A HIGH-RESOLUTION SOLID-STATE NMR AND DSC STUDY OF MISCIBILITY AND CRYSTALLIZATION BEHAVIOR OF POLY(VINYL ALCOHOL)/POLY(N-VINYL-2-PYRROLIDONE) BLENDS

Blends of crystallizable poly(vinyl alcohol) (PVA) with poly(N-vinyl-2-pyrrolidone) (PVPy) were studied by C-13 cross-polarization/magic angle spinning (CP/MAS) n.m.r. and d.s.c. The C-13 CP/MAS spectra show that the blends were miscible on a molecular level over the whole composition range studied, and that the intramolecular hydrogen bonds of PVA were broken and intermolecular hydrogen bonds between PVA and PVPy formed when the two polymers were mixed. The results of a spin-lattice relaxation study indicate that blending of the two polymers reduced the average intermolecular distance and molecular motion of each component, even in the miscible amorphous phase, and that addition of PVPy into PVA has a definite effect on the crystallinity of PVA in the blends over the whole composition range, yet there is still detectable crystallinity even when the PVPy content is as high as 80 wt%. These results are consistent with those obtained from d.s.c. studies.

MISCIBILITY OF POLY(N-VINYL-2-PYRROLIDONE) WITH POLY(ETHER SULFONE) AND 2 PHENOLPHTHALEIN-BASED POLYMERS

Blends of poly(N-vinyl-2-pyrrolidone) (PVP) with poly(ether sulphone) and two phenolphthalein-based polymers, viz. phenolphthalein poly(ether ether sulphone) and phenolphthalein poly(ether ether ketone) were prepared by casting from a common solvent and studied by differential scanning calorimetry. It was found that all the PVP blends are miscible and show a single, composition-dependent glass transition temperature (T(g)). The T(g)-composition dependence has been analysed by the use of the Gordon-Taylor equation. The values of the k parameter in the Gordon-Taylor equation obtained are all not high for the three pairs, in accordance with the fact that there is no strongly specific interaction between PVP and any of the other polymers.

MISCIBILITY OF POLY(N-VINYL-2-PYRROLIDONE) WITH A COPOLYAMIDE

Blends of poly(N-vinyl-2-pyrrolidone) (PVP) with a copolyamide (CoPA) randomly composed of 1:1:1 (wt) nylon 6, nylon 66 and nylon 610 structural units were prepared by casting from a common solvent. They were found to be miscible and show a single, composition-dependent glass transition temperature (T(g)). The addition of PVP to CoPA significantly lowers the crystallinity owing to an increasing T(g) of the system. The observed miscibility is proposed to be the result of specific interactions between the proton acceptor groups of PVP and the amide groups of CoPA.

Pretreatment of polymer-supported Pd-Co and its catalytic activity

Various pretreatments of poly (N-vinyl-2-pyrrolidone) (PVP) protected palladium-cobalt system result in different catalytic activities in the hydrodechlorination of chlorobenzene.

One-pot, high-yield synthesis of size-controlled gold particles with narrow size distribution

Here, we first report a facile one-step one-phase synthetic route to achieve size-controlled gold micro/nanoparticles with narrow size distribution by using o-diaminobenzene as a reducing agent in the presence of poly(N-vinyl-2-pyrrolidone) via a simple wet-chemical approach. All experimental data including that from scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques indicates that the gold micro/nanoparticles with a narrow size distribution were produced in high yield (similar to 100%).

Large-scale, rapid synthesis and application in surface-enhanced Raman spectroscopy of sub-micrometer polyhedral gold nanocrystals

Macromolecule-protected sub-micrometer polyhedral gold nanocrystals have been facilely prepared by heating an aqueous solution containing poly (N-vinyl-2-pyrrolidone) (PVP) and HAuCl4 without adding other reducing agents. Scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), ultraviolet-visible-near-infrared spectroscopy (UV-vis-NIR), and x-ray diffraction (XRD) were employed to characterize the obtained polyhedral gold nanocrystals. It is found that the 10:1 molar ratio of PVP to gold is a key factor for obtaining quasi-monodisperse polyhedral gold nanocrystals. Furthermore, the application of polyhedral gold nanocrystals in surface-enhanced Raman scattering (SERS) was investigated by using 4-aminothiophenol (4-ATP) as a probe molecule. The results indicated that the sub-micrometer polyhedral gold nanocrystals modified on the ITO substrate exhibited higher SERS activity compared to the traditional gold nanoparticle modified film. The enhancement factor (EF) on polyhedral gold nanocrystals was about six times larger than that obtained on aggregated gold nanoparticles (similar to 25 nm).

