Thermal Imidization Kinetics of Ultrathin Films of Hybrid Poly(POSS-imide)s

In the thermal imidization of an alternating inorganic–organic hybrid network, there is an inverse relationship between the length and flexibility of the organic bridges and the extent of the layer shrinkage. The hybrid material studied here consists of polyhedral oligomeric silsesquioxanes that are covalently bridged by amic acid groups. During heat treatment, shrinkage of the materials occurs due to the removal of physically bound water, imidization of the amic acid groups, and silanol condensation. For five different bridging groups with different lengths and flexibilities, comparable mass reductions are observed. For the shorter bridging groups, the dimensional changes are hindered by the limited network mobility. Longer, more flexible bridging groups allow for much greater shrinkage. The imidization step can be described by a decelerating reaction mechanism with an onset at 150 °C and shows a higher activation energy than in the case of entirely organic polyimides. The differences in the imidization kinetics between hybrid and purely organic materials demonstrates the need for close study of the thermal processing of hybrid, hyper-cross-linked material

Hyper-cross-linked, hybrid membranes via interfacial polymerization

Hyper-cross-linked, hybrid membranes consist of covalent networks of alternating organic and inorganic, or biological groups. This thesis reports on the preparation of such hybrid networks via interfacial polymerization. The structure-property relationships of the hybrid networks depend strongly on the type, size and flexibility of the constituents. The collection of polymers that can be synthesized via interfacial polymerization includes polyamides, polyurethanes, polyureas, polyanilines, polyimides, and polycarbonates. In addition, the technique can be used to prepare defect-free, ultrathin films of metal organic frameworks, organic-inorganic hybrids, and bio-hybrids. \ud Here, inorganic-organic network materials based on polyhedral oligomeric silsesquioxanes (POSS) that are covalently bound by imide bridges have been prepared. The membranes are characterized by a high degree of cross-linking, as a result of the large number of functional groups on the POSS cages. Even at temperatures up to 300 °C, macromolecular dynamics of the hybrid networks based on short imide bridges is limited. This is illustrated by the relatively small shrinkage during heat treatment of the poly[POSS-(amic acid)] precursors and the high permselectivities in gas separation applications at a broad temperature range. Poly(POSS imide)s with long, flexible imide bridges display a higher degree of network flexibility. The flexibility of the hybrid network materials prepared with relatively long imide bridges is reflected by the unique sorption behavior of fluoroalkane based poly(POSS-imide). The membrane layers sorb large amounts of CO2 and CH4, up to an extent that the molar volume of the adsorbed gas exceeds that of the liquid molar volume of these gases. \ud The interfacial polymerization method used for the inorganic-organic networks has been extended towards biological hybrids. The preparation of all-protein layers that consist of enzymatically active and fluorescently active films is reported. The broad applicability of interfacial polymerization for the preparation of ultrathin hybrid films provide prospect for further development of materials with unique functionalities

A molecular characterization of hyper-cross-linked hybrid polyPOSS-imide networks

Hybrid hyper-cross-linked membranes based on inorganic polyhedral oligomeric silsesquioxanes (POSS) covalently bonded with organic imides have been shown to maintain remarkable molecular sieving abilities and gas separation performances up to 300 C. These films are obtained through the interfacial polycondensation of POSS with a dianhydride, leading to a polyPOSS-(amic acid) network, which is then converted to a polyPOSS-imide network by thermal imidization. Using the pyromellitic (PMDA) dianhydride as a test case, the underlying molecular structures have been generated by molecular dynamics (MD) simulations and specific algorithms which closely mimicked the mixing, polycondensation and imidization steps of the experimental scheme. This allowed realistic models of the final cross-linked imide networks to be compared with their un-cross-linked monomer mixtures and their intermediate amic-acid precursors. Both the formation of the network and the subsequent imidization decreased the density as the systems became sterically more constrained. The volume shrinkage during imidization was less than expected considering the amount of water removal. This led to a larger void space and an improved gas solubility for the polyPOSS-imide films. Although the networks were constructed with the experimentally-found average of four linked arms per POSS, the distribution of the number of links per POSS were quite wide with a range from zero to the maximum possible of eight links per POSS. There was also considerable heterogeneity in the POSS imide POSS angles, which was related to the flexible aliphatic linker between the organic and inorganic moieties. Thermomechanical analyses confirmed that these cross-linked materials were well-suited for high-temperature applications. When subjected to uniaxial tension, they strain hardened at large deformations and their elastic moduli remained solid-like at high temperatures

Sorption Behavior of Compressed CO2 and CH4 on Ultrathin Hybrid Poly(POSS-imide) Layers

Sorption of compressed gases into thin polymeric films is essential for applications including gas sensors and membrane based gas separation. For glassy polymers, the sorption behavior is dependent on the nonequilibrium status of the polymer. The uptake of molecules by a polymer is generally accompanied by dilation, or swelling, of the polymer material. In turn, this dilation can result in penetrant induced plasticization and physical aging that affect the nonequilibrium status of the polymer. Here, we investigate the dilation and sorption behavior of ultrathin membrane layers of a hybrid inorganic−organic network material that consists of alternating polyhedral oligomeric silsesquioxane and imide groups, upon exposure to compressed carbon dioxide and methane. The imide precursor contains fluoroalkene groups that provide affinity toward carbon dioxide, while the octafunctionalized silsesquioxane provides a high degree of cross-linking. This combination allows for extremely high sorption capacities, while structural rearrangements of the network are hindered. We study the simultaneous uptake of gases and dilation of the thin films at high pressures using spectroscopic ellipsometry measurements. Ellipsometry provides the changes in both the refractive index and the film thickness, and allows for accurate quantification of sorption and swelling. In contrast, gravimetric and volumetric measurements only provide a single parameter; this does not allow an accurate correction for, for instance, the changes in buoyancy because of the extensive geometrical changes of highly swelling films. The sorption behavior of the ultrathin hybrid layers depends on the fluoroalkene group content. At low pressure, the apparent molar volume of the gases is low compared to the liquid molar volume of carbon dioxide and methane, respectively. At high gas concentrations in the polymer film, the apparent molar volume of carbon dioxide and methane exceeds that of the liquid molar volume, and approaches that of the gas phase. The high sorption capacity and reversible dilation characteristics of the presented materials provide new directions for applications including gas sensors and gas separation membranes

Swelling of 9 polymers commonly employed for organic solvent nanofiltration: a comprehensive dataset

This dataset contains all the data used for researching the swelling behaviour of 9 different polymers in a variety of solvents. The measurements were performed by employing spectroscopic ellipsometry. This dataset therefore includes the raw experimental data, the analysed data and the model used for the analysis of the data