Molecular Architecture and its role in Silica Sol-Gel Polymerization
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MOLECULAR ARCHITECTURE AND iTS ROLE IN SILICA SOL-GEL POLYMERIZATION
P. C. CAGLE, W. G. KLEMPERER AND C. A. SIMMONS School of Chemical Sciences and Materials Research Laboratory, University of Illinois, Urbana, IL 61801
ABSTRACT Sol-gel polymerization of [Si 8O1 2](OCH 3) 8 in CH3 CN under neutral conditions yields very high surface area (SBET > 900 m2 /g) xerogels. This property is seen to result from the structure of the gel on the molecular level. According to N2 adsorption studies, model studies, and TEM studies, the large size and rigidity of the cubic [Si 8 0 1 2] core structure leads to polymers whose rigidity inhibits extensive crosslinking of the type observed in orthosilicate derived xerogels.
I.
INTRODUCTION
An enormous body of research has been devoted to optimizing silica sol-gel polymerization conditions for the processing of films, fibers, monoliths, and aerogels by controlling the conditions of tetralkylorthosilicate, Si(OR) 4 (a), hydrolysis/condensation [1,2]. Relatively little attention has been devoted, however, to the architecture of sol-gel derived silica on the molecular size scale. We have recently addressed this issue through the synthesis of the cubic octamethyl octasilicate [Si8Ol2](OCH3)8 (b), with the hope that sol-gel polymerization of
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