(A) Gelation of aqueous solutions of 18%[P407], 3CPE-18%[P407], 18%[P407-PBP], and 3CPE-18%[P407-PBP], as a function of temperature. 3CPE: 2% LIM, 1% SDS, and 0.5% BUP. Data are means ± SD (n = 4). (B) TEM images of micelle formation. Scale bars, 100 nm. (C) Synthesis steps for P407-PBP and chemical structures of the ABCBA penta-block copolymers. (D) Schematic of the gelation of P407-PBP aqueous solution, facilitated by hydrophobic interactions of PPE end groups at elevated temperature. (E) FTIR spectra of P407, P407-PBP with n-butyl groups, and P407-PBP with s-butyl groups. (F) Effect of n- or s-butyl phosphoester and DP on G′ and G″ of 18% aqueous solution of P407 derivatives, as a function of temperature. Data are means ± SD (n = 4).