Effect Of Block Order Of NIPAAm/HEMA Triblock Copolymers On Thermoresponsive Behavior Of Solutions

ABA- and BAB- type triblock thermoresponsive copolymers (A=N-isopropylacrylamide, B=2-hydroxyethyl methacrylate) were synthesized by atom transfer radical polymerization (ATRP) and the formation of copolymers were confirmed. The differences in the thermo-sensitiveness of copolymer solutions were studied, and the effect of block order on the thermo-sensitive transition was explored. The main contents of this thesis include the following parts:(1) ABA and BAB triblock copolymers were synthesized by ATRP via sequential monomer addition, and the reaction kinetics indicated the"living character"of the polymerization. The copolymers characterized by FT-IR, 1H NMR and GPC were shown to have low polydispersities in the range of 1.13-1.54 for selected target degrees of polymerization. The lower polydispersities and higher conversion of the BAB copolymers compared with corresponding ABA copolymers implied that a better controllability could be realized in BAB system.(2) Turbidimetry and differential scanning calorimetry (DSC) were used to determine the lower critical solution temperature (LCST) of copolymer solutions, which was increased while the solution concentration was raised or HEMA contents in the copolymer was decreased. With the same composition and concentration, BAB exhibited higher transition temperature and a good solubility in water in comparison with ABA. Above LCST, copolymer solution at a critical concentration was capable of forming free-standing gel. Rheological measurement revealed that the moduli of ABA copolymer solution were higher than those of BAB above gel point.(3) The results of surface tension indicated that the critical micellar concentration (CMC) of ABA was lower than that of BAB, suggesting that the micellization occurred more readily for ABA in aqueous solution. Transmission electronic microscope (TEM) showed that the micelle size of BAB was a little smaller than that of ABA with the same unit compositions.(4) It was speculated that ABA and BAB copolymers formed branch and flower micelles in water, respectively, which ultimately influenced the course of phase transition. Temperature-varied 1H NMR and phase diagram were used to examine the effect of micelle type on the temperature-responsive transition of copolymer solutions.