Stimuli responsive gels based on interpenetrating network of chitosan and poly(vinylpyrrolidone)

New spherically shaped crosslinked IPN hydrogels based on chitosan and poly(vinylpyrrolidone) were prepared. The IPN hydrogels were synthesized in two steps: (1) chitosan (CHT) crosslinked beads were obtained by reaction of chitosan with ethyleneglycol diglycidyl ether (EGDE); (2) absorption of a suitable amount of a solution of vinylpyrrolidone (VP) monomer from the porous CHT beads followed to VP polymerization and crosslinking inside the network. Sequential IPN's at different composition were obtained: they reversibly swell in water at various pH and show sensitive volumetric behaviour.     

Adsorption behavior of poly(vinylpyrrolidone) toward fuller's earth suspensions

The adsorption of poly(vinylpyrrolidone) (PVP) onto Fuller's earth surface was studied at fixed pH (4.2) and room temperature (27 ± 0.2°C). The kinetics of the adsorption process was monitored and various adsorption and kinetic parameters such as the adsorption coefficient, the rate constants for adsorption and desorption, the diffusion constant, and the penetration constant were evaluated. The effects of various experimental factors such as the pH and the presence of inorganic and organic anions or aliphatic alcohols were also studied on the adsorbed amounts of PVP. The role of temperature was also investigated and various thermodynamic parameters such as the standard Gibb's free energy, enthalpy, and entropy were also evaluated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2122–2133, 2000     

Complexation of poly(vinylpyrrolidone) and gelatin with some transition metal chlorides in aqueous solution

Complexation of poly(vinylpyrrolidone) and gelatin with certain metal chlorides (HgCl₂, CdCl₂, CoCl₂, and ZnCl₂) have been investigated by viscosimetric and spectrophotometric techniques in aqueous solutions. While the change in intrinsic viscosity, [η], of poly(vinylpyrrolidone) has shown a discontinuity with a concentration of metal chlorides, gelatin showed a steady decrease with increasing metal chloride concentration. The decreasing order of effectiveness of cations in complex formation is Hg²⁺ > Cd²⁺ > Co²⁺ > Zn²⁺ for poly(vinylpyrrolidone) and Zn²⁺ > Co²⁺ > Cd²⁺ > Hg²⁺ for gelatin solutions. It has been suggested that the poly(vinylpyrrolidone)/metal cation interaction is a charge-controlled reaction, and gelatin/metal cation is a covalent coordination in character. A similar metal cation effect has been observed for poly(vinylpyrrolidone) by UV-VIS spectrophotometry. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 891–895, 1998     

Self diffusion of small molecules in aqueous solution of poly(vinylpyrrolidone)

The self-diffusion coefficients of small penetrants were measured in aqueous solutions at varying concentrations of poly(vinylpyrrolidone). Measurements have been performed using the n.m.r. pulsed-gradient spin-echo (PGSE) technique and the classical gradient diffusion (CGD) method, modified for ternary systems. A good agreement was found between the two, confirming the validity of the latter. The results have been quantitatively analysed by a free-volume approach adapted for diffusion of a solute in moderately concentrated polymer solutions. From this model a linear relationship is predicted between ln $\text{D}\text{D}{}_{\mathrm{<mtext>o</mtext>}}$ and ?^?1, the reciprocal volume fraction of solvent, which was also found experimentally for all diffusants studied. An enhanced concentration dependence of penetrant diffusion with increasing size of the diffusing molecules was observed. These findings are in agreement with predictions from the free-volume theory.     

Characterization of poly(vinylpyrrolidone)–konjac glucomannan blend films

Blend films of konjac glucomannan (KGM) and poly(vinylpyrrolidone) (PVP) were prepared by using a conventional solvent‐casting technique and dried at room temperature. The structure and physical properties were studied by infrared spectroscopy (IR), wide‐angle X‐ray diffraction (WAXD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscope (SEM), and by measurement of mechanical properties. The changes of carbonyl stretching bands of KGM and PVP and hydroxyl stretching region of KGM were detected by FTIR analysis. WAXD analysis revealed that the film KP‐2 got the lowest crystallinity of all the films. The tensile strength and breaking elongation of the blend films reaches the maximum value at 10 wt % PVP content. The DTA curves indicated the existence of interaction between two kinds of macromolecules. Higher thermal stability was attained by konjac glucomannan through blending with PVP. These improvements are attributable to the existence of a certain degree of interaction between KGM and PVP molecules resulted from intermolecular hydrogen bonds. Air surface morphology of the films observed by SEM was consistent with the results mentioned above. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1049–1055, 2001     

Effects of curing temperature on poly(ethylene terephthalate)

The effect on poly(ethylene terephthalate) (PET) of thermal curing in a particular temperature range (T max =280-350C) in air have been studied. The changes in the structure were monitored using various characterization techniques such as differential scanning calorimetry, thermogravimetric analysis, optical microscopy equiped with hot-stage, and scanning electron microscopy. It was observed that when (PET) is cured at very high temperature above its original melting point, cross-linking of the (PET) samples occurs. The cross-linking takes place in the melt in this case. With increasing the curing temperature, the area of the higher melting peak temperature decreases due to the increase in cross-linking of (PET). In terms of spherulitic texture, it was found that with increasing the curing temperature more inter-lamellar intra-spherulitic inclusions are observed in the material.     

