Study On The Thermoresponsive Property And Application Of New Functional Hyperbranched Thermoresponsive Polymers

In this dissertation, a series of new functional hyperbranched thermoresponsive polymers with different lower critical solution temperature were synthesized from hyperbranched polyethyleneimine （HPEI）. The factors influencing the thermoresponsive property of the aqueous solution of these polymers were studied in detail, such as the structures of the polymers, the pH of the solutions and the existence of various salts. It was found that there was obvious difference between the hyperbranched thermoresponsive polymers and the traditional linear thermoresponsive ones in the thermoresponsive property. Based on these results these polymers were used to form themoresponsive composites with gold nanoparticles. The solution properties of these thermoresponsive composites and their applications as colorimetric sensors and recoverable catalysts were further researched. The details were as follows:1. In the process of the modification of the terminal amino groups of HPEI with isobutyric amide （IBAm） groups, the amidation agents were optimized and it was found that isobutyric anhydride was the best one. A series of HPEI-IBAm hyperbranched thermoresponsive polymers were successfully prepared by changing the molecular weight of HPEI core and the degree of substitution （DS） of IBAm groups.2. The cloud point （CP） of the aqueous solution of HPEI-IBAm polymers was sensitive to the alteration of molecular weight and the DS of the polymers and the pH of the aqueous media. Lowering the molecular weight and the DS value of the polymer and increasing the pH of the system can effectively increase the CPof the solution. The CP value can be controlled in a broad temperature range of 0¹00℃.3. The CP of HPEI-IBAm was more sensitive to the salts compared with that of linear thermoresponsive polymer. At high salt concentration, the specific ranking of inorganic anions in salting-out HPEI-IBAm polymer was as follows: PO43- >CO3^2- >SO4^2- >S₂O₃^2- >F- >Cl- >Br- ^NO₃^->I- >SCN^-. This sequence is in accordance with the well-known Hofmeister series. However, at low salt concentration, the specific ranking of inorganic anions in salting-out HPEI-IBAm polymer was as follows: PO43- ^CO3^{2- S}CN^- >I- >NO₃^- >S₂O₃^2- >SO4^2- >Br- >F- >Cl-. Anti-Hofmeister phenomenon can be found in both monovalent and divalent inorganic anions. The cations’effect on the CP of HPEI-IBAm aqueous solutions was not so significantly as anions, however, the cations ranking ordering for HPEI-IBAm also showed obvious difference from that of the linear thermoresponsive polymers. The specific ranking order of inorganic cations in salting-out HPEI-IBAm polymer was as follows: Sr^{2+ B}a²⁺ >Na^{+ K+ R}b+ >Cs⁺ >NH₄^{+ C}a²⁺ >Li^{+ M}g²⁺. The organic ammonium salt showed obvious salting-in effect in the certain salt concentration region. The salting-in effect of ammonium chloride salts can be enhanced significantly by increasing the length of their aliphatic chains.4. The composites of gold nanoparticles with HPEI-IBAms were thermoresponsive, and their CPs could be adjusted in a broad temperature range. Upon raising the temperature near the CP, the color of the obtained thermoresponsive composites changed sharply in a narrow temperature range. Thus, the obtained thermoresponsive composites were suitable to be used as colorimetric sensors for detecting the environmental temperature variation. Furthermore, the solution colors of the thermoresponsive composites were also sensitive to the pH and salts of the system, resulting that they could also be used as colorimetric sensors for detecting the variation of pH and salt concentration.5. The obtained thermoresponsive gold nanoparticles could be used as responsive catalysts for the catalytic reduction reaction of 4-nitrophenol. The advantages are as follows: （1） catalysts could be recycled several times. （2） Appropriate HPEI-IBAm polymer could improve the catalytic activity of the gold nanoparticles. （3） The sudden significant increase of the reaction temperature above the pre-set one could be avoided.