End-group control in catalytic chain transfer polymerization

The application of catalytic chain transfer polymerization as a technique to produce end-functionalized low-molecular weight polymers is discussed in terms of simple kinetic models and illustrated by practical examples. Since end-functionalities other than vinyl groups need to be introduced via a functional monomer it is shown to be necessary and possible to control the endgroup by careful selection of a comonomer. Simple kinetic modeling reveals the required properties of this comonomer to be a high affinity of its derived radical to react with Co(II) rather than with other monomers, and that the other present monomers need to possess the opposite properties. The use of a-methyl styrene as a monomer to selectively introduce end-functionalities is discussed in detail. Furthermore it is shown that the use of α-hydroxy methyl functionalized monomers in catalytic chain transfer polymerization lead to the introduction of aldehyde endgroups, which are very versatile building blocks for post-polymerization modifications. The a-methyl styrene analogue, i.e., 2-phenyl allyl alcohol, has great promise for the selective introduction of these aldehyde endgroups.