Amphiphilic Block Copolymer Networks by Sequential Branching-Extension-Crosslinking Atom Transfer Radical Polymerization

Crosslinked block copolymer (BCP) gel networks are synthesized by chain extension of a branched macroinitiator with a second monomer and crosslinker under atom transfer radical polymerization (ATRP) conditions. Specifically, crosslinked poly(tert-butyl acrylate)-b-poly(n-butyl acrylate) (PtBA-b-PnBA) gels are synthesized by photoinduced ATRP with the aim of forming amphiphilic block copolymer gels via deprotection of the tert-butyl acrylate group. By using a controlled polymerization method such as ATRP, the gel point of the first (co)polymerization of a tBA/crosslinker mixture can be delayed and reached only once the second monomer (nBA) and extra crosslinker are added. The BCP gels can be made successfully both in a one-pot polymerization and with purification of the initial block before chain extension. These gels are subjected to thermomechanical and swelling analysis, before and after deprotection with trifluoroacetic acid (TFA). Rheology, swelling, and thermogravimetry all confirmed the incorporation of both monomers in the gel structure. Furthermore, after deprotection, three T_g values were observed by differential scanning calorimetry (DSC) of a crosslinked BCP, compared with a single T_g value for a statistical analogue of the same composition, thus corroborating the difference in their morphology.