Novel Luminescent Electrospun Fibers Prepared From Conjugated Rod–Coil Block Copolymer of Poly[2,7‐(9,9‐dihexylfluorene)]‐block‐Poly(methyl methacrylate)

Novel luminescent electrospun (ES) fibers have been successfully prepared from a conjugated rod–coil block copolymer, poly[2,7‐(9,9‐dihexylfluorene)]‐block‐poly(methyl methacrylate) (PF‐b‐PMMA) using a single‐capillary spinneret. Experiment results indicate that PF‐b‐PMMA ES fibers prepared from THF, THF/DMF (50/50), and DMF contain PF block aggregated structures of dot‐like (5–10 nm), line‐like (10–20 nm), and ellipse‐like structure (25–50 nm), respectively. Such variation of aggregation size leads to a red‐shift of the absorption or luminescence spectra. In addition, the fiber diameters decrease upon enhancing the DMF content. The present study demonstrates that blue light‐emitting ES fibers are successfully prepared from conjugated rod–coil diblock copolymers and their aggregate morphology and photophysical properties could be tuned through use of selective solvent.

     

Dimensional Control of Block Copolymer Nanofibers with a π‐Conjugated Core: Crystallization‐Driven Solution Self‐Assembly of Amphiphilic Poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine)

With the aim of accessing colloidally stable, fiberlike, π‐conjugated nanostructures of controlled length, we have studied the solution self‐assembly of two asymmetric crystalline–coil, regioregular poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine) (P3HT‐b‐P2VP) diblock copolymers, P3HT₂₃‐b‐P2VP₁₁₅ (block ratio=1:5) and P3HT₄₄‐b‐P2VP₁₁₅ (block ratio=ca. 1:3). The self‐assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu‐catalyzed azide–alkyne cycloaddition reactions of azide‐terminated P2VP and alkyne end‐functionalized P3HT homopolymers. When the block copolymers were self‐assembled in a solution of a 50 % (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP‐selective alcoholic solvent (MeOH<iPrOH<nBuOH). Very long (>3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain‐extended P3HT blocks. The crystallinity and π‐conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide‐angle X‐ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT₂₃‐b‐P2VP₁₁₅ resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT₂₃‐b‐P2VP₁₁₅ unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L_w/L_n <1.11) and lengths from about 100‐300 nm, that were dependent on the unimer‐to‐seed micelle ratio.     

聚(3-己基噻吩)作为光谱增感层在有机太阳电池光谱响应增强中的应用

报道了利用聚(3-己基噻吩)(P3HT)作为前置缓冲层来弥补(4,8-双-(2-乙基己氧基)-苯并[1,2-b:4,5-b']二噻吩)-(4-氟代噻并[3,4-b]噻吩(PBDT-TT-F):[6,6]-苯基-C₆₁-丁酸甲酯(PC₆₁BM)共混体相异质结(BHJ)电池对450-600 nm处光谱响应不足的新的器件结构设计思路. 光谱带隙为1.8 eV的PBDT-TT-F 在550-700 nm处有很强的光谱吸收, 在有机太阳电池器件上有很好的应用潜能. 但其在350-550 nm处的吸收不强, 影响了器件对太阳光谱的利用效率. 与此相比, P3HT薄膜的光谱吸收主要在450-600 nm范围内, 同PBDT-TT-F 形成良好的互补关系. 新设计的器件外量子效率(EQE)研究结果表明, 利用P3HT 作为前置缓冲层可以与PBDT-TT-F:PC₆₁BM薄膜中的PC₆₁BM形成平面异质结, 从而拓展了器件在450-600 nm处的光谱响应范围,实现光谱增感作用. 优化P3HT的厚度为20 nm左右, 器件对外输出的短路光电流密度从11.42 mA·cm^-2提高到12.15 mA·cm^-2, 达到了6.3%的提升.     

Poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene): Synthesis,microphase separation,thin film transistors,and photovoltaic applications

We report the synthesis, characterization, microphase separation, field‐effect charge transport, and photovoltaic properties of regioregular poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene) (P3HT‐b‐P3cHT). Two compositions of P3HT‐b‐P3cHT (HcH63 and HcH77) were synthesized with weight‐average molecular weights of 155,500 and 210,800 and polydispersity indices of 1.45 and 1.57, respectively. Solvent‐casted HcH77 was found to self‐assemble into nanowires with a width of 12.5 ± 0.9 nm and aspect ratios of 50–120, as observed by TEM imaging. HcH77 and HcH63 annealed 280 °C were observed by small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) to be microphase‐separated with characteristic length scales of 17.0–21.7 nm. The microphase‐separated domains were shown to be crystalline with interlayer backbone (100) d‐spacings of 1.69 and 1.40 nm, which correspond to the P3HT and P3cHT blocks, respectively. Field‐effect transistors fabricated from P3HT‐b‐P3cHT thin films showed a mobility of holes (0.0019 cm²/Vs) which is independent of thermal annealing. Bulk heterojunction solar cells based on HcH77/fullerene (PC₇₁BM) blend thin films had a maximum power conversion efficiency of 2.45% under 100 mW/cm² AM1.5 solar illumination in air. These results demonstrate that all‐conjugated block copolymers are suitable semiconductors for applications in field‐effect transistors and bulk heterojunction solar cells. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 614–626, 2010     

Morphology and pH Sensing Characteristics of New Luminescent Electrospun Fibers Prepared from Poly(phenylquinoline)‐block‐Polystyrene/Polystyrene Blends

New luminescent electrospun (ES) fibers for pH‐tunable colorimetric sensors were prepared from binary blends of poly(phenylquinoline)‐block‐polystyrene (PPQ‐b‐PS)/polystyrene (PS) with a single‐capillary spinneret. The PPQ‐b‐PS aggregated domain sizes in the ES fibers prepared from dichloromethane (CH₂Cl₂), chlorobenzene (CB) and chloroform (CHCl₃) were 1.5 ± 0.5, 2.2 ± 0.4 and 4.1 ± 1.1 µm, respectively. Such variation on the aggregation size led to the red‐shifting photoluminescence spectra changing from green, to yellow, and orange. ES fibers prepared from CH₂Cl₂ exhibited pH‐tunable photoluminescence and the emission maximum varied from 532 to 560 nm as the pH value changed from 7 to 1. The study demonstrated that the ES fibers prepared could have potential applications for sensory devices.

     

Synthesis of all‐conjugated poly(3‐hexylthiophene)‐block‐ poly(3‐(4′‐(3″,7″‐dimethyloctyloxy)‐3′‐pyridinyl)thiophene) and its blend for photovoltaic applications

New all‐conjugated block copolythiophene, poly(3‐hexylthiophene)‐block‐poly(3‐(4′‐(3″,7″‐dimethyloctyloxy)‐3′‐pyridinyl)thiophene) (P3HT‐b‐P3PyT) was successfully prepared by Grignard metathesis polymerization. The supramolecular interaction between [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) and P3PyT was proposed to control the aggregated size of PCBM and long‐term thermal stability of the photovoltaic cell, as evidenced by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and optical microscopy. The effect of different solvents on the electronic and optoelectronic properties was studied, including chloroform (CL), dichlorobenzene (DCB), and mixed solvent of CL/DCB. The optimized bulk heterojunction solar cell devices using the P3HT‐b‐P3PyT/PCBM blend showed a power conversion efficiency of 2.12%, comparable to that of P3HT/PCBM device despite the fact that former had a lower crystallinity or absorption coefficient. Furthermore, P3HT‐b‐P3PyT could be also used as a surfactant to enhance the long‐term thermal stability of P3HT/PCBM‐based solar cells by limiting the aggregated size of PCBM. This study represents a new supramolecular approach to design all‐conjugated block copolymers for high‐performance photovoltaic devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Synthesis and self‐assembly of diblock copolymers composed of poly(3‐hexylthiophene) and poly(fluorooctyl methacrylate) segments

Regioregular poly(3‐hexylthiophene)‐b‐poly(1H,1H‐dihydro perfluorooctyl methacrylate) (P3HT‐b‐PFOMA) diblock copolymers were synthesized by atom transfer radical polymerization of fluorooctyl methacrylate using bromoester terminated poly(3‐hexylthiophene) macroinitiators in order to investigate their morphological properties. The P3HT macroinitiator was previously prepared by chemical modification of hydroxy terminated P3HT. The block copolymers were well characterized by ¹H NMR spectroscopy and gel permeation chromatography. Transmission electron microscopy was used to investigate the nanostructured morphology of the diblock copolymers. The block copolymers are able to undergo microphase separation and self‐assemble into well‐defined and organized nanofibrillar‐like micellar morphology. The development of the morphology of P3HT‐b‐PFOMA block copolymers was investigated after annealing in solvent vapor and also in supercritical CO₂. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

