Solid state structure and gas transport behavior of semicrystalline poly(ethylene terephthalate) and barrier coatings based on polyhydroxylated dendritic polymers

The existence of rigid amorphous fraction (RAF) in semicrystalline poly(ethylene terephthalate) (PET) is associated with the lamellar stack crystalline morphology of this polymer, the regions where several crystalline lamellas are separated by very thin (20–40Å) amorphous layers. In contrast, regular or mobile amorphous fraction (MAF) is associated with much thicker interstack regions. The specific volume of RAF in cold and melt crystallized PET was probed at 25°C using oxygen solubility measurements, and showed a direct correlation with the crystallization temperature. It was shown that upon crystallization from either melt or glassy state, RAF vitrifies at the crystallization temperature and resembles the glassy behavior despite high temperature. When cooled to room temperature, the RAF preserves a memory about the melt state of polymer, which is uniquely defined by the crystallization temperature. Consistent results were demonstrated by positron annihilation lifetime spectroscopy (PALS) study. Moreover, correlations between PALS and oxygen transport parameters suggested that the dominant free volume parameter which controls the diffusion process is the hole volume, whereas the dominant parameter controlling the solubility is the hole density.; Oxygen transport properties were assessed for a series of hydroxyl-functional hyperbranched polyesters (HBPs) at both 0% and 50% relative humidity (RH). At 0% RH, all HBPs showed outstanding oxygen barrier properties, with the permeability coefficients more than one order magnitude smaller than that of the amorphous PET. It was found that the oxygen diffusion process was mainly determined by the free volume and characteristic jump length of gas molecules from one core to another core. On the other hand, the oxygen sorption was related with the glass transition temperature, following dual-sorption model. The different amount of volume fraction of periphery layers contributed to the difference in oxygen solubility among HBPs of different generations. Due to the plasticization of the polymers by moisture, both diffusivity and solubility coefficients increased for all HBPs at 50% RH. With highest hydroxyl group density, H20 showed largest increase in both diffusivity and solubility coefficients at 50% RH.; The mechanical properties of HBPs were significantly improved by crosslinking. The polarity index calculated based on the concentration of hydroxyl and amine groups was found to be a good predictor of the diffusivity of crosslinked H40: higher the polarity index, lower the oxygen diffusivity coefficients. The oxygen sorption of crosslinked H40 showed similar behavior as that of neat H40, and it is related with the T_g of crosslinked H40.; A dynamic gas permeation system using mass-spectrometer (DGPS-MS) was successfully developed, based on the principles of the dynamic differential approach. The permeation results of various gases through different polymer membranes demonstrated that DGPS-MS has the capability to measure from very fast (no more than a few minutes) to slow (a couple of days) diffusion of different gases, and gas mixtures as well. The data obtained from DGPS-MS agreed well with the literature value.