Nm For Poly Research Articles

On the Structure of Poly(N-isopropylacrylamide) Microgel Particles

This investigation presents a study of the internal structure of poly(NIPAM/xBA) microgel particles (NIPAM and BA are N-isopropylacrylamide and N,N'-methylene bisacrylamide, respectively). In this study, x is the wt % of BA used during microgel synthesis. Two values of x were used to prepare the microgels, 1 and 10. The microgel dispersions were investigated using photon correlation spectroscopy (PCS) and small-angle neutron scattering (SANS). These measurements were made as a function of temperature in the range 30-50 degrees C. Scattering maxima were observed for the microgels when the dispersion temperatures were less than their volume phase transition temperatures. The SANS data were fitted using a model which consisted of Porod and Ornstein-Zernike form factors. The analysis showed that the macroscopic hydrodynamic diameter of the microgel particles and the submicroscopic mesh size of the network are linearly related. This is the first study to demonstrate affine swelling for poly(NIPAM/xBA) microgels. Furthermore, the mesh size does not appear to be strongly affected by x. The data suggest that the swollen particles have a mostly homogeneous structure, although evidence for a thin, low segment density shell is presented. The study confirms that poly(NIPAM/xBA) microgel particles have a core-shell structure. The shell has an average thickness of approximately 20 nm for poly(NIPAM/1BA) particles which appears to be independent of temperature over the range studied. The analysis suggests that the particles contained approximately 50 vol % water at 50 degrees C. The molar mass of the poly(NIPAM/1BA) microgel particles was estimated as 6 x 10(9) g mol(-1).

Holographic grating recorded by He–Ne laser operating at 632.8 nm in polymer film containing push–pull azo dye

Holographic gratings were optically recorded by two beams from a He–Ne laser operating at 632.8 nm in poly (methyl methacrylate) (PMMA) film containing push–pull azo dye. The holographic characteristics of the recorded gratings were dependent on the polarization direction of the recording beams and the relationship between the diffractive signals and the power density of recording beams was investigated. The formation of holographic gratings accompanied by 532 nm (double-frequency of Nd:YAG laser) irradiation was studied in detail. It was found that the effect of 532 nm laser to the holographic grating lay in two aspects. The acceleration effect of 532 nm laser to the formation of holographic grating is predominant when the power density of 532 nm laser is low. While at relatively high power density of 532 nm laser, the erasure is the main factor to the holographic grating. Moreover, the holographic grating was probed by 532 nm laser at low power density and the dependence of the first order diffractive signal on the recording beam power density was also presented.

Influence of chain length and temperature on UV-Vis absorption and degradation behavior of poly(diethyl dipropargylmalonate) with an alternating cis-trans-1,2-(cyclopent-1-enylene)vinylene structure

Cyclopolymerization of diethyl dipropargylmalonate (DEDPM) with Mo(N-2,6-i-Pr2-C6H3) (CHCMe2Ph)(OC(CH3)3)2 in the presence of quinuclidine yields poly(DEDPM) with an alternating cis-trans-1,2-(cyclopent-1-enylene)vinylene structure. Poly(DEDPM) n with different degrees of polymerization (n = 5–90) and PDI < 1.4 was prepared. A linear plot of number of monomers (N) added versus molecular weight as determined by light scattering (data were collected at λ = 690 nm) suggests that the cyclopolymerization of DEDPM proceeds in a living manner. A degree of polymerization (DP)-dependent UV-Vis absorption is found. At 25°C, the absorption maximum λmax for poly(DEDPM) n for n ≥ 50 is 591 nm. Thus, a maximum effective conjugation length N eff of 52 can be calculated. Increasing chain length results in a highly resolved fine structure in the UV-Vis spectrum with absorption maxima at 550 and 590 nm and a shoulder at around 513 nm for poly(DEDPM)70. In the solid state, absorption maxima were in the range of 478-574 nm for poly(DEDPM)5–90. Poly(DEDPM)10 and poly(DEPM)90 showed glass transition temperatures of 25.8 and 26.5°C, respectively. The measurement of λmax of poly(DEDPM)50 solutions in chloroform within a temperature range of 30°C reveals a reversible thermoresponsive behavior with changes in λmax of 8 nm. Poly(DEDPM) is stable under air over months in the solid state, as well as in solution using non-acidic solvents (e.g. CH2Cl2). In contrast, values for λmax for poly(DEDPM) solutions in CHCl3 decrease, if the solutions are exposed to air and light, yet remain constant in the absence of light and air. Changes in molar mass of poly(DEDPM) solutions in CHCl3 and CH2Cl2 were investigated by SEC measurements using light scattering detection and correlated with their time-dependent UV-Vis absorption behavior. Finally, poly(DEDPM)10–90 is thermally stable up to 185°C under a helium atmosphere.

