Thermoresponsive MPC-b-NIPAM Diblock Star Copolymers

Diblock star tri-arm copolymer, poly(2-methacryloyloxyethyl phosphorylcholine -b-N-isopropylacrylamide) were synthesized via atom transfer radical polymerization (ATRP) using the so-called two steps approach. The formation and composition of copolymer were confirmed by FT-IR and 1H NMR, and the thermo-sensitive behaviors of their solutions were studied. The main contents were summarized in the following:(1) The surface tension of varied copolymer solutions was measured. The results indicated that the critical micellar concentration (CMC) decreased gradually when the N-propylacrylamide contents in the copolymer increased. Transmission electronic microscope (TEM) showed that the copolymer solutions could form globular micelles whose diameter were around 100 nm. The hydrodynamic diameter (Dh) determined by dynamic light scattering (DLS) revealed Dh was temperature sensitive. When temperature was raised, the size of the micelles was increased.(2) The cloud point (CP) and low critical solution temperature (LCST) were determined by turbidimetry and differential scanning calorimetry (DSC). The CP and LCST decreased upon increasing solution concentration or NIPAM contents in the copolymer.(3) Phase diagram of copolymer solutions disclosed that 1:8 (MPC/NIPAM) copolymer solution was unable to form gel, 1:16 solution could only form weak-gel and 1:32 sample could form free standing-gel. The copolymer solutions obtained showed a fast thermo-responsive behavior, and the 1:32 copolymer had a good ability to hold water.(4) The rheological properties of copolymer solutions were dependent on temperature. After sol-gel transition, the variation in the storage modulus G'was significant with about four orders of magnitude increase; while the increment in loss modulus G''and shear viscosity was around 3 orders of magnitude.(5) The cytotoxicity assay demonstrated that the concentration had no influence on the cytotoxicity of MPC-b-NIPAM block copolymer solutions in a wide range, implying good biocompatibility. The result suggests the great potential application of these materials in the field of embolic agents.