Original Polymer Solution Research Articles

Enzyme encapsulation in freeze-dried bionanocomposites prepared from chitosan and xanthan gum blend

Freeze-dried hydrogel was prepared from a colloidal suspension of chitosan and xanthan gum blend in order to encapsulate an enzyme (firefly luciferase), and the release behavior of the enzyme from the prepared hydrogels was investigated. Selected amount of firefly luciferase was homogenized with the original polymer solution, and was then stabilized in the resultant freeze-dried samples. The encapsulated enzymes showed their enzymatic activities through bioluminescence reaction and in terms of encapsulation stability, prepared samples were found to be sensitive to the buffer pH, that is, the release rate of the enzyme was larger in pH 6.0 than in pH 8.0. The addition of the montmorillonite nanoclay (MMT) significantly lowered the enzyme release rate due to strong influence on the structural modification of the bionanocomposites. Small angle X-ray scattering measurements suggested that this was due to the modification of polymeric network structures, and the polymer network affected the release behavior of the enzyme. Further, enzymatic activities of the encapsulated and the released enzyme were confirmed for over 30 days, suggesting that the hydrogel formulation could be an excellent support structure for encapsulating bioactive substances such as enzymes.

“On–off” switching of dynamically controllable self‐assembly formation of double‐responsive block copolymers with tunable LCSTs

AbstractWe report here a reversible self‐assembly formation system using block copolymers with thermo‐tunable properties. A series of double‐responsive block copolymers, poly(N‐isopropylacrylamide (NIPAAm))‐block‐poly(NIPAAm‐co‐N‐(isobutoxymethyl)acrylamide (BMAAm)) with two lower critical solution temperatures were synthesized by one‐pot atom transfer radical polymerization via sequential monomer addition. When dissolved in aqueous solution at room temperature, the block copolymers remained unimeric. Upon heating above room temperature, the block copolymers self‐assembled into micellar structures. The micelle formation temperature and the resulting diameter were controlled by varying the BMAAm content. 1H Nuclear Magnetic Resonance, dynamic light scattering, field‐emission scanning electron microscopy, and fluorescence spectra revealed the presence of a monodisperse nanoassembly, and demonstrated the assembly formation/inversion process was fully reversible. Moreover, a model hydrophobic molecule, pyrene, was successfully loaded into the micelle core by including pyrene in the original polymer solution. Further heating resulted in mesoscopic micelle aggregation and precipitation. This dual micelle and aggregation system will find utility in drug delivery applications as a thermal trigger permits both aqueous loading of hydrophobic drugs and their subsequent release. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Shear and extensional rheology of solutions of modified hydroxyethyl celluloses and sodium dodecyl sulfate

This work reports on the rheology of aqueous solutions of hydroxyethyl cellulose (HEC) and three derivatives, in the presence of sodium dodecyl sulfate (SDS). The polymers employed were: a hydrophobically modified hydroxyethyl cellulose (HMHEC) containing hexadecyl grafts, a cationically modified hydroxyethyl cellulose (cat-HEC), containing glycidyl-trimethyl-ammonium grafts, and a polymer with both modifications (cat-HMHEC). Rheological measurements were performed in simple shear flow, oscillatory shear flow, opposed-jets flow and flow through porous media. The addition of surfactant increases intermolecular interactions between HMHEC molecules due to the formation of mixed micelles that bridge hydrophobic side groups from different polymer chains. These interactions lead to phase separation in an intermediate SDS concentration range and, at higher surfactant concentrations when a homogeneous phase was obtained, to higher shear and apparent extensional viscosities. Further surfactant addition eventually inhibits hydrophobe interactions due to electrostatic repulsion between micelles, leading to shear viscosities that are even lower than that of the original polymer solution. Hydrophobe interactions are inhibited by the relatively strong nature of flow in opposed-jets. The addition of cationic side groups confers the polymer a polyelectrolytic nature, which translates into higher shear and apparent extensional viscosities. Interchain interactions are strengthened by the presence of surfactant by the formation of intermolecular cross-links between polymer chains.

Multiple pH-Induced Morphological Changes in Aggregates of Polystyrene-block-poly(4-vinylpyridine) in DMF/H2O Mixtures