A Semiflexible Polymer Model Applied to Loop Formation in DNA Hairpins

A statistical mechanical “zipper” model is applied to describe the equilibrium melting of short DNA hairpins with poly(dT) loops ranging from 4 to 12 bases in the loop. The free energy of loop formation is expressed in terms of the persistence length of the chain. This method provides a new measurement of the persistence length of single-stranded DNA, which is found to be ∼1.4 nm for poly(dT) strands in 100 mM NaCl. The free energy of the hairpin relative to the random coil state is found to scale with the loop size with an apparent exponent of ≳7, much larger than the exponent of ∼1.5–1.8 expected from considerations of loop entropy alone. This result indicates a strong dependence of the excess stability of the hairpins, from stacking interactions of the bases within the loop, on the size of the loop. We interpret this excess stability as arising from favorable hydrophobic interactions among the bases in tight loops and which diminish as the loops get larger. Free energy profiles along a generalized reaction coordinate are calculated from the equilibrium zipper model. The transition state for hairpin formation is identified as an ensemble of looped conformations with one basepair closing the loop, and with a lower enthalpy than the random coil state. The equilibrium model predicts apparent activation energy of ∼−11 kcal/mol for the hairpin closing step, in remarkable agreement with the value obtained from kinetics measurements.

Synthesis and Characterization of Polythiophene Derivatives Containing Electron Transporting and Hole Transporting Moieties

Novel luminescent copolymers, poly(3-(2-benzotriazoloethyl)thiophene-co-octylcarbazolylene) ([(BET)m-OcCz2]n) that contain both electron transporting benzotriazole and hole transporting octylcarbazole moiety were synthesized by oxidation of ferric chloride with changing the composition ratio of BET and OcCz. The absorption peak of UV-VIS was blue-shifted from λmax=440 nm in poly(3-(2-benzotriazoloethyl)thiophene) (PBET) to λmax= 412 nm in [(BET)4-OcCz2]n. The photolumine scence (PL) and electroluminescence (EL) intensities of the polymers were decreased with presence of carbazole moieties in the copolymer.

Role of the structure on the photo and cathodo-luminescence of poly(ethylene naphthalate): PEN

The photoluminescence in the blue emission band at 430 nm of poly(ethylene naphthalate), assigned in literature to the formation of excimers states involving the naphthalene groups, is shown to be very sensitive to the disorder induced by irradiations. The cathodoluminescence, excited by a beam of 4 keV electrons, exhibits two components: a rapidly decreasing fluorescence at 430 nm and a broad and more stable one at 640 nm assigned to short chain segments. The influence of mechanical stretching and temperature on the fluorescence of non-treated PEN films has been investigated. The enhancement of the fluorescence with film elongation is attributed to the increase of the polymer chain ordering along the stretching direction, whereas the decrease of the fluorescence with temperature is correlated to the β ∗ relaxation associated in dielectric spectroscopy to the movements of the naphthalene groups, known to be responsible for the excimer fluorescence. The dependence of the blue and red fluorescence components on the polymer structural organization provides efficient probes to study the local order and degradation stage of PEN and accounts for the results reported in literature according to the different film histories.

