Effects of the addition of dimer acid alkyl esters on the properties of ethyl cellulose.

In this study, we synthesized dimer acid (DA) esters, having short to long alkyl chains, (DA-Cn) by the Diels-Alder reaction and subsequent esterification reaction of fatty acids that were prepared by the hydrolysis of waste vegetable oil. It was found that the DA-Cn were thermally more stable than common petroleum-based plasticizer DOP. When the DOP, DA, or DA-Cn with short alkyl chains were added to ethyl cellulose (EC), the optical clarity and SEM images of the samples showed their good miscibility with those additives in a micro-scale. It was also found that the rubbery modulus of the EC decreased with increasing amount of additives; the type of the additives did not affect the rates of the decrease in the rubbery modulus. The main transition temperatures of the EC containing either DA or DA-C1 or DA-C4 decreased with increasing amounts of those additives and were comparable to that of the DOP-containing EC. The above findings suggested that the DA and its esters with short alkyl chains could act as effective plasticizer and, thus, could be used instead of the DOP. In addition, the results obtained from tensile testing and leaching experiments implied that the DA might be better plasticizer than the DA-C1 and DA-C4, at least in some cases, because of hydrogen-bonding with the EC.

Influence of charge densities of randomly sulfonated polystyrene surfaces on cell attachment and proliferation.

Attachment and proliferation of NIH-3T3 fibroblast cells on random polymer surfaces, polystyrene sulfonated acid (PSSAx) with five different degrees of sulfonation (x = 0%, 5%, 10%, 15% and 33%) and on a tissue culture polystyrene (TCPS) surface were studied. The surface properties, wettability and roughness were measured by water-contact angle and atomic force microscopy measurement. The wettability and surface roughness increased with increasing the content of sulfonic acid groups on the surfaces. The number of cells attached on the surface after seeding increased with increasing x and reached to the maximum value on PSSA15. The cell proliferation also increased with increasing x. However, cell proliferation was slow down on PSSA33 in comparison to PSSA10 and PSSA15 surfaces after 48 h culture.

Unipolar bistable switching of organic non-volatile memory devices with poly(styrene-co-styrenesulfonic acid Na).

We demonstrated unipolar organic bistable memory devices with 8 x 8 cross-bar array type structure. The active material for the organic non-volatile memory devices is poly(styrene-co-styrenesulfonic acid Na) (PSSANa). From the electrical measurements of the PSSANa organic memory devices, we observed rewritable unipolar switching behaviors with a stable endurance and narrow cumulative probability. Also the PSSANa memory devices exhibited a uniform cell-to-cell switching with a high ON/OFF ratio of approximately 10(5) and good retention time of approximately 10(4) seconds without significant degradation.

Effects of the type of solvents on the morphology of styrene-methacrylic acid random copolymers cast onto silicon wafer.

The effects of the type of solvents on the aggregation behavior of poly(styrene-ran-methacrylic acid) (PSMAA) cast onto silicon wafer were studied using a SEM method. It was found that polystyrene prepared from DMF formed non-spherical aggregates but that PSMAA formed mixtures of ellipsoids and spheres. As the acid content increased, the spheres having a distinct boundary started contacting each other, and the average size of spherical particles decreased. Upon neutralization, the spherical particles became contacted spheres covered with much smaller spheres (ca. 20 nm in their sizes) and formed micro-gels. These results were compared to the data in the previous study of samples obtained from either water or THF. It was observed that the solubility parameters of the copolymers and ionomers, and polarity of solvents were some of key factors that determine the aggregation behavior of the polymers. The volatility of the solvent was also found to be an important factor for the aggregation behavior of polymers.

Application of column-switching HPLC method in evaluating pharmacokinetic parameters of zaltoprofen and its salt.

The objective of this study was to compare the pharmacokinetic parameters of zaltoprofen and those of its sodium salt in rats. Zaltoprofen, a potent non-steroidal anti-inflammatory agent, was virtually insoluble in water, but its sodium salt had excellent water solubility. To investigate the effect of aqueous solubility differences upon their pharmacokinetic parameters, minicapsules containing the drug powders were administrated orally to rats, and blood samples were taken via the common carotid artery. A column-switching high-performance liquid chromatographic analytical procedure was developed and validated for the quantitation of zaltoprofen in rat plasma samples. Our study demonstrated that the time required to reach maximum plasma concentration (T(max)) of zaltoprofen sodium was significantly reduced and its maximum plasma concentration (C(max)) was increased 1.5-fold, relative to the values for zaltoprofen. It is anticipated that the sodium salt of zaltoprofen will allow the rapid onset of the drug's action in the treatment of inflammatory diseases.

Effects of the neutralization degree on morphologies in "drying-mediated" samples of sodium neutralized poly(styrene-ran-methacrylic acid) copolymers in THF.

