Linear and nonlinear optical properties of trans- and cis-poly(1-ethynylpyrene) based sonogel hybrid materials

The synthesis of sol-gel materials induced by ultrasonic action (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic and optical properties. The resulting SiO₂ glass exhibits high porosity and allows the inclusion of organic compounds in the colloidal sol-state. In this work, optical properties of trans-poly(1-ethynylpyrene) (trans-PEP) and cis-poly(1-ethynylpyrene) (cis-PEP) (M_w=24,000 g/mol) incorporated in this kind of gels were studied by absorption and fluorescence spectroscopies. Absorption spectra of the polymers showed that trans-PEP possesses a higher degree of conjugation than its homologue cis-PEP in sol-gel. Intramolecular interactions occur between adjacent pendant pyrene units (associated pyrenes) present in each polymer, giving rise to static excimer emissions, strongest in cis-PEP because of the shorter distances between aromatic rings. The results were compared to those previously reported for these polymers in solution. Besides, trans- and cis-PEP exhibited nonlinear optical properties like third harmonic generation (THG), which were measured in sol-gel phase for spin-coated film samples.     

Synthesis and physicochemical characterization of a well-defined poly(butadiene 1,3)-block-poly(dimethylsiloxane) copolymer

For the first time, order-order and order-disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D₃), and subsequently characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size exclusion chromatography (SEC), Fourier Transform infrared spectroscopy (FTIR), Small-Angle X-ray scattering (SAXS) and rheology. SAXS combined with rheological experiments shows that the order-order and order-disorder transitions are thermoreversible. This fact indicates that the copolymer has sufficient mobility at the timescale and at the temperatures of interest to reach their equilibrium morphologies.     

Thermal properties of poly(ethylene succinate) nanocomposite

This article describes the thermal properties of clay-containing poly(ethylene succinate) (PES) nanocomposite. The nanocomposite of PES with organically modified montmorillonite (o-mmt) has been prepared by solution-intercalation-film-casting technique. Small-angle X-ray scattering patterns and transmission electron microscopy observations show the homogeneous dispersion of silicate layers in the PES matrix. The crystallization and melting behaviors of the PES matrix in the presence of dispersed silicate layers have been studied by differential scanning calorimeter, polarized optical microscope, and wide-angle X-ray scattering. Results show that the incorporation of o-mmt stops the super-cooling effect and accelerates the mechanism of nucleation and crystal growth of PES matrix significantly. The incorporation of o-mmt also improves the thermal stability of neat PES dramatically.     

Developing coarse-grained force fields for cis-poly(1,4-butadiene) from the atomistic simulation

Computational methods are described and applied to study how to develop coarse-grained force fields for cis-poly(1,4-butadiene) from the atomistic simulation. We developed an iterative method for potential inversion from distribution functions for the polymer systems. Then, we analyzed the static character and dynamic character from atomistic simulation and coarse-grained (CG) simulation as a simple application, the results also testified the coarse-grained modeling is effective.     

Precise preparation of four-arm-poly(ethylene glycol)-block-poly(trimethylene carbonate) star block copolymers via activated monomer mechanism and examination of their solution properties

The polymerization of trimethylene carbonate (TMC) in the presence of HCl·Et₂O via activated monomer mechanism was performed to synthesize 4a-PEG-b-PTMC star block copolymers composed of poly(ethylene glycol) (PEG) and poly(trimethylene carbonate) (PTMC) using four-arm (4a) PEG as an initiator. The TMC conversion and molecular weight of PTMC increased linearly with the polymerization time or the feed ratios of the TMC to 4a-PEG in the presence of HCl·Et₂O in CH₂Cl₂ at 25 °C. The obtained PTMC had molecular weights close to the theoretical value calculated from TMC to PEG molar ratio and exhibited monomodal GPC curve. We prepared successfully 4a-PEG-b-PTMC star block copolymers without metal catalyst at room temperature via living ring-opening polymerization (ROP) of TMC from 4a-PEG as an initiator in the presence of HCl·Et₂O as a monomer activator. The CMCs of the 4a-PEG-b-PTMC star block copolymers determined from fluorescence measurements. The CMCs of the 4a-PEG-b-PTMC star block copolymers decreased in the order of the increase in the PTMC segment. The partition equilibrium constant, K_v, which is an indicator of the hydrophobicity of the micelles of the 4a-PEG-b-PTMC star block copolymers in aqueous media, increased with the increase in the PTMC segment. In conclusion, we confirmed that the 4a-PEG-b-PTMC star block copolymers form micelles and hence may be potential hydrophobic-drug delivery vehicles.     

