Da-Kong Lee

Polyurethane dispersions derived from polycarbonatediols and a carboxylic polycaprolactonediol

Aqueous polyurethane dispersions derived from various polycarbonatediols, a carboxylic polycaprolactonediol, PLACCEL205BA, and isophorone diisocyanate (IPDI) were prepared. The effect of dispersing procedure on the molecular weight was investigated. It was found that a modified dispersing procedure gave polyurethane dispersions with higher molecular weight and better tensile strength. Comparing with polyurethane dispersions derived from dimethylolpropionic acid (DMPA), PLACCEL205BA gave polyurethane dispersions with finer particle size indicating that PLACCEL205BA imparted better dispersibility. It was also found that the chemical structure of the polycarbonatediols affected the tensile properties significantly.

Synthesis and Thermal Properties of Block Copolyetheresters with Poly(pentamethylene p,p'-bibenzoate) Segments

The block copolyetheresters with hard segments of poly(pentamethylene p,p′-bibenzoate) and soft segments of poly (tetramethylene ether) were prepared by melt polycondensation of dimethyl-p,p′-bibenzoate, 1,5-pentanediol and poly (tetramethyene ether) glycol (PTMEG) with molecular weights of 650, 1000 and 2000. The results by NMR indicate that the polymer composition is determined by the charge molar ratio (x) of PTMEG to dimethyl-p,p′-bibenzoate. The thermal transitions of the block copolyetheresters were investigated by DSC in combination with X-ray diffraction and polarized microscopy. Some block copolyetheresters exhibit a monotropic smectic phase due to the presence of the poly (pentamethylene p,p′-bibenzoate) segments. As the molar content of PTMEG increases, the average sequence length of the polyester segments decreases, the isotropic-smectic transition temperature and the smectic order decrease accordingly. When x is as high as 0.3, the block copolyetheresters exhibit no liquid crystallinity.

Effect of Annealing Poly(4-Methylpentene) and of Oxidative Degradation during Annealing

Injection molded specimens of a poly(4-methylpentene) (TPX) were annealed at temperatures between 140 and 220°C for times up to 500 min in air, and the annealed TPX specimens were characterized by the differential scanning calorimeter, UV–visible spectrometry, FT-IR, and X-ray diffraction. The annealing of the TPX specimens at 140–180°C for 50 min showed little effect on their thermal properties. However, the thermal properties were significantly affected by annealing at 200–220°C, and the change was dependent on the annealing time. Besides the annealing effect, the thermal properties were also affected by oxidative degradation. Severe oxidative degradation can destroy the crystalline structure and thus decreases the crystallinity. The oxidative degradation phenomenon of the TPX specimens during annealing can be simulated by isothermal scanning of the weight loss in air by thermal gravimetric analysis.

Effect of molecular weight on two smectic polyesters

The liquid crystalline transitions of two kinds of smectic polyesters with different molecular weights were investigated by DSC, polarized microscopy and X-ray diffraction. The molecular weight affects the transitions significantly for these two kinds of polyesters. With a high enough molecular weight, both poly (pentamethylenep,p′-bibenzoate) and poly(hexamethylenep,p′-bibenzoate) exhibit an enantiotropic smectic phase, but the two endothermic transition peaks of the DSC heating curve seem to overlap. The polyesters tend to exhibit a monotropic smectic phase as the molecular weight decreases. From the DSC cooling curve, the isotropic-smectic transition can be seen more clearly. As the molecular weight decreases, the smectic order decrease significantly. The molecular weight affects the transitions in a different way for these two different kinds of polyesters.

Effect of Annealing on an Amorphous Polyetheretherketone Film

The effect of annealing on an amorphous polyetheretherketone (PEEK) film is described in this article. PEEK film samples of different crystallinity were obtained by annealing originally amorphous PEEK films. The annealed PEEK film samples were characterized a differential scanning calorimeter (DSC), ultra-violet (UV)-visible spectrometry and X-ray diffraction. The annealing temperature affected the crystallinity of PEEK film greatly after an annealing time of 50 min. Thus, an annealing temperature of 163°C was chosen for obtaining PEEK film samples of different crystallinity. It can be seen that as the annealing temperature or time increases, the crystallinity follows an increasing trend. The DSC and light transmittance data show that the crystallization rate seems to reach a maximum around 40-50 min at an annealing temperature of 163°C. Furthermore, the crystllinity affects the tensile properties of the PEEK film significantly.

IR Analysis of the Polyurethane Resins by a Modified Method

Three moisture curable polyurethane resins with different NCO (isocyanate) contents were prepared by reacting a poly(tetramethylene ether) glycol (PTMEG) with excess Isophorone diisocyanate (IPDI), and they were characterized by the IR (infra red) spectroscopic analysis by a modified method with the quartz plate as the sample carrier. A quartz plate was scanned as the background in the FTIR in the range of 4000 to 2100 cm^(-1), and IR spectra of the moisture curable polyurethane resin coated quartz plates were scanned. In this IR range of 4000 to 2100 cm^(-1), the characteristic peaks of NH, CH and NCO groups of the polyurethane resins can be seen clearly. Thus, the use of the quartz plate as the sample carrier is proved to be successful in the IR analysis of the moisture curable polyurethane resins. The relationship between the relative absorbance of the resin coated quartz plate and the NCO content shows good linearity, indicating that the NCO content of the moisture curable polyurethane resins can be quantitatively determined by this modified method. It can be also seen that the quantitative analysis of the moisture curable polyurethane resins by this modified method is better than the conventional salt plate method.