Highly alkoxylated PPV copolymers for PLEDs: Syntheses, optical properties and enhancement of device lifetimes

A series of solution processible light-emitting copolymers composed of tetraalkoxy-phenylenevinylene (TALK-PPV) and dialkoxy-phenylenevinylene (DALK-PPV) has been synthesized using the Gilch polymerization route. Thermal, optical and electrochemical properties of the synthesized copolymers [poly(TALKPV-co-DALKPV)s] have been investigated and compared with those of each homopolymers, poly[2-(3,7-dimethyloctyloxy)-3,5,6-trimethoxy]-1,4-phenylenevinylene] (TALK-PPV) and poly[2-(3′,7′-dimethyloctyloxy)-5-methoxy-1,4-phenylenevinylene] (DALK-PPV). The synthesized copolymers showed a high molecular weight (Mn=∼2-3.0×10⁵) and narrow polydispersity indices (∼3). Electroluminescent devices using the copolymers as the emissive layer have been fabricated with a configuration of ITO/PEDOT:PSS/polymers/Ca/Al. Interestingly the copolymer devices resulted in a more than 4-fold increase in device lifetime than the homopolymers, which might be due to the highly reduced steric hindrance of the polymer backbone by introducing DALKPV units between the adjacent highly alkoxylated TALKPV repeating units in the polymer backbone.     

Preparation and Surface Properties of Fluorinated Acrylates Copolymers

Copolymerization of acrylates and styrene (St) with perfluorooctylacyloxyethyl methacrylate (FA) monomer, prepared from the reaction of perfluorooctanoic acid and hydroxymethyl methacrylate, was carried out by solution polymerization. The fluorinated acrylate and St copolymers (PFA) were examined by GPC, FT-IR, and ¹H NMR. The surface tension of the PFA solution in N-methyl pyrrolidone was tested by the drop volume method. The results showed that the surface tension of the PFA solution decreased in exponential decay with increase of the PFA concentration, and the surface tension of the solution also decreased with increased addition of the FA monomer in the copolymer at the same concentration. Meanwhile, the adsorption of the PFA macromolecules in the air–solution interface increased and enrichment of the fluorinated segments on the solution surface occurred. The studies of the surface free energy, polarity, fluorine content, and morphology of the PFA films illustrated that the surface free energy and polarity of the PFA films were decreased with the augment of the FA monomer in the copolymers, and that the fluorine content and the surface roughness were increased. The surface free energy of the PFA film was as small as 16.6 mN·m^?1. The surface properties of the PFA copolymers obtained by one shot feed during polymerization were superior to those obtained by continuing feed procedure. More fluorine segregation occurred and induced the formation of a fluorine-enriched surface if the PFA copolymer was postheated. The posttreatment was thus beneficial to the improvement of the surface properties of the PFA film.     

Synthesis, characterization, and corrosion protection properties of poly(N-(methacryloyloxymethyl) benzotriazole-co-methyl methacrylate) on mild steel

The copolymers from different feed ratios of N-(methacryloyloxymethyl) benzotriazole (MMBT) and methyl methacrylate (MMA) has been synthesised using free radical solution polymerization technique and characterized using FT-IR and ¹³C NMR spectroscopy. The thermal stability of the polymers was studied using theremogravimetrtic analysis (TGA). The corrosion behaviors of mild steel specimens dip coated with different composition of copolymers have been evaluated by potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) method. These electrochemical properties were observed in 0.1 M HCl medium. The polarization and impedance measurements showed different corrosion protection efficiency with change in composition of the copolymers. It was found that the corrosion protection properties are owing to the barrier effect of the polymer layer covered on the mild steel surfaces. However, it was observed that the copolymer obtained from 1:1 mole ratio of MMBT and MMA exhibited better protection efficiency than other combinations.     

Designing and Characterization of Poly(L-Lactide)/Poly(ϵ-Caprolactone) Multiblock Copolymers

A series of poly(L-lactide)/poly(?-caprolactone) (PLA/PCL) biodegradable multiblock copolymers was synthesized by a two-step process and characterized. Ring-opening polymerization was used to prepare a series of HO-PLA-PCL-PLA-OH copolymers initiated by hydroxyl-terminated PCL. Then the triblock copolymers and 1,6-hexamethylene diisocyanate (HDI) were reacted with different copolymer/HDI weight ratios. Consequently, a series of PLA/PCL multiblock copolymers with designed molecular chain structure was obtained. Gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and ¹H NMR were used to characterize these copolymers and the results showed that the designed PLA/PCL copolymers had been synthesized. Dynamic mechanical analysis (DMA) was applied to characterize their thermal properties. Stress–strain curves showed that a PLA/PCL copolymer with adjustable mechanical properties had been achieved.     

New approach in synthesis,characterization and release study of pH-sensitive polymeric micelles,based on PLA-Lys-<Emphasis Type="Italic">b</Emphasis>-PEGm,conjugated with doxorubicin

Amphiphilic block copolymers are well established as building blocks for the preparation of micellar drug carriers. The functional polymer micelles possess several advantages, such as high drug efficiency, targeted delivery, and minimized cytotoxicity. The synthesis of block copolymers using nano-structured templates has emerged as a useful and versatile approach for preparing drug carriers. Here, we report the synthesis of a smart polymeric compound of a diblock PLA-Lys-b-PEG copolymer containing doxorubicin. We have synthesized functionalized diblock copolymers, with lysinol, poly(lactide) and monomethoxy poly(ethylene glycol) via thermal ring-opening polymerization and a subsequent six-step substitution reaction. A variety of spectroscopic methods were employed here to verify the product of our synthesis. ¹H-Nuclear magnetic resonance and Fourier transform infrared studies validated the expected synthesis of copolymers. Doxorubicin is chemically loaded into micelles, and the ex vitro release can be evaluated either in weak acidic or in SBF solution by UV–vis spectroscopy. Dynamic light scattering, thermo gravimetric analysis, and size exclusion chromatography have also been used.     

Mössbauer studies of solid state decomposition of methyl methacrylate-ethyl methacrylate copolymers containing ferric chloride

Methyl methacrylate (MMA)-ethyl methacrylate (EMA) copolymers of different monomer concentrations containing anhydrous ferric chloride were prepared by bulk polymerization at 70°C. TGA studies showed that inclusion of iron salt increases the thermal stability of copolymers by 50°C. Mössbauer spectra of copolymers heated at different temperatures showed the presence of Fe³⁺ species only, in different environments. The mechanism of thermal stabilization of copolymer has been proposed on the basis of IR, TGA and Mössbauer spectroscopy studies.     

Influence of Grafting Density of Diblock Copolymers on Interfacial Assembly Behavior and Interfacial Shear Strength of Glass Fiber/Polystyrene Composites

To investigate the influence of the grafting density and the molecular structure of block copolymers on the interfacial assembly behavior and interfacial shear strength, macromolecular coupling agents, hydroxyl-terminated poly(n-butyl acrylate-b-styrene) (HO-P(BA-b-S)) were synthesized by atom transfer radical polymerization, and then chemically anchored on the glass fiber surfaces to form a well-defined monolayer. The phase separation and 'hemispherical' domain morphologies of diblock copolymer brushes at the polystyrene/glass fiber interface were observed. The interfacial assembly morphology differs with changes in the grafting density of diblock copolymers. When the grafting density is greatest, the highest height difference of the hemispherical domain and the largest surface roughness are achieved, as well as the best interface shear strength. It was also found that the copolymer brush with a PBA block of the polymerization degree (Xn) about 77 is the optimal option for the interfacial adhesion of PS/GF composites. Thus, the grafting density and molecular structure of diblock copolymers determines the interfacial assembly behavior of copolymer brushes, and therefore the interfacial shear strength.     

Preparation and Characterization of Poly (Acrylonitrile-co-1-Acryloylpyrrolidine- 2-Carboxylic Acid) with High Molecular Weight

1-acryloylpyrrolidine-2-carboxylic acid (APCA) monomer was copolymerized with acrylonitrile (AN) by aqueous suspension polymerization. High molecular weight (HMW) copolymers of AN and APCA [poly(AN-co-APCA)] with different copolymer composition were successfully prepared by employing azobisisobutyronitrile (AIBN) as initiator and polyvinyl alcohol (PVA) as dispersant in a H₂O/N,N-dimethylformamide (DMF) mixture at 60°C. The PAN homopolymer and copolymers were characterized by elemental analysis (EA), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The EA results indicated that the content of oxygen increased significantly in PAN copolymers with increasing APCA content. The APCA copolymer composition calculated from the EA was higher than that from ¹H NMR spectra. The FTIR spectra of PAN and poly(AN-co-APCA) with different monomer ratios confirmed that the contents of APCA units in the copolymer chains increased with increasing APCA content in the feed. The DSC exotherms revealed that copolymerization with APCA could slow the rate of the exothermic reactions during the heat-treatment processes. The XRD results indicated that the PAN homopolymer and copolymers poorly crystallized and the crystallinity decreased with increasing APCA contents.     