Synthesis,optical and electrochemical properties of ZnO nanowires/graphene oxide heterostructures

Large-scale vertically aligned ZnO nanowires with high crystal qualities were fabricated on thin graphene oxide films via a low temperature hydrothermal method. Room temperature photoluminescence results show that the ultraviolet emission of nanowires grown on graphene oxide films was greatly enhanced and the defect-related visible emission was suppressed, which can be attributed to the improved crystal quality and possible electron transfer between ZnO and graphene oxide. Electrochemical property measurement results demonstrated that the ZnO nanowires/graphene oxide have large integral area of cyclic voltammetry loop, indicating that such heterostructure is promising for application in supercapacitors.     

Poly(4-diphenylaminostyrene) with a well-defined polymer chain structure: Controllable optical and electrical properties

The effect of polymer chain structure on the optical and electrical properties are reported for poly(4-diphenylaminostyrene) (PDAS), which was prepared by the living anionic polymerization of 4-diphenylaminostyrene (DAS) with the benzyllithium (BzLi)/N,N,N′,N′-tetramethylethylenediamine (TMEDA) system. The optical properties of PDAS are strongly affected by the stereoregularity of the PDAS polymer chain; intramolecular excimer-forming fluorescence was observed from PDAS with a syndiotactic-rich configuration. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PDAS were approximately −5.4 and −2.0 eV, respectively, regardless of the polymer chain structure. The hole and electron drift mobilities for PDAS were in the order of 10⁻⁴ to 10⁻⁵ (cm²/V s) and 10⁻⁵ (cm²/V s), respectively, with negative slopes. The distance of each triphenylamino (TPA) group in the polymer chain was a major factor influencing the drift mobility of PDAS. The current-voltage (I-V) characteristics of PDAS were controllable according to the polymer chain structure of PDAS.     

Synthesis and characterization of amphiphilic graft copolymer poly(ethylene oxide)-graft-poly(methyl acrylate)

A novel well-defined amphiphilic graft copolymer of poly(ethylene oxide) as main chain and poly(methyl acrylate) as graft chains is successfully prepared by combination of anionic copolymerization with atom transfer radical polymerization (ATRP). The glycidol is protected by ethyl vinyl ether first, then obtained 2,3-epoxypropyl-1-ethoxyethyl ether (EPEE) is copolymerized with EO by initiation of mixture of diphenylmethyl potassium and triethylene glycol to give the well-defined poly(EO-co-EPEE), the latter is deprotected in the acidic conditions, then the recovered copolymer [(poly(EO-co-Gly)] with multi-pending hydroxyls is esterified with 2-bromoisobutyryl bromide to produce the ATRP macroinitiator with multi-pending activated bromides [poly(EO-co-Gly)_(ATRP)] to initiate the polymerization of methyl acrylate (MA). The object products and intermediates are characterized by NMR, MALDI-TOF-MS, FT-IR, and SEC in detail. In solution polymerization, the molecular weight distribution of the graft copolymers is rather narrow (M_w/M_n < 1.2), and the linear dependence of Ln [M₀]/[M] on time demonstrates that the MA polymerization is well controlled.     

Poly(9,9-dihexylfluorene) derivatives containing electron-transporting aromatic triazole segments: Synthesis, optical and electrochemical properties

We prepared three new poly(9,9-dihexylfluorene) derivatives (P1–P3) containing kinked aromatic triazole (triphenyl-1,2,4-triazole derivative) via Suzuki coupling polymerization. These copolymers were soluble in common organic solvents and showed high decomposition temperatures (T_d = 416–454 °C). The optical and electrochemical properties of P1–P3 were compared with poly(9,9-dihexylfluorene) (PFO) and P4 and P5 in which the linkages of the aromatic triazole were different. After introducing the triazole units, absorption spectra showed blue shift (388 nm → 372 nm) due to reduced conjugation, but PL spectra remained almost unchanged (417–418 nm). The linkages of triazole with fluorene segments in P1–P5 were different: (1) fluorene segments linked with triazole through a kinked angle (P1 and P2), (2) triazole as a branch unit (P3) and as terminal groups (P4), (3) fluorene segments linked with triazole in a linear way (P5). As estimated from semi-empirical MNDO calculation, two twisted conformations (ca. 90° each) exist between triazole core and fluorene groups. These kinked conformation and twisted structure increased the PL efficiency (Φ_PL = 0.60–0.73, Φ_PL = 0.58 for PFO) and partially inhibited annealing-induced excimer formation. From cyclic voltammetric results, P1–P3 exhibited better electron affinity (LUMO: −2.75 to −2.82 eV) than PFO (LUMO: −2.52 eV).     

