Thermodynamics of poly(α-olefin) solutions

The Maron theory of polymer solutions was used to examine the 30°C vapor pressure data of Tait and Livesey on solutions of polyheptene-1, polydecene-1, polydodecene-1, and polyoctadecene-1 in toluene. For polyheptene-1 and polydecene-1, excellent agreement was obtained between theory and experiment over the entire concentration range studied. However, for the other two polymers, deviations were observed between the calculated and observed vapor pressures at higher solution concentrations. These deviations were used to show the presence of crystallinity in these and to ascertain the amounts. Further, it was shown that only one crystalline form of the polymer was present in the polydodecene-1, whereas in the polyoctadecene-1 two crystalline forms were detected. These observations, confirmed by measurements with a differential thermal analyzer (DTA), indicate that for polydodecene-1 and one of the crystalline forms in polyoctadecene-1 the crystallization involves alignment of both backbone and side chains; however, the lower melting form in polyoctadecene-1 appears to have only the side chains aligned in the crystal lattice.     

β-Phase of poly(vinylidene fluoride) formation in poly(vinylidene fluoride)/poly(methyl methacrylate) blend from solutions

The effect of single and mixed solvent on the crystallization behavior of the PVDF/PMMA blend from solutions was investigated. The films cast from the good solvent N,N-dimethylformamide (DMF) dominantly yielded the β-phase crystal with the highest crystallinity of PVDF. Those deposited from the methyl ethyl ketone (MEK) and tetrahydrofuran (THF) exhibited a mixture of α- and some extra β-phase crystals and presented the low crystallinity of PVDF. The crystallization behavior and morphology of the films cast from the mixed solvent (THF/DMF) revealed an enormous dependence on the DMF content. The increased DMF content in the mixed solvent enhanced the interactions between polymers and solvents, and favored the β-crystal of PVDF formation but hindered the α-phase of PVDF formation. Thus, the total crystallinity of PVDF in the blend film was decreased with the DMF content increasing, because of the decreased α-phase of PVDF. In addition, the morphological feature revealed that the voids between the PVDF spherulites were eliminated remarkably by blending with PMMA. The average size of the connected spherulite on top surface of the film can grow into larger as DMF content increased.     

Improvement of ammonia sensing properties of poly(pyrrole)–poly (n-methylpyrrole) composite by ion irradiation

In the present investigation we have electrochemically synthesized polypyrrole–poly (n-methylpyrrole) composite film with optimized process parameters (viz. concentration of monomers and dopant, applied current density, deposition time, pH of electrolyte etc.) on platinum substrate. The composite film of polypyrrole–poly (n-methylpyrrole) was subjected to electrical, spectral and morphological characterizations and its sensing response to various concentration of ammonia was also studied. Later, the synthesized composite films were irradiated under high vacuum (∼5×10⁻⁶ Torr) at room temperature with 85 MeV O⁷⁺ ion beam at various fluences from 1×10⁵ to 1×10⁷ ions/cm². We have observed remarkable improvements in electrical and morphological properties suitable for gas-sensing applications. The irradiated composite film was evaluated for the sensing of various concentrations of ammonia and excellent improvement in terms of sensitivity, lower detection limit and response time was observed.     

Laser transmission welding of poly(ethylene terephthalate) and biodegradable poly(ethylene terephthalate) – Based blends

Joining of Poly(Ethylene Terephthalate) PET and its biodegradable derivatives is of high relevance to ensure good productive rate, low cost and operational safety for fabrication of medical and electronic devices, sport equipments as well as for manufacturing of food and drug packaging solutions. In the present investigation, granules of PET and PETs modified by organic additives, which promote biodegradation of the polymeric chains, were prepared by extrusion compounding. The achieved granules were subsequently re-extruded to shape thin (330 μm) flat sheets. Substrates cut from these sheets were joined by Laser Transmission Welding (LTW) with a continuous wave High Power Diode Laser (cw-HPDL). First, based on a qualitative evaluation of the welded joints, the most suitable operational windows for PETs laser joining were identified. Second, characterization of the mechanical properties of the welded joints was performed by tensile tests. Accordingly, Young's modulus of PET and biodegradable PET blends was studied by Takayanagi's model and, based on the experimental results, a novel predicting analytical model derived from the mixture rule was developed. Lastly, material degradation of the polymeric joints was evaluated by FT-IR analysis, thus allowing to identify the main routes to thermal degradation of PET and, especially, of biodegradable PET blends during laser processing.     

