Regioregular improvement on the oxidative polymerization of poly‐3‐octylthiophenes by slow addition of oxidant at low temperature

Many pathways can be used to synthesize polythiophenes derivatives. The polycondensation reactions performed with organometallics are preferred since they lead to regioregular polymers (with high content of heat‐to‐tail coupling) which have enhanced conductivity and luminescence. However, these pathways have several steps; the reactants are highly moisture sensitive and expensive. On the other hand, the oxidative polymerization using FeCl₃ is a one‐pot reaction that requires less moisture sensitive reactants with lower cost, although the most common reaction conditions lead to polymers with low regioregularity. Here, we report that by changing the reaction conditions, such as FeCl₃ addition rate and reaction temperature, poly‐3‐octylthiophenes with different the regioregularities can be obtained, reaching about 80% of heat‐to‐tail coupling. Different molar mass distributions and polydispersivities were obtained. The preliminary results suggest that the oxidative polymerization process could be improved to yield polythiophenes with higher regioregularity degree and narrower molar mass distributions by just setting some reaction conditions. We also verified that it is possible to solvent extract part of the lower regioregular fraction of the polymer further improving the regioregularity degree. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Imidazolium-substituted ionic (co)polythiophenes: Compositional influence on solution behavior and thermal properties

A series of ionic polythiophenes, in homopolymer and random copolymer configurations, is prepared via the Grignard metathesis (GRIM) polymerization protocol and subsequent substitution on the bromohexyl side chains with N-methylimidazole. The introduced structural variations – comonomer ratio, side chain composition, counter ions – allow tuning of the thermal properties and solution behavior of the resulting conjugated polymers. As expected, the solubility depends majorly on the number of ionic groups and the counter ions. The most peculiar behavior is observed for the P3HT-P3(MIM)HT-Br 50/50 random copolymer, which shows organization of the polymer chains in solution and thin film dependent on the preparation conditions. Dynamic light scattering studies confirm that the ordered solid-state structure is somewhat maintained when the copolymer is dissolved in a bad solvent mixture. The ionic (co)polythiophenes are generally more resistant to thermal degradation than their precursors. The precursor polymers all show a clear semi-crystalline behavior, with a decrease in crystallinity upon decreasing the number of regular 3-hexylthiophene units. On the other hand, the studied ionic (co)polythiophenes are fully amorphous. Changes in the counter ions have dramatic effects on the thermal properties. Bromine counter ions render the polymers strongly hygroscopic. The novel materials are of particular appeal in the field of organic photovoltaics, in which the imidazolium-substituted (co)polythiophenes can be beneficially applied as constituents of either active layers or electron transport layers. Their processability from green solvents is also of major importance for the field.     

Poly(2,7-carbazole)s: structure-property relationships

Conjugated polymers combine the interesting optical and electrical properties of metals with the processing advantages and mechanical properties of traditional synthetic polymers. With clever use of a variety of synthetic tools, researchers have prepared highly pure polymers with optimized physical properties during the past 30 years. For example, the synthesis of well-defined polyacetylenes, polyphenylenes, polythiophenes, polyfluorenes, and other conjugated polymers have significantly improved the performance of these polymeric materials. However, one important class of conjugated polymers was missing from this chemical inventory: easy access to well-defined poly(2,7-carbazole)s and related polymers. This Account highlights advances in the synthesis of poly(2,7-carbazole) derivatives since they were first reported in 2001. Starting from 2-nitro-biphenyl derivatives, 2,7-functionalized carbazoles are typically obtained from Cadogan ring-closure reactions. In a second step, Yamamoto, Stille, Suzuki, or Horner-Emmons coupling polymerization leads to various poly(2,7-carbazole) derivatives. We discuss the characterization of their optical and electrical properties with a strong emphasis on the structure-property relationships. In addition, we carefully evaluate these polymers as active components in light-emitting diodes, transistors, and photovoltaic cells. In particular, several low band gap poly(2,7-carbazole) derivatives have revealed highly promising features for solar cell applications with hole mobilities of about 3 x 10(-3) cm2 V(-1) s(-1) and power conversion efficiencies up to 4.8%. Finally, we show how these new synthetic strategies have led to the preparation of novel poly(heterofluorene) derivatives and ladder-type conjugated polymers.     