Thermosensitive poly(allylamine)-g-poly(N-isopropylacrylamide): synthesis, phase separation and particle formation

Grafting of poly(N-isopropylacrylamide) (PNIPAAm) having carboxylic groups at one end onto poly(allylamine) (PAH) in the presence of water soluble carbodiimide has yielded PAH-g-PNIPAAm copolymers with grafting ratios of 50, 29 and 18, respectively. These thermosensitive copolymers exhibit a lower critical solution temperature (LCST) at 34 °C at a temperature increase cycle regardless of their grafting ratios, a temperature identical to that of PNIPAAm-COOH oligomers. Temperature cycling reveals completely reversible polymer aggregation and dissolution above and below the LCST, respectively. Much smaller particle sizes are observed by scanning force microscopy and transmission electron microscopy compared to dynamic light scattering. A porous sphere model is suggested to depict the structure of the particles formed above the LCST, by which the dependence of the particle sizes on their grafting ratios is interpreted taking into account the surface tension and the spatial aggregation distance. Finally, to demonstrate the capability of the copolymers being used as thermosensitive polyelectrolytes, assembly onto multilayers is conducted and the increase of layer thickness is confirmed by small angle X-ray scattering and ellipsometry characterizations.     

Blends of bacterial poly(3-hydroxybutyrate) and a poly(epichlorohydrin-co-ethylene oxide) copolymer: thermal and CO2 transport properties

In this work the miscibility and the carbon dioxide transport properties of a bacterial, isotactic poly(3-hydroxybutyrate) (iPHB) and its blends with a copolymer of epichlorohydrin and ethylene oxide (ECH-co-EO) have been studied. Blends were prepared by solution/precipitation. The aim to obtain miscible blends of iPHB with a rubbery second component (such as the ECH-co-EO copolymer) is to have mixtures with glass transition temperatures below room temperature. In these conditions, the iPHB chains not involved in the crystalline regions retain its mobility. This mobility seems to be necessary for the attack of microorganisms and the corresponding biodegradability.Miscibility is the general rule of these mixtures, as shown by the existence of a single glass transition temperature for each blend and by the depression of the iPHB melting point. The interaction energy density stabilising the mixtures, calculated using the Nishi-Wang treatment, was similar to those of other polymer mixtures involving different polyesters and poly(epichlorohydrin) (PECH) and ECH-co-EO copolymers. The so-called binary interaction model has been used in order to simulate the evolution of the interaction energy density with the ECH-co-EO copolymer composition. Previously reported experimental data on blends of iPHB with PECH and poly(ethylene oxide) (PEO) have been used to quantify the required segmental interaction energy densities.In the determination of the CO₂ transport properties of the mixtures, only iPHB rich blends containing up to 40% of copolymer were considered. The effect of the ECH-co-EO copolymer is to increase the sorption and the diffusion of the penetrant (and, consequently, the permeability) with respect to the values of the pure iPHB. This is primarily due to the reduction of the global crystallinity of the blends and to the low barrier character of the ECH-co-EO copolymer. Sorption data can be reasonably reproduced using an extension of the Henry's law to ternary systems.     

Branched poly(arylene ether ketone)s with tailored thermal properties: Effects of AB/AB2 ratio, core (B3) percentage, and reaction temperature

A series of poly(ether ketone) copolymers were prepared by nucleophilic aromatic polymerization reactions of the AB monomer 4-fluoro-4′-hydroxybenzophenone, 1, and the AB₂ monomer bis(4-fluorophenyl)-(4-hydroxyphenyl)phosphine oxide, 2, in the presence of 3 or 5 mol% of a highly reactive core molecule, tris(3,4,5-trifluorophenyl)phosphine oxide (B₃), 4. All of the copolymers prepared in the presence of a core molecule were sufficiently soluble in N-methylpyrrolidinone, NMP, to allow the determination of their molecular weights and polydispersity indices, PDIs. Number-average molecular weights, M_ns, of 3200-6800 Da were determined and the PDI values ranged from 1.41 to 4.07. The M_n was controlled by the mol% of 4 present in the reaction mixture with higher molar percentages leading to lower M_n values. Lower reaction temperatures and lower ratios of AB/AB₂ monomers afforded copolymers with lower PDI values. As expected, the crystallinity of the samples decreased with an increasing AB₂ content or an increase in PDI. The copolymers also exhibited excellent thermo-oxidative stability with a number of samples suffering 5% weight losses at temperatures, in air, well in excess of 450 °C.     

