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The transport of small gases (H2, CO2, N2, O2) through a series of novel membranes based on necklace-shaped inorganic polymers (DMS@POSS), in which a polyhedral oligomeric silsesquioxane (POSS) cage unit and soft chains of oligo-dimethyl siloxane (DMS) were alternately connected, was investigated. The influence of the DMS chain length and crosslinking density of the DMS@POSS on membrane properties were studied. The membranes revealed characteristic structure-property relation towards both glass transition and gases transport. Specifically, clear dependence of properties from the length of DMS units (or overall siloxane content) was revealed. Gas transport properties, when compared to state-of-art polydimethylsiloxane and commercial silicone rubber, demonstrated significantly higher selectivity of DMS@POSS for carbon dioxide (in CO2/N2), hydrogen (in H2/N2) and oxygen (in O2/N2) but lowered permeability, proportional to the amount of POSS in the material. With a precise control over mechanical and thermal properties compared to conventional silicone rubbers, described materials could be considered as materials of choice in niche gas separation or other applications.