis was studied for solid samples in deionized water at physiological temperature for 12 weeks. The starting pH was 6.3 and the final pH ranged between 5.2 and 6.8. Polymer film mass decreased between ∼8.7 and 26 percent during the 12 week period, while the molecular weights decreased ∼57 to 99 percent.

Microstructure-stability relations studies of porous chitosan microspheres supported palladium catalysts

In this study, polyethylene glycol (PEG) with different molecular weight, polyvinyl pyrrolidone (PVP), and polyvinyl alcohol (PVA), are chosen as porogens for preparing chitosan base porous microsphere supported palladium catalyst for coupling reactions. The pore structure of the microspheres was controlled by the compatibility of chitosan and counterpart polymers. The prepared porous chitosan microspheres supported palladium heterogeneous catalysts have been evaluated using the well-established Ullmann reductive homocoupling and the Heck cross-coupling reactions. The activities, stabilities and recyclability of the porous chitosan microspheres supported palladium catalysts are not only highly dependent upon the surface areas of the solid supports, but also upon the chemical properties of the water-soluble polymers. The degradation of the prepared heterogeneous palladium catalysts is mainly caused by a combination of the palladium leaching and the morphological transformation of the palladium species from the amorphous into the crystals.

Ketalized poly(amino ester) for stimuli-responsive and biocompatible gene delivery

Stimuli-triggered degradation and facilitated intracellular release of nucleic acids are key design factors in developing efficient and biocompatible nonviral gene carriers. In this study, a cationic polymer was developed with aims to achieve enhanced gene transfection and low cytotoxicity via rapid biodegradation and subsequent intracellular de-complexation in response to dual stimuli in a cell. Diaminoethane was polymerized to synthesize cationic and hydrolytically degradable poly(amino ester), and then it was further conjugated with acid-degradable amino ketal branches. The resulting polymer, ketalized poly(amino ester) (K-PAE), differentially degrades via rapid hydrolysis of the ketal branches in the mildly acidic endosome and subsequent gradual degradation of the polyester backbone in the cytoplasm. DNA/K-PAE polyplexes underwent acid-triggered de-complexation at an endosomal pH, leading to efficient intracellular release of DNA and significantly enhanced transfection efficiency. In addition, DNA/K-PAE polyplexes demonstrated low cytotoxicity and serum-resistant gene transfection, in comparison with commercial counterpart polymers, promising for efficient and safe gene delivery in vivo. This study presents insightful design clues for developing efficient, versatile, stimuli-responsive, and biocompatible polymers for nonviral gene delivery.

Synthesis of Poly(fluorene-alt-thieno[3,4-b]thiophene) for Photovoltaic Devices

Polymer-based bulk heterojunction solar cells have been fabricated using blended films composed of an electrondonating conjugated polymer and an electron-accepting material such as a fullerene derivative; they are promising low-cost, flexible renewable energy sources. A solar cell’s power conversion efficiency (PCE) is the product of the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) divided by the incident light power density. The Voc of polymer solar cells is generally proportional to the energy difference between the highest occupied molecular orbital (HOMO) of the electron donor and the lowest unoccupied molecular orbital (LUMO) of the electron acceptor, suggesting that polymers with deep HOMO levels are advantageous if conditions are otherwise similar. Photovoltaic cells have had PCEs of ca. 5% reported when a mixture of poly(3-hexylthiophene) (P3HT) and a fullerene derivative were respectively used as the electron donor and acceptor. Interesting low band gap polymers consisting of alternating ester or ketone-substituted thieno[3,4-b]thiophene and alkoxybenzo[1,2-b:4,5-b']dithiophene units have been developed. Among them, a polymer consisting of a fluorinated ketone-substituted thieno[3,4-b]thiophene and alkoxybenzo[1,2-b:4,5-b']dithiophene units, whose band gap and HOMO level were 1.77 eV and −5.22 eV, respectively, exhibited a maximum PCE of 7.73%. We have also synthesized conjugated polymers for photovoltaic applications. Especially, a polymer consisting of alternating carbazole and ester group-substituted thieno[3,4b]thiophene units (PCTT1) showed a band gap of 2.1 eV and HOMO level of −5.52 eV. This polymer, blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), when used as the photoactive layer of solar cells, yielded a maximum PCE of 2.53%. Polyfluorenes have advantages such as thermal and oxidation stabilities. They can also form films easily and have good hole-transporting properties. The band gaps and HOMO levels of fluorene-containing polymers have been reported to be similar to those of carbazole-containing counterpart polymers, though different PCEs were shown by resulting polymer-based solar cells. Thus poly(fluorenealt-thieno[3,4-b]thiophene polymer) (PFTT) was synthesized as a counterpart of PCTT1. This work describes the synthesis and characterization of the polymer along with preliminary tests of resulting polymer-based photovoltaic devices. Experimental Section