To understand the effect of neutralization degree on surface morphologies of drying-mediated samples, un-neutralized, partially and fully Na-neutralized poly(styrene-ran-methacrylic acid) (PSMAA) prepared from THF solutions were investigated using a scanning electron microscope (SEM). We varied the content of acid groups as well as the degree of neutralization of the PSMAA copolymers. The neutralization degree changed the surface morphologies of the polymers significantly. When the acid group content was low (<9.4 mol%), the morphologies of PSMAA were found to be very similar to that of homo-PS, forming a continuous matrix with a number of circular pores. Upon neutralization, the shape of the pores changed to non-circular form and the porous matrix was mingled with the congregated aggregates. With increasing neutralization degrees, the boundary between porous films and deformed sphere-shaped aggregates became unclear. For fully neutralized forms, only highly porous layered films were formed, indicating micro phase separation between solvent and aggregated copolymer networks.

Determination of three characteristic regimes of weakly charged polyelectrolytes monolayers.

We have demonstrated that monolayer films of randomly charged polystyrene sulfonated acid (PSSA) can be produced by the Langmuir technique, and observed the micro-domain structures, produced by the phase separation of electrostatically charged moieties and the hydrophobic moieties. Using atomic force microscopy and Langmuir isotherm, we found three specific regimes for the polyelectrolytes with various degrees of sulfonation (4-35%); very low charged PSSA (4-5%) in the hydrophobic regime, moderately charged PSSA (6-16%) which possessed a well-balanced nature between electrostatic and the hydrophobic interactions, and strongly amphiphilic nature of PSSA (6-16%) in the ionomer regime. Finally, we could categorize PSSA 35% in the polyelectrolyte regime, due to the dominance of the electrostatic interactions over the hydrophobic interactions.

Preparation and biophysical characterization of pluronic F127-dendrimer conjugate as a delivery agent of antisense oligonucleotides.

A series of pluronic F127 conjugated PAMAM dendrimer generation 5 were prepared to evaluate the potential use of dendrimer-pluronic conjugates as a delivery agent of antisense oligonucleotides. The structural features of the conjugates were identified by FT-IR and 1H-NMR spectra. The prepared dendrimer generation 5-pluronic F127 conjugates showed particle size in the range of 50 to 130 nm with reduced zeta potential. The electrophoretic property of conjugates was further confirmed by capillary zone electrophoresis (CZE), demonstrating the decrease in electrophoretic mobility of conjugates as the number of pluronic F127 on surface of dendrimer increases. The number of free amino groups on a pluronic F127 conjugated dendrimer was quantitatively determined by fluorescamine assay, measuring the fluorescence intensity of amino groups reactive to fluorescamine on dendrimer generation 5-pluronic F127 conjugates. In MTT assay, dendrimer G5-pluronic F127 conjugates were safe on gingival fibroblast cells and acute toxicity was reduced as the mole ratio of dendrimer to pluronic increased. Complex formation of dendrimer G5-pluronic F127 conjugates with oligonucleotides was dose dependent.

Effects of molecular weights of sulfonated polystyrene ionomers on the formation of stable colloidal particles in tetrahydrofuran/water (1/99) mixture.

The effects of the molecular weights (MWs) of sulfonated polystyrene copolymers on the colloidal particle sizes and the size distributions were investigated. It was found that the size of colloidal particle of acid copolymer of relatively low MW, being largest in comparison with higher MW sample, decreased strongly and then remained constant at ca. 11 nm upon dilution. These findings implied that at relatively high concentrations the colloids aggregated together due to the interactions between particles having relatively non-polar surface and that the colloids might contain more than one polymer chain. In the cases of copolymers of high MWs, the colloid sizes did not change much with the solution concentration, but the particle size of the higher MW copolymer was slightly larger than that of the lower MW sample. This was understood; the higher MW copolymer, the longer polymer chain, and the larger colloid. The size of the ionomeric colloids was found to increase slightly upon dilution, which was due to the repulsion of ionic groups on the surface. As expected, the size of the particles of the ionomers showed a similar trend found in the acid samples.

Small-angle X-ray scattering study on poly(ethyl acrylate-co-itaconate) ionomers neutralized with various cations.

The morphology of poly(ethyl acrylate-co-itaconate) ionomers neutralized partly and fully with Na(I), Li(I) and Zn(II) was studied using a small-angle X-ray scattering (SAXS) technique. It was found that the SAXS peak position for the ionomers shifted to lower angle with increasing degree of neutralization for the ionomers containing 5.8 mol% of ionic repeat units. In the case of 11.9 mol% ionomers, with increasing degree of neutralization from 50% to 100% the SAXS peak shifted to slightly higher angles. With the density data and the space-filling concept for a simple cubic lattice, the average radii of multiplets of the ionomers were calculated. For 5.8 mol% ionomers, the radius of the Li-ionomer increased from 0.35 nm to 0.43 nm with increasing neutralization degree from 50% to 100%, and that of the Na-ionomer changed from 0.34 to 0.53 nm. In the case of the 11.9 mol% ionomers, the radius changed from 0.51 to 0.49 nm for the Li-ionomer and from 0.42 nm to 0.47 nm for the Na-ionomer. For the Zn-ionomers, only 100% neutralized ionomers showed a SAXS peak. From the SAXS profiles, the persistence lengths of the polymer chains attached to the scattering centers were also obtained.

