Properties of nanometric and submicrometric multilayered films of poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole)

Multilayered films formed by 3, 5 and 7 alternated layers of poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole) have been prepared by chronoamperometry under a constant potential of 1.4 V using a layer-by-layer electrodeposition technique. In order to examine influence of the interface:bulk dimensional ratio, the thickness of the yielded films was reduced from the submicrometric to the nanometric scale by decreasing the polymerization time of each layer from 100 s to 10 s. The electroactivity, electrochemical characteristics and morphologies of the resulting multilayered films have been compared with those obtained for both single-component poly(3,4-ethylenedioxythiophene) films prepared using identical experimental conditions and previously reported multilayered films with thickness within the micrometric scale [Estrany F, Aradilla D, Oliver R, Alemán C. Eur Polym J 2007;43:1876].     

Properties of nanometric and micrometric multilayered films made of three conducting polymers

The electrochemical, electrical and morphological properties of multilayered films formed by alternated layers of poly(3,4-ethylenedioxythiophene), polypyrrole, and poly[N-(2-cyanoethyl)pyrrole], which were prepared by electrochemical layer-by-layer deposition, have been investigated and compared with those of multilayered films formed by two conducting polymers. Results indicate that the electrochemical behavior of the films formed by three conducting polymers depends on the micrometric or nanometric thickness of the layers. Thus, the electroactivity increases until the thickness of these films reaches a threshold value (∼2 μm), while the electrostability of the films is very remarkable when their thickness is close to ∼4 μm or higher. On the other hand, comparison between multilayered systems made of two and three conducting polymers indicates that the third component introduces heterogeneity in the interfaces between consecutive layers, reducing the ability to store charge. Among the latter, multilayered films formed by poly(3,4-ethylenedioxythiophene) and polypyrrole have been found to be particularly electroactive and electrostable. The surface morphology and topography of the layers have been used to rationalize the electrochemical properties of the different materials.     

Conducting poly(3,4-ethylenedioxythiophene)-montmorillonite exfoliated nanocomposites

Exfoliated nanocomposites formed by poly(3,4-ethylenedioxythiophene) and different concentrations of non-modified montmorillonite (bentonite), which range from 1% to 10% w/w, have been prepared by anodic electropolymerization in aqueous solution. Analyses of the electrochemical and electrical properties reveal that the electroactivity of the nanocomposites is higher than that of the individual homopolymer, while the electrical conductivity of the two systems is practically identical. On the other hand, the exfoliated distribution of the clay in the polymeric matrix and the morphology of the prepared materials have been characterized using transmission electron microscopy, X-ray diffraction and atomic force microscopy. The overall of the results represents a significant improvement with respect to other nanocomposites constituted by conducting polymers and clays, including those involving poly(3,4-ethylenedioxythiophene), and evidences the reliability of the preparation procedure employed in this work.     

Poly(N-isopropylacrylamide)/poly[(N-acetylimino)ethylene] thermosensitive block and graft copolymers

Block and graft copolymers with poly(N-isopropylacrylamide) and poly[(N-acetylimino)ethylene] (PNAI) sequences were synthesized via PNAI derivatives (macroinitiators or macromers). The polymerization yields for block copolymers synthesized in ethanol, using the PNAI macroinitiator, were low (<10%), except where photochemical polymerization was applied. By contrast, for the copolymerizations of N-isopropylacrylamide with the PNAI macromers, performed in alcoholic solution, quite high polymerization yields, around 80-90%, were reached. ¹H-NMR and IR spectral and differential scanning calorimeter thermal data confirmed the copolymer formation. Thermosensitivity of the copolymers was investigated by means of turbidimetric technique as a function of their nature, average molecular weight and composition. It was found that the length of the chain of the PNAI macromer and the content in hydrophilic PNAI units of the resulted copolymer affected this behavior.     

