The synthesis and characterization of two groups of novel networks prepared from cyclolinear polysiloxanes are described. The first group of networks from cyclolinear polysiloxanes (N-CLPSs) was synthesized by the hydrosilation of vinyl-terminated cyclolinear polyorganosiloxanes [prepared from diacetoxydiethyltetramethyl-cyclotetrasiloxane (D4Et2OAc2) or diacetoxyltriethylpentamethylcyclopentasiloxane (D(5)Et(3)OAC(2))] with a copolymer of dimethylsiloxane and methylhydrosiloxane as the crosslinking agent. Hydrosilation was effected with a platinum carbonyl catalyst with a cyclovinylsiloxane moderator. The second group of networks (N-eCLPSs) was prepared similarly with extended cyclolinear polysiloxanes. The mechanical properties of the novel networks were comparable to those of polydimethylsiloxane networks (N-PDMS). The oxygen permeabilities were similar to or slightly higher than that of N-PDMS. The glass-transition temperatures of D(4)Et(2)OAC(2)- and D5Et3OAc2-based N-CLPSs were -67.8 and -90.8 degrees C, respectively, whereas the incorporation of polydimethylsiloxane spacers into similar N-eCLPSs lowered their glass-transition temperatures to -109.7 and -115.0 degrees C. Upon heating to 800 degrees C in air, N-CLPSs yielded more residue than N-eCLPSs, which in turn yielded more residue than N-PDMS. These results may have been due to the presence of T units in the cyclic siloxane units, which may have inhibited chain degradation or the formation of volatile products. (c) 2006 Wiley Periodicals, Inc.