Poly(3,4-alkylenedioxypyrrole)s: Highly Stable Electronically Conducting and Electrochromic Polymers

A series of poly(3,4-alkylenedioxypyrrole)s are reported as a new class of electronically conducting polymers exhibiting especially low oxidation potentials from ca. −0.6 to −0.4 V vs Fc/Fc+ (equivalent to −0.15 to +0.05 V vs SCE) as desired for ambient stability of the doped and conducting states. These polymers exhibit unique combinations of multicolor electrochromism, switching from a red or orange neutral state to a light blue/gray doped state, passing through a darker intermediate state (brown), as examined by in situ colorimetry. High spectral contrast ratios have been measured throughout the visible region with a maximum Δ%T = 76% at 534 nm for poly[3,4-(2,2-dimethylpropylenedioxy)pyrrole) (PProDOP−(CH3)2). PProDOP−(CH3)2 exhibits outstanding redox switching stability, being able to undergo 40 000 deep double-potential switches between its doped and neutral states (1 s, Δ%Tmax = 76%) while retaining more than 90% of its electroactivity. A high level of stability to overoxidation has also been observed as these materials show limited degradation of their electroactivity at potentials 2 V above their half-wave potential. Triflate-doped free-standing films of PEDOP and PProDOP, having high electrical conductivities of 83 and 95 S/cm, respectively, have been obtained by galvanostatic deposition at low temperature (−7 °C).

Microscopic visualization on crystalline morphologies of thin films for poly[( R)-3-hydroxybutyric acid] and its copolymer

Thin films with average layer thickness 100 nm of poly[( R)-3-hydroxybutyric acid] (P[( R)-3HB]) and poly[( R)-3-hydroxybutyric acid- co-10 mol% 6-hydroxyhexanoic acid] were isothermally crystallized at a given crystallization temperature after melting at 200°C. The spherulitic and lamellar morphologies of polyester thin films were investigated by means of optical microscopy, transmission electron microscopy and atomic force microscopy. After isothermal crystallization, the uniform two-dimensional spherulites which have the stacking texture of flat-on lamellae were developed throughout both polyester thin films. Each flat-on crystal gave a well-resolved electron diffractogram, and all electron diffractograms were identical. Accordingly, the 6-hydroxyhexanoic acid units were rejected from the tightly packed region of lamellar crystals. Both the lamellar periodicity and lamellar width of polyester thin films increased with a rise in the crystallization temperature. At the growth front of crystalline lamellae, microfibril crystals with 30–50 nm width were present. The enzymatic hydrolysis of thin films was carried out at 25°C using an aqueous solution of PHB depolymerase from Alcaligenes faecalis. After enzymatic degradation, the jagged texture along the crystal long-axis could be observed at the ends of crystalline lamellae on the surface of the thin films. These observations suggest that the lamellar crystals of P[( R)-3HB] is composed of both tight molecular packing regions of microfibril crystals and loose molecular packing boundary regions.

Quasi-Elastic Light Scattering Study of the Synthesis of Tailor-Made Suspensions of Uniform Polyaniline-Based Nanoparticles

The understanding of the mechanism of aniline oxidative polymerization allows one to regulate the synthesis of the colloidal panicle suspensions in such a way that a product of controlled average particle size and panicle size distribution is obtained. Quasi-elastic light scattering was used to determine these parameters for the panicles taken from a reaction mixture at various stages of the polymerization. It has been found that the panicle size and the panicle size distribution of the product depend on the reactiveness of the monomer (m-, o-toluidine. or aniline), on the concentrations of the monomer, oxidant and stabilizer-poly(vinyl alcohol-co-acetate). and on the temperature. The panicles of uniform size are formed within a limited period of time during the polymerization: in some cases until termination. Their sizes lie within the range of 200–600 nm for the polyaniline and within 400–3000 nm for poly(m-toluidine). Comparison of the prepared samples with commercially available uniform polystyrene latex standards shows that the polyaniline- and poly(toluidine)-based panicle suspensions exhibit at least the same but in most cases narrower panicle size distributions. The obtained color panicles can be used in many practical applications, for example, as markers for studies of the transport phenomena in colloidal suspensions.

