Electroluminescence and photovoltaic properties of poly(p‐phenylene vinylene) derivatives with dendritic pendants

A copolymer of dendronized poly(p‐phenylene vinylene) (PPV), poly{2‐[3′,5′‐bis (2′‐ethylhexyloxy) bnenzyloxy]‐1,4‐phenylene vinylene}‐co‐poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene vinylene] (BE‐co‐MEH–PPV), was synthesized with the Gilch route to improve the electroluminescence and photovoltaic properties of the dendronized PPV homopolymer. The polymer was characterized by ultraviolet–visible absorption spectroscopy, photoluminescence spectroscopy, and electrochemical cyclic voltammetry and compared with the homopolymers poly{2‐[3′, 5′‐bis(2‐ethylhexyloxy) benzyloxy‐1,4‐phenylene vinylene} (BE–PPV) and poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH–PPV). Polymer light‐emitting diodes based on the polymers with the configuration of indium tin oxide (ITO)/poly(3,4‐ethylene dioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS)/polymer/Ca/Al were fabricated. The electroluminescence efficiency of BE‐co‐MEH–PPV reached 1.64 cd/A, which was much higher than that of BE–PPV (0.68 cd/A) and a little higher than that of MEH–PPV (1.59 cd/A). Photovoltaic properties of the polymer were studied with the device configuration of ITO/PEDOT : PSS/polymer : [6,6J‐phenyl‐C₆₁‐butyric acid methyl ester] (PCBM)/Mg/Al. The power conversion efficiency of the device based on the blend of BE‐co‐MEH–PPV and PCBM with a weight ratio of 1 : 3 reached 1.41% under the illumination of air mass 1.5 (AM1.5) (80 mW/cm²), and this was an improvement in comparison with 0.24% for BE–PPV and 1.32% for MEH–PPV under the same experimental conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of novel phenyl‐substituted poly(p‐phenylene vinylene) derivatives

Two novel phenyl‐substituted poly(p‐phenylene vinylene) derivatives, poly{2‐[3′,4′‐(2″‐ethylhexyloxy)(3″,7″‐dimethyloctyloxy)benzene]‐1,4‐phenylenevinylene} (EDP‐PPV) and poly{2‐[3′,4′‐(2″‐ethylhexyloxy)(3″,7″‐dimethyloctyloxy)benzene]‐5‐methoxy‐1,4‐phenylenevinylene} (EDMP‐PPV), and their copolymer, poly{2‐[3′,4′‐(2″‐ethylhexyloxy)(3″,7″‐dimethyloctyloxy)benzene]‐1,4‐phenylene‐vinylene‐co‐2‐[3′,4′‐(2″‐ethylhexyloxy)(3″,7″‐dimethyloctyloxy)benzene]‐5‐methoxy‐1,4‐phenylenevinylene} (EDP‐co‐EDMP‐PPV; 4:1, 1:1, and 1:4), were successfully synthesized according to the Gilch route. The structures and properties of the monomers and the resulting conjugated polymers were characterized with ¹H‐NMR, ¹³C‐NMR, elemental analysis, gel permeation chromatography, thermogravimetric analysis, ultraviolet–visible absorption spectroscopy, and photoluminescence and electroluminescence (EL) spectroscopy. The EL polymers possessed excellent solubility in common solvents and good thermal stability with a 5% weight loss temperature of more than 380°C. The weight‐average molecular weights and polydispersity indices of EDP‐PPV, EDMP‐PPV, and EDP‐co‐EDMP‐PPV were 1.40–2.58 × 10⁵, and 1.19–1.52, respectively. Double‐layer light‐emitting diodes with the configuration of indium tin oxide/polymer/tris(8‐hydroxyquinoline)aluminum/Al devices were fabricated, and EDP‐co‐EDMP‐PPV (1:1) showed the highest EL performance and exhibited a maximum luminance of 1050 cd/m² at 19.5 V. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1259–1266, 2005     

Synthesis and properties of polyether with short alternating conjugated and nonconjugated blocks containing oxadiazole units

