Preparation Of PH/Temperature-sensitive Polymer Fluorescent Material And Performance Research

Poly(N-isopropyl acrylamide), PNIPAAm, shows thermoresponsive features withreversible phase transition behavior, lower critical solution temperature (LCST) about32oC in pure water. Acylhydrazone bond with the pH responsibility is one of dynamiccovalent bonds and more stable than the weak intermolecular interactions. It can beused to generate multifunctional polymers.In this paper,2-(2’-pyridyl) benzimidazole was hydroformylated by Ullmannreaction. Poly(N-isopropyl acrylamide-co-acylhydrazide)(PNIPAAm-co-AH) wasobtained by hydraziding Poly(N-isopropylaerylamide-co-methylaerylate). PNIPAAm-co-AN with pH/temperature-responsive was obtained through acylhydrazonation of4-(2-(2’-pyridyl) benzaldehyde) benzimidazole and PNIPAAm-co-AH. Fluorenemolecule was introduced onto PNIPAAm-co-AH copolymer through the formation ofdynamic covalent acylhydrazone bonds to obtain pH/thermoresponsive preparedPNIPAAm-co-AN.The structures and properties of PNIPAAm-co-MA, PNIPAAm-co-AH, PNIPA-Am-co-AN were characterized by1H-NMR, FI-IR, FL, GPC and DLS. Resultssuggested that small fluorescent molecule4-(2-(2’-pyridyl) benzaldehyde) benzimida-zole was successfully connected to the polymer side groups. Copolymer has bettertemperature sensitive. LCST of PNIPAAm-co-MA and PNIPAAm-co-AN increasedwith MA increasing, as opposed to PNIPAAm-co-AH. LCST of PