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Acrylic acid(AA) was grafted onto cellulose in homogeneous media by using ammonium persulfate as an initiator in the presence of N,N 0 -methylenebisacrylamide as a crosslinker under microwave (MW) irradiation. The powerful and highly efficient direct solvent, 1-butyl-3-methylinidazolium chloride ionic liquid was used as the solvent for the dissolution of cellulose and the media for the homogeneous graft polymerization of AA onto cellulose. The use of MW resulted in a drastic reduction of reaction time: 3 min irradiation was sufficient, compared with 30 min to 5 h, as conventional heating was used. Investigation was conducted on the effect of reaction parameters, such as monomer concentration, crosslinker dosage, exposure temperature and exposure time. The structure of the graft copolymer was confirmed by IR spectrum, thermogravimetric analyzer, and scanning electron microscope. The results show that the MW irradiation method can increase the reaction rate. And the graft copolymer is also an effective metal ion adsorbent.

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The concentration effect on aggregation and dissolution behavior of poly(N-isopropylacrylamide) (PNIPAM) in water was studied. Three concentration regimes with different phase behavior were identified by differential scanning calorimetry (DSC). Further optical, light-scattering, and rheological studies indicated that the appearance of different regimes arose from their corresponding solution structures below lower critical solution temperature (LCST): free chains and small clusters in regime I, large clusters in regime II, and a gel-like network in regime III. Different solution structures below LCST led to different phase-separated patterns formed above LCST: colloidal particles in regime I, large precipitate in regime II, and the sponge-like solid in regime III, which was well understood based on the overlapping parameter P. Different phase-separated patterns therefore resulted in different remixing behavior as observed by DSC. This work suggests that the swelling and collapse behavior of PNIPAM based hydrogels was controlled through the design of their phase-separated patterns, and therefore provided a way to develop high performance thermo-sensitive materials.

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