A polyether, poly[(2,5‐dimethylene‐1,3,4‐oxadiazole)dioxy‐1,4‐phenylene‐1,2‐ethenylene‐1,4‐phenylene‐1,2‐ethenylene‐1,4‐phenylene], based on short alternating conjugated oxadiazole units, has been synthesized, which is a kind of PPV derivative that emits blue light. The resulting polymer is fairly soluble in chloroform. The synthesized polymer shows a UV–visible absorbency maximum wavelength around 310 nm in solution. The photoluminescence maximum wavelength for the resulting polymer appears around 470 nm. The polymer also exhibits good thermal stability up to 300°C under N₂ atmosphere. It is also observed that the onset temperature of thermal decomposition is as high as 355°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2682–2686, 2002     

Synthesis and characterization of highly fluorescent phenylene vinylene containing perfluorocyclobutyl (PFCB) aromatic ether polymers

4-(Trifluorovinyloxy)benzaldehyde was treated under Wittig conditions with 4-dihexyloxy-2,5-xylenebis(triphenylphosphoniumbromide) to form 1,4-bis(2′-(4-trifluorovinyloxyphenyl)ethenyl)-2,5-dihexyloxybenzene, a novel phenylene vinylene-bistrifluorovinyl ether monomer. Cyclopolymerization afforded an insoluble, non-luminescent material likely due to cross-addition reactions between phenylene vinylene olefin and trifluorovinyl ether (TFVE). However, 1,2-bis(4-formylphenoxy)hexafluorocyclobutane was polymerized with 1,4-dihexyloxy-2,5-xylenebis(triphenylphosphoniumbromide) and 1-methoxy-4-(2-ethylhexyloxy)-2,5-xylenebis(triphenylphosphoniumbromide) under Wittig conditions to yield two novel poly(perfluorocyclobutyl-co-phenylene vinylene) polymers. The polymers are of moderate molecular weight (8600-8700 M_n), show excellent thermal stability (T_d = 390-405 °C), and are readily soluble in common organic solvents. The materials are highly fluorescent in both solution and thin film with solution quantum yields of 68 and 71%.     

Effect of thermal annealing in atmosphere on photoluminescence of BTEO–PPV films

The photoluminescence (PL) spectra of poly[2,5‐bis‐(tri‐ethoxy)‐1,4‐phenylene vinylene] (BTEO–PPV) films are blue‐shifted with increasing thermal annealing temperature. It is known from the UV–vis absorption spectra that thermal annealing decreases the conjugation length of the polymer. For BTEO–PPV films, unlike with MEH–PPV films, the symmetric triethoxy side groups further block aggregation of the polymer chains. The absorption Fourier transfer infrared spectra showed that thermal annealing in atmosphere destroyed the chain structure of BTEO–PPV film by thermal oxidation to form aldehyde groups, which resulted in low PL efficiency of the annealed films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Poly(p-phenylene vinylene) derivatives with ester- and carboxy-functionalized substituents: a versatile platform towards polar functionalized conjugated polymers

A polar functionalized poly(p-phenylene vinylene) (PPV) derivative, ester containing poly(1,4-(2-(pentyloxy-5-carboxy methylester)-5-methoxyphenylene)vinylene), has been prepared via the sulfinyl precursor route. Subsequently, the carboxylic acid containing poly(1,4-(2-(5-carboxypentyloxy)-5-methoxyphenylene)vinylene) is readily obtained by the basic hydrolysis of the ester side groups. This carboxylic acid substituted polymer exhibits significantly improved optical properties as compared to previously reported similar polymers. To obtain polar functionalized PPV derivatives with more complex tailored substituents a versatile novel approach is presented based on the Mitsunobu reaction conditions via a post-polymerization functionalization of the carboxylic acid side groups. Using these reaction conditions substituents containing various ester groups, i.e. 4-nitrobenzyl, 2-nitrobenzyl, 5-(methyl)furfural and 3-N,N-dimethylamino-1-propane, have been covalently attached to the phenylene ring. Analytical data of the functionalized polymers are consistent with a quantitative functional group substitution. The results demonstrate that the employed functionalization method allows for the introduction of a large variety of polar substituents in a straightforward manner.     