电活性和生物活性多巴-胰岛素样生长因子-1@聚(乙交酯-丙交酯)/聚(3-己基噻吩)静电纺丝纤维的制备及神经组织工程应用

理想型神经修复材料应具备与正常神经相似的导电性、仿生细胞外基质结构以及释放特定的生长因子等性能。 本研究将不同质量分数(0、3%、5%、10%)的聚(3-己基噻吩)(P3HT)加入到聚(乙交酯-丙交酯)(PLGA)中,采用静电纺丝工艺,制备了具有电活性和仿生结构的复合纤维。 利用酪氨酸羟化酶,将不同质量浓度(10、50、100 ng/mL)的含多巴接头的胰岛素样生长因子-1(DOPA-IGF-1)绑定在纤维表面,实现生长因子长效稳定的作用。 通过扫描电子显微镜、接触角表征了纤维直径、分布以及表面亲疏水性。 利用细胞培养、荧光染色实验评估了纤维在体外的生物相容性和生物活性。 结果表明,该电活性纤维能有效促进大鼠肾上腺嗜铬细胞瘤细胞(PC12)增殖,其中,PLGA/P3HT-5%纤维表现出更好的细胞响应性。 结合DOPA-IGF-1质量浓度为10 ng/mL的纤维更利于PC12细胞的黏附、生长。 兼具电活性和生物活性的纳米纤维DOPA-IGF-1@PLGA/P3HT在神经组织修复领域具有潜在的应用价值。     

Synthesis of Poly(3‐hexylthiophene) with a Narrower Polydispersity

Summary: The polymerization of 2‐bromo‐3‐hexyl‐5‐iodothiophene ( 1 ) with isopropylmagnesium chloride and Ni(dppp)Cl₂ was quenched with 5 M hydrochloric acid instead of water to yield head‐to‐tail poly(3‐hexylthiophene) (HT‐P3HT) with a very low polydispersity. The of the polymer was controlled by the feed ratio of 1 to Ni(dppp)Cl₂. Quenching with 5 M hydrochloric acid seemed to promote protonolysis of HT‐P3HT‐Ni complexes before the coupling reaction between HT‐P3HT.

GPC profiles of HT‐P3HT obtained after quenching with water and 5 M hydrochloric acid, respectively.     

Preparation,Characterization and Electromagnetic Shielding Effectiveness of Conductive Polythiophene/Poly(ethylene terephthalate) Composite Fibers

Conductive polythiophene (PTh)/poly(ethylene terephthalate) (PET) composite fibers were prepared by polymerization of thiophene in the presence of PET fibers in acetonitrile medium using FeCl₃. The effects of polymerization conditions such as oxidant/monomer mol ratio and polymerization temperature and time on PTh content and surface electrical resistivity of PTh/PET composite fiber were investigated in detail. It was observed that the usage of preswelled PET fibers in dichloromethane increased the PTh content and decreased surface resistivity of composite fiber. Composite fiber having the highest PTh content (5.7%) and the lowest surface resistivity (80 kΩ) was obtained at 20°C with 1.25 M FeCl₃ and 0.42 M thiophene concentrations. The washing effects of laundering detergent and dry cleaning liquid on surface resistivity of composite fibers were investigated. The electromagnetic shielding effectiveness (EMSE) and relative shielding efficiency by absorption and reflection of composite fibers were measured in the radio and microwave frequency range. The results show that the EMSE values decreased with increasing frequency from radio waves to microwaves with an attenuation of 21 dB to 4 dB.     