Microstructural studies on BaCl2 doped poly(vinyl alcohol)

We have studied the effect of BaCl₂ dopant on the optical and microstructural properties of a polymer poly(vinyl alcohol) (PVA). Pure and BaCl₂ doped PVA films were prepared using solvent casting method. These films were characterized using FTIR, UV-visible, XRD and DSC techniques. The observed peaks around 3425 cm⁻¹, at 1733 cm⁻¹ and 1640 cm⁻¹ in the FTIR spectra were assigned to O-H, CC stretching and acetyle CO group vibrations, respectively. In the doped PVA shift in these bands can be understood on the basis of intra/inter molecular hydrogen bonding with the adjacent OH group of PVA. The UV-visible spectra shows the absorption bands around 196 nm and shoulders around 208 nm with different absorption intensities for doped PVA, which are assigned to n→π* transition. This indicates the presence of unsaturated bonds mainly in the tail-head of the polymer. Optical band energy gap is estimated using UV-visible spectra and it decreases with increasing dopant concentration. The powder XRD shows an increase in crystallinity in the doped PVA, which arises due to the interaction of dopant with PVA causing a molecular rearrangement within the amorphous phase of polymer. These modifications also influence the optical property of the doped polymer. The DSC study also supports increasing crystalline thickness and degree of crystallinity due to doping.     

Synthesis,optical, electrochemical,and thermal stability properties of poly(azomethine-urethane)s

In this study, the novel low band gap and thermally stable poly(azomethine-urethane)s (PAMUs) were synthesized to investigate aliphatic and aromatic group effects on some physical properties such as thermal stability, optical and electrochemical properties. For this reason, we firstly synthesized the new Schiff bases via condensation reaction of 5-nitrovanilin with aromatic and aliphatic diamines. Then, these monomers were converted to PAMUs derivatives by the step-polymerization reaction with aromatic and aliphatic diisocyanates. The structures of the compounds were confirmed by FT-IR, UV–vis, ¹H NMR, and ¹³C NMR techniques. The molecular weight distribution parameters of the compounds were determined by the size exclusion chromatography (SEC). The compounds were also characterized by solubility tests, TG–DTA, and DSC techniques. Cyclic voltammetry (CV) measurements were carried out and HOMO–LUMO energy levels and electrochemical band gaps (E^′g${E^{\prime }}_g$) were calculated from their absorption edges. Additionally, optical band gaps (E_g) were determined by using UV–vis spectra of the materials. Fluorescence measurements were carried out in THF, DMF, and DMSO solutions to determine the optimum concentrations and the maximal emission and excitation intensities.     

Poly(N-vinylguanidine): Characterization, and catalytic and bactericidal properties

Poly(N-vinylguanidine) (PVG) is one of the simplest guanidine-bearing polyelectrolytes, but is virtually unknown in the scientific literature. An efficient synthetic route for poly(N-vinylguanidine) (PVG) is described that involves free-radical polymerization of N-vinylformamide (NVF) followed by basic hydrolysis of the PNVF and guanidinylation of the resulting polyvinylamine (PVAm). The molecular weights can be varied by altering the initial NVF/azo initiator ratio. Characterization of the PVG by ¹H and ¹³C NMR, FTIR and FT-Raman spectroscopy methods supports the PVG structure. The PVG possesses an average pK_a of 13.4 and is an active hydrolyzing species for diisopropyl fluorophosphate (DFP), an organophosphate mimic for combat nerve agents. The second-order rate constant of the DFP hydrolysis by PVG at pH 7.8 and 25 °C was measured to be 3.9 × 10⁻³ M⁻¹ s⁻¹, expressed per concentration of the catalytic amino or imino moieties in each PVG monomer. The hydrolysis occurs via the general S_N2 mechanism of base catalysis. The guanidinylation of PVAm affords PVG with 10- to 40-fold lower minimum inhibition concentration (MIC) when tested against four Gram-positive and four Gram-negative bacteria relative to the PVAm itself. Hence, the PVG is effective both as a hydrolyzing agent against toxic organophosphates and as a bactericide, thus exhibiting potential as a material for use in chemical and biological defense as well as a disinfectant in clinical and industrial applications.     