Formation of the colloidal particles of sulfonated polystyrene ionomers neutralized with either Na(I) or Ba(II) in ThF/water (1/99) mixture.

The sizes of colloidal particles in THF/water (1/99 v/v) of the sulfonated polystyrene copolymers containing 2.1, 5.1 and 9.4 mol% of either acidic or ionic repeat units were determined using a dynamic light scattering technique. It was observed that for the acid copolymer containing 2.1 mol% of acidic units the size of the particle and size distribution decreased significantly as the solution concentration decreased from 2.0 x 10(-4) to 5.0 x 10(-6) g/mL. However, when the content of acidic units increased to 5.1 and 9.4 mol%, the size of the particles and size distribution increased slightly with decreasing solution concentrations. It was also found that the neutralization of the acid group with Na(I) induced the slow increase in the diameter of colloidal particles of the ionomers with decreasing solution concentration, and that the size of the colloids decreased with increasing ion contents. Thus, it was suggested that the former and latter findings could be understood using the polyelectrolyte effect and charge density concepts, respectively. For the ionomers neutralized with Ba(II), it was found that the size of the single colloidal particles was similar to that of the Na(I) ionomer. However, the aggregates of the colloids were not easily separated by the ultrasonication. Thus, it was speculated that the Ba(II) cations placed inside the aggregates of hydrophobic environment acted as the links between colloidal particles.

Aggregation behavior of Na-neutralized styrene-ran-methacrylic acid copolymers in aqueous solution.

The aggregation behavior of un-neutralized, partly and fully Na-neutralized poly(styrene-ran-methacrylic acid) copolymers in aqueous solution was investigated using a SEM technique. It was observed that the un-neutralized copolymer formed spherical particles on the Si wafer, and the average size of particles was ca. 160 nm. The particle sizes did not change much with acid content. Upon the neutralization of the acid groups of the copolymer with NaOH, the copolymer became more hydrophilic, leading to the formation of network-like feature consisting of much smaller particles (< 50 nm), compared to those of the acid copolymers. With increasing ionization, the boundary of the particles forming networks faded away, implying the formation of tubular structures.

Surface modification for polystyrene colloidal particles with controlled charge densities.

A significant amount of polystyrene sulfonated acid (PSSA) and poly(styrene-ran-acrylic acid) (PSAA) random copolymer can be adsorbed by dispersion of PS particles via a swelling-quenching process. A THF-water mixed solvent was used in the swelling process and a large amount of pure water was used, to give a low concentration of THF% in quenching process. Our results showed that functional PSSA groups were randomly and tightly adsorbed to the PS particles. When the mol.% of charged segments was increased, the progressive adsorption of PSSA chains to the PS particles leads to an increase in the electrophoretic mobility and zeta-potential of aqueous dispersions. Thus, we were able to obtain well-distributed surface charge density on the PS particles.

Effect of the charge on the morphology of sodium salt form of the randomly sulfonated polystyrene ionomer cast onto silicon wafers.

The morphology of the sodium salt form of randomly copolymerized polystyrene sulfonate (Na-PSS) in water/THF(99/1 v/v) cast onto silicon wafers, was studied by using scanning electron microscope (SEM). The contents of the sulfonate repeat units in Na-PSS were 1.1, 2.4, 4.6, 10.8, and 15.6 mol%. Based on the observed SEM images, the morphology of the Na-PSS changed with increasing ionic group content. For 1.1 and 2.4 mol%, sphere-shaped aggregates were formed with average sizes of 90 nm and of 77 nm, respectively. For 4.6 mol% and 10.8 mol%, 20-30 nm-sized aggregates were close-packed and fused together, resulting a surface with large roughness and ca. 10 nm-sized pores were formed. As the mol% increased to 15.6, the surface became smoother and flat films were formed.

Self-assembly of mixtures of block copolymers of poly(styrene-b-acrylic acid) with random copolymers of poly(styrene-co-methacrylic acid).

The effects of the addition of random copolymers of poly(styrene-co-methacrylic acid) [P(S-co-MAA)] on the self-assembly of block copolymers of poly(styrene-b-acrylic acid) (PS-b-PAA) are described. The effects of variation of five factors, including the MAA content, the weight fraction and molar mass of the P(S-co-MAA), the initial concentration of the mixture, and the length of the PAA segment in the block copolymer, were investigated. With increasing MAA content, the localization of the random copolymer in the aggregate changed from the core to the interface, which led to a morphological transition from spheres to vesicles. Vesicles, mixtures of vesicles and large spheres, and large spheres alone were formed with increasing weight fraction of the random copolymer. When the molar mass of the random copolymer was high, both rods and vesicles were observed at low water contents; otherwise, only vesicles were observed. The vesicle size increased (from 100 to 140 nm) with increasing initial polymer concentration, whereas the vesicle membrane thickness remained constant. The size of the vesicles prepared from the mixtures increased with water content but decreased with the length of PAA in the diblock.