Influence of Strong Electron-Donor Monomers in Sequence-Controlled Polymerizations

A series of styrenic monomers containing strong donor substituents (i.e., 4-methylstyrene, 4-acetoxystyrene, and 4-tert-butoxystyrene) were tested in sequence-controlled radical copolymerizations in the presence of acceptor comonomers (i.e., N-substituted maleimide). The copolymers were synthesized by nitroxide-mediated polymerization using the commercially available alkoxyamine BlocBuilder MA. This technique allowed synthesis of copolymers with controlled molecular weights and molecular weight distributions for all monomers. Moreover, a beneficial effect of the donor substituents on the sequence-controlled copolymerization was noted. Indeed, all studied styrenic derivatives led to a very precise incorporation of functional N-substituted maleimides in the copolymer chains. The most favorable donor/acceptor copolymerization was observed with 4-tert-butoxystyrene. This particular monomer was therefore tested in the presence of various functional N-substituted maleimides (i.e., N-benzyl maleimide, 4-(N-maleimido) azobenzene), N-(1-pyrenyl)maleimide, and N-(2-(amino-Boc)ethylene)maleimide). In all cases, sequence-controlled microstructures were obtained and characterized. Moreover, the formed copolymers were hydrolyzed into poly(4-hydroxystyrene-co-N-substituted maleimide) derivatives. In all cases, it was verified that the sequence-controlled microstructure of the copolymers is preserved after hydrolysis.