Nano-network with dual temperature and pH responsiveness based on copolymers of 2-hydroxyethyl methacrylate with 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane

Abstract  

This study refers to the synthesis of a nano-network with dual temperature and pH responsiveness based on the 2-hydroxyethyl methacrylate (HEMA) copolymers with a comonomer with spiroacetal moiety and crosslinking capacity, namely 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane (U). The copolymers were synthesized by radical emulsion polymerization, using 4,4′-azobis(cyanopentanoic acid) as initiator, in the presence of sodium lauryl sulfate as tensioactive agent and poly(vinyl alcohol) as protective colloid. Three copolymer variants were taken into study resulted from the different ratio between the comonomers (HEMA/U), which was about 98/2, 95/5, and 90/10, respectively. The copolymers were characterized by FTIR and thermal analysis. The copolymers sensitivity was evidenced by studying the evolution of the hydrodynamic radius and zeta potential of the polymeric particles as a function of pH. Thus, the particles size increases with the comonomer amount, from 193 nm in case of the homopolymer up to 253 nm for the copolymer with maximum content of the comonomer (10%). The increase of the particle hydrodynamic radius with the growth of temperature was also put into evidence.     

Self—assembly behaviour of amphiphilic diblock copolymer in selective solvents studied by synchrotron small—angle x—ray scattering

The aggregation behaviour of styrene-vinyl benzoic acid (PS_m-b-PVBA_n) amphiphilic diblock copolymers in selective solvents with different m and n was investigated by synchrotron small-angle x-ray scattering (SAXS). We have carried out a detailed analysis of scattering intensity, dimension, shape and microstructure of the diblock copolymers of narrow distribution in water, methanol, ethanol and isopropanol selective solvents, respectively. We have found that the aggregation behaviour of the copolymer depends on the nature of the solvent and the micelle forms flat disc objects with the ratio of radius ω=0.4. The average radius gyration R_g of the copolymer decreases as solvents change from isopropanol to ethanol and to methanol, and increases with increasing pH in aqueous solution, but decreases with the addition of CoCl_2 in ethanol solvent. The scattering intensity of diblock copolymer micelle follows I(h)∝h^{-α} in different selective solutions, suggesting that the PS_m-b-PVBA_n coils have self-similar structure behaviour or a fractal structure in the selective solvents. All of these revealed that the aggregation behaviour of the diblock copolymer changes dramatically with experimental condition in the selective solvent. The increase of mass fractal dimension (D_m) from 2.12 to 2.47 indicates that the copolymer chain changes from a swollen coil to a rather compact disc in the course of changing solvents, decreasing surface fractal dimension (D_s) from 2.98 to 2.58 indicates that the copolymer micelle change from a rather rough surface to a smooth form in the course of increasing pH in aqueous solutions, and increasing D_m and D_s from 2.29 to 2.35 and 2.70 to 2.90, respectively, indicates the shrinkage of copolymer micelle to a rather compact and rough disc form by adding CoCl_2 in ethanol solvents.     

Complex nanostructured materials from segmented copolymers prepared by ATRP

The development of new controlled/living radical polymerization processes, such as Atom Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated polymerization and degenerative transfer processes, including RAFT, opened the way to the use of radical polymerization for the synthesis of well-defined, complex functional nanostructures. The development of such nanostructures is primarily dependent on self-assembly of well-defined segmented copolymers. This article describes the fundamentals of ATRP, relevant to the synthesis of such systems. The self-assembly of block copolymers prepared by ATRP is illustrated by three examples. In the first, block copolymers of poly(butyl acrylate) with polyacrylonitrile phase separate, leading to spherical, cylindrical or lamellar morphologies, depending on the block copolymer composition. At a higher temperature, polyacrylonitrile block converts to nanostructured carbon clusters, whereas poly(butyl acrylate) block serves as a sacrificial block, aiding the development of designed nanostructures. In the second example, conductive nanoribbons of poly(n-hexylthiophene) surrounded by a matrix of organic polymers are formed from block copolymers prepared by ATRP. The third example describes an inorganic-organic hybrid system consisting of hard nanocolloidal silica particles (20 nm) grafted by ATRP with well-defined polystyrene-poly(benzyl acrylate) block copolymer chains (1000 chains per particle). Silica cores in this system are surrounded by a rigid polystyrene inner shell and softer polyacrylate outer shell. Received 9 July 2002 Published online: 11 March 2003     

