Aqueous Solutions of Native and Hydrophobically Modified Polysaccharides: Temperature Effect

Feasibility of Processing Hot-Melt Pressure-Sensitive Adhesive (HMPSA) with Solvent in the Lab

Hot-melt pressure-sensitive adhesive (HMPSA) is an environmentally benign adhesive which is typically processed without solvent in industries. However, casting solution method is commonly used for experimental purposes in the lab for convenience. Therefore, seven types of solvent with different polarities, including toluene as the most commonly used solvent, were investigated in this work to study the feasibilities. Quick bond strength and holding power were tested with different types of solvents and different adhesive weight percent in the prepared solutions. Through viscosity measurement, thermal analysis, and compositional analysis, the correlation between the chosen solvents and adhesive performance was further explored. It was found that the differences in the obtained bond strength of HMPSA treated with a variety of solvents were due to physical reasons instead of chemical reactions, and a solvent with similar polarity to toluene (e.g., tetrachloride, octane) should be considered as an option because a similar polymer chain relaxation could be maintained as the original HMPSA without solvent treatment. In this study, the mechanism of choosing toluene as common solvent for HMPSA testing was analyzed, and the feasibility of optional solvents was discussed.

Pullulan derivative with cationic and hydrophobic moieties as an appropriate macromolecule in the synthesis of nanoparticles for drug delivery

A new amphiphilic pullulan derivative (DBAP-PO) was obtained by grafting tertiary butyl amine and octanoyl groups on the pullulan backbone as cationic and hydrophobic moieties, respectively. The structural characteristics of the modified polymer were investigated by FT-IR and ¹H and ¹³C NMR spectroscopy. The self-association ability in aqueous solution of DBAP-PO was studied by viscosity and fluorescence methods. The intrinsic viscosity of the polymer was determined by Wolf model. The critical aggregation concentration (CAC) value of 0.028 g/dL, determined by fluorescence measurements in the presence of pyrene, was confirmed by capillary viscosimetry and dynamic laser scattering (DLS). Dialysis method was used to demonstrate the capacity of the pullulan derivative to form spherical nanoparticles (d ~ 200 nm) loaded with model drug, sodium diclofenac (DF) (74% entrapment efficiency). The DF release was sustained and pH-dependent. In vitro cytotoxicity as well as morphological studies conducted on the human skin fibroblasts showed that DBAP-PO/DF nanoparticles do not exhibit cytotoxic effects at the pharmacologically relevant concentration of DF, maintaining the typical morphology of the cells.

Self-assembly of amphiphilic copolymers containing polysaccharide: PISA versus nanoprecipitation, and the temperature effect

The self-assembly methods and the temperature have a considerable impact on the morphology of the resulting nanoobjects in the case of amphiphilic glycopolymers.

Synthesis of 2-alkenyl-3-butoxypropyl guar gum with enhanced rheological properties

A new guar gum derivative was synthesized though the nucleophilic substitution of sodium hydroxide-activated guar gum with n-butyl glycidyl (BGE) ether. The physicochemical properties of 2-alkenyl-3-butoxypropyl guar gum (ABPG) were characterized by attenuated total reflection Fourier transform infrared spectrometry (ATR-FTIR), X-ray diffraction (XRD) and thermal gravimetric analyses (TGA). The results showed that sodium hydroxide can be effectively substituted with BGE to form the ABPG. The steady and dynamic rheological properties of the aqueous solution and ABPG gel were determined using an RS6000 rheometer. Compared with the guar gum, ABPG enhanced the thickening property and improved the solution stability. The ABPG gel exhibited good temperature resistance and shear stability properties.

Synthesis of an Amphiphilic Polysaccharide Derivative and Its Micellization for Drug Release

A new route for the synthesis of novel amphiphilic polysaccharides was developed, in which a synthetic biodegradable poly(ε-caprolactone) was capped with a phenylalanine group (PCL-phenylalanine). The ring-opening polymerization of ε-caprolactone (ε-CL) was carried out in the absence of a metal catalyst with L-phenylalanine as the initiator; this was followed by a coupling reaction with biodegradable dextran in the presence of carbonyldimidazole. The FTIR and 1H NMR analyses confirm the coupling reaction. Fluorescence, transmission electron microscopy (TEM), and dynamic light scattering (DLS) confirm that in aqueous solution the amphiphilic polysaccharides self-assemble into the nanoscale spherical micelles with good stability. The in vitro drug release behavior of the nonsteroidal indomethacin drug exhibits sustained drug release profile as described by the Higuchi model without a burst effect.

Rheology of a reversible supramolecular polymer studied by comparison of the effects of temperature and chain stoppers

The rheology of a reversible supramolecular polymer is studied by comparing the effects of an increase in temperature and the addition of chain stoppers. The dependence of the zero-shear viscosity and the terminal relaxation time on temperature is exponential, and the activation energy for viscous flow can be calculated. Above a critical stopper fraction, power laws describe the stopper dependence of the viscosity and relaxation time. A simple model for the effect of the addition of chain stoppers on the average degree of polymerization adequately describes the results. A comparison of flow curves at several temperatures and stopper fractions reveals considerable differences between solutions with the same zero-shear viscosity. These are mainly associated with differences in the terminal relaxation time. A mechanism of shear-induced alignment and subsequent elongation of chains is proposed, with which the experimental results are consistent.