Silica-based microporous membranes can be successfully processed by sol¿gel techniques. However tailor making of such membranes is still not possible because of the unavailability of systematic studies on membrane oriented sol processing and characterization. The present series of papers aims to give a systematic understanding of silica polymeric growth, synthesis chemistry, and finally membrane characterization. Polymeric silica sols were prepared by hydrolysis and condensation of alkoxide. The fractal growth of the polymers during sol¿gel transition is monitored with the help of small angle X-ray scattering. Fractal dimensions and radii of gyration of sols and gels with different synthesis chemistry are compared. The type of aggregation mechanism prevailing in these systems is identified as cluster¿cluster aggregation with reaction limitations during synthesis and reaction and diffusion limitations during aging.