Dual Gas-responsive Fluorescent Diblock Copolymer Synthesized via RAFT Polymerization

Stimulus-responsive polymers with luminescence properties have a wide range of applications in the fields of controlled drug release, fluorescent probes, and biological stents. In this paper, carbon dioxide (CO₂)/oxygen (O₂) dual-responsive fluorescent diblock copolymers were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization method with two fluorescent monomers synthesized as its luminescence source, DEAEMA (CO₂ responsive monomer) and tFMA (O₂ responsive monomer). An experimental study demonstrated that the synthesized stimulus-responsive fluorescent polymer had a high sensitivity to CO₂; the double-responsive fluorescent diblock copolymer could form and achieve the reversal of polymer micelles in the aqueous solution when it was sequentially subjected to the introduction of CO₂ and O₂.

     

Amphiphilic block copolymer nanocontainers as bioreactors

Self-assembly of an amphiphilic triblock copolymer carrying polymerizable end-groups is used to prepare nanometer-sized vesicular structures in aqueous solution. The triblock copolymer shells of the vesicles can be regarded as a mimetic of biological membranes although they are 2 to 3 times thicker than a conventional lipid bilayer. Nevertheless, they can serve as a matrix for membrane-spanning proteins. Surprisingly, the proteins remain functional despite the extreme thickness of the membranes and that even after polymerization of the reactive triblock copolymers. This opens a new field to create mechanically stable protein/polymer hybrid membranes. As a representative example we functionalize (polymerized) triblock copolymer vesicles by reconstituting a channel-forming protein from the outer cell wall of Gram-negative bacteria. The protein used (OmpF) acts as a size-selective filter, which allows only for passage of molecules with a molecular weight below 400 g mol^-1. Therefore substrates may still have access to enzymes encapsulated in such protein/polymer hybrid nanocontainers. We demonstrate this using the enzyme β-lactamase which is able to hydrolyze the antibiotic ampicillin. In addition, a transmembrane voltage above a given threshold causes a reversible gating transition of OmpF. This can be used to reversibly activate or deactivate the resulting nanoreactors. Received 22 August 2000     

Solid-state dye lasers based on copolymers of 2-hydroxyethyl methacrylate and methyl methacrylate doped with rhodamine 6G

Rhodamine 6G has been dissolved in copolymers of 2-HydroxyEthyl MethAcrylate (HEMA) and Methyl MethAcrylate (MMA) and the resulting solid-state solutions have been pumped at 337 nm and 532 nm. Lasing efficiencies similar to those found in ethanol solution have been obtained with a 1:1 vol/vol HEMA: MMA copolymer matrix, and lifetimes of ca. 10 000 (337 nm pumping) and ca. 75 000 (532 nm pumping) pulses at repetition rates up to 15 Hz and 10 Hz, respectively, have been demonstrated.     

Improving polymeric microemulsions with block copolymer polydispersity

Recent experiments have demonstrated that block copolymers are capable of stabilizing immiscible homopolymer blends producing bicontinuous microemulsion. The stability of these polymeric alloys requires the copolymer to form flexible, nonattractive monolayers along the homopolymer interfaces. We predict that copolymer polydispersity can substantially and simultaneously improve the monolayers in both of these respects. Furthermore, polydispersity should provide similar improvements in systems, such as colloidal suspensions and polymer/clay composites, that utilize polymer brushes to suppress attractive interactions.     

Preparation of lotus-like superhydrophobic fluoropolymer films

Styrene and 2,2,3,4,4,4-hexafluorobutyl methacrylate copolymers were synthesized by bulk polymerization, and the superhydrophobic copolymer films were prepared subsequently using phase separation technique. The copolymer was dissolved in tetrahydrofuran, and then added ethanol into the solution thereafter, to induce phase separation. The microstructures of the polymer films were controlled by the degree of phase separation, which was enhanced properly by the concentration of ethanol. The surface morphology of the films, observed by environmental scanning electron microscope, is similar to that of the lotus leaf. The contact angle and sliding angle were measured as 154.3° and 5.8°, respectively. The excellent superhydrophobic property demonstrated that the phase separation technique is useful for preparing lotus-like fluoropolymer films.     