Electrochemical recognition and trace-level detection of bactericide carbendazim using carboxylic group functionalized poly(3,4-ethylenedioxythiophene) mimic electrode

The electrochemical recognition and trace-level detection of bactericide carbendazim (MBC) in paddy water and commercial juice were realized using carboxylic group functionalized poly(3,4-ethylenedioxythiophene) (PC4-EDOT-COOH) film electrode. PC4-EDOT-COOH film was prepared by one step, low-cost, and green electrosynthesis in aqueous microemulsion system and characterized by FT-IR, cyclic voltammetry, UV–vis and SEM. In comparison with poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(hydroxymethylated-3,4-ethylenedioxylthiophene) (PEDTM), PC4-EDOT-COOH exhibited the best electrochemical recognition towards MBC and the recognition mechanism was proved by quantitative calculation. Sensing parameters such as pH values, accumulation potential, accumulation time, supporting electrolyte, and scan rate on the current response of MBC were discussed. In addition, the sensor can be applied to quantification of MBC in the concentration range of 0.012–0.35 μM with a low detection limit of 3.5 nM (S/N = 3). Moreover, PC4-EDOT-COOH film electrode showed good stability, high selectivity, and satisfactory anti-interference ability. Satisfactory results indicated that PC4-EDOT-COOH film is a promising sensing platform for the trace-level analysis of bactericide residue carbendazim in agricultural crops and environment.     

Synthesis and phase separation of amine-functional temperature responsive copolymers based on poly(N-isopropylacrylamide)

Free radical copolymerizations of N-isopropyl acrylamide (NIPAM) and cationic N-(3-aminopropyl) methacrylamide hydrochloride (APMH) were investigated to prepare amine-functional temperature responsive copolymers. The reactivity ratios for NIPAM and APMH were evaluated in media of different ionic strength (r_NIPAM = 0.7 and r_APMH = 0.7-1.2). Phase separation behavior of the random copolymers with only 5 mol% of the APMH was found to be suppressed in pure water at temperatures up to 45 °C due to electrostatic repulsion among the cationic amine groups randomly distributed along the copolymer chain. Alternate sequential addition of PNIPAM/APMH mixtures and pure NIPAM was used to provide increased control of the location of APMH units along the chain. Consequently (close to) homo-PNIPAM block(s) were formed as evidenced by its characteristic phase transition at 33 °C. The influences of the monomer feeding time and feeding interval time to the APMH distribution were investigated to prepare copolymers with thermo-induced phase separation under physiologically relevant temperature and to determine the extent of conjugation to poly(ethylene oxide).     

Thermosensitive superabsorbents based on poly(N,N-diethylacrylamide-co-sodium acrylate)

A series of poly(N,N-diethylacrylamide-co-sodium acrylate) with a degree of crosslinking of 1 mol%have been prepared as thermosensitive superabsorbents for water.The critical swelling temperatures or the volume phase transition temperature(VPTT) and the water absorption capacity of the polymers can be modulated by varying the amount of sodium acrylate(0-60 mol%) in the copolymers.The water absorption and swelling properties of the different hydrogels have been studied as function of temperature.The crosslinked copolymers can absorb large amounts of water at ambient temperatures and dehydrate at higher temperatures with relative ease,making the absorbent materials thermally responsive and thus reusable.The water absorption capacity of the copolymers depends on the pH of the media as the acrylate monomer has a higher water absorption in its deprotonated state.Added urea in the media raises and sharpens the VPTT values of the copolymers containing sodium acrylate.     

