Synthesis and characterization of electrolytic amphiphilic model networks based on cross-linked star polymers: Effect of star architecture

Amphiphilic model networks of a new structure, that of cross-linked in-out star copolymers, were synthesized by a one-pot preparation using group-transfer polymerization. The networks comprised hydrophobic methyl methacrylate and hydrophilic 2-(dimethylamino)ethyl methaerylate (DMAEMA) moieties. Ethylene glycol dimethacrylate served as the cross-linker. Two heteroarm star-, two star-block-, and one statistical star copolymerbased networks were prepared. The synthesis of the heteroarm star-based networks involved a four-step addition of monomer/cross-linker/monomer/cross-linker. The simultaneous or sequential addition of two monomers between cross-linking gave statistical- or block-copolymer-based star networks, respectively. The linear, arm-first and in-out star network precursors were characterized in terms of their molecular weight distribution by gel permeation chromatography. Static light scattering was used to assess the absolute weight-average molecular weight of the star network precursors. The compositions of the in-out star precursors were determined by H-1 NMR. The effects of network architecture (heteroarm, block, and statistical), solvency (THF and water), and pH on the swelling behavior of the networks were investigated. The degrees of swelling increased at low pH because of the ionization of the DMAEMA residues. The higher degree of swelling of the statistical-copolymer-based network as compared to the swelling of the star-block and heteroarm star analogues is attributed to the proposed microphase-separated structure of the latter in the aqueous medium compared to the disordered structure of the former.