Oligomer Blends Research Articles

Studies on the Simultaneous Solid-State Polymerization and Exchange Reactions of PET/PEN Oligomer Blends

Poly(ethylene terephthalate) (PET) and poly(ethylene-2,6-naphthalate) PEN oligomers were obtained by degrading high molecular weight PET and PEN. Crystalline PET/PEN blends of varying compositions were prepared by melt blending and then crystallizing at 175°C. Simultaneous solid-state polymerization (SSP) and exchange reactions were performed on these blends by heating just below the melting temperature under a nitrogen flow. 1H NMR spectroscopy was used to study the progress of exchange reactions between terephthalic and naphthalate units. The inherent viscosity was measured to monitor the progress of SSP. WAXS studies indicated that the condensation and exchange reactions occurred in the amorphous phase, leaving the PET and PEN crystallites unaffected. Detailed thermal characterization showed that the crystallization behavior of the copolymers depended strongly on the extent of the exchange reaction.

Shear effect on the phase behaviour and morphology in oligomer blend of polystyrene/poly(methyl methacrylate)

The phase behaviour of an oligomer mixture of polystyrene/poly(methyl methacrylate) (PS/PMMA), which shows an upper critical solution temperature (UCST) type phase diagram, has been investigated under simple shear flow. The cloud points were strongly affected by the values of the applied shear rate. The phase diagrams under different values of shear rate, indicated shear-induced mixing for all measured compositions, and the magnitudes of the depression of the cloud points under the effect of shear rate were found to be composition dependent. The dramatic decrease of the homogenization temperature was investigated as a function of shear rate (γ̇), and the normalised shift in the cloud point |ΔT(γ̇)/T(0)| versus γ̇ was also studied and compared with that of simple liquid mixtures and polymer solutions, as well as high molecular weight polymer blends. The cloud points of this oligomer mixture showed high sensitivity to change under the effect of shear rate; a much higher sensitivity than both simple liquid mixtures and polymer solutions, on the other hand, slightly less sensitivity than the high molecular weight polymer blend (PMMA/poly(styrene-co-acrylonitrile)). The morphology of PS/PMMA=30/70 blend was also studied under different values of shear rate at 35°C below its quiescent cloud point, using the transmission electron microscopy (TEM). The results showed that the shear-induced mixing occurred at a high critical shear rate value (34s−1), below which the dispersed PS-rich domains were slightly elongated and broken-up into very small domain sizes with very good particle distribution.

Novel Microporous Poly(vinylidene fluoride) Blend Electrolytes for Lithium‐Ion Batteries

In the present paper, novel microporous poly(vinylidene fluoride)‐hexafluoropropylene copolymer (PVDF-HFP) blend electrolyte/electrode films were obtained as the result of phase separation between PVDF-HFP and polyethylene oxide (PEO) oligomer additives, which were cast from a common solvent. Upon solvent evaporation and removal of the additives, an interconnected microporous morphology was formed. The additives can either be removed from the films by vacuum evaporation or methanol extraction. The conductivities of the methanol extracted microporous (pore sizes range from 1 to 5 μm) films formed from PVDF-HFP/PEO oligomer blends after electrolyte activation are more than 70% higher than those of the methanol extracted nanoporous (pore size in range from 10 to 100 nm) films prepared from PVDF-HFP/dibutyl phthalate blends. Microporous films formed by vacuum evaporation had conductivities similar to solvent extracted nanoporous separators. Battery performance tests were carried out using lithium cobalt dioxide as the cathode and mesocarbon microbeads as the anode. The cells prepared using extracted microporous PVDF-HFP/PEO oligomer blend films as separators show more than 40% higher specific discharge capacity at the C/2 rate, and 70% higher rate capability than those using extracted nanoporous separators. © 2000 The Electrochemical Society. All rights reserved.

