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Novel regular network polyesters were prepared from pentaerythritol (Xp) and aliphatic dicarboxylic acids of different numbers of methylene groups (HOOC(CH2) n - 2COOH, n = 4, 6, 8, 9, 10, 12, 14, 16, and 20). Prepolymer prepared by melt polycondensation was cast from dimethylformamide solution and postpolymerized at 270 °C for various times to form a network. The resultant films were transparent, flexible, and insoluble in organic solvents. The network polyesters obtained were characterized by infrared absorption spectra, wide angle X-ray diffraction analysis, density, thermomechanical analysis, differential scanning calorimetry, tensile test, water absorption, and alkali hydrolysis. The enzymatic degradation estimated by weight loss of the network polyester films in a buffer solution of various kinds of lipases at 37 °C was studied. The enzymatic degradation of Xpn films was compared with that of the network polyester films of glycerol with various aliphatic dicarboxylic acids reported earlier. After a 6 day incubation in Rhizopus delemar lipase solution, the weight loss was hardly observed for Xp4−8, while it increased gradually for Xp9−14 and showed the maximum weight loss of 13 g/m2 for Xp14; then the weight loss decreased abruptly for Xp16−20. Other lipases of porcine pancreas and Candida rugosa hardly degraded Xpn films.

In the injection molding of polymer lenses, the demolding resistance may cause problems, such as deformation, cracks, and scratches, in these products. To examine the method of decreasing the demolding resistance of polymer lenses, a method of precisely measuring the demolding resistance should be established. In this study, we designed and fabricated a mold equipped with high-sensitivity quartz force sensors for demolding resistance measurement that is customized for the injection molding of polymer lenses. In addition, we evaluated the performance of the mold. Using this mold, we measured the demolding resistance of fluorine-based polyester lenses. As a result, it was clarified that (1) the preload applied to the quartz force sensors before the start of mold closing has a significant effect on the generation of demolding resistance, (2) the draft angle of a cavity wall has an effect on the demolding resistance, and (3) the maximum demolding resistance increases with increasing holding pressure, injection rate, heating cylinder temperature, and mold temperature.

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