Effect of thermal annealing on surface morphology and physical properties of poly(3-octylthiophene) films

An unusual morphology observed in poly(3-octylthiophene) (P3OT) films, solution grown at room temperature, which is previously shown by highly regioregular-poly(3-alkylthiophenes) (rr-P3ATs), is reported. Upon thermal annealing a rare well-arranged corrugated-rod-type (CRT) morphology, comes up gradually. It is observed by soft-heat treatment of pristine P3OT films, which is not reported for any members of polythiophenes family. This novel CRT morphology, observed by scanning electron microscopy (SEM), is supported by photoluminescence (PL) quenching, red shift of λ_max (π-π* absorption) in UV-vis spectra, and increase in conductivity. These improvements in physical properties are perhaps due to the increase in the planarity and 3D-π-π stacking of polymer chains by gradual soft-thermal annealing. It is worthwhile to mention here that the P3OT synthesized for the present investigation, with changed polymerization parameters, is comparable with its rr-P3ATs counterparts. The improvement in the quality of P3OT may induce self-assembling nature in former which results due to increased π-π interactions.     

聚噻吩衍生物的合成及改性研究

首先利用Kumada反应合成了3种噻吩单体,即3-丁基噻吩、3-苯基噻吩和3-十六烷基噻吩;然后采用三氯化铁(FeCl3)氧化法合成了对应的3种聚噻吩;最后将3种聚噻吩与富勒烯(C60)进行溶液复合,得到了光电性能和溶解性能俱佳的聚噻吩/C60复合材料。采用红外光谱(FT-IR)、扫描电镜(SEM)、热失重分析(TGA)和伏安循环(CV)曲线等方法对聚噻吩及其复合材料的化学结构、溶解性能、热性能和电性能等进行了表征,并探讨了不同噻吩取代基对聚合物分子链共轭效应的影响规律。结果表明:3种改性聚噻吩具有良好的溶解性、耐热性和导电性;C60在3种改性聚噻吩中分散性良好,并使聚噻吩的电导率提高了10个数量级左右,其中聚3-十六烷基噻吩/C60复合材料的电化学能隙为1.70eV。     

New regioregular polythiophenes functionalized with sulfur-containing substituents for bulk heterojunction solar cells

Organic photovoltaic devices fabricated with polythiophenic derivatives and single-walled carbon nanotubes (SWCNT)s have been assembled and tested. For this purpose, some new regioregular polythiophenes with different sulfur-containing groups in the terminal position of a hexamethylenic side chain were prepared using direct and indirect polymerization routes. The optical features of the synthesized polymers were examined and compared by registering their UV–Vis spectra in different solvent/non-solvent systems and in film; their thermal stability, electrical conductivity, cyclic voltammetry and photovoltaic properties were carefully analyzed. In particular, the two samples bearing the sulfinyl group in side chain showed better chromic responses, enhanced self-assembling capabilities, more extended conjugation length, higher electrical conductivity and very promising photovoltaic performances, when compared to those of analogous systems reported on up to now.     

Synthesis of Conjugated Polymers in Chiral Nematic Liquid Crystal Fields

This review presents the progress made on current research in the synthesis of π-conjugated polymers in chiral nematic liquid crystal (N*-LC) fields through either chemical or electrochemical polymerization. The following are noteworthy advances in the field of π-conjugated polymers. (i) Helical aliphatic conjugated polymers of helical polyacetylene (H-PA) were synthesized using asymmetric interfacial polymerization in N*-LC fields. (ii) Helical aromatic conjugated polymers with electroactive properties, such as poly(3,4-ethylenedioxythiophene) (PEDOT) and polybithiophene (PBT), were synthesized using asymmetric electrochemical polymerization in N*-LC fields. (iii) Chiral aromatic conjugated copolymers, such as the poly(bithienylene-phenylene) (PBTP) derivative, were synthesized using the asymmetric Stille polycondensation reaction in N*-LC fields. Throughout the document, it has been emphasized that by using N*-LC systems as asymmetric polymerization fields, helix formation is possible for aliphatic and aromatic π-conjugated polymers without chiroptical substituents on the side chains.     

Quinolinyl‐moiety‐containing 3‐ester‐substituted polythiophenes showing fluorescence efficiency

Polythiophenes with ester substituents at the 3‐position of the thiophene ring were synthesized by ferric chloride oxidative polymerization. The polythiophenes are partially soluble in tetrahydrofuran, and these solutions were used to characterize the polythiophenes using Fourier transform infrared, ¹H NMR, UV‐visible and fluorescence spectroscopy, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry and cyclic voltammetry. The electrochemical band gap of the polymers is in the range 1.6–2.3 eV. The effect of the various substituents on the fluorescence behaviour was studied in detail. The quinolinyl‐moiety‐containing polythiophene ester has the highest fluorescence quantum yield. The incorporation of Al³⁺ and Zn²⁺ ions increases greatly the fluorescence intensity. The electroluminescence properties of the polymers were evaluated with a device configuration of ITO/PEDOT:PSS/polymer/LiF/Al. The polymers show a yellow emission in electroluminescence spectra. The results suggest that the quinoline‐containing ester‐substituted polythiophene is a promising electronic and optoelectronic material. Copyright © 2011 Society of Chemical Industry     

