Investigation of Enhanced Free Volume in Nanosilica-Filled Poly(1-trimethylsilyl-1-propyne) by 129Xe NMR Spectroscopy

Polymer Nanocomposite Membranes

Based on the results of research works reflected in the scientific literature, the main examples, methods and approaches to the development of polymer inorganic nanocomposite materials for target membranes are considered. The focus is on membranes for critical technologies with improved mechanical, thermal properties that have the necessary capabilities to solve the problems of a selective pervaporation. For the purpose of directional changes in the parameters of membranes, effects on their properties of the type, amount and conditions of nanoparticle incorporation into the polymer matrix were analyzed. An influence of nanoparticles on the structural and morphological characteristics of the nanocomposite film is considered, as well as possibilities of forming transport channels for separated liquids are analyzed. Particular attention is paid to a correlation of nanocomposite structure-transport properties of membranes, whose separation characteristics are usually considered within the framework of the diffusion-sorption mechanism.

Gas Transport Properties of ODPA-TAPOB Hyperbranched Polyimide-Silica Hybrid Membranes

Physical and gas transport properties of novel hyperbranched polyimide-silica hybrid membranes were investigated. Hyperbranched polyamic acid as a precursor was prepared by polycondensation of a triamine monomer, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and a dianhydride monomer, 4,4′-oxidiphthalic anhydride (ODPA), and subsequently modified the end groups by 3-aminopropyltrimethoxy-silane (APTrMOS). Hyperbranched polyimide-silica hybrid membranes were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) by the sol-gel method and thermal imidization. The 5% weight-loss temperature and glass transition temperature of the hybrid membranes determined by TGDTA measurements considerably increased with increasing silica content, indicating effective cross-linking at polymer-silica interface mediated by APTrMOS. CO2, O2, N2, and CH4 permeability coefficients of the hybrid membranes increased with increasing silica content. In addition to the increased permeability, CO2/CH4 selectivity of the hybrid membranes increased with increasing silica content. It was concluded that the ODPA-TAPOB hyperbranched polyimide-silica hybrid membranes have high thermal stability and good gas selectivity, and are expected to apply to a high-performance gas separation membrane.

Interfacial regions in spherical nanoparticle-doped glassy polymers: interfaces or interphases?

By computational simulation, we provide new evidence supporting a high-free-volume interphase in spherical nanoparticle-doped glassy polymers and offer a generic framework for understanding how this interphase is shaped.

Effect of End Group Modification on Gas Transport Properties of 6FDA-TAPOB Hyperbranched Polyimide-Silica Hybrid Membranes

Physical and gas transport properties of end group-modified 6FDA-TAPOB hyperbranched polyimide (HBPI)-silica hybrid membranes were investigated. Hyperbranched polyamic acids as precursors were synthesized by polycondensation of triamine, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and the molecular end groups were subsequently allowed to react with 3-aminopropyltrimethoxysilane (APTrMOS) and fluorine compound, 3,5-bis(trifluoromethyl)aniline (6FMA) and 1H,1H-heptadecafluorononylamine (17FN). The HBPI-silica hybrids were prepared by sol-gel reaction using the polyamic acids, water, and tetram-ethoxysilane (TMOS). The 5% weight-loss and glass transition temperatures of the hybrids considerably increased with increasing silica content, indicating effective crosslinking at polymer-silica interface mediated by APTrMOS moiety. The CO2, O2, N2, and CH4 permeability coefficients of the hybrids increased with increasing silica content. In particular, 6FMA-modified and 17FN-modified 6FDA-TAPOB HBPI-silica hybrids showed high gas permeability, arising from their high fractional free volumes. The CO2/CH4 selectivity of the hybrids increased remarkably with increasing silica content, whereas their O2/N2 selectivity remained almost constant against silica content. It was concluded that the HBPI-silica hybrids have high thermal stability, high gas permeability, and excellent CO2/CH4 selectivity, and are expected to apply to high-performance gas separation membranes.

Reverse-selective diffusion in nanocomposite membranes

The permeability of certain polymer membranes with impenetrable nanoinclusions increases with the particle volume fraction [T. C. Merkel, Science 296, 519 (2002)10.1126/science.1069580]. The discovery contradicts qualitative expectations based on Maxwell's classical theory of conduction or diffusion in composites with homogeneous phases. This Letter presents a theory based on an hypothesis that polymer chains are repelled from the inclusions during membrane casting. The accompanying increase in free volume, and hence solute diffusivity, yields bulk transport properties that are in good agreement with experiments.