Synthesis and characterization of novel soluble alternating copoly(phenylene vinylene) derivative for light‐emitting electrochemical cell

A novel alternating copolymer, poly{[2,5‐di(2‐(2‐ethoxy ethoxy)ethoxy)‐1,4‐phenylene vinylene]‐alt‐1,4‐[phenylene vinylene]}, has been synthesized through the Wittig condensation as electroluminescent material. In this copolymer, one component is phenylene vinylene with flexible oligo(ethylene oxide) side chain that facilitates ion transportation and phase miscibility between nonpolar and polar part of composite luminescent layer, and another is a rigid phenylene vinylene moiety to improve luminescent quantum efficiency and tune color. The copolymer shows good solubility and thermal stability for device fabrication compared to poly(phpeylene vinylene)(PPV). The band gap value of copolymer is between those of corresponding homopolymers, which indicates that alternating copolymerization is a suitable way to obtain luminescent polymer with desired band gap. The maximum wavelength of photoluminescence of copolymer is 539 nm (yellowish‐green). The HOMO and LUMO energy levels obtained by cyclic voltammetry measurement indicate that the electron injection ability of copolymer has been greatly improved compared with that of the PPV. A more balanced carrier injection and higher quantum efficiency are proved by electroluminescent properties of corresponding light‐emitting devices. The turn‐on voltage of LEC device (ITO/copolymer + PEO + LiClO₄/Al) is found to be 2.3 V, with current comparative to LED (ITO/copolymer/Al) at 9.5 V. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1350–1356, 2003     

Synthesis and characterization of the soluble luminescent poly[2-decyloxy-5-(4’-ethoxyphenyl)-1,4-phenylenevinylene]

Summary A new soluble luminescent poly[2-decyloxy-5-(4^′-ethoxyphenyl)-1,4-phenylene-vinylene] (DEP-PPV) is prepared by the dehydrohalogenation of 1,4-bis(bromo-methyl)-2-decyloxy-5-(4^′-ethoxyphenyl) benzene in this study. The structure and properties of the DEP-PPV are examined by ¹H NMR, FT-IR, UV/VIS, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The incorporation of a decyloxy substituent in the 2-position of phenylene ring makes the DEP-PPV soluble in organic solvents and eliminates tolan-bis-benzyl structure defects. The energy band gap of DEP-PPV in tetrahydrofuran is 2.36 eV. The PL peak of DEP-PPV solution shifts to higher wavelength as the solution concentration increases. The PL spectrum of the DEP-PPV film shows a peak at 546 nm and the one of the pristine PPV film does at 540 nm. This red shift of PL peak for the DEP-PPV as compared with that for the PPV indicates that the incorporation of a conjugated ethoxyphenyl group on the phenylene ring can increase the conjugation length of phenylenevinylene units in the DEP-PPV. With the DEP-PPV acting as a light-emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DEP-PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 530 nm, which corresponds to the yellowish-green light. The turn-on voltage of the device is about 16 V. Its maximum brightness is 46 cd/m² at a voltage of 18 V.     

Origin of the methylene bonds in poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] prepared according to Gilch's method: novel applications

Impurities containing methylene bridges between 2‐((2′‐ethylhexyl)oxy)‐5‐methoxy‐benzene molecules are inevitably formed during the synthesis of 1,4‐bis(chloromethyl)‐2‐((2′‐ethylhexyl)oxy)‐5‐methoxy‐benzene, the monomer used in the preparation of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV), but they can be removed by double recrystallization of the monomer prior to polymerization. When impurities containing methylene bridges participate in a Gilch polymerization, the methylene bonds formed in the main chains are prone to break at 200 °C, that is, at least 150 °C below the major degradation temperature of defect‐free MEH‐PPV. Interestingly, the thermal treatment used to break the methylene bonds present reduces the chain aggregation of MEH‐PPV during film formation and induces its blends with poly(2,3‐diphenyl‐5‐octyl‐p‐phenylene‐vinylene) (DPO‐PPV) to form a morphology similar to that of block copolymers. Both significantly enhance the luminescence properties. Copyright © 2006 Society of Chemical Industry     

Synchrotron radiation ablation of polymers having double bonds in their main chains