Novel Copolyamides Containing [60]Fullerene in the Main Chain

Abstract Novel copolymers, poly(1,4-oxybisphenylene fullerenobisacetamide-co-1,4-oxybisphenylene isophthalamide)s, which contained [60]fullerene in the main chain, were synthesized by the direct copolycondensation of a mixture of [60]fullerenobisacetic acid and isophthalic acid with 4,4′-diaminodiphenyl ether in the presence of triphenylphosphite and pyridine. Light scattering measurements for the copolymers showed a weight-average molecular weight Mw of about 5-6 × 104. The UV-visible spectra of the copolymers exhibited the characteristics of the parent fullerene derivative. The absorption edge red-shifted from 370 nm for poly(1,4-oxybisphenylene isophthalamide) to about 700 nm for the copolymers.

Changes in the optical spectra of poly(vinyl chloride) as a result of gamma irradiation

In the present work, the effect of different doses of gamma rays ranging from 50 to 500 kGy on the transmission spectra and the tristimulus transmittance as well as the absorption coefficient in the range 400–700 nm of poly(vinyl chloride) (PVC) were studied by the optical transmission spectra. Variation in the group coordination in the near infrared region (700–3000 nm) were also studied. The data indicated that measurable and remarkable changes in the transmittance of the irradiated samples, as well as decrease in the tristimulus transmittance values, as compared to the unirradiated PVC sample were detected. Moreover, the irradiated samples acquire various colors depending on the radiation doses. Linear empirical formulae are estimated to determine gamma doses from the values of CIE translucency and the absorption coefficients of PVC at 550 and 650 μm.

Modifying a Polystyrene/Poly(methyl methacrylate) Interface with Poly(styrene-co-methyl methacrylate) Random Copolymers

Joints of polystyrene (PS) and poly(methyl methacrylate) (PMMA) modified with ∼50 nm of poly(styrene-co-methyl methacrylate) random copolymer [P(S-ran-MMA)] were investigated. Copolymers having styrene compositions of fS = 0.48 and fS = 0.73 were used. Transmission electron microscopy reveals that the copolymers phase separate to form a distinct layer at the joint such that there is an interface with each homopolymer. Interfacial fracture toughness measurements, using the asymmetric double cantilever beam geometry, show a strong effect of the PS to PMMA sheet thickness ratio; that is, the phase angle influences the measured interfacial toughness. Reflection infrared spectroscopy on fracture surfaces indicates that the crack propagates at or near the PS/copolymer interface for all thickness ratios and for both copolymers. In-plane crazing was not observed in front of the crack tip for these systems. Rather, strengthening appears to be exclusively a consequence of oblique crazes in the more compliant PS sheet which form at 45° or 135° relative to the crack direction. Joints modified with P(S0.73-ran-MMA) exhibit denser oblique crazes than those modified with P(S0.48-ran-MMA), resulting in a higher measured fracture toughness at all sheet thickness ratios or phase angles.

