Macromers and Monofunctional Silicones

Macromers are relatively high molecular weight species with a single functional polymerizable group which, although used as monomers, have high enough molecular weight or internal monomer units to be considered polymers. A macromer has one end-group which enables it to act as a monomer molecule, contributing only a single monomeric unit to a chain of the final macromolecule. The term macromer is a contraction of the word macromonomer. Copolymerization of macromers with traditional monomers offers a route to polymers that are usually associated with grafting. Macromers provide a mechanism for introducing pendant groups onto a polymer backbone with conditions consistent with radical, condensation, or step-growth polymerization but result in pendant groups that are usually associated with significantly different polymerization conditions and significantly different physical properties than the main polymer chain. Siloxane macromers afford a mechanism for introducing a variety of desirable properties without disrupting the main chain integrity of an organic polymer.

Two general classes of siloxane macromers are available: asymmetric and symmetric. Asymmetric macromers have been the most widely used, but symmetric monomers, which open a path for hyper-branched polymers, are anticipated to have increased commercial utilization. Macromers are primarily defined by the functional group anticipated to be the reactive functionality in a polymerization. Other modifications usually effect a greater degree of compatibility with the proposed bulk polymer. These include modifying or replacing the most widely used siloxane building block, dimethylsiloxane, with other siloxanes, typically trifluoropropylmethylsiloxane.