GAS-PERMEABILITY OF MODEL POLYURETHANE NETWORKS AND HYBRID ORGANIC-INORGANIC MATERIALS - RELATIONS WITH MORPHOLOGY

Various polyurethane (PU) and hybrid organic-inorganic networks based on isocyanate chemistry were synthesized using a two-stage method. All the networks were amorphous. For PU membranes the morphology and the permeability coefficients of different gases (H-2, N-2, O-2) were a fu nction of the polarity and the chain length of the soft segment and a function of the composition of the networks. The membranes based on th e same soft segment chain length and on the same molar composition wer e structurally nanoheterogeneous systems for the less polar soft segme nts (alpha,omega-hydroxyterminated hydrogenated polybutadiene and a fa tty acid oligoester). They were homogeneous for a polycaprolactone typ e soft segment. The gas diffusion was appreciably hindered in the case of better miscibility between the soft chains and the hard crosslinks . Decreasing the soft segment length decreased the gas permeability co efficient of the network. As the chemical compositions were changed by increasing the soft segment content, an increase in permeability coef ficients was observed. The morphology and transport properties of PU n etworks and hybrid organic-inorganic networks with low inorganic conte nt were compared for the same soft segment content. The similarities o bserved between the two types of networks led us to conclude that the organic or inorganic nature of the crosslinking agent has no influence on the gas transport properties of these networks. (C) 1997 John Wile y & Sons, Inc.