Polyacetylene (PA), poly(cis- and trans-1,4-butadiene)s (cis- and trans-PBs), and poly(p-phenylene vinylene) (PPV) were ablated by synchrotron radiation (SR), aiming to deposit thin, uniform films of each on a substrate. When PA was irradiated by SR, gaseous phenyl compounds were produced, and a thin amorphous film was deposited on the substrate, exhibiting no characteristics of PA. In the cases of PPV and trans-PB, the source materials were reproduced in the form of thin film on the substrate by SR ablation. When alkali halides, e.g. NaCl and KBr, were used as deposition substrates, PPV was deposited, in an ordered way, on their cleavage surfaces. However, the deposited film of trans-PB by SR ablation was non-crystalline, because it was produced as a copolymer by 1,4- and 1,2-addition polymerizations of ablated butadiene-based fragments. In comparison, thin films of these polymers were also prepared by thermally evaporating them in a vacuum. When trans-PB and PPV were thermally evaporated, thin films with chemically and structurally identical features to the source polymers were produced, respectively. In contrast, a deposited film from cis-PB by SR ablation consisted of carbon compounds, showing no sign of hydrocarbon compounds in it, while trans-PB was produced from cis-PB by thermal vapor deposition.     

Synthesis and Characterization of Poly(tetramethyl-1,4-silphenylenesiloxane) Derivatives with Oxyethylene Substituent on Phenylene Moiety

Summary Novel poly(tetramethyl-1,4-silphenylenesiloxane) derivatives having 2-methoxy-ethoxy or 2-(2-methoxyethoxy)ethoxy substituents at both 2- and 5-positions on phenylene moieties were synthesized and characterized by differential scanning calorimetry and thermogravimetry analyses. Poly(tetramethyl-1,4-silphenylene-siloxane) derivatives were obtained by condensation polymerization of the corresponding disilanol derivatives, i.e., 1,4-bis(dimethylhydroxysilyl)-2,5-bis(2-methoxyethoxy)benzene and 1,4-bis(dimethylhydroxysilyl)-2,5-bis[2-(2-methoxy-ethoxy)ethoxy]benzene, which were prepared by the Grignard reaction using chlorodimethylsilane and the corresponding dibromobenzene derivatives followed by the hydrolyses, catalyzed by palladium on charcoal. The introduction of 2-methoxyethoxy groups on the phenylene moiety made the melting point high, compared with poly(tetramethyl-1,4-silphenylenesiloxane); however, that of 2-(2-methoxyethoxy)ethoxy groups made it low, indicating the longer oxyethylene moiety induced the lowering of the melting point. There were no significant differences in the thermostabilities of both present polymers, suggesting the length of oxyethylene moiety would not affect the thermostability, though the introduction of polar oxyethylene group onto the phenylene moiety induced a decline of thermostability.     

Photodegradation mechanism and stabilization of polyphenylene oxide and rigid‐rod polymers

Poly(2,4‐dimethyl‐1,4‐phenylene oxide) (PPO), poly(benzo[1,2‐d:5,4‐d′]bisoxazole‐2,6‐diyl‐1,4‐phenylene) (PBO) and poly(benzo[1,2‐d:4,5‐d′]bisthiazole‐2,6‐diyl‐1,4‐phenylene) (PBZT), which are polymers with extended conjugated structures, undergo a self‐sensitized photo‐induced electron‐transfer reaction. A second component is not required. This article presents many similar observations on these polymers when they are exposed to light and evidence to support the proposed photo‐induced electron‐transfer mechanism. Methods to stabilize these polymers against photo‐oxidation are also described. Workers investigating other conjugated polymeric systems may find the experimental methods, observations and polymer stabilization approaches discussed in this review useful. Copyright © 2005 Society of Chemical Industry     

Synthesis, characterization and liquid-crystal-aligning properties of novel aromatic polypyromellitimides bearing (n-alkyloxy)biphenyloxy side chains

Novel aromatic polypyromellitimides bearing (n-alkyloxy)biphenyloxy side chains were prepared by two-step polycondensation of 1,4-phenylenediamine (PDA) and biphenyl-4,4′-diamine (BZ) with 3,6-bis[4′-(n-alkyloxy)biphenyl-4-oxy]pyromellitic dianhydrides (C_mB-PMDAs, m = 6, 8, 10, 12), which had been synthesized by the nucleophilic substitution of N,N′-diphenyl-3,6-dibromopyromellitimides with sodium 4-(n-alkyloxy)biphenoxides. Inherent viscosities of the poly(amic acid)s were in the 0.26-0.62 dL/g range. Poly{1,4-phenylene-3,6-bis[4′-(n-alkyloxy)biphenyl-4-oxy]pyromellitimide}s (C_mB-PPIs) and poly{4,4′-biphenyl-3,6-bis[4′-(n-alkyloxy)biphenyl-4-oxy]pyromellitimide}s (C_mB-BPIs) obtained in films by thermal imidization of the corresponding poly(amic acid)s were characterized by FT-IR spectroscopy and elemental analysis, and their crystalline structure and thermal properties were measured and discussed with respect to the side chain length. After the polyimide films were surface-treated by rubbing with velvet fibers, standard liquid crystal (LC) cells containing 4-cyano-4′-n-pentylbiphenyl (5CB) were fabricated and their LC-aligning properties were investigated in terms of pretilt angle. The pretilt angles were remarkably affected by side chain length and on surface of the polyimides with m = 6 and 8 LCs aligned parallel to the rubbing direction while on surface of the polyimides with m = 10 and 12 they aligned nearly or completely vertical to the rubbing direction.     