Light Scattering Studies on Dilute Solutions of Semiflexible Polyelectrolytes

Abstract Poly(1,4-phenylene-2,6-cis-benzobisoxazole) and poly(2,5-benzoxazole) represent examples of semiflexible chains, forming polyelectrolytes in solution in protic acids. Dilute solutions of these have been studied by static and dynamic light scattering and viscometry. Solutions have been prepared in acidic solvents over a wide range of ionic strength, and hence of Debye electrostatic screening length K −1. The data reveal electrostatic interactions among the protonated chains through a thermodynamic segment diameter dT that depends markedly on K −1. The analysis suggests that the electrostatic component d e to d τ must be large enough to offset a neutral component d n in d τ, providing the mechanism for dissolution of the charged chains. The persistence length ρ ≈ 40 nm for poly(1,4-phenylene-2,6-cis-benzobisoxazole), is essentially independent of K −1. Thus, for this chain the electrostatic component ρe to ρ must be small in comparison with the neutral component ρn, to ρ. This appears to be in reasonable accord with estimates of ρn based on conformational analyses, and ρ, using an electrostatic model. By contrast, ρ is found to depend markedly on K −1 for poly(2,5-benzoxazole), with ρ much larger than ρn for all of the systems studied. The observed Kρ vary from 20 to 50 with K −1 increasing from 0,8 to 8 nm for poly(2,5-benzoxazole). Thus, it may be considered to be a wormlike semiflexible chain in solvents with low K −1 (high ionic strength), and rodlike in solvents with larger K −1. By comparison, values of Kρ calculated with an electrostatic model based on a charged wormlike cylinder are about ten-fold smaller. The discrepancy is attributed to the failure of the model to account for the discrete rotational states available to the poly(2,5-benzoxazole) chain.

A study of the effect of ultrasonic agitation during development of poly(methylmethacrylate) for ultrahigh resolution electron-beam lithography

Experiments on poly(methylmethacrylate) electron resist have been performed in order to understand how ultrasonic agitation during development affects sensitivity, contrast, and resolution. A modified JEOL 4000 EX electron microscope with a beam diameter of 1 nm was used for writing the resist patterns. First, the development/exposure characteristics of the ultrasonic development process were measured using large area (2×2 μm) patterns. With a 5 s develop in a mix of 3:7 cellosolve:methanol, it was found that ultrasonic agitation increases the effective sensitivity of the resist by roughly 20% but resist contrast does not change significantly (5.7±0.5). It was also found that the sensitivity increases approximately linearly with accelerating voltage from 75 to 400 kV but contrast does not change with voltage significantly. Resolution was explored by writing fine lines at progressively increasing doses in 60 nm of poly(methylmethacrylate) and examining these lines with high resolution scanning electron microscopy. Complete development to the substrate was verified by wet etching a thin chromium layer underneath the resist. The narrowest lines that developed to the substrate had a width of about 10 nm although at this width considerable ‘‘bridging’’ of the lines was observed. We were unable with the ultrasonic agitation conditions used in our experiments to reduce the degree of bridging or the minimum linewidth.

Structural and electrical properties of soluble conducting poly(3-pentylthiophene)

A solution of processible poly (3-pentylthiophene) (P3PT) was synthesized by chemical polymerization. The structure of the resulting polymer was investigated by gel permeation chromatography (GPC); infrared;1H and13C nuclear magnetic resonance; Ultraviolet visible spectroscopy (UV-Vis) and wide-angle X-ray scattering (WAXS) techniques. It was found that the microstructure of the chains has a low number of irregular couplings and thus has desirable electrical properties. In the small-angle region of X-ray scattering, a pronounced peak was observed with ad (coherence length) value of 1.51 nm for P3PT and 1.835 nm for poly (3-heptylthiophene (P3Hept). Electron spin resonance measurements showed that P3PT has 1018 spins g−1, ag value 2.0039, and a δHpp of about 6 Gauss. The Pauli-like susceptibility after doping P3PT with I2 is of the same order as for poly paraphenylene (PPP) doped with AsF5, and corresponds to a density of states at the Fermi level about 0.01 states eV−1 per carbon atom in the thiophene ring. The current-voltage (I–V) characteristics obtained for different temperatures were always linear. The dark room temperature conductivity was 10−8 Sm−1 and distinctly increased after doping. The P3PT studied is a good candidate for potential commercial applications.

