Behavior of ATRP-derived styrene and 4-vinylpyridine-based amphiphilic block copolymers in solution

The reaction sequence of (i) styrene (St) and (ii) 4-vinylpyridine (4VP) employing atom transfer radical polymerization (ATRP) with Cu(I)Cl/Me₆TREN as the catalyst is known to lead to poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymers with narrow molecular weight distributions and is well-controlled for both the styrene and the successive 4VP polymerization. Block copolymers derived by this reaction sequence can easily be converted to amphiphilic species by quarternization of the P4VP block. It was found that the behavior of ATRP-derived PS_n-b-P4VP_m⁺⋅MeI⁻ ionomers in solution is similar to the behavior of anionically derived ionomers. This indicates that the minor difference in polydispersity and chain termini in particular does not influence the colloidal characteristics significantly. Thus, ATRP was proven to be a valuable alternative to sensitive anionic polymerization technique to produce amphiphilic block copolymer systems. Additionally, it was found that PS_n-b-P4VP_m⁺⋅MeI⁻ ionomers with short P4VP_m⁺⋅MeI⁻ and long PS blocks self-assemble in dioxane to “inverse” amphiphilic micelles and undergo a morphological transition to “regular” micelles upon slow addition of ethanol.