How to measure absolute P3HT crystallinity via 13C CPMAS NMR

We outline the details of acquiring quantitative ¹³C cross‐polarization magic angle spinning (CPMAS) nuclear magnetic resonance on the most ubiquitous polymer for organic electronic applications, poly(3‐hexylthiophene) (P3HT), despite other groups' claims that CPMAS of P3HT is strictly nonquantitative. We lay out the optimal experimental conditions for measuring crystallinity in P3HT, which is a parameter that has proven to be critical in the electrical performance of P3HT‐containing organic photovoltaics but remains difficult to measure by scattering/diffraction and optical methods despite considerable efforts. Herein, we overview the spectral acquisition conditions of the two P3HT films with different crystallinities (0.47 and 0.55) and point out that because of the chemical similarity of P3HT to other alkyl side chain, highly conjugated main chain polymers, our protocol could straightforwardly be extended to other organic electronic materials. Variable temperature ¹H NMR results are shown as well, which (i) yield insight into the molecular dynamics of P3HT, (ii) add context for spectral editing techniques as applied to quantifying crystallinity, and (iii) show why T_1ρ^H, the ¹H spin–lattice relaxation time in the rotating frame, is a more optimal relaxation filter for distinguishing between crystalline and noncrystalline phases of highly conjugated alkyl side‐chain polymers than other relaxation times such as the ¹H spin–spin relaxation time, T₂^H, and the spin–lattice relaxation time in the toggling frame, T_1xz^H. A 7 ms T_1ρ^H spin lock filter, prior to CPMAS, allows for spectroscopic separation of crystalline and noncrystalline ¹³C nuclear magnetic resonance signals. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Synthesis,morphology, and field‐effect transistor characteristics of new crystalline–crystalline diblock copolymers of poly(3‐hexylthiophene‐block‐steryl acrylate)

We report the synthesis, morphology, and charge‐transporting characteristics of new crystalline–crystalline diblock copolymers, poly(3‐hexylthiophene‐block‐stearyl acrylate) (P3HT‐b‐PSA). Three different diblock copolymers, P1 , P2 , and P3 , with P3HT/PSA polymerization degree block ratios of 60/26, 60/50, and 60/360, respectively, were prepared for investigating the morphology‐property relationship and the dependence of optoelectronic properties on the block copolymer structure. Small‐ and wide‐angle X‐ray scattering indicated the presence of both P3HT and PSA crystalline domains and the presence of microphase separation among blocks. The transmission electron microscopy and atomic force microscopy results revealed that the diblock copolymers cast from chlorobenzene, tended to form needle‐like morphologies. The field‐effect mobilities of the diblock copolymers deposited on untreated SiO₂ substrates, decreased with increasing PSA block length. In a sharp contrast, the mobilities enhanced with increasing PSA content when the P3HT‐b‐PSA was deposited on phenyltrichlorosilane (PTS)‐treated substrates. The copolymers with a 60/360 P3HT/PSA ratio showed a good mobility of 4 × 10^?3 cm² V^?1 s^?1 and a high on/off ratio of 7 × 10⁶ on PTS‐treated substrates. This study highlighted the importance of the block ratio, the substrate and self‐assembly structures on the charge transport characteristics of the crystalline–crystalline conjugated diblock copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

One‐pot synthesis of conjugated poly(3‐hexylthiophene)‐b‐poly(phenyl isocyanide) hybrid rod–rod block copolymers and its self‐assembling properties

In this article, the synthesis of a series of conjugated rod–rod block copolymers based on poly(3‐hexylthiophene) (P3HT) and poly(phenyl isocyanide) (PPI) building blocks in a single pot is presented. Ni‐catalyzed Grignard metathesis polymerization of 2,5‐dibromo‐3‐hexylthiophene and subsequent addition of 4‐isocyanobenzoyl‐2‐aminoisobutyric acid decyl ester in the presence of Ni(dppp)Cl₂ as a single catalyst afford P3HT‐b‐PPI with tunable molecular weights and compositions. In solid state, microphase separation occurred as differential scanning calorimetric analysis of P3HT‐b‐PPI revealed two glass transition temperatures. In solutions, the copolymers can self‐assemble into spherical aggregates with P3HT core and PPI shell in tetrahydrofuran and exhibit amorphous state in CHCl₃. However, atomic force microscopy revealed that the block copolymers self‐assemble into nanofibrils on the substrate. These unique features warrant the resultant conjugated rod–rod copolymers' potential study in organic photovoltaic and other electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2939–2947     

Effect of Device Fabrication Conditions on Photovoltaic Performance of Polymer Solar Cells Based on Poly(3‐hexylthiophene) and Indene‐C70 Bisadduct