Mechanical and Thermal Properties of Poly(Phthalazinone Ether Sulfone)/Poly(Ether Sulfone) Blends

The mechanical and thermal properties of poly(phthalazinone ether sulfone) (PPES)/poly(aryl ether sulfone) (PES) blends prepared by melt-mixing were investigated by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The dynamic mechanical thermal analysis results show that the incorporated PES has a large influence on the heat stability of PPES. The DMTA results display that the blends with a single glass transition temperature, which increases with increasing PPES content, indicates that PPES and PES are completely miscible over the studied composition range. The thermodegradative behavior of PPES/PES blends was used to analyze their thermal stability. The Friedman technique was used to determine the kinetic parameters (i.e., the apparent activation energy and order of reaction of the degradation process). The results indicate that the presence of the PES component influences the thermal stability of the PPES. On the basis of the kinetic data derived from Friedman' approach, the lifetime estimates for pure PPES, pure PES, and the blends generated from the weight loss of 5% were constructed.     

Synthesis, crystallization and tensile properties of poly(ethylene terephthalate-co-2,6-naphthalate)s with low naphthalate units content

A series of poly(ethylene terephthalate-co-naphthalate)s (PETN copolymers) with low naphthalate units content was synthesized. A melting point depression was observed, while the glass transition temperatures were slightly higher than that of Polyethylene terephthalate (PET). Crystallization rates of the copolymers decreased with increasing comonomer content. WAXD patterns showed that only PET crystals were formed. Co-crystallization behaviour was evaluated on the basis of the Wendling–Suter model. The tensile properties of the copolymers PETN 97/3 and PETN 94/6, Young's modulus yield stress and elongation at break was significantly improved compared to PET. WAXD showed that some crystalline precursor was generated during drawing of the specimens. DSC traces of the drawn specimens showed enhanced crystallization rates compared to that of the original amorphous specimens.     

Thermal properties of poly(styrene-block-ε-caprolactone) in blends with poly(vinyl methyl ether)

The thermal characteristics of a styrene-ε-caprolactone diblock copolymer, P(S-b-CL), in blends with poly(vinyl methyl ether) (PVME) were studied by DSC. The glass transition temperatures show that PVME is only dissolved in the PCL block. It segregates from the PCL block at low temperatures. The addition of PVME leads to increasing crystallinity of the PCL block in a certain range of composition. However, degrees of crystallinity do not change significantly with crystallization temperature. Optical inspection revealed that the PCL block does not form spherulites. The crystallization kinetics of the PCL block has been systematically studied. The rate constants of crystallization for different blends decrease exponentially with crystallization temperature, whereas the rates of crystallization are scarcely affected by PVME content. The Avrami exponents were found close to two.     

Crosslinkable poly(aryl ether ketone)s containing pendant phenylethynyl moieties: Synthesis, characterization and properties

A novel phenylethynyl-contained bisphenol monomer, (2,5-dihydroxyphenyl)(4-(2-phenylethynyl)phenyl)methanone (PEBP), has been synthesized and characterized. The resultant monomer was copolymerized with hydroquinone and 4,4′-difluorobenzophenone by means of an aromatic nucleophilic substitution reaction to provide a series of crosslinkable poly(aryl ether ketone)s containing pendant phenylethynyl moieties (PE-PAEKs). The solubility of PE-PAEKs tended to be improved with the increase in PEBP content. Wide-angle X-ray diffraction (WAXD) results showed that introduction of bulky pendant groups into molecular chains led to decrease in crystallinity. PE-PAEKs were successfully cured upon heating. Dynamic mechanical analysis (DMA) results indicated that the glass-transition temperature (T_g) of the cured PE-PAEKs was increased. Thermogravimetric analysis (TGA) results implied that the thermal stability of the cured PE-PAEKs was excellent.     

Synthesis of porphyrin end-capped water-soluble poly(phenylene ethynylene) and study of its optical properties

A novel Porphyrin End-Capped poly(phenylene ethynylene) (P-PPE) was synthesized by palladium-catalyzed cross-coupling reaction. Porphyrin was successfully introduced to the polymer backbone, which was confirmed by ¹H NMR, UV–Vis and Fluorescence spectroscopy. The degree of polymerization of P-PPE was characterized by both ¹H NMR and GPC analysis. UV–Vis absorption and fluorescence studies in organic solvent indicate that there is significant energy transfer between the PPE backbone and the terminal porphyrin end group, and the PPE backbone works as an antenna transferring photo energy to ZnTPP terminal. The aggregation state of P-PPE in water was also investigated by UV–Vis and fluorescence studies.