Surface-Initiated Controlled Radical Polymerization in Ordered Mesoporous Silicas

Recent advances in the synthesis of well-defined high-surface-area mesoporous silica/polymer composites via surface-initiated polymerization (“grafting from” method) and via attachment of preformed polymer chains (“grafting to” method) to surfaces of ordered mesoporous silicas (OMSs) are reviewed in the context of related research areas. Prior work on polymerizations in nanoscale confinements of OMSs is outlined and surface-initiated polymerization in disordered mesoporous silicas is briefly discussed. Early work on the surface-initiated radical polymerization initiated from OMS surface is reviewed and recent work involving OMS supports with large mesopores is discussed to illustrate the ability to form well-defined polymer brushes in nanopores using atom transfer radical polymerization (ATRP). The synthesis of polymer brushes in mesopores through the combination of ATRP or other polymerizations and the “click” chemistry is also outlined.     

Thermal and mechanical properties of homogeneous ternary nanocomposites of regioregular poly(3‐hexylthiophene)‐wrapped multiwalled carbon nanotube dispersed in thermoplastic polyurethane: Dynamic‐ and thermomechanical analysis

An interesting correlation between initial loading and nature of wrapping of regioregular poly(3‐hexylthiophene) (rrP3HT) on multiwalled carbon nanotube and their combined effect on dynamic‐ and thermomechanical properties in ternary system (thermoplastic polyurethane as matrix) is highlighted. Wrapping of rrP3HT on carbon nanotube (CNT) makes the hexyl side chains thermally nonequivalent and composites more stable. Dynamic‐ and thermomechanical analysis ascertained the miscibility (single T_g = ?40°C), large mechanical reinforcement, and improved storage modulus of nanocomposites in the presence of CNT compared to its blends. Two breaks at ～ ?100 and ～ ?40°C for TPU‐P3HT composites (PHs) and TPU‐P3HT‐MWCNT composites (PHCs) in the loss modulus vs. temperature plot indicates two different types of transitions in P3HT chains. Dimensional stability by expansion probe technique measures low coefficient of thermal expansion of PHCs compared to its blends. Softening property by penetration probe technique suggests that 2.5 wt % loading of P3HT exhibits lowest degree of penetration compared to other nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of donor-acceptor type 4,4′-bis(2,1,3-benzothiadiazole)-based copolymers

A series of novel donor-acceptor type polymers based on 4,4′-bis(2,1,3-benzothiadiazole) were synthesized and characterized. Two soluble regioregular tail-to-tail and head-to-head coupled polymers, poly[7,7′-bis(3-octyl-2-thienyl)-4,4′-bis(2,1,3-benzothiadiazole)] poly[3TBB3T], and poly[7,7′-bis(4-octyl-2-thienyl)-4,4′-bis(2,1,3-benzothiadiazole)] poly[4TBB4T] were synthesized by FeCl₃-mediated oxidative polymerization. To further decrease the band gap of the polymers, vinylene spacers were incorporated into the polymer backbone by Stille coupling of the corresponding monomers and (E)-1,2-bis(tributylstannyl)ethene. A crystal structure of a monomer analog shows near planar arrangement of the aromatic units in the solid state. The optical properties of the monomers and polymers were investigated by steady-state absorption and photoluminescence spectroscopy. Cyclic voltammetry measurements indicate that the polymers could be employed as acceptor materials in polymer-polymer bulk heterojunction solar cells due to their low LUMO energy of about −4.0 eV. A maximum photovoltaic power conversion efficiency of about 0.3% was observed for a 1:1 blend of regioregular poly(3-hexylthiophene) (rr-P3HT) and poly[4TBB4T] and the origin of the moderate efficiency is discussed by interpreting the device current-voltage characteristics, external quantum efficiency and incident light intensity dependence of the power conversion efficiency.     

