ADMET with Volatile Monomers

If a volatile monomer is used in an ADMET polymerization, a condenser should be used to return monomer vapor to the reaction mixture. The kinetics of step-growth polymerization dictate that the concentration of monomer falls very quickly to produce dimer, trimer, and so forth. Nevertheless, monomer will be present for some time after the start of the polymerization. If the monomer is particularly volatile, a dry ice-isopropanol condenser is useful. This can be constructed in any glass shop by attaching a cup-shaped cooling reservoir to a vacuum valve or other cylindrical glass tube with the required joints and valve. If the monomer is only slightly volatile, or the carrier gas method is used, a water-cooled condenser is sufficient to retain monomer in the flask, while allowing ethylene to escape. 

Liquid ADMET monomers often become so viscous that magnetic stirring is impossible. There are several solutions to this. One is to attach a strong horseshoe or other magnet to a mechanical stirrer and rotate it very slowly under the vessel and temperature bath to slowly agitate the polymer melt. Another solution is to use a high viscosity mechanical stirrer if the polymer is a viscous melt Vacuum adapters for the stirring shaft are available, so that the vacuum method may be used with mechanical stirrers. 

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ADMET of this monomer, 2-butene, was much less volatile than ethylene hence, polymerization of this monomer in bulk proved difficult Polymerization in a high-boiling solvent at reflux facilitated removal of the 2-butene, albeit with reduced molecular weights, which was attributed to a rapid catalyst death due to the elevated temperature. Despite their low molecular weights, these well-defined poly(3-hexylthiophene vinylenes) exhibited properties that were in agreement with other reported examples. 

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