Synthesis and Characterization of Terpolymers of poly(L-lactide-glycolide-ε-caprolactone)

Random terpolymers of poly(L-lactide-glycolide-ε-caprolactone) (PLLGC) was prepared by ring-opening polymerization of L-lactide, glycolide and ε-caprolactone monomers initiated with stannous octanoate. Fourier transform infrared spectra, nuclear magnetic resonance and gel permeation chromatography were employed to characterize the obtained PLLGC terpolymers. The effects of polymerization temperature, reaction time, the amount of initiator and the polymerization pressure on the weight average molecular mass and polydispersity index of the PLLGC were investigated. In addition, the water contact angle of the PLLGC was also tested. The characterization of chemical structure showed that the PLLGC was successfully synthesized. For instance, a PLLGC terpolymer with a weight average molecular mass of about 12.435?×?10⁴?Da and a polydispersity index of 1.28 was obtained when the polymerization was conducted with a molar ratio of monomer to initiator ([M]/[I]) of 2000, polymerization temperature of 140?°C, polymerization pressure of 5.0?Pa and reaction time of 24?h. The random incorporation of ε-CL monomer units decreased the wettability of the PLGA copolymers.     

三链核酸poly(U)·poly(A)·poly(U)主链的振动位移

基于三链核酸 poly(U)· poly(A)·poly(U)的螺旋对称性 ,利用晶格动力学方法 ,计算了三链核酸分子 poly(U)·poly(A)·poly(U)主链振动的本征矢 ,探讨了振动位移矢量和线二色光谱的关系。结果表明 ,对应着磷酸双氧的反对称振动谱线可以用于直接确定磷酸根的取向 ,精度大约为 1°。其他谱线必须通过对分子的简正分析来帮助确定分子的结构。     

三螺旋DNA分子poly(dT)·poly(dA)·poly(dT)的构型和振动谱

我们计算了ｐｏｌｙ（ｄＴ）·ｐｏｌｙ（ｄＡ）·ｐｏｌｙ（ｄＴ）的Ｈｏｗａｒｄ模型的原子笛卡尔坐标，并利用晶格动力学方法对模型进行了简正分析。结果发现其０ Ｐ ０对称振动模式位于８０４ｃｍ－１，这和８１０ｃｍ－１附近没有拉曼和红外谱线的实验结果不符。在８００～１０００ｃｍ－１的范围内只有四个振动模式，明显少于拉曼和红外光谱在该范围内的谱线数目。所以我们认为Ｈｏｗａｒｄ模型需要进一步地完善和修正，ｐｏｌｙ（ｄＴ）·ｐｏｌｙ（ｄＡ）·ｐｏｌｙ（ｄＴ）必须具有三条不完全一致的脊骨     

Piezoelectric property of hot pressed electrospun poly(γ-benzyl-α, L-glutamate) fibers

Since the 1960s, the piezoelectricity in biopolymers (e.g. proteins and polynucleotides) has attracted considerable scientific attention. In particular, poly(glutamate)s have been one of the most popular targets for this research due to their well-defined helical structure and permanent polarity along the helical axis. To date, films of poly(glutamate)s have been shown to exhibit piezoelectricity only in shear mode (d₁₄), mainly due to the limitation in fabricating electrically poled polymer samples. This paper describes a combined electrospinning and hot press method that allows production of poled poly(??-benzyl-??,L-glutamate) (PBLG) films with piezoelectricity in all d₃₃, d₃₁ and d₁₄ modes for the first time. It is found that this PBLG film belongs to the matrix structure of C_??v group, which is the same as that of poled PVDF film. The moderately high piezoelectric coefficients in both d₃₃ and d₁₄ modes as well as their thermal stability make the poled PBLG film an excellent candidate for use in flexible transducers and small energy harvesting devices.     