Study of chain sequence in the controlled radical telomerization of vinyl acetate with Co(acac)2 catalyst in bulk

A series of porphyrin-containing polymers with triazole rings as linkers have been successfully synthesized by click polymerization. The polycycloadditions of porphyrin-containing dialkyne 1 and 1,4-diazidobenzene 2 were initiated either by simple heating or by Cu(I)-catalyst, affording polymers P1-P8 with relatively high molecular weight. The polymerization process was monitored by gel permeation chromatography analysis. The polymer prepared by thermally initiated click polymerization has unimodal molecular weight distribution and moderate polydispersity index after prolonging reaction time to 170?h. Compared with the metal-free click polymerization, the rate of molecular weight growth in Cu(I)-catalyzed click polymerization declined, leading to relatively low molecular weight of the resulting polymer. The as-synthesized polymers are soluble in common organic solvents and stable at a temperature up to 350?°C. The photophysical properties of the porphyrin monomer and the polymer were investigated by UV?Cvis and fluorescence spectroscopy. This approach offers practical advantages over other synthetic methods used to prepare main-chain porphyrin-containing polymers with regard to the absence of byproducts generated during the polymerization reaction.     

Regioregular poly(3-alkylthiophene) conducting block copolymers

Regioregular poly(3-alkylthiophenes) (PATs) represent an important class of polymers that are environmentally stable and display high electrical conductivity. Despite their excellent electrical properties, PATs do not exhibit very good mechanical and processing properties. This issue is addressed here by integrating poly(3-alkylthiophene) in copolymer structures with various polymer blocks that display better mechanical properties, leading to a variety of polymeric materials with desired properties. We describe a new method for the synthesis of poly(3-alkylthiophene) block copolymers using vinyl terminated regioregular poly(3-alkylthiophene) as precursors via atom transfer radical polymerization (ATRP).     

Self-assembly of conjugated oligomers and polymers at the interface: structure and properties

In this review, we give a brief account on the recent scanning tunneling microscopy investigation of interfacial structures and properties of π-conjugated semiconducting oligomers and polymers, either at the solid-air (including solid-vacuum) or at the solid-liquid interface. The structural aspects of the self-assembly of both oligomers and polymers are highlighted. Conjugated oligomers can form well ordered supramolecular assemblies either at the air-solid or liquid-solid interface, thanks to the relatively high mobility and structural uniformity in comparison with polymers. The backbone structure, substitution of side chains and functional groups can affect the assembling behavior significantly, which offers the opportunity to tune the supramolecular structure of these conjugated oligomers at the interface. For conjugated polymers, the large molecular weight limits the mobility on the surface and the distribution in size also prevents the formation of long range ordered supramolecular assembly. The submolecular resolution obtained on the assembling monolayers enables a detailed investigation of the chain folding at the interface, both the structural details and the effect on electronic properties. Besides the ability in studying the assembling structures at the interfaces, STM also provides a reasonable way to evaluate the distribution of the molecular weight of conjugated polymers by statistic of the contour length of the adsorbed polymer chains. Both conjugated oligomers and polymers can form composite assemblies with other materials. The ordered assembly of oligomers can act as a template to controllably disperse other molecules such as coronene or fullerene. These investigations open a new avenue to fine tune the assembling structure at the interface and in turn the properties of the composite materials. To summarize scanning tunneling microscopy has demonstrated its surprising ability in the investigation of the assembling structures and properties of conjugated oligomers and polymers. The information obtained could benefit the understanding of the elements affecting the film morphology and helps the optimization of device performance.     

Polymer structures and properties of new heat resistant films and fibers

Commercial films, elastomers, and fibers have valuable in-use properties below 300°C. Astronautic requirements, however, may evaentually call for materials that withstand 500 hrs at 300°C or 100 hrs at 500°C while fully retaining their useful properties. The most significant advances in the synthesis and preparation of heat resistant polymer have been made since 1959 with new synthetic methods such as interfacial polymerization, cyclopolymerization, and intramolecular polymer post-cyclopolymerization, and intramolecular olymer post-cyclization reactions. It is the purpose of this paper to discuss the structural relationships among those heat resistant, orgainc polymers that were reported to give strong films and fibers. Those heat resistant polymers, which have not yet been fabricated into films and fibers are not included in this review.     