Copolyacrylates with phenylalanine and anthracene entities prepared by ATRP and microwave irradiation

In this study, two amino acid copolymers containing anthracene incorporated either on the one end, poly(N-acryloyl-l-phenylalanine-co-methyl methacrylate)-1 or as pendant groups, poly-(N-acryloyl-l-phenylalanine-co-methyl methacrylate)-2 were prepared directly from N-acryloyl-l-phenylalanine (APhe) and methyl methacrylate (MMA) through atom transfer radical polymerization (ATRP) and microwave-assisted synthesis. In the first case, 9-(chloromethyl)anthracene was used as an ATRP-initiator to obtain a copolymer that contains amino acid sequences and anthracene end-capped units (0.03 molar fraction). Rapid synthesis of copolymer under microwave irradiation (250 W) in the presence of 1,1′-azobis(cyclohexanecarbonitrile) used as an initiator was followed of a functionalization of the formed copolymer with an anthracene derivative yielding copolyacrylate with pendant anthracene (0.02 molar fraction). The structure of the copolymers was verified by ¹H NMR, UV-Vis and FTIR spectroscopy, gel permeation chromatography (GPC), and fluorescence spectroscopy. The fluorescence quenching process of anthracene which exists in copolymers by FeCl₃, cobalt acetate, nitrobenzene, maleic anhydride, diethylaniline and nitromethane in DMF solutions shows that this involves an electron transfer between the excited state anthracene and the present transitional metal cations, more efficiently being FeCl₃ for poly-(APhe-co-MMA)-1 and cobalt acetate for the latter copolymer.     

An approach to hybrid inorganic nanoparticles in reactive PS-b-PMSMA amphiphilic copolymers

A series of well-defined amphiphilic poly(styrene)-block-poly 3-(trimethoxysilyl) propyl methacrylate (PS-b-PMSMA) copolymers with controlled molecular weight and block length were prepared by the atom transfer free radical polymerization. The cadmium sulfide (CdS) nanoparticles were fabricated in the spherical micelles self-assembled from these prepared PS-b-PMSMA copolymers. Then, the CdS/PS-b-PMSMA films were obtained by spin coating the CdS/PS-b-PMSMA solution on silicon wafer. The experimental results showed the addition of Cu(II) could decrease the value of polydispersity index for the prepared copolymers. Nuclear magnetic resonance and Fourier transform infrared spectra showed the synthesis of PS-b-PMSMA copolymer. The average roughness and mean square roughness of the prepared CdS/PS-b-PMSMA films obtained from the atomic force microscopy analysis were 3.0–3.4 nm and 1.7–2.0 nm, respectively, indicating the excellent surface planarity. On the other hand, the ratio of block length between PS and PMSMA had a great influence on the micelle size. The larger ratio of PS to PMSMA block length resulted in the larger size of micelles and CdS nanoparticles that caused a red-shift of ultraviolet–visible and photoluminescence spectra. The red-shift of spectra was explained by the quantum confinement effect associated with the tiny size of the CdS nanoparticles.     

超声引发苯乙烯微乳液聚合转化率的紫外光谱法分析

研究了苯乙烯微乳液聚合体系中苯乙烯浓度和转化率的测定方法,探讨了紫外光谱法分析测定苯乙烯浓度的影响因素。实验结果表明：以95%乙醇为溶剂和参比液,紫外吸收波长为247 nm时,苯乙烯浓度的范围在9.70×10-6 mol·L-1～6.95×10-5mol·L-1内,其吸光度与浓度呈良好的线性关系,其最大摩尔吸光系数ε 为1.384×104 L·mol-1·cm-1。微乳液聚合体系中十二烷基硫酸钠、正戊醇的存在对苯乙烯浓度的分析测定没有影响。苯乙烯微乳液聚合体系中的聚苯乙烯可以通过加95%乙醇进行沉淀分离,残余的微量聚苯乙烯对分析结果无影响。将紫外光谱法与化学法和重量法比较,表明紫外光谱法测定苯乙烯的转化率是可行的,该方法操作简便,灵敏度高。