Reversible polymer cross-linking system utilizing radical crossover reaction

Living radical copolymerization of MMA and methacrylic ester containing TEMPO-based alkoxyamine unit has been controlled to afford the copolymers (1, 2) with alkoxyamine units at the side chain. Cross-linking reactions have been performed by heating an anisole solution of the mixture of 1 and 2 at 100°C at various concentration conditions. Cross-linking behavior remarkably depends on the concentration and the gelation occurred under high concentration condition. Reaction behavior has also evaluated by the determination of cross-linking points, and characteristic behavior of thermodynamic reaction has been observed. The reverse reaction, transformation from gel to solution, has been examined by heating the gel swelled with anisole solution of excess amount of alkoxyamine derivative 3. After heating, the sample transformed from gel state to colorless solution. Interestingly, the M_n of the resulted polymer almost corresponds to the initial M_n of the mixture of 1 and 2, indicating that the covalent cross-linking is reversible under equilibrium control.