Self-Association Behavior of Cell Membrane-Inspired Amphiphilic Random Copolymers in Water

Water-soluble and amphiphilic random copolymers (P(MPC/DMA_x)) composed of hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC) and hydrophobic n-dodecyl methacrylate (DMA) were prepared via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. The compositions of DMA unit (x) in the copolymer were in the range of 0 to 38 unit mol %. The degree of polymerization of P(MPC/DMA_x) was adjusted to about 200. Since the monomer reactivity ratios of MPC and DMA are 1.01 and 1.00, respectively, ideal free radical copolymerization occurred. In aqueous solutions, interpolymer aggregation occurred due to the hydrophobic pendant n-dodecyl groups. The aggregation number (N_agg) increased with an increasing x. The mobilities of the DMA and MPC pendant groups in aqueous solutions were restricted, as confirmed by ¹H NMR relaxation time measurements, because a part of the MPC units were trapped in the hydrophobic microdomain formed from the pendant n-dodecyl groups. The polarity of the hydrophobic microdomain formed from P(MPC/DMA₃₈) in water was similar to that of ethyl acetate according to fluorescence probe experiments. No specific interactions were found in water between P(MPC/DMA_x) and bovine serum albumin because the surface of the interpolymer aggregates contained only hydrophilic MPC units.