Hui-An Tsai

Factors affecting the nodule size of asymmetric PMMA membranes

Abstract Several factors that may affect the surface nodule size of a polymeric membrane were under investigation. The increase of polymer concentration and molecular weight were found to increase the surface nodule size. The increase of casting temperature also resulted in an increase in nodule size. These results supported that the radius of gyration and the collision frequency between polymer chains were the key factors affecting the nodule size. However, when the radius of gyration was reduced by the use of a poor solvent or by pre-adding nonsolvent in the casting solution, the surface nodule size increased. It suggested that there existed other factors affecting the nodule size on membrane surface besides the gyration radius and the collision frequency of polymer chains. In this study, we found in most cases that the surface nodule size decreased along with the surface tension difference between the casting solution and the coagulant. To demonstrate the effect of surface tension, we examined the nodule size inside the membranes where the nodule formation was not significantly affected by the interfacial tension. Opposite to what was observed on the surface, the nodule size increased with the solvation power of the solvent. This result suggested that it was the interfacial tension that overpowered the gyration radius in affecting the surface nodule size.

Synthesis of biodegradable polycaprolactone/polyurethane by curing with H2O

To prepare a pre-polymer in this study, the following materials were used: 4,4′-diphenylmethane diisocyanate, poly(ε-caprolactone) diol (PCL), and polytetramethylene ether glycol. The pre-polymer was then cured using H2O to form a new type of polyurethane (PU), PCL/H2O-PU. Fourier transform infrared analysis confirmed the successful synthesis of PCL/H2O-PU. Results from thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis showed that the thermal resistance and glass transition temperature of PCL/H2O-PU increased with the H2O and the hard segment content. Stress–strain curves for the PCL/H2O-PU specimens showed that with increasing H2O content, the tensile strength and Young’s modulus increased, but the elongation at break decreased. WAXD patterns indicated that with a higher H2O content, the polymer chains were in a more ordered arrangement, although the morphology was still amorphous. The degree of swelling in an aqueous ethanol solution and the hydrolytic degradation rate increased with the PCL content. Scanning electron microscopic images showed that during the degradation period, the original wrinkled surface of PCL/H2O-PU became smooth, and then cracks were formed. The cracks became more severe when the degradation was at a higher temperature.

Synthesis and crystal structure of 2-D silver coordination polymers containing aminopyrazine

Two supramolecules of Ag(I), [Ag(NO3)(APZ)] n (1) and {[Ag(APZ)2][CF3COO] · H2O} n (2) (APZ = aminopyrazine) have been prepared by self-assembly of Ag(I) salts with APZ in MeOH/H2O. EA, IR, and TGA spectra have been recorded and the complexes have been structurally characterized by X-ray crystallography, confirming that 1 and 2 are 2-D pleated rectangular grid coordination polymers. The in 1 is coordinated to Ag+, bidentate, and μ2,η1- , while CF3COO− in 2 is not coordinated. Ag ··· O interactions, hydrogen bonds, and π ··· π stacking interactions support the supramolecular structures.

catena-Poly[[bis­(nitrato-κO)copper(II)]-μ-1,4-bis­(4,5-dihydro-1,3-oxazol-2-yl)­benzene-κ2N:N′]

In the title coordination polymer, [Cu(NO3)2(C12H12N2O2)]n, the CuII ion, situated on an inversion center, is coordinated by two O atoms from two nitrate anions and two N atoms from two 1,4-bis(4,5-dihydro-1,3-oxazol-2-yl)benzene (L) ligands in a distorted square-planar geometry. Each L ligand also lies across an inversion center and bridges two CuII ions, forming a polymeric chain running along the [101] direction. The three O atoms of the nitrate group are disordered over two positions in a 3:2 ratio.