Amphiphilic graft copolymers based on ultrahigh molecular weight poly(styrene-alt-maleic anhydride) with poly(ethylene glycol) side chains for surface modification of polyethersulfone membranes

Amphiphilic graft copolymers having ultrahigh molecular weight poly(styrene-alt-maleic anhydride) (SMA) backbones and methoxyl poly(ethylene glycol) (MPEG) grafts were synthesized via the esterification between anhydride groups with hydroxyl groups. The synthesized graft copolymers, SMA-g-MPEGs, were used as additives in the preparation of polyethersulfone (PES) membranes via phase inversion process. X-ray photoelectron spectroscopy (XPS) analysis showed the comb-like graft copolymers spontaneously segregated to membrane surface during membrane formation. Water contact angle measurements and water absorbance experiments indicated the PES/SMA-g-MPEG blend membranes were much more hydrophilic than pure PES membrane. The blend membranes had stronger protein adsorption resistance than pure PES membrane did. After washed using de-ionized water for 25 days, the blend membranes exhibited higher hydrophilicity and stronger protein adsorption resistance. This phenomenon was attributed to the further accumulation of SMA-g-MPEG additives on membrane surface in aqueous conditions. SMA-g-MPEGs can be well preserved in membrane near-surface and not lost during membrane washing due to their high molecular weight and comb-like architecture.     

Enzymatic synthesis and characterization of a water-soluble, conducting poly(o-toluidine)

An enzymatic method for the synthesis of a water-soluble, conducting poly(o-toluidine) (POT) in the presence of sulfonated polystyrene (SPS) is presented. The enzyme horseradish peroxidase was used to polymerize o-toluidine to form a water-soluble, conducting POT/SPS complex, which exhibits moderate electrical conductivity. The synthesis is simple and the conditions are mild. The polymerization may be carried out at room temperature in pH 4.3 buffered aqueous solution with stoichiometric amount of monomer, SPS, hydrogen peroxide and catalytic amount of enzyme. The UV-Vis absorption spectra of the products display a distinct absorption peak at 740 nm at pH 4.3 that indicates the formation of the conducting, emeraldine salt form of POT. The structure and electrochemical behavior of the polymer was investigated with FT-IR and cyclic voltammetry method.     

Studies on cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes

New ultrafiltration membranes based on chemically and thermally stable arylene main-chain polymers have been prepared by blending the sulfonated poly(ether ether ketone) with cellulose acetate in various compositions in N,N^′-dimethylformamide as solvent by phase inversion technique. Prepared membranes have been subjected to ultrafiltration characterizations such as compaction, pure water flux, water content, and membrane hydraulic resistance. The pore statistics and molecular weight cut-off (MWCO) of the membranes have been estimated using proteins such as trypsin, pepsin, egg albumin and bovine serum albumin. The pore size increased with increasing concentrations of sulfonated poly(ether ether ketone) in the casting solution. Similarly, the MWCOs of the membranes ranged from 20 to 69 kDa, depending on the various polymer compositions. Surface and cross-sectional morphologies of membranes were analyzed using scanning electron microscopy. The effects of polymer compositions on the above parameters were analyzed and the results are compared and discussed with those of pure cellulose acetate membranes.     

Layer-by-layer films of enzymatically synthesized poly(aniline)/bacterial poly(γ-glutamic acid) for the construction of nanocapacitors

Poly(aniline) (PANi) and poly(γ-glutamic acid) (γ-PGA) have been synthesized by enzymatic catalysis and natural bacterial reactions, respectively. Layer-by-layer films have been prepared on glass or quartz slides by alternative immersions of the substrate in dilute solutions of γ-PGA and PANi, with several rinsing in between each deposition. UV-vis spectroscopy has been used to follow the evolution of the self-assembly process as well as to characterize the oxidative states of PANi. The linear dependence of the absorbance vs. the number of layers indicates a constant increase of thickness layer-by-layer. The morphology of the multilayer films, analyzed by atomic force microscopy, is granular type. Enzymatically synthesized PANi nanofilms present good electrical conductivity while γ-PGA acts as an insulating material. These differences in electrical properties and the possibility to obtain alternated multilayered films permit the construction of entirely “biological” nanocapacitors.     

