Synthesis And Characterization Of Sensitive Poly (N-isopropylacrylamide)/Poly(Acrylic Acid) IPN Microgels

In recent years, there have considerable research attention been focused on the preparation of novel responsive microgels because of their wide applications in many fields, such as drug controlled release, environmental cleanup, separation ,and colloidal crystals, etc. Among them, the temperature- and pH-responsive microgels have attracted great interest from both scientific and industrial communities at present. Therefore ,in this thesis, we intend to prepare a series of novel temperature- and pH-sensitive microgels based on NIPAM and AAc via surfactant-free emulsion polymerization and interpenetrating network technique. The structure and properties of these hydrogels were preliminarily explored. The main results achieved are as follows:1 ,The novel temperature- and pH- sensitive semi-interpenetrating network (semi-IPN) microgels were prepared via the preparation of the temperature-sensitive linear poly(N-isopropylacrylamide)(PNIPAM) by surfactant-free emulsion polymerization and then introducing the other pH-sensitive poly(acrylic acid)(PAAc) network into the polymer by interpenetrating technique. The results from the study of structure and properties proved that both the components were existed in a semi-IPN structure which had good temperature- and pH-sensitivity. At acidic condition ,these hydrogels exhibited "thermo-induced contraction" behavior similar to the traditional PNIPAM hydrogel. At alkalescent condition and the temperature below the VPTT of PNIPAM microgel(≈32℃),the diameter of the microgel particles increased with elevating temperature until reached up to the VPTT, and then tended to decrease as the temperature to be further elevated. It also showed that the microgels were easy toward aggregation at strong acidic condition.2, The novel temperature- and pH- sensitive IPN microgels were prepared via the preparation of the temperature-sensitive cross-linked PNIPAM microgel by surfactant-free emulsion polymerization and then introducing the other PAAc network into it by IPN technique. The experimental results indicated that both the components were existed in an IPN structure which had good temperature- and pH-sensitivity. The VPTT of these microgels was at 31.69℃, which is consistent with that of the cross-linked PNIPAM microgel. As the temperature above 25℃, the hydrogels thus prepared were easy toward aggregation.3, The novel temperature- and pH- sensitive semi-IPN microgels were prepared via the preparation of the temperature-sensitive cross-linked PNIPAM microgels by surfactant-free emulsion polymerization and then introducing the other pH-sensitive linear PAAc into it by IPN technique. The experimental results showed that both the components were formed a semi-IPN structure which had good thermosensitivity and had VPTT at 32.2℃.As the temperature above 25℃,the hydrogels were easy toward aggregation. However , as the AAc amount was 0.8ml,and at pH=4,the microgel could exhibit the "thermo-inducing contraction" behavior similar to the traditional PNIPAM microgel, meanwhile, exhibit pH-sensitivity.