High-speed curing by laser irradiation

Laser-assisted processing of multifunctional systems is a very efficient method for achieving high-speed curing of photosensitive resins. With acrylate functionalized monomers and polymers, crosslinking was achieved upon a few millisecond exposure to a UV laser beam, in the presence of a radical-type photoinitiator. The polymerization reaction was followed in real-time by infrared spectroscopy and shown to proceed with long kinetic chains (up to 20,000 functional groups polymerized per initiating radical). An acrylate functionalized polyester proved to be the most reactive system, with formation of a tightly cross-linked and strickly insoluble polymer. Its high sensitivity makes this photoresist particularly well suited for laser direct imaging applications. Similar results have been obtained with epoxy and vinyl ether functionalized polymers, which undergo a fast cationic polymerization in the presence of a photogenerated protonic acid. Interpenetrating polymer networks have been synthetized by laser irradiation of blends of acrylate and epoxy-functionalized oligomers to obtain polymers that combine the elastomeric character of cross-linked polyurethanes and the toughness of epoxy polymers. These laser-sensitive polymers are to be used as photoresists to produce microcircuits, as protective coatings of optical fibers, as recording media in holography and as photocurable resins in stereolithography.

Potentiometric detection in capillary electrophoresis with a conducting oligomer electrode

A conducting oligomer-based electrode was used as a potentiometric detector for capillary electrophoresis. The electrodes were made by coating copper wires (250 μm diameter) with conducting oligomer blends. The oligomer was of the phenylene vinylene type. The potential changes occurring at the surface of the conducting oligomer electrode were measured in a wall-jet configuration. A mixture of 10 linear saturated fatty acids was separated using different buffers as running electrolytes. For hexanoic acid, the calibration curve showed linearity up to injected concentrations of 7×10 −4 M and a detection limit of 1×10 −6 M was obtained. The intra-electrode variation was 1.7%. The electrode showed a lifetime of at least three weeks. A theoretical model was given to describe the behaviour of the potentiometric detector.

White Light Emitting Electroluminescence Devices with Organic Oligomers

AbstractWe report on the properties of white light emitting electroluminescence (EL) devices fabricated by combining blue and orange light emitting organic materials, parahexaphenyl (PHP) and a new isothianaphthen-S-oxide (ITSO) oligomer. The EL spectrum of this oligomer blend covers the range from 400 to 650 nm. When the concentration ratios of these materials are suitably adjusted a pure white light emission (CIE coordinates of x=0.333 and y= 0.338) and a high external EL quantum efficiency of 1.2% photons/electron can be obtained. The mechanism of the white light generation is ascribed to an internal self-absorption of part of the blue PHP light emission by ITSO and a subsequent photoluminescence emission process of ITSO. The results of photoinduced absorption, which is sensitive to charged species and triplet states of these guest-host systems, are discussed.

Solid-state-concentration effects on the optical absorption and emission of poly(p-phenylene vinylene)-related materials.

We present measurements of the optical absorption and emission properties of poly(p-phenylene vinylene) (PPV) -related materials focusing on the differences between molecules isolated by dispersion in an inert host and concentrated molecular films. Optical absorption spectra, photoluminescence (PL) spectra, PL efficiency, and time-resolved PL spectra of dilute blends of PPV oligomers with 2--5 phenylene-phenyl rings are compared with those of dense oligomer and polymer films. In dilute oligomer-poly(methyl methacrylate) (PMMA) blends with high PL efficiency, the PL decay is exponential, independent of both temperature and oligomer length. This implies that the fundamental radiative lifetime of PPV oligomers is essentially independent of oligomer length. Concentrated spin-cast oligomer films and polymers have a faster and strongly temperature-dependent PL decay that approaches that of the dilute oligomer results at low temperature. The differences in PL decay correspond to changes in PL efficiency. The efficiency of the oligomer-PMMA blend is high and only weakly temperature dependent, whereas that of concentrated films is lower and strongly temperature dependent, decreasing by more than a factor of 3 from 10 to 350 K. The quenching of the PL efficiency in concentrated films is due to migration to extrinsic, impurity related centers as opposed to an intrinsic intermolecular recombination process. The PL spectrum of a dilute oligomer blend redshifts substantially, both as the excitation energy is decreased and as the emission time increases. This spectral redshift is due to disorder-induced site-to-site variation and not to diffusion to lower-energy sites. In contrast, no spectral shift with excitation energy or emission time was observed for dense oligomer films. \textcopyright{} 1996 The American Physical Society.