The dipolar and exchange contributions to the spin-lattice relaxation of the imino protons in poly(rA)· poly(rU)

Selective, semiselective, and biselective excitation has been used to study the spin-lattice relaxation of the hydrogen-bonded imino protons in the sonicated, double-stranded RNA polymer poly(rA)· poly(rU). The spin-lattice relaxation of the imino protons has contributions from both dipolar interactions and exchange with the solvent, and the relative contribution of each to the observed rate depends on temperature. When exchange is slow compared to the dipolar contribution, the two components can be resolved by measuring the relaxation rate with and without prior inversion of the solvent peak. When exchange is fast, the contributions can be resolved by comparing the initial selective relaxation rate with the rate of saturation transfer when the solvent peak is inverted. This allows the exchange and dipolar contributions to be separated at temperatures well below the duplex melting temperatures and provides an easy way to study the mechanism of proton exchange with the solvent.     

Studies on structural,optical and cluster size of poly(m-toluidine)–polyvinyl chloride blends

Poly(m-toluidine) (PmT), a derivative of polyaniline, has been prepared by chemical oxidation polymerization method. The synthesized PmT powder is blended with plasticized polyvinyl chloride (PVC) to achieve 20 μm thick self-supported films. These films were irradiated with 60 MeV Si⁵⁺ ions at three different fluences whose S _e (electronic energy loss) value is found to be 1.988×10³ KeV/μ m, an order of magnitude larger than 60 MeV C⁵⁺ (2.958×10² KeV/μ m). Fourier transform infrared (FTIR), X-ray diffraction (XRD) and ultraviolet-visible (UV) absorption studies of pre- and post-irradiated films of PmT–PVC blends were carried out to study the heavy ion irradiation effects on these polymer blends. An overall change in the structure of the polymer blend has been observed from FTIR studies. UV-visible spectra show a decrease in the optical band gap (E _g) and an increase in cluster size with increasing fluence. An effort is made to compare these results with our earlier studies. We found that the variation in S _e plays an important role in the structural and optical properties of PmT–PVC blends.     

Control on β conformation of poly(9,9-di-n-octylfluorene)via solvent annealing

Films of poly(9,9-dioctylfluorene)(PFO) are of great importance in fabricating light emitting diodes.In practice, theβ-phase of PFO is expected due to its high efficiency in the transport of charge carrier.To promote the formation of β-phase,PFO films are immersed and annealed in the mixture of solvent/nonsolvent.The effects of temperature, solvent/nonsolvent ratio, and annealing time are examined systematically.It is found that the fraction of β-phase can be highly improved by increasing the ratio of solvent/nonsolvent.The reconfiguration of PFO molecules for β-phase in annealing is generally finished in 10 min.The finding in this study demonstrates that solvent-assisted annealing offers a fast and economic approach for mass annealing.     

Nanostructured Thermosetting Blends of Phenolic Thermosets and Poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) Triblock Copolymer

The amphiphilic triblock copolymer, poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (PEO‐b‐PPO‐b‐PEO) was incorporated into novolac resin to prepare thermosetting blends. The morphology of the thermosetting blends was investigated by means of atomic force microscopy (AFM) and small‐angle x‐ray scattering (SAXS) and the nanostructures were obtained. It was identified that the reaction‐induced phase separation occurred in the blends of phenolic thermosets with the model poly(propylene oxide) (PPO), whereas poly(ethylene oxide) (PEO) was miscible with novolac resin after and before the curing reaction. In terms of miscibility and phase behavior of the subchains of the triblock copolymer with novolac resin, it was demonstrated that the formation of nanostructures in the thermosets followed a mechanism of reaction‐induced microphase separation.     