Synthesis and polymerization of 1-(2-N-aziridinoethyl)-4-vinylbenzene

An addition reaction of aziridine onto 1,4-divinylbenzene (DVB) catalyzed by lithium aziridide was studied. It was found that 1-(2-N-aziridinoethyl)-4-vinylbenzene (AEVB) and 1,4-bis (2-N-aziridinoethyl)-benzene(BAEB) can be prepared selectively under appropriate conditions. On the basis of kinetic studies, the reactivity of aziridine toward DVB was compared with that of diethylamine. Vinyl polymerization and ringopening polymerization of AEVB were also carried out to obtain poly [1-{4-(2-aziridinoethyl)phenyl}ethylene] (poly(AEPE)) and poly[{(4-vinylphenethyl) imino}-ethylene](poly(VPIE)), respectively.     

Deformation studies of single rigid-rod polymer-based fibres. Part 1. Determination of crystal modulus

This series of papers covers several aspects related to the influence of external stresses on the crystalline microstructure of rigid-rod polymer-based fibres. For the study, the main three fibres of this type have been selected, namely poly(p-phenylenebenzobisoxazole) (PBO fibres), poly(p-phenylenebenzobisthiazole) (PBT or PBZT fibres) and the novel poly{2,6-diimidazo[4,5-b:4′-5′-e]pyridinylene-1,4(2,5-dihydroxy)phenylene} (PIPD or M5 fibres). Synchrotron radiation was employed to record high-quality wide-angle X-ray scattering patterns from single fibres. The present paper deals mainly with the evaluation of lattice strain along the fibre axis (c-)direction. Crystal moduli of the different fibres were calculated from the variation with stress of the lattice strain determined from the shift of the major meridional (00l) reflections. This procedure rendered values of approximately 440 GPa for the crystal modulus of PIPD and PBO fibres, and 350 GPa for the PBT one. The difference between these two values was explained in terms of specific molecular conformation of the monomers in the unit cell. Discrepancies between the crystal and macroscopic (calculated from tensile tests) moduli are due to imperfections generated during the manufacture of the fibres.     

Polymeric coatings for photostability enhancement of poly(p‐phenylene vinylene) derivative films

Poly(p‐phenylene vinylene) (PPV) derivatives are an important class of conjugated polymers, known for their applications as electroluminescent materials for light‐emitting devices and sensors. These derivatives are highly susceptible to photodegradation by the combined action of oxygen and light. Here, the use of various commercial polymers as protective coatings against the photodegradation of PPV derivatives was explored. Cast films of two similar PPV derivatives, poly[(2‐methoxy‐5‐n‐hexyloxy)‐p‐phenylene vinylene] and poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐p‐phenylene vinylene], were submitted to photodegradation by exposure to white light under atmospheric conditions in order to verify if the type of side chain (linear or branched) had an effect on the photodegradation. No significant differences in the photodegradation behaviour between the two polymers were noticed. The following commercial polymers were tested as protective coatings for the PPV derivative cast films: 99 and 80% hydrolysed poly(vinyl alcohol) (PVA) and starch. The best results were achieved using coatings of 99% hydrolysed PVA, which increased about 700 times the time necessary for complete degradation of the PPV derivative films. The results show the effectiveness of this coating in minimizing and, possibly, controlling the effects of the photodegradation of PPV derivative films, which can be useful in many applications, e.g. oxygen sensors. Copyright © 2009 Society of Chemical Industry     

Synthesis,characterization, and photophysical properties of novel poly(p‐phenylene vinylene) derivatives with conjugated thiophene as side chains