Multiple changes in the aggregate morphologies of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblocks have been observed as a function of the apparent pH (pH*) in DMF/H2O mixtures. The pH* changes were induced by adding HCl (in the concentration range 400 nM−20 mM) or NaOH (100 nM−20 mM). On the acid side, as the pH* increases from 7 (20 mM HCl) to 12.3 (the pH* of the original polymer solution without any additional microions), the aggregate morphology changes from large compound micelles (LCMs) to a mixture of spheres, rods, and vesicles (pH* = 8), to spheres (pH* = 8.4), to rods (pH* = 11.8), and then back to spheres (pH* = 12.3). In the presence of NaOH, as the pH* increases from 12.3 to 18 (20 mM NaOH), the morphology changes to rods (pH* = 12.6), then back to spheres again (pH* = 17.5), and finally to a mixture of spheres, rods, lamellae, and vesicles (pH* = 18). This level of morphological complexity as a function of pH* is unprecedented. The reasons for the behavior can be ascribed to the amphiprotic nature of P4VP in DMF. The addition of either an acid or a base introduces ionic groups into the corona chains. Thus electrostatic repulsion is introduced and the aggregate morphology changes generally in the direction of bilayers to spheres. However, due to the existence of multiple equilibria, some of the added microions are free, which decreases the steric−solvation interaction and decreases the electrostatic repulsion by shielding. This decrease in the corona repulsion tends to decrease the coil dimensions in the corona. As a result, the morphology is driven in the direction of spheres to bilayers. Therefore, a competition between unshielded electrostatic repulsion and shielding coupled with a decrease of the steric−solvation interaction is induced. At relatively low concentrations, the decrease of the steric−solvation interaction dominates, while at relatively high concentrations, the shielding dominates. In intermediate regions, the unshielded electrostatic repulsion is dominant. The morphological transitions induced by extremely low concentrations of HCl or NaOH (100 nM−1 μM) are very surprising. The effect of a neutral salt (NaCl) on the neutral copolymer and the effect of pH* on a quaternized copolymer were also explored.

Formation of locust bean gum hydrogel by freezing-thawing

The gelation process of locust bean gum (LBG) aqueous solution has been studied by rheological and calorimetric measurements. The storage modulus of the gel was found to be dependent on repeating cycles of the freezing–thawing process and freezing speed. When freezing–thawing was repeated more than three times, the dynamic rigidity of the hydrogel was about 50% more than that of the original polymer solution. Furthermore, the storage modulus was greater for the hydrogel prepared by 12°C min-1 freezing than that by 1°C min-1 freezing. These observations are explained in terms of the formation of ice crystals during the freezing process, observed by differential scanning calorimetry (DSC). © 1998 SCI.

STUDIES ON THE PRODUCTION OF ACRYLIC FIBER BY WET SPINNING

The properties of the dope solution of acrylonitrile-methyl acrylate copolymer of 0.95 to 0.05 which was prepared by 50% aqueous solution of NaCNS were studied.(1) The specific gravity of the dope was measured at 30°C in the concentration range from 0.63% to 11.93%.(2) Hygroscopic behaviours of the 50% aqueous solution of NaCNS and the dope sulution with the polymer concentration of 9.5% were measured and compared at the relative humidity of 60% and at 25°C.(3) Microscopic measurement was utilized to evaluate the dissolving rate of acrylonitrile fiber and polymer particle. The minimum concentration of NaCNS to dissolve the polymer is presumed to be around 46%.(4) The viscosity of the dope solution was measured by the ball fall method in the polymer concentration range from 7% to 13%, and in the temperature range from 0.8°C to 65°C. At 30°C, the modified Baker equation obtained is as follows.where η is the viscosity (sec.), M: molecular weight obtained by using the Staudinger equation, ηBP/C=1.5×10-4M (C: 0.5 mole/l), C: the polymer concentration of the dope (%).(5) A linear relationship was observed between the logarithm of the viscosity and the recipr ocal of the absolute temperature in the temperature range from 30°C to 65°C. This relationship did not hold at the temperature below 10°C.(6) The Copolymers of different molecular weights were mixed in various ratios to prepare six dope solutions of the copolymer mixture and the viscosity of the solutions were measured.The relationship of the viscosity of each of the original polymer solution to those of the mixed polymer solutions may be expresed as: where η: the viscosity of the mixed polymer solution (sec.), η1: the viscosities of the original polymer solutions (sec.), W1: the weight fractions of the original polymer solutions (%).

Reduced viscosities of polyelectrolytes in the presence of added salts

AbstractTwo different techniques for diluting polyelectrolyte solutions with salt solutions are discussed. The first is the so‐called isoionic dilution and the second is a method using salt solutions of concentrations so chosen as to make the reduced viscosity a linear function of polymer concentration.For isoionic dilutions, in which the total counterion concentration is kept constant, the reduced viscosity curves are not linear over the whole range but are rather sharply curved at the early stages of dilution. However, it is observed that the viscosity of solutions subject to such dilutions can be expressed by an empirical equation similar in form to that of Fuoss and Strauss.The second method is carried out by diluting the polymer solution with a simple salt solution whose concentration, c1, is selected by trial and error to make the reduced viscosity a linear function of concentration. The ratio r = c1/c0 where c0 is the concentration of counterions from the original polymer solution, increases as the charge density of the polyelectrolyte decreases and is rather insensitive to c0. The values of 1 − r obtained for the partially neutralized polyacrylate were compared with the degrees of counterion fixation obtained by electrolytic methods, and good agreement was found between the two.