Designation, Synthesis And Characterization Of Novel Multi-responsive Polymers Based On Semi-rigid Chains

Stimuli responsive polymers can provide a variety of applications for the biomedical fields. Due to their promising potential, scientists'interests on these polymers have exponsentially increased. Among them, double- or multi- responsive polymers have attracted more attention in this area.Bis(N-ethyl piperazinly) 2-vinylterephthal amide) (NEPVTA) was synthesized in this thesis, and then novel semi-rigid multi-responsive polymers were prepared via the solution radical polymerization. The phase transition behaviors of PNEPVTA were investigated by dynamic light scattering analysis. The aqueous solutions of PNEPVTA at pH 7.0 exhibited a lower critical solution temperature (LCST) at 63.7 oC. Dynamic light scattering studies indicated some aggregations of polymer chains below the LCST. For PNEPVTA in aqueous solution under the same condition, the relaxation time distribution was bimodal in correspondence with two well-separated modes. The phase transition temperature of PNEPVTA responded to pH changes. Lower critical solution temperatures (LCSTs) of PNEPVTA solution depended on polymer concentration and salts. The LCST of PNEPVTA was influenced by the addition of cationic surfactants. The behavior was attributed to enhanced polymer-surfactant interactions as the critical aggregation concentration (cac) of the system was approached. The behaviour of PNEPVTA was studied by scattering intensity in mixtures of water with ethanol. It was found that the well-known lower critical solution temperature-type cononsolvency properties of PNEPVTA in water–ethanol mixtures.To study the effect of substitutional alkyl on the thermal phase behavior in aqueous solution, we synthesized successfully another monomer bis(N-isopropyl piperazinly) 2-vinylterephthal amide) (NIPPVTA). NIPPVTA polymer with 1 mg/mL exhibited sharp phase transition at 47.6 oC. It was lower than LCST of PNEPVTA. The introduction of isopropyl increased hydrophobic interaction, and lower the LCST of PNIPPVTA. The effect of cationic surfactants on LCST of PNIPPVTA was familiar to PNEPVTA solution. The LCST could be controlled efficiently by the addition of cationic surfactants. PNIPPVTA also responded to pH change, and the sensitivity of PNIPPVTA was promoted. Similar to what was observed in PNEPVTA aqueous solution, the LCST of PNIPPVTA aqueous solution were lowered by the addition of salts. The cononsolvency properties of PNIPPVTA in water–ethanol mixtures were shifted to lower temperatures and became more obvious compared with PNEPVTA.In summary, the increase of substitutional alkyl will reduce the LCST of polymers. The increase of stereo-hindrance will make these polymers become sensitive to stimuli. The LCST of PNIPPVTA was controlled more exactly than PNEPVTA.