Photoluminescence of Oligomer and Polymer Blends

Abstract We have measured the photoluminescence(PL) of polymer and oligomer blends using partially converted poly-(p-phenylene vinylene) (PC-PPV) and a kind of p-phenylene vinylene oligomer, 1,4-distyrylbenzene in the solution of N-methyl-2-pyrrolidinone(NMP). The PL spectra of this blended material showed that the amounts of oscillator strength of oligomer peak at 2.79eV shifted to red, near 2.49eV, which is responsible for PC-PPV. This changing of oscillator strength results the enhancement of initially weak PL intensity of PC-PPV and eventually changing the color. In order to explain the excitonic migration effect occurring more seriously in blended system, as we believed, we compared this data to that of PC-PPV/oligomer multi-layered film as well as of oligomer itself. Those results will be also compared with that of another blended material, oligomer and polyaniline(PANI), and the differences will be discussed.

Interfacial Tension of Oligostyrene/Oligo(dimethylsiloxane) near the Critical Point

Interfacial tension γ of an oligomer blend, oligostyrene (M w =600) and oligo(dimethylsiloxane) (M w =460), was measured by the sessile-drop method. The interfacial tension near the critical point could be fitted to γ=γ 0 E 1/Tμ , where e 1/T is the reduced temperature distant e 1/T (=T c /T-1) from the critical point T c . The critical exponent μ was determined to be 1.27, which was exactly of the Ising type, showing an importance of critical fluctuations. The critical amplitude γ 0 was 5.05 mN m -1 . The critical amplitude of the mean-field type theory was calculated with the interaction parameter χ evaluated from the coexistence curve. The theoretical prediction was reasonably consistent with the experimental result, taking into account that the critical behavior was of the Ising type

Coexistence curves of polystyrene/ poly(dimethylsiloxane) blends

The coexistence curves of blends of polystyrene (PS, M w = 600 and 2.2 × 10 3 g mol −1) and poly(dimethylsiloxane) (PDMS, M w = 460, 1400, 3700 and 2.3 × 10 5 g mol −1) were determined using a specially designed refractometer. The coexistence curve of the oligomer blend PS ( M w = 600)/PDMS ( M w = 460) was of the upper critical solution temperature type, and sensitively reflected molecular-weight polydispersity of the PS, although the polydispersity index M w/ M n was less than 1.10. The coexistence curve at the critical composition could be fitted to φ ± = a ± ε β + b ± ε β+ Δ , where φ + and φ − are the volume fractions of PDMS of the coexisting phases ( φ + > φ −), the exponent Δ is 0.5 and ε is the reduced temperature. The critical exponent β was determined to be 0.33 6, which was that for non-renormalized Ising behaviour, showing no polydispersity effect. The Flory—Huggins theory could reasonably describe the coexistence curves of blends with different molecular weights, although it showed a slight discrepancy for the effects of molecular-weight asymmetry on the coexistence curve. By fitting the calculated coexistence curves to the experiments, the interaction parameter % was evaluated as a function of temperature. The obtained % parameter involved a large enthalpy term, dominating the entropy term, and indicated that PS/PDMS was an extremely immiscible blend compared with other reported blends. Critical fluctuation effects on the coexistence curve were also discussed.