The impact of point thermal absorbers in ablation of poly(methyl methacrylate)

Molecular dynamics (MD) simulations are used to study the interactions of photons with a poly(methyl methacrylate), or PMMA, substrate and point thermal absorbers. The point thermal absorbers are embedded within the polymer matrix which can be excited and transfer energy to the surrounding particles through an internal vibrational mode. Using a fluence above the ablation threshold, two excitation channels are studied—one includes a direct heating of the polymer and the other includes the excitation of the thermal absorbers. Although the yield of ejected particles is similar for both simulations, the plume composition differs. For the simulation of the excitation of the point thermal absorbers, the plume consists of a greater number of smaller substrate fragments due to local high temperature regions.     

Silica coating of Co–Pt alloy nanoparticles prepared in the presence of poly(vinylpyrrolidone)

This article describes a method for silica coating of Co–Pt alloy nanoparticles prepared in the presence of poly(vinylpyrrolidone) (PVP) as a stabilizer. The Co–Pt nanoparticles were prepared in an aqueous solution at 25–80 °C from CoCl₂ (3.0 × 10⁻⁴ M), H₂PtCl₆ (3.0 × 10⁻⁴ M), PVP (0–10 g/L), and NaBH₄ (4.8 × 10⁻³–2.4 × 10⁻² M). The silica coating was performed for the Co–Pt nanoparticle colloid containing the PVP ([Co] = [Pt] = 3.0 × 10⁻⁵ M) at 25 °C in (1/4) (v/v) water/ethanol solution with tetraethoxyorthosilicate (TEOS) (7.2 × 10⁻⁵–7.2 × 10⁻³ M) and ammonia (0.1–1.0 M). Silica particles, which had an average size of 43 nm and contained multiple cores of Co–Pt nanoparticles with a size of ca. 8 nm, were produced at 1.4 × 10⁻³ M TEOS and 0.5 M ammonia after the preparation of Co–Pt nanoparticles at 80 °C, 5 g/L PVP, and 2.4 × 10⁻² M NaBH₄. Their core particles were fcc Co–Pt alloy crystallites. Their saturation magnetization was 2.0-emu/g sample, and their coercive field was 12 Oe.     

Electrical properties, structure, and surface morphology of poly(p-xylylene)–silver nanocomposites synthesized by low-temperature vapor deposition polymerization

The crystalline structure, surface morphology, electrical, and optical properties of thin films of nanocomposites consisting of silver nanoparticles embedded in poly(p-xylylene) matrix prepared by low-temperature vapor deposition polymerization were studied. Depending on the filler content, the average size of silver nanoparticles varied from 2 to 5 nm for nanocomposites with 2 and 12 vol.% of silver, correspondingly. The optical adsorption in the visible region due to surface plasmon resonance also exhibited a clear correlation from silver content, revealing a red shift of the adsorption peak with the increase of the metal concentration. The temperature dependences of the dc resistance of pure p-xylylene condensate and p-xylylene–silver cocondensates during polymerization as well as temperature dependences of the formed poly(p-xylylene)–silver nanocomposites were examined. The observed variation of the temperature dependences of electrical resistance as a function of silver concentration are attributed to different conduction mechanisms and correlated with the structure of the composites. The wide-angle X-ray scattering and AFM measurements consistently show a strong effect of silver content on the nanocomposite structure. The evolution of the size of silver nanoparticles by thermal annealing was demonstrated.     

Influence of photoexcitation pathways on the initiation of ablation in poly (methyl methacrylate)

Experimental and theoretical studies of laser ablation of polymers, under various processing conditions, have identified many possible photoexcitation pathways and consequently many likely processes responsible for the onset of ablation. We investigate the role of these processes—namely the thermal, mechanical and chemical processes—occurring in a polymeric substrate during UV irradiation. Molecular dynamics simulations with an embedded Monte Carlo-based reaction scheme were used to study ablation of Poly (methyl methacrylate) at 157 nm. Laser-induced heating and chemical decomposition of the polymeric substrate are considered as ablation pathways. For the heating case, the mechanism of ejection is thermally driven limited by the critical number of bonds broken. This fragmentation process is well reproduced by the existing bulk photothermal ablation model. Alternatively, if the photon energy goes toward direct bond breaking, it initiates chemical reactions, polymer unzipping, and formation of gaseous products leading to near complete decomposition, loss of strength and cohesiveness of the top layers of the polymeric substrate. The ejection of small gaseous molecules weakens and hollows out the substrate, facilitating liftoff of larger fragments of material. These larger clusters are thermally ejected and the photochemical ablation process can be described by the two-step model proposed by Kalontarov.     

