FUNCTIONAL POLYMERS SUPPORTED ON POROUS SILICA .2. RADICAL POLYMERIZATION OF VINYLBENZYL CHLORIDE FROM GRAFTED PRECURSORS

Vinylbenzyl chloride was chosen as a model monomer for grafting a functional polymer onto silica carrying radical active precursors, such as monomer, transfer agent or initiator, previously grafted onto silica via a suitable coupling agent. The grafting efficiency was studied as a function of the texture of the initial silica, the nature of the active precursor and the polymerization conditions. Evidence for grafting was obtained from FTIR and Si-29 CP-MAS NMR spectra, and the thickness of the grafted layer was estimated from surface area and porosimetry measurements. From molecular weight measurements of nongrafted polymer it can be deduced that there is a trend toward the elongated conformation of the grafted polymer. Attempts to separate the grafted polymer, through digestion of the silica with HF, failed to give a soluble linear polymer except when the active precursor was a transfer agent; in the two other cases a crosslinked polymer with a low crosslink density was obtained, which kept the morphology of the initial silica.