Shear influence on the phase separation of oligomer blends

AbstractShear influences on the phase separation behaviour of four different blends of ethylene glycol/propylene glycol oligomers, exhibiting upper critical solution temperatures, were investigated. Cloud point curves at rest (turbidity measurements) are reported for all systems, spinodal conditions (light scattering) and tie‐lines (analysis of the coexisting phases) are given for some examples. Phase diagrams under shear were obtained from rheological data. They demonstrate that the demixing temperatures of systems where both glycols bear OH end‐groups are lowered up to ca. 1°C by shear rates of 1000s−1; the critical composition, generalized to the non‐equilibrium conditions of flow, is markedly shifted. These observations are explained in terms of the generalized Gibbs energy (containing the mechanical energy the system stores during flow) as a consequence of the strongly interacting end‐groups of the glycols. This interpretation is backed by the fact that the shear effects disappear when the glycols are methylated.

Thermodynamics of oligomer blends of poly(methylphenylsiloxane) and polystyrene

Heats of mixing to infinite dilution ΔH M(∞), excess volumes V E and cloud-point curves were experimentally determined for an upper critical solution temperature type of system, the poly(methylphenyl-siloxane)/polystyrene oligomer blend. ΔH M(∞) was positive and V E negative. Flory's equation-of-state theory with modified combining rules was applied to this system. The theory with the positive value of the exchange enthalpy parameter reproduced the experimental thermodynamic properties except for the location of the maximum point in the cloud-point curves.

Incompatible ternary blends containing unsaturated polyester resins. II. Interfacial properties

AbstractThe interfacial tension (γ) in ternary blends of unsaturated polyester (UP) and rubber oligomers in styrene have been measured using three different techniques: tensiometric plate, capillary height, and drop profile methods. These experimental methods give similar results, but it has been shown that γ values “with or without skimming” are very different. The presence of small molecules, inhibitors, impurities, etc., in the interphase region can explain this discrepancy. We have observed a good correlation between γ and the Flory‐Huggins interaction parameter. The elastomer chain ends have an influence on the interfacial tension: γ is reduced when the oligomers possess hydroxyl groups. An epoxy terminated butadiene–acrylonitrile copolymer, ETBN, was prepared from a large excess of diglycidyl ether of bisphenol A, DGEBA, and carboxyl terminated butadiene–acrylonitrile copolymer, CTBN, at 150°C, and without a catalyst. The excess of DGEBA was eliminated by successive precipitation in the selective solvent ethanol. Since the DGEBA blocks are miscible with the UP resin, the introduction of the ETBN copolymer drastically reduces the interfacial tension of the ternary blend of UP and rubber in styrene.

SANS investigations of critical phenomena and phase separations: Two examples of blends with high and low molecular weights

The method of SANS was applied to study critical fluctuations and precipitates in blends of large molecules. The critical behaviour has been investigated for an oligomer blend: n-hexane/n-perfluorohexane; furthermore, for a blend with high molecular weight, PVME/d-PS, the growth of precipitates was measured by means of a double crystal diffractometer with a resolution of 10 -5 Å -1.

Adsorption of polymer mixtures from solutions on solids: I. Polybutylmethacrylate-butadiene-nitrile rubber-aerosil

Until the present time the adsorption of polymer mixtures (1-5) has not been systematicaUy investigated. Meanwhile the practical application of polymer or oligomer blends has a great importance for producing filled polymers, coatings, glues, etc. (6, 7). Therefore the investigation of the selective adsorption of one of the components from a polymer mixture in a common solvent is of great interest, especially so that an insight into the structure and properties of adsorption and boundary layers may be obtained (8). Earlier, as a result of investigation of the system rubber-epoxy resin-NH4C1, we experimentally established that the selective adsorption of one of the mixture components (9, 10) leads to nonuniformity of distribution of macromolecules of different chemical nature in the absorption and boundary layers at various distances from the surface, this factor being very important for understanding physical properties of composite materials. In the present work we investigate in more detail the adsorption and the structure of adsorption layers in the model system. For such a system the mixture polybutylmethacrylate and butadiene nitrile rubber was chosen.