Structural,optical and electrical properties of 60 MeV C5+ ion-irradiated poly(3-methylthiophene) films

The structural, optical and electrical properties of 60 MeV C⁵⁺ ion-irradiated poly(3-methylthiophene) (P3MT) synthesized by the chemical oxidation polymerization method have been studied. The P3MT powder was dissolved in chloroform (CHCl₃), and thin films of thickness 2 μm were prepared on glass and Si substrates. The polymerization was confirmed by the FTIR spectrum. Then films were irradiated by 60 MeV C⁵⁺ ions at different fluences. FTIR spectra show methyl group evolution after irradiation. The optical band gap decreases slightly after irradiation and the DC conductivity increases by about one order of magnitude after irradiation at the highest fluence. The role of S _e has also been discussed when compared with 60 MeV Si⁵⁺ ion irradiation of P3MT. The morphological changes are observed using SEM.     

Study on third-order nonlinear optical properties of a soluble poly(p-phenylene vinylene) derivative

Recently, π-conjugated polymers with large π-electrondelocalization have received much attention because oftheir larger and ultra faster nonlinear optical (NLO)response due to the distortion of π-conjugated elec-tronic charge distribution along the main chain[1-3].Poly(p-phenylene vinylene) (PPV) and its derivativesare typical π-conjugated polymers that have been de-scribed in the literature for the possibility of using themin light-emitting device and large-area multicolor dis-play, whi…     

Preparation and characterization of biodegradable poly(ε-caprolactone)-based gel polymer electrolyte films

Biodegradable polymer electrolyte films based on poly(ε-caprolactone) (PCL) in conjunction with lithium tetrafluoroborate (LiBF₄) salt and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) ionic liquid were prepared by solution cast technique. The structural, morphological, thermal, and electrical properties of these films were examined using X-ray diffraction (XRD), optical microscopy (OM), differential scanning calorimetry (DSC), and impedance spectroscopy. The XRD and OM results reveal that the pure PCL possesses a semi-crystalline nature and its degree of crystallinity decreases with the addition of LiBF₄ salt and EMIMBF₄ ionic liquid. DSC analysis indicates that the melting temperature and enthalpy are apparently lower for the 40 wt% EMIMBF₄ gel polymer electrolyte as compared with the others. The ambient temperature electrical conductivity increases with increasing EMIMBF₄ concentration and reaches a high value of ～2.83?×?10^?4 S cm^?1 for the 85 PCL:15 LiBF₄ + 40 wt% EMIMBF₄ gel polymer electrolyte. The dielectric constant and ionic conductivity follow the same trend with increasing EMIMBF₄ concentration. The dominant conducting species in the 40 wt% EMIMBF₄ gel polymer electrolyte determined by Wagner’s polarization technique are ions. The ionic conductivity of this polymer electrolyte (～2.83?×?10^?4 S cm^?1) should be high enough for practical applications.     

The effects of photochemical oxidation and chain conformation on green emission of poly(9,9-dioctylfluorene)

The effects of chain conformation on the photo-oxidation and green emission of poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) has been investigated at both single-molecule and ensemble levels. Single-molecule studies reveal the conformation of PFO chains to be more globular when cast from THF than from toluene solutions. Intensity transients of the single molecules show that the elongated molecules cast from toluene have more fluctuations due to limited energy transfer along the polymer chains. The more globular chains show monotonic decays with isotropic polarization. Emission spectra of the single molecules show that photochemical oxidation leads to a reduction in the emission of the molecule with no change in the emission spectra. No green emission is ever detected for single molecules, indicating that formation of emissive ketone defects is a rare event. Ensemble studies of chains show that molecules cast from THF develop some green emission upon photodegradation, while those cast from toluene do not. The increase in green emission in the globular molecules suggests that interchain contacts improve energy transfer for emissive ketone defects in the PFO cast from THF.