Synthesis and reactivity of functionalized alkoxyamine initiators for nitroxide‐mediated radical polymerization of styrene

The synthesis and examination of different functionalized (2,2,6,6‐tetramethyl‐1‐piperidinyloxy free radical) TEMPO‐containing alkoxyamine initiators for nitroxide‐mediated radical polymerization of styrene are reported. Initiators with ester and carbonate functional groups were synthesized by a low‐temperature radical‐abstraction reaction of the functionalized ethylbenzene in the presence of TEMPO to introduce the functional groups onto the initiating chain‐end of polystyrene. An initiator with two alkoxyamine groups symmetrically located at each end of a carbonate bond was also synthesized and used for nitroxide‐mediated styrene polymerization. Styrene polymerization using these initiators followed first‐order kinetics up to approximately 60 min at 140 °C or 30% monomer conversion. Alkoxyamines bearing an acetoxy or tert‐butylcarbonate group at the p‐position of 1‐(2,2,6,6‐tetramethyl‐1‐piperidinyloxy)ethylbenzene behave in a similar way to the unfunctionalized initiator. With an initiator containing two alkoxyamine groups, the resulting polymer molecular weight was twice that of the polymer obtained from initiators with only one alkoxyamine group, as expected from propagation from both chain‐ends. Upon hydrolysis of the carbonate bond, it was revealed that equivalent polymer chain growth occurred from each alkoxyamine site in the difunctional initiator.