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Both “condensation” and “hydrosilylation” reactions have been successfully applied for the synthesis of silicon-based interpenetrating polymer networks (IPNs) consisting of a stable Si−O and Si−C linkage. We adopted a ladder silsesquioxane oligomer (LDS 1; commercial name, Glass Resin GR100) and a polycarbosilane (PCS) by hydrosilylation polymerization of bifunctional Si−H and Si−vinyl monomers as the two components for the IPN. The combined LDS/PCS curing system was studied to try to obtain homogeneously cured material, which may lead to IPN formation, by using both reactions selectively in one pot for chain-extending and cross-linking of both components, respectively. We synthesized the cured LDS/PCS; LDS/PCS = 8/2, 5/5, and 2/8 [wt/wt]. Tuning the rates of the two reactions to each other was important for obtaining a transparent cured product. The morphology of the cured LDS/PCS (8/2) was examined by TEM and AFM. TEM analysis showed a good miscibility with an nm level of LDS/PCS (8/2). The thermal and mechanical properties of the LDS/PCS (8/2) cured sample were better than the calculated values from each component's value. The experimental data imply the IPN structure of the cured LDS/PCS.

Several organic oligomers (Mw = 103–104 order) containing SiH bonds of the general formula 1 have been successfully synthesized by platinum‐catalyzed partial hydrosilylation reaction of an allyloxy (or an allyl carbonate) end‐blocked linear organic oligomer 2 with 2,4,6,8‐tetramethylcyclotetrasiloxane, [CH3(H)SiO]4 (3) (hereafter called hydrocyclotetrasiloxane). 1H‐NMR spectroscopy confirmed the introduction of hydrocyclotetrasiloxane moiety into the oligomers through SiC linkage by hydrosilylation reaction. 13C‐NMR analysis revealed that the cyclic structure of the starting hydrocyclotetrasiloxane 3 was retained intact in product 1. As the precursor for 1, allyloxy (or allyl carbonate) end‐blocked oligomers 2 could be prepared from hydroxyl‐terminated oligomers 4. The storage stability of product 1 was significantly influenced by the platinum catalyst still remaining in it. The poor stability was improved by decreasing the amount of the platinum catalyst and/or by adding coordinating compounds. As a result, an excellent stability of product 1 was obtained. © 1993 John Wiley & Sons, Inc.

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