Stabilization and characterization of pernigraniline salt: the "acid-doped" form of fully oxidized polyanilines

The electrochemical polymerization of 2-methylaniline and 2-ethylaniline gave uniform electroactive polymer films which were analyzed in different acidic conditions. It has been found that the fully oxidized polymers undergo an acid-base transition at pH∼0 which leads to the formation of a protonated (bipolaronic) form. This electronic structure is characterized by an absorption band at 630 and 680 nm for poly(2-methylaniline) and poly(2-ethylaniline), respectively. A similar structure was obtained in the fully oxidized poly(N-methylaniline)

Cure monitoring of a photosensitive polymer using the luminescent organometallic complex fac-CIRe(CO) 3(4,7-Ph 2-phen)

The organometallic complex fac-CIRe(CO) 3(4,7-Ph 2-phen) exhibits a bright yellow-orange phosphorescence centred at 576 nm in poly(methyl methacrylate)/trimethylolpropane triacrylate (PMMA/TMPTA) solutions. This luminescence feature is shown to be a useful spectroscopic probe of the acrylate crosslinking reactions in the u.v. photochemical curing of a model PMMA/TMPTA thin film system.

Stark spectroscopy of the Rhodobacter sphaeroides reaction center heterodimer mutant.

The effect of an electric field has been measured on the absorption spectrum (Stark effect) of the heterodimer mutant (M)H202L of Rhodobacter sphaeroides reaction centers, where the primary electron donor consists of one bacteriochlorophyll alpha and one bacteriopheophytin alpha. The electronic absorption spectrum of the heterodimer mutant from 820-950 nm is relatively featureless in a poly(vinyl alcohol) film, but it exhibits some structure in a glycerol/water glass at 77 K. A feature is seen in the Stark effect spectrum of the heterodimer at 77 K centered at 927 and 936 nm in poly(vinyl alcohol) and a glycerol/water glass, respectively. This feature has approximately the same shape and width as the Stark effect for the primary electron donor of the wild type, which consists of a pair of bacteriochlorophyll alpha molecules. The angle zeta A between the transition moment at the frequency of absorption and the difference dipole delta muA is 36 +/- 2 degrees in the wild type and 32 +/- 2 degrees for that feature in the heterodimer. A range of values for [delta muA] = (13-17)/f Debye units (where f is the local field correction) is obtained for the 936-nm feature in glycerol/water, depending on analysis method. This feature is interpreted as arising from a transition to the lower exciton state of the heterodimer, which is more strongly mixed with a low-lying charge transfer transition than in the wild type.

Studies on dilute solutions of rodlike macroions. II. Electrostatic effects

AbstractA group of rodlike polymers soluble only in strong protic acids was studied using light scattering and viscosity techniques. These include poly(1,4‐phenylene benzobisoxazole), poly(1,4‐phenylene benzobisthiazole) and poly(1,4‐phenylene terephthalamide). The solution properties were dependent on the ionic strength of the acid used as solvent. In a low ionic strength acid such as chlorosulfonic acid, the polymer solutions exhibited decreased unpolarized scattering, an extremely small translational diffusion coefficient, and high viscosity. All of these effects could be eliminated by the addition of a salt such as lithium chlorosulfonate, which increased the ionic strength of the solvent. The effects were attributed to a pseudo ordering of the polymer solvent system caused by electrostatic repulsions between protonated polymer chains effective over large distances (ca. 100 Å) in the low ionic strength solvent. This type of ordering is distinct from actual anisotropic phase formation, which occurs at higher concentrations in these systems. Analysis of data at infinite dilution gave a persistence length of at least 45 nm for poly(1,4‐phenylene terephthalamide), larger than previous experimental results, but in accord with recent rotational isomeric state calculations and similar to experimental data for poly(p‐benzamide).

Absorption and luminescence spectra of poly (N,N′-bis-phenoxyphenyl)pyromellitimide, the initial polyamic acid and some model compounds

A spectrophotometric study was made of absorption in the range of 220–500 nm of poly(N,N′-bis-(phenoxyphenyl)pyromellitimide), its prepolymer and solutions of a number of model compounds. Proposals were made for the interpretation of absorption bands in the spectrum of the polyimide. It was established that the prepolymer shows blue fluorescence, while polyimide shows none. The absence of fluorescence is hypothetically explained by the high efficiency of intercombination conversion, which is due to the existence of a low level of triplet state of nρ ∗ type. A spectrophotometric method was developed for evaluating the degree of cyclization.