Improved synthesis of oxymethylene-linked poly(oxyethylene)

Polyethylene glycol 400 was reacted with CH₂Cl₂ in the presence of KOH to form oxymethylene-linked chains. The method gave a high yield of colourless high-molecular-weight elastomer. The ionic conductivity of a mixture of the polymer with LiCF₃SO₃ ([O]/[Li] = 25) was about 5 × 10^?5S cm^?1 at 25°C.     

Properties of aqueous salt solutions of poly(vinylpyrrolidone). II. Polymer dimensions and thermodynamic quantities

The unperturbed dimensions and thermodynamic parameters of poly(vinylpyrrolidone) (PVP) have been studied in aqueous salt solutions, e.g. phosphates, mono- and dihydrogen phosphates, carbonates, sulphates of sodium and potassium. Values of K₀ ( = [η]_ΘM^-1/2, where [η]_Θ is intrinsic viscosity at the theta temperature and M is molecular weight) with M_w = 78 000 g mol^-1 were found to range from 4·63×10^-4 to 5·56×10^-4 dl g^-1, and root-mean-square end-to-end distances, 〈r²〉₀^1/2, ranging from 1·61×10^-6 to 1·68×10^-6cm were evaluated. Values of the characteristic ratio, C_n, the steric parameter, σ, and the enthalpy and the entropy of dilution parameters, χ_H and χ_S, have also been calculated, and the interaction parameter was found to be χ-0·5<-0·001 for aqueous salt solutions of PVP. ©1997 SCI     

Polymer micelle-like aggregates of novel amphiphilic biodegradable poly(asparagine) grafted with poly(caprolactone)

Novel amphiphilic graft copolymers composed of poly(asparagine) (PAsn) as the hydrophilic backbone and poly(caprolactone) (PCL) as the hydrophobic segment were successfully synthesized by grafting PCL-HMDs to poly(succinimde). After tosylating PCL-diol with p-toluenesulfonylchloride (TsCl), tosylated poly(caprolactone) (PCL-OTs) was then reacted with hexamethylenediamine (HMD). The reaction of the amine terminated PCL with poly(succinimide) (PSI) and the following aminolysis resulted in poly(aspargine)-graft-poly(caprolactone) (PAsn-g-PCL). The degree of substitution (DS) and grafting reaction was confirmed by ¹³C NMR, FT-IR spectroscopy and elemental analysis. X-ray diffraction and DSC thermogram showed that the crystalline domain originated from PCL became apparent with an increase of DS. The amphiphilic comb-type graft polymer formed self-aggregates in aqueous solution when precipitated and dialysed against distilled water. Strong hydrophobic interaction of associated PCL grafts facilitated primary aggregate formation with DS, significantly reducing critical aggregation concentration and secondary aggregates also appeared in DLS measurements. Self-aggregates showed a bimodal size distribution originated from the self-aggregation and kinetically controlled particle aggregation, although the smaller primary aggregates was predominant. Spherical and dispersed aggregates of about 20 nm in diameter were observed by a transmission electron microscope.     

One-pot synthesis and characterization of aliphatic poly(oxytetramethylene) ionene

One-pot synthesis of poly(oxytetramethylene) ionene (POI) composed of one dimethylammonium group in each repeating unit is described. POI was prepared by using the cationic polymerization of tetrahydrofuran, followed by the chain extension reaction of living poly(oxytetramethylene) (POTM) chain with N,N-dimethylaminotrimethylsilane. The weight average molecular weight of the ionene with bromide counter-anion (POI-Br) was 48,000 g/mol and the molecular weight of POTM between the ionic sites was ca. 2100. POI-Br showed polyelectrolyte behavior in polar solvent. The elastomeric film of POI-Br was prepared: its tensile strength at break and elongation at break were ca. 11 MPa and ca. 1900% at 19 °C, respectively. Small-angle X-ray scattering, differential scanning calorimetry and dynamic mechanical analysis suggested the formation of microphase-separated structure for POI-Br film.