Synthesis of degradable miktoarm star copolymers via atom transfer radical polymerization

Both nondegradable and degradable miktoarm star copolymers were synthesized via ATRP using the in-out method. The synthesis consisted of three steps: synthesis of a linear macroinitiator (MI) using the first monomer, a core-forming reaction with a divinyl compound, and then further chain extension with the second monomer. Various characterization methods, including GPC, NMR, and GC, were used to analyze the initial star polymers and to identify the optimal experimental conditions for the synthesis of the multifunctional star initiators and the miktoarm star copolymers. During the synthesis of miktoarm star copolymers, both interstar and intrastar arm-arm couplings were observed. The initiating efficiency of the alkyl bromide sites in the core of the star polymers was determined by analysis of the linear block copolymers, obtained after cleavage of the degradable star and miktoarm star copolymers. The results confirmed that the initiation efficiency was reduced by the highly cross-linked star core. In the case of degradable miktoarm star copolymers, only 19% of the total Br functionality incorporated into the first star copolymer initiated the polymerization of the second monomer.