Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Linear relationships among molecular weight, polymerization time, and gelation for the condensation of any monomer, including those of unknown size and functionality, are developed and applied to data on soluble silicic acids generated from tetraethyl silicate and from sodium silicate. The results suggest the formation of monomers containing ca. 12-15 —OSi units with functionality of ca. 2.05 that condense with a rate constant of ca. 10-4 liter/mole sec and an activation energy of 40-70 kJ/mole. One model compatible with these characteristics and the stoichiometry involved is a ladder polymer ca. 3 —SiO units wide. Polymer isolation was achieved by replacing residual —OH with (CH3)3Sio—, as well as by freezing of of aqueous solutions, which yielded fibers under special conditions. Solutions of the uncapped and capped polymers and melts of the latter had low viscosity even for fractions with M̄n ∼100,000. This implies a coiled or globular nature for the polymers, which is supported by their limited propensity for film and fiber formation. Attemps to improve this situation by copolymerization, the use of other capping agents, and by the polymerization of precapped monomers were unsuccessful.
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