Two novel poly(p‐phenylene vinylene) (PPV) derivatives with conjugated thiophene side chains, P1 and P2, were synthesized by Wittig‐Horner reaction. The resulting polymers were characterized by ¹H‐NMR, FTIR, GPC, DSC, TGA, UV–Vis absorption spectroscopy and cyclic voltammetry (CV). The polymers exhibited good thermal stability and film‐forming ability. The absorption spectra of P1 and P2 showed broader absorption band from 300 to 580 nm compared with poly[(p‐phenylene vinylene)‐alt‐(2‐methoxy‐5‐octyloxy‐p‐phenylene vinylene)] (P3) without conjugated thiophene side chains. Cyclic voltammograms displayed that the bandgap was reduced effectively by attaching conjugated thiophene side chains. This kind of polymer appears to be interesting candidates for solar‐cell applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

聚[2-甲氧基-5-(3′-甲基)丁氧基]对苯乙炔的合成及性能研究

以对甲氧基苯酚和溴代异戊烷为原料,经过三步反应制备了大π共轭高分子聚[2 甲氧基 5 (3′ 甲基)丁氧基]对苯乙炔(MMB PPV),摩尔产率为48%。聚合反应投料比为n(双氯苄)∶n(叔丁醇钾)=1∶5。利用1H NMR、FT IR和元素分析等对产物及中间体的结构进行了表征。UV Vis光谱表明,MMB PPV在波长450～550nm具有显著的吸收。TG曲线显示,MMB PPV的失重主要由两个部分组成,245℃对应于聚合物的分解温度。分别用H2SO4、FeCl3和I2对MMB PPV粉末进行掺杂,掺杂后MMB PPV的电导率依次为0 34、8 5×10-2和4 7×10-3S/cm。此外,采用分光光度计对MMB PPV的光学禁带宽度(Eg)进行测量,线性拟合的结果分别为2 02eV及2 07eV。     

Synthesis of MDI and PCL-diol-based polyurethanes containing [2] and [3]rotaxanes and their properties

We have successfully synthesized novel polyurethanes where PU1 contains a [3]rotaxane that consists of N-3,5-di-tert-butylbenzyl-N-3-hydroxypropylammonium hexafluorophosphate (AOH1) and N,N′-Dimethyl-N,N′-bis(dibenzo-24-crown-8)-terephthalamide (BisC) as well as PU2 contains a [2]rotaxane that consists of AOH1 and dibenzo-24-crown-8 ether. Diphenylmethanediisocyanate (MDI), 1,4-butanediol (BD) and poly(ε-caprolactone)diol (PCL) were used as an isocyanate, chain expander, and soft segment, respectively. A polyurethane without any rotaxane structures (PU0) were also prepared as a reference polymer. The existence of the rotaxanes in the polyurethanes was confirmed by ¹H NMR spectroscopy and TGA measurement. ATR-FT-IR spectral measurement revealed that the rotaxanes disturb the formation of hydrogen bonding between the polyurethane chains. From the DSC result, the rotaxanes retard the recrystallization of the PCL unit whereas no influence on the glass transition temperatures of the polyurethanes was observed. The retarding effect appeared remarkably with PU1. These thermal behaviors of the polyurethanes were also supported by viscoelastic measurement. In tensile test, the tensile strength and break of strain of PU1 were larger than those of PU2.     

Thermooxidative stability of spectra of fluorene-based copolymers

The origin of the low-energy emission of fluorene-based homo- and copolymers still remains controversial. In this work, the effect of thermal treatment on the emission properties of poly[(9,9-dihexylfluorene)-alt-co-(1,4-phenylene)] (PF6P) and its four derivatives modified by attaching different lengths of alkoxy side chains on the phenylene rings has been systematically investigated. By comparing the photoluminescence (PL) spectra of PF6P and the modified polymers, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and PL lifetime measurements have revealed that the long wavelength emission could be attributed to the formation of fluorenone-based excimers rather than to the localized fluorenone π-π* transition, the energy transfer from fluorene segments to the fluorenone moieties, or the fluorenone defects generated by thermal oxidation during thermal treatment. Compared with PF6P, the attachment of alkoxy side chains on the phenylene rings effectively inhibits the aggregation of backbone chains, thus restrains the formation of fluorenone-based excimers and remarkably improves thermal stability of the spectra.