Effect of the device fabrication conditions on photovoltaic performance of the polymer solar cells based on poly(3‐hexylthiophene) (P3HT) as donor and indene‐C₇₀ bisadduct (IC₇₀BA) as acceptor was studied systematically. The device fabrication conditions we studied include pre‐thermal annealing temperature, active layer thickness, and the P3HT:IC₇₀BA weight ratios. For devices with a 188‐nm‐thick active layer of P3HT:IC₇₀BA (1:1, w:w) blend film and pre‐thermal annealing at 150°C for 10 min, maximum power conversion efficiency (PCE) reached 5.82% with V_oc of 0.81 V, I_sc of 11.37 mA/cm², and FF of 64.0% under the illumination of AM1.5G, 100 mW/cm².     

Synthesis and Characterization of Poly(p-phenylene benzobisoxazole)/Poly(pyridobisimidazole) Block Copolymers

Poly(p-phenylene benzobisoxazole)/poly(pyridobisimidazole) block copolymers (PBO-b-PIPD) were prepared by introducing poly(pyridobisimidazole) (PIPD) moieties into the main chains of poly(p-phenylene benzobisoxazole) (PBO) in order to enhance its photostability. PBO and copolymer fibers were directly prepared from the polymerization solutions by dry-jet wet-spinning. Chemical structures and molecular chains arrangement of the block copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, solid-state ¹³C-NMR and wide angle X-ray diffraction (WAXD). Thermal stability of the copolymers was investigated by thermogravimetric analysis (TGA) in nitrogen. Thin films of PBO and copolymers were cast from methanesulfonic acid (MSA) solutions. Both the films and fibers were exposed to UV light to determine their photostability. Changes in the chemical structures and surface morphologies of the films were characterized by FTIR spectra and scanning electronic microscopy (SEM), respectively. After UV light exposure, the retention of strength for copolymer fibers is improved compared to PBO fibers. The results revealed that copolymers suffered less photodegradation in comparison with homopolymer. The mechanism for the improved photostability of the copolymers was discussed.     

聚3-甲基噻吩及聚3-己基噻吩修饰钛酸盐纳米管的光电化学性能研究

采用水热法制备了钛酸盐纳米管, 并将钛酸盐纳米管制备成纳米结构电极进行光电化学研究. 钛酸盐纳米管产生阳极光电流, 具有n-型半导体特性. 结果表明, 聚3-甲基噻吩[poly(3-methylthiophene), PMeT]、聚3-己基噻吩[poly(3-hexylthiophene), P3HT]修饰钛酸盐纳米管后产生的光电流均较纯钛酸盐纳米管的光电流高, 且使产生光电流的波长向长波区移动. 钛酸盐纳米管/PMeT、钛酸盐纳米管/P3HT的光电转换效率分别达11.40%, 0.91%(未校正光子损失). 钛酸盐纳米管/PMeT的光电转换效率较钛酸盐纳米管/P3HT的光电转换效率高10.5%. 钛酸盐纳米管/PMeT、钛酸盐纳米管/P3HT中存在p-n异质结, 在一定条件下p-n异质结的存在有利于光生电子/空穴的分离.     

Enhanced electrochromic properties of hybrid P3HT/WO3 composites with multiple colorations

We investigated the enhanced electrochemical and electrochromic properties of P3HT (poly 3-hexylthiophene)/WO₃ composites. Nanoporous WO₃ layers were prepared using electrochemical anodization. P3HT was spin coated on these layers to obtain hybrid P3HT/WO₃ composites. After annealing at 300 °C for 1 h, the monoclinic phase of the WO₃ layer and self-organized lamella structure of P3HT were examined. The P3HT/WO₃ composites exhibited enhanced current densities and three different reflective colors with a combination of pristine P3HT and WO₃ during the redox reaction. Furthermore, the composites exhibited faster switching speeds compared with WO₃ layers, which might be attributed to the easy Li⁺ insertion/extraction resulting from the incorporation of P3HT.     

