Preparation And Characterization Of Thermoresponsive Hyperbranched Polyethylenimine With Plenty Of Reactive Primary Amine Groups

In this dissertation thermoresponsive hyperbranched polyethylenimine (HPEI)having plenty of reactive primary amines was prepared through three-step reactionswith HPEI as the raw material. Its thermoresponsive properties in water were studiedsystematically. The details were as follows:Certain amount of primary amine groups of HPEI were first protected by Bocgroups. Subsequently, the residual reactive amine groups were reacted withisobutyric anhydride to introduce isobutyramide (IBAm) groups to HPEI. Finally,Boc groups were deprotected to result in HPEI-IBAm-NH2.1H NMR characterization proved the successful preparation of the product ineach step. Compared with its spatial isomer HPEI-IBAm0.80without primary aminegroups,1H NMR spectra verified that more IBAm groups were located in the interiorof HPEI-IBAm0.80-NH2. The further modification of HPEI-IBAm0.80-NH2andHPEI-IBAm0.80with p-nitrobenzaldehyde demonstrated that HPEI-IBAm0.80-NH2was more reactive than HPEI-IBAm0.80due to its possession of primary amines.Turbidimetry measurement showed that HPEI-IBAm0.80-NH2wasthermoresponsive in water. In the pH range of9.5—10its cloud point temperature(Tcp) was constant, and it increased obviously upon decreasing the pH below9.5.The thermoresponsive HPEI-IBAm0.8exhibited the similar trend, but the pHthreshold to achieve the constant Tcpwas around8.5. Moreover, HPEI-IBAm0.8-NH2showed higher Tcpand broader phase transition than HPEI-IBAm0.8.Moreover, the influence of organic acids on the thermoresponsive properties ofHPEI-IBAm0.80-NH2was explored.