A New Free Radical Approach to the Synthesis of Polydimethylsiloxane-Vinyl Monomer Block Polymers

Abstract

The platinum catalyzed condensation of bis(silylpinacolate) free radical initiators bearing vinyl groups attached to silicon with α,ω-hydrogen functional polydimethylsiloxane oligomers, i.e., oligomers containing terminal Si-H bonds, leads to the preparation of high molecular weight macroinitiators. The thermolysis of these macroinitiators in the presence of various vinyl monomers provides a direct synthesis of block polymers. Depending on the monomer chosen, simple triblock and/or multisequence block polymers can readily be prepared. Analysis of the products of the block polymerizations using styrene monomer shows that only block polymers are formed. These block polymers display unusual properties such as intense iridescence, reversible stress crazing and solvent dependent mechanical properties. The stress-strain properties of the block polymers have been measured and found to be related to both the relative proportions of the hard and soft blocks and to their respective block lengths. At hard block contents of less than approximately 50%, the block polymers are thermoplastic elastomers while at compositions greater than 50% the block polymers are rubber modified thermoplastics.