Phase structure of electrospun poly(trimethylene terephthalate) composite nanofibers containing carbon nanotubes

Nanofibrous composite mats were prepared by electrospinning of poly(trimethylene terephthalate), PTT, with multi-walled carbon nanotubes (PTT/MWCNT). Trifluoroacetic acid (TFA) and methylene chloride (MC) with volume ratio of 50/50 is a good solvent for PTT and was used as the electrospining solution. Scanning electron microscopy was used to investigate the morphology of electrospun (ES) nanofibers with 0, 0.2, 1.0, or 2.0 wt% of MWCNTs. Crystal structure of the ES mats was determined from wide angle X-ray diffraction. Thermal properties were investigated using heat capacity measurements from differential scanning calorimetry (DSC) using the three-runs method for baseline correction, heat flow amplitude calibration, and sample heat capacity determination. A model comprising three phases, a mobile amorphous fraction (MAF), rigid amorphous fraction (RAF), and crystalline fraction (C), is appropriate for ES PTT/MWCNT fibers. The phase fractions, W _i (for i = RAF, MAF or C) were determined by DSC. Crystallinity decreases very slightly with the amount of MWCNT. At the same time, a large increase in RAF was observed: W _RAF of PTT fiber with 2% MWCNT is twice that of neat PTT fiber. The addition of MWCNTs enhanced the PTT chain alignment and increased RAF as a result. Changes of vibrational band absorbance at 1358 and 1385 cm⁻¹, corresponding to characteristic groups, were obtained with infrared spectroscopy. The increased absorbance at 1358 cm⁻¹ and decreased absorbance at 1385 cm⁻¹, with the addition of MWCNTs, strongly supports the three-phase model for ES PTT/MWCNT nanocomposites.     

Structural transitions of nanocrystalline domains in regioregular poly(3‐hexyl thiophene) thin films

The effects of solution processing and thermal annealing on thin film morphology and crystalline structures of regioregular poly(3‐hexyl thiophene) (RR P3HT) are studied in terms of molecular weight (M_w). Using grazing‐incidence X‐ray diffraction, π‐conjugated planes in drop‐cast films from chloroform solutions are found to be preferentially oriented parallel to the substrates regardless of M_w. However, the mesoscale nanocrystalline morphology of the drop‐cast films is significantly affected by M_w, exhibiting a distinctive morphological transition from short nanorods to long nanofibrils above a critical number‐averaged M_w (～ 3.6 kDa). This is probably due to the change in a conformation change from an extended‐chain to a folded‐chain, as M_w of RR P3HT increases. In contrast, spin‐casting of high M_w RR P3HT produces less ordered films with a lower crystallinity and mixed parallel/perpendicular orientations of π‐conjugated planes. The crystallinity and parallel π‐conjugated orientation of RR P3HT in spin‐cast films could be improved by thermal treatments at high‐temperatures either (1) above the glass transition temperature or (2) above the melting temperature of RR 3PHT followed by recrystallization upon cooling under vacuum. However, the charge mobility of the spin‐cast films for a field‐effect transistor application is still lower than that of the drop‐cast films. This would be attributed to the chain oxidation and the development of distinct grain boundaries between RR P3HT nanofibrils during the thermal treatments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1303–1312, 2007     

Base Hydrolysis of Poly(Ethylene Terephthalate) in Methanolic and Aqueous Solutions

Abstract

Hydrolysis of poly(ethylene terephthalate) fibers (intrinsic viscosity: 0.819 dL/g) using methanolic sodium methoxide was compared to that using aqueous sodium hydroxide. Weight and tenacity loss occurred more rapidly with methanolic NaOCH₃. After the methanolic NaOCH₃ treatment, the surface appeared far rougher, much of which was due to low molecular weight material present on the fibers. Intrinsic viscosity measurements indicated virtually no difference between the two treatments in the small amount of chain cleavage obtained at a given weight loss. Fiber density increased after the reaction with methanolic NaOCH₃, probably due to the presence of the methyl ester end groups formed during the ester interchange reaction, while fiber density was essentially unaffected by treatment in aqueous NaOH. Density decreased after the methanolic NaOCH₃-treated fiber was hydrolyzed with aqueous NaOH. Thermal analysis revealed a small increase in the melting temperature after methanolic NaOCH₃ treatment. The shoulder present in the melting region of this sample was markedly affected by chloroform extraction of low molecular weight products resulting from the reaction. While hydrolysis using methanolic NaOCH₃ was more severe than that using aqueous NaOH, both reactions appeared to be confined to the fiber surface.