Synthesis and properties of novel poly(p-phenylenevinylene) copolymers for near-infrared emitting diodes

A series of novel near-infrared (NIR) electroluminescence (EL) copolymers based on a host poly(p-phenylenevinylene) (PPV) derivative of poly(2-methoxy-5-octyloxy-p-phenylenevinylene) (PMOPV) with different content of narrow band-gap (NBG) unit 4,7-bis(2-thienyl)-2,1,3-benzothiadiazolevinylene (DBTV) or 4,7-bis(2-thienyl)-2,1,3-benzoselenadiazolevinylene (TBSV) was prepared by Stille coupling reaction. All the copolymers are soluble in common organic solvents, most of which emit NIR light accompanied by gradually red-shifting with increasing the content of the NBG units. The peak EL emission of the copolymers with around 30% TBSV content is at about 800 nm.     

Study on interaction between Tb(III) and poly(N-isopropylacrylamide)-g-poly(N-isopropylacrylamide-co-styrene) core-shell nanoparticles

Based on the synthesis of poly(N-isopropylacrylamide-co-styrene) P(NIPAM-co-St) and poly(N-isopropylacrylamide) (PNIPAM) grafted P(NIPAM-co-St) core-shell nanoparticle, a new kind of thermoresponsive and fluorescent complex of Tb(III) and PNIPAM-g-P(NIPAM-co-St) (PNNS) was successfully prepared. The PNNS-Tb(III) complex was characterized with the different techniques. It was found that when PNNS with the core-shell structure interact with Tb(III), Tb(III) mainly bonded to O of the carbonyl groups of PNNS, forming the novel PNNS-Tb(III) complex. After forming the complex, the emission fluorescence intensity of Tb(III) in the complex is significantly enhanced. Especially, the maximum emission intensity of the PNNS-Tb(III) complex at 545 nm is enhanced about 223 times comparing to that of the pure Tb(III) because the effective intramolecular energy transfer from PNNS to Tb(III). The intramolecular energy transfer efficiency from PNNS to Tb(III) reaches 50%. The fluorescence intensity is related the weight ratio of Tb(III) and PNNS in the PNNS-Tb(III) complex. When the weight ratio of Tb(III) and the PNNS is 12 wt%, the enhancement of the emission fluorescence intensity at 545 nm is highest. This novel fluorescence characterization of the PNNS-Tb(III) complex may be useful in the fluorescence systems and the biomedical field.     

Amphiphilic biodegradable poly(CL-b-PEG-b-CL) triblock copolymers prepared by novel rare earth complex: Synthesis and crystallization properties

Amphiphilic biodegradable poly(CL-b-PEG-b-CL) triblock copolymers have been successfully prepared by the ring-opening polymerization of ε-caprolactone (CL) employing yttrium tris(2,6-di-tert-butyl-4-methylphenolate) [Y(DBMP)₃] as catalyst and double-hydroxyl capped PEGs (DHPEG) as macro-initiator. The triblock architecture, molecular weight, thermal and crystallization properties of the copolymers were characterized by NMR spectra, SEC, DSC and WAXD analyses. The isothermal crystallization behavior of the copolymers was investigated by POM analysis in detail, which is greatly influenced by the length of PCL and PEG blocks. On the POM micrograph of PEG_10,000-(PCL₈₆₀₀)₂, a unique morphology of concentric spherulites was observed due to the sequent crystallization of the PCL and PEG blocks.     

Synthesis and hydrolytic degradation of poly(ethylene succinate) and poly(ethylene terephthalate) copolymers

The conditions of synthesis of statistical poly(ethylene succinate-co-terephthalate) copolymers (2GTS) and high molecular weight poly(ethylene succinate) (PES) with good hydrolytic and optical parameters, designed for the production of biodegradable products and resins, are presented in this article. Copolymers were prepared by melt polycondensation of bis-(β-hydroxyethylene terephthalate) (BHET) and succinic acid (SA) with excess of ethylene glycol (2G) in the presence of a novel titanium/silicate catalyst (C-94) and catalytic grade of germanium dioxide (GeO₂) as cocatalyst. The chemical structure and physical properties of those materials were characterized by ¹H NMR, FT-IR, dynamical-mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), solution viscosity and spectroscopic methods. The hydrolytic degradation was performed in a water solution with variable pH, also in garden soil and in compost. The highest hydrolytic degradation rate was observed for pH 4 and for compost. Better hydrolytic degradation values in compost medium were observed for copolyester prepared in the presence of GeO₂ as polycondensation cocatalyst. The copolyester with 40 mol% of aliphatic units was chosen for industrial syntheses which were performed in ELANA and subsequently the processing parameters and compatibility with potato starch of this polyester were checked by BIOP Biopolymer Technologies AG.     

