Design And Preparation Of Temperature-sensitive PNIPAAm Fluorescence Probe

In this paper, poly(N-isopropylacrylamide) (PNIPAAm) with a Cl or Br end group was synthesized by atom transfer radical polymerization (ATRP) using ethyl-2-chloropropionate (ECP) or ethyl-2-bromopropionate (EPN-Br) as initiator, CuCl or CuBr as catalyst, N,N,N′,N″,N″-pentamethyl diethylenetriamine (PMDETA) or tris[2-(dimethylamino) ethyl]amine (Me6TREN) as ligand in different solvents such as 2-propanol, dimethyl sulfoxide (DMSO), water and mixed solvents (VDMF/VH2O=1:1, VDMF/VH2O=1:2). The effects of catalyst, ligand, initiator and solvent types on ATRP reaction were discussed. Structure and number-average molecular weight of the PNIPAAm were characterized by means of nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC).It was found that the molecular weight distribution of the resulting PNIPAAm was low in 2-propanol at 40℃under n[ECP]:n[CuCl]:n[Me6TREN] =1:1:2 condition. The low critical solution temperature (LCST) of PNIPAAm was dramatic decrease with increasing number-average molecular weight.The polymeric fluorescence probe was successfully obtained through nucleophilic substitute of PNIPAAm-Cl with fluorescein (FL) in ethanol, which was proved to be temperature/ pH-sensitive. The structure and properties of the fluorescence probe was characterized by1H-NMR, infrared spectroscopy (FI-IR), UV-visible spectrophotometer (UV), GPC and fluorescence spectrophotometer. It was found that the molecular weight of PNIPAAm could affect LCST based on the characterization by UV. The LCST fell when the molecular weight increase. The fluorescent response property of PNIPAAm was determined by fluorescent spectroscopy. It was found that the fluorescent intensity grew with increasing pH.(2) In this paper, two-arm initiator (9-AA-Br) with two bromine atoms was synthesized by reaction of 9-aminoacridine (9-AA) and bromoacetyl bromide. The structure of 9-AA-Br was characterized by FT-IR and 1H-NMR. The obtained result indicated that 9-AA-Br had been synthesized successfully.9-AA-PNIPAAm was synthesized by ATRP of NIPAAm using 9-AA-Br as initiator, CuCl/5,5,7,12,12,14–hexamethyl-1,4,8,11-tetraazamacrocyclotetradecan (Me6[14]aneN4) as catalytic system in THF at room temperature. The molecular weight and the molecular weight distribution of 9-AA-PNIPAAm were characterized by GPC. It was found that polymerization process of NIPAAm was basically in accordance with the law of ATRP. The structure of 9-AA-PNIPAAm was characterized by FT-IR and 1H-NMR. The LCST fell when the liquid concentration increase or when the molecular weight increase. The 9-AA-PNIPAAm fluorescence probe fluorescent intensity grew with increasing pH in alkaline conditions. At the same time, the emission summits red shift with increasing of pH. The PNIPAAm had good fluorescent response property due to fluorescent group in molecules structure of PNIPAAm.