Oxidative carbonylation of aniline over a polymer-supported palladium-copper catalyst

The polymer-supported bimetallic catalyst FVP-PdCl2-2CuCl(2) (PVP, poly(N-vinyl-2-pyrrolidone), obtained in situ by the addition of CuCl2 to an alcoholic solution of PVP-PdCl2, exhibits high selectivity and activity for the oxidative carbonylation of aniline with carbon monoxide and oxygen to ethyl N-phenylcarbamate in the presence of a base (NaOAc) under atmospheric pressure. The strong synergic effect of Pd-Cu gives rise to a clear increase in the selectivity and activity. (C) 2000 Elsevier Science B.V. All rights reserved.

Polymer-supported palladium-manganese bimetallic catalyst for the oxidative carbonylation of amines to carbamate esters

The polymer-supported bimetallic catalyst PVP-PdCl2-MnCl2 (PVP=poly(N-vinyl-2-pyrrolidone)) exhibits high activity and selectivity for the oxidative carbonylation of amines with carbon monoxide and oxygen to carbamate esters under atmospheric pressure in the presence of a base (NaOAc). This catalyst is prepared by the addition of MnCl2 to the alcoholic solution of PVP-PdCl2 in situ. A remarkable bimetallic synergic effect and the role of PVP in PVP-PdCl2-MXn (MXn=the second transition metal component such as NiCl2, CoCl2, MnCl2 and FeCl3) gives rise to an obvious increase in the conversion and selectivity for the reaction. Among the second metal components tested, Mn-Pd exerts the strongest synergic effect. (C) 1999 Elsevier Science B.V. All rights reserved.

Medicated wound dressings based on poly(vinyl alcohol)/poly(N-vinyl pyrrolidone)/chitosan hydrogels

Poly(vinyl alcohol) /poly(N-vinyl pyrrolidone) (PVP)/chitosan hydrogels were prepared by a low-temperature treatment and subsequent Co-60 -gamma-ray irradiation and then were medicated with ciprofloxacin lactate (an antibiotic) and chitosan oligomer (molecular weight = 3000 g/mol). The gel content, swelling ratio, tensile strength, and crystallinity of the hydrogels were determined. The effects of the chitosan molecular weight, the low-temperature treatment procedure, and the radiation dosage on the hydrogel properties were examined. The molecular weight of chitosan was lowered by the irradiation, but its basic polysaccharide structure was not destroyed. Repeating the low-temperature treatment and gamma-ray irradiation caused effective physical crosslinking and chemical crosslinking, respectively, and contributed to the mechanical strength of the final hydrogels. The incorporation of PVP and chitosan resulted in a significant improvement in the equilibrium swelling ratio. and elongation ratio of the prepared hydrogels. The ciprofloxacin lactate and chitosan oligomer were soaked into the hydrogels. Their in vitro release behaviors were examined, and they were found to follow diffusion-controlled kinetics.

Hybridization of poly(4-vinyl pyridine)-b-polystyrene-b-poly(4-vinyl pyridine) aggregates in dioxane/water solution

Self-assembly of binary blends of two triblock copolymers of poly(4-vinyl pyridine)-b-polystyrene-b-poly(4-vinyl pyridine), i.e., P4VP(43)-b-PS260-b-P4VP(43) (P1) and P4VP(43)-b-PS366-b-P4VP(43) (P2), in dioxane/water solution was studied. These two triblock copolymers individually tend to form vesicles (P2) and cylindrical micelles (P1) in dilute solution. It was found that copolymer components in the blend, sample preparation method, and annealing time had significant effect on hybridization aggregate morphology. By increasing P1 content in the copolymer blends, fraction of looped and stretched cylinders increased, while fraction of bilayers decreased. Nearly no bilayer was observed when P1 content was above 85 wt%.

Synthesis and characterization of color-stable electroluminescent polymers: Poly(dinaphtho [1,2-a : 1 ',2 '-g]-s-indacene)s

Two new stepladder conjugated polymers, that is, poly(7,7,15,15-tetraoctyldinaphtho[1,2-a:1',2'-g]-s-indacene) (PONSI) and poly(7,7,15,15-tetra(4-octylphenyl)dinaphtho[1,2-a:1',2'-g]-s-indacene) (PANSI) with alkyl and aryl substituents, respectively, have been synthesized and characterized. In comparison with poly(indenofluorene)s, both polymers have extended conjugation at the direction perpendicular to the polymer backbone because of the introduction of naphthalene moieties. The emission color of the polymers in film state is strongly dependent on the substituents. While PONSI emits at a maximum of 463 nm, PANSI with the same backbone but aryl substituents displays dramatically redshifted emission with a maximum at 494 nm.

Mechanism-transformation synthesis and characterization of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer

By mechanism-transformation (anionic --> cationic) poly(styrene-6-2-ethyl-2-oxazoline) diblock copolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene block capped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of 2-ethyl-2-oxazoline. The products were thoroughly characterized by various methods, such as H-1-NMR, IR, DMA, TEM and SAXS. The results show that the copolymer obtained possesses high molecular weight and narrow molecular weight distribution.