Complexation between poly(N,N-diethylacrylamide) and poly(acrylic acid) in aqueous solution

The complexation between poly(N,N-diethylacrylamide) (PDEA) and poly(acrylic acid) (PAA) in aqueous solution was studied by viscometric, potentiometric, and fluorescence techniques. It was found that an interpolymer complex formed between the two polymers through hydrogen bonding interactions with the stoichiometry of r=0.6 (r is unit molar ratio of PAA/PDEA), and the complex formation show the dependence on pH values. The phase behaviour studies showed that the lower critical solution temperature of the PDEA-PAA aqueous solution gradually increased with the increasing of r from 0.01 to 0.15, until a soluble system in the whole temperature region was obtained, which remained in the range of r=0.15-0.3. At higher PAA concentrations, when r is above 0.3, the system appeared phase separation, and almost no temperature dependence was observed. Based on these conclusion and structure characteristics of PDEA and PAA, a model containing only short sequences of monomer residues was proposed for the structure of PDEA-PAA complex.     

Rapid swelling and deswelling in cryogels of crosslinked poly(N-isopropylacrylamide-co-acrylic acid)

Thermally sensitive hydrogels of poly[N-isopropylacrylamide (NIPA)-co-acrylic acid (AA)] hydrogels with N,N-methylene bisacrylamide (BIS) as crosslinker have been synthesized via a two-step procedure in which, the initial polymerisation is conducted for various times at 18 °C, this step being followed by polymerisation for one fixed time at −22 °C. The gravimetrically determined rates of swelling/deswelling for these materials termed “cryogels” prepared by this two-step polymerisation are much higher than those for the same type of hydrogel prepared via conventional methods (30 °C for 24 h). For example the time for the former xerogel to take up 70% of its final water content at 25 °C is just 18 min, compared with a time 300 min for the latter to attain the same uptake of water. During deswelling (shrinking) at 50 °C, which is above the lower critical temperature, the hydrogel loses 60 and 90 wt% water in 1 and 10 min respectively, compared to a timescale for the corresponding crosslinked copolymers prepared by conventional methods of about 100 min for 50 wt% water loss. A third type of hydrogel was made by a cold treatment (CT), for which the hydrogel prepared by conventional polymerization was stored in the frozen state. The swelling rate of these CT xerogels was the same as that for xerogels prepared by conventional polymerization, but the deswelling rate of the former was higher than that of the latter; for example, during deswelling, a loss of 90% water is attained within a few minutes.Scanning electron microscopy, digital photographs and flotation experiments together with swelling ratio studies reveal that the polymeric network of cryogel produced by the two-step polymerization method is characterized by an open structure with more pores and higher swelling ratio but lower mechanical strength compared to the conventional hydrogels. Such rapid response hydrogels have potential applications in separation and drug release technologies for example.     