The further understanding of chain topology effect on the properties of single polymer in good solvent: Special behaviors of single tadpole chain

Chain topology strongly affects the static and dynamic properties of polymer melts and polymers in dilute solution. For different chain architectures, such as ring and linear polymers, the molecular size and the diffusion behavior are different. To further understand the chain topology effect on the static and dynamic properties of polymers, we focus on the tadpole polymer which consists of a cyclic chain attached with one or more linear tails. It is found that both the number and the length of linear tails play important roles on the properties of the tadpole polymers in dilute solution. For the tadpole polymers with fixed linear tail length and number, with increasing the degree of polymerization of tadpole polymers, a transition from linear-like to ring-like behavior is observed for both the static and dynamic properties. By studying the radii of gyration for different chains, we define a ratio of the number of monomers in linear tails (N_tail) to the total degree of polymerization (N), and found that when the ratio N_tail/N is more than about 0.73, tadpole chains behave as linear chains, while, when N_tail/N is less than about 0.29, they behave as ring chains. This result will be helpful in further understanding of the chain topology dependence on the static and dynamic properties of polymer in dilute solution. Furthermore, the tadpole polymers behave as what Zimm theory expected before they deviate from the linear-like regime, or after they reach the ring-like regime, however, in the intermediate regime, the behavior of tadpole polymer does not show what Zimm model expected.     

Synthesis of functionalizable derivatives of 3,4‐ethylenedioxythiophene and their solid‐state polymerizations

Four polythiophenes based on poly(3,4‐ethylenedioxythiophene) (PEDOT) framework have been successfully prepared by the facile thermal activated solid‐state polymerization (SSP) process from their corresponding dibromothiophene derivatives, which were efficiently obtained using our improved methodology. Rates of polymerizations of these precursors were varied and most of the processes were incomplete under the reaction condition chosen for the synthesis. Raising the reaction temperature of the SSP further advanced the polymerization progress and improved the conductive properties of the polymer. The polymer of 3,4‐ethylenedioxythiophene‐methanol (EDTM) and its two related derivatives with functionalizable groups were prepared for the first time by the SSP method. The process and these new SSP‐derived polymers could help solving the fabrication difficulty and expand the scope of their applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42233.     

Graft polymers with macromonomers. I. Synthesis from methacrylate-terminated polystyrene

Pure graft polymers having uniform molecular weight polystyrene side chains were prepared by free radical copolymerization of methacrylate-terminated polystyrene macromonomers (MA-CROMER) with ethyl acrylate, butyl acrylate, or other suitable monomers. The MACROMER monomer was synthesized by living anionic polymerization under conditions that led to very narrow molecular weight distributions. Very effective end capping produced a material that was highly monofunctional. The graft copolymers were prepared by several techniques such as free radical solution polymerization, by aqueous suspension polymerization which produced beads, or by emulsion reactions which yielded stable latices. Polymerizations were reproducible. High conversion of the MACROMER monomer into pure graft polymers was achieved, and the product was contaminated with only a little homopolymer. The milled and molded phase-separated graft polymers had optical clarity and physical properties characteristic of polystyrene-reinforced triblock polymers. Compositions of 20-30% polystyrene were thermoplastic elastomers with good recovery. When polystyrene contents were increased, the graft products were strong, flexible thermoplastics with well defined yield strengths and increased permanent set. Copolymers of polystyrene macromers with acrylonitrile or vinyl chloride produced transparent polystyrene homopolymer-free graft polymer products having improved processing over polyacrylonitrile or poly(vinyl chloride) homopolymers.     

Surface functionalization by smart coatings: Stimuli-responsive binary polymer brushes

Heterogeneous binary polymer brushes consist of an assembly of polymer chains of two incompatible polymers that are attached by one end to the surface with sufficient grafting density. They have been investigated experimentally only for a short time. Those brushes can be used in the form of ultrathin polymeric layers as a versatile tool for surface engineering to tune physico-chemical surface characteristics as wettability, surface charge, chemical composition or morphology, and furthermore to create switchable and responsive surface properties. For the fabrication of these layers “grafting-from” (as radical polymerization at the interface) and “grafting-to” (as tethering of the polymer chains from solution) methods were developed and investigated in detail.     

Synthesis and characterization of poly(3‐hexylthiophene)–poly(3‐hexyloxythiophene) random copolymers with tunable band gap via Grignard metathesis polymerization

A series of 3‐substituted polythiophene copolymers having different side chain arrangements of hexyl and hexyloxy groups has been synthesized via the Grignard metathesis (GRIM) method and systematically studied. Despite differences in monomer reactivity ratios for the nickel‐catalyzed chain transfer polymerization, random sequences of hexyl‐ and hexyloxy‐substituted polythiophenes with different monomer compositions and adjustable band‐gap energies can be synthesized according to their respective comonomer feed ratio, as evidenced from NMR, UV, electrochemical measurements, and computational calculations. Structural characterization from X‐ray diffraction measurements reveals that the flexible hexyloxy side chains of the monomer significantly affect the crystallinity and molecular packing of the random copolymers. This study shows potential for synthesizing random copolymers with different monomer reactivities via the GRIM method for future optoelectronic applications. © 2014 Society of Chemical Industry