Synthesis,characterization, and biodegradation of copolymers of unsaturated and saturated poly(ester amide)s

A new family of biodegradable copolymers of unsaturated poly(ester amide)s (UPEAs) and saturated poly(ester amide)s (SPEAs) based on L ‐phenylalanine, aliphatic dicarboxylic acids, and aliphatic dialcohols was synthesized by solution polycondensation and characterized. These unsaturated/saturated poly(ester amide) copolymers (USPEAs) were obtained in fairly good yields with N,N‐dimethylacetamide as the solvent. The molecular weights (M_n and M_w) of the USPEAs measured by GPC ranged from 15 to 60 kg/mol with a molecular weight distribution of 1.07–1.63. The chemical structures of the USPEAs were confirmed by both IR and NMR spectra. The USPEA copolymers had glass transition temperatures lower than that of pure UPEA but higher than that of pure SPEA. An increase in the unsaturated component in the USPEA copolymers led to an increase in their glass transition temperatures. The solubility of the copolymers was good in N,N‐dimethylacetamide and dimethyl sulfoxide but poor in water, acetone, methanol, and ethyl acetate. The preliminary in vitro biodegradation properties of the USPEA copolymers were investigated in both pure phosphate buffered saline (PBS) buffer and α‐chymotrypsin solutions. The copolymers showed significantly faster weight loss in an enzyme solution than in a pure PBS buffer. Upon the adjustment of the unsaturated‐to‐saturated diester monomer feed ratio, the obtained USPEA copolymers could have controlled chemical and physical properties, such as glass transition temperatures, solubility, and biodegradability, which could easily extend their applications to biomedical and pharmaceutical areas. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1595–1606, 2007     

Rapid swelling and deswelling in cryogels of crosslinked poly(N-isopropylacrylamide-co-acrylic)

Thermally sensitive hydrogels of poly[N-isopropylacrylamide (NIPA)-co-acrylic(AA)] hydrogels with N,N-methylene bisacrylamide (BIS) as crosslinker have been synthesised via a two-step procedure in which, the initial polymerisation is conducted for various times at 18 °C, this step being followed by polymerisation for one fixed time at −22 °C. The gravimetrically determined rates of swelling/deswelling for these materials termed “cryogels” prepared by this two-step polymerisation are much higher than those for the same type of hydrogel prepared via conventional methods (30 °C for 24 h). For example the time for the former xerogel to take up 70% of its final water content at 25 °C is just 18 min, compared with a time 300 min for the latter to attain the same uptake of water. During deswelling (shrinking) at 50 °C, which is above the lower critical temperature, the hydrogel loses 60 and 90 wt.% water in 1 and 10 min respectively, compared to a timescale for the corresponding crosslinked copolymers prepared by conventional methods of about 100 min for 50 wt.% water loss. A third type of hydrogel was made by a cold treatment (CT), for which the hydrogel prepared by conventional polymerisation was stored in the frozen state. The swelling rate of these CT xerogels was the same as that for xerogels prepared by conventional polymerisation, but the deswelling rate of the former was higher than that of the latter; for example, during deswelling, a loss of 90% water is attained within a few minutes.Scanning electron microscopy, digital photographs and flotation experiments together with swelling ratio studies reveal that the polymeric network of cryogel produced by the two-step polymerisation method is characterised by an open structure with more pores and higher swelling ratio but lower mechanical strength compared to the conventional hydrogels. The polymerisation was taking place on moderate freezing condition and the hydrogel was stored in a frozen state and subsequent thawing of polymer to be very useful the acceleration the response rate of this kind hydrogels. Such rapid response hydrogels have potential applications in separation and drug release technologies for example.     

Chitosan-N-poly(ethylene glycol) brush copolymers: Synthesis and adsorption on silica surface

Chitosan-N-poly(ethylene glycol) brush copolymers with different degree of substitution (DS) were synthesized via reductive amination of chitosan by methoxy poly(ethylene glycol) (MPEG) aldehyde. Chitosan-N-MPEG copolymers were high-molecular-weight products with desirable DS; solubility and solution viscosity of those copolymers depended on the method of the synthesis of MPEG aldehyde and on DS. Synthesis of MPEG aldehyde by the use of TEMPO radical/BAIB was not suitable because of partial oxidation of methoxy groups of MPEG resulting in bifunctional PEG derivatives leading to cross-linking. Adsorption studies of chitosan-N-MPEG graft copolymers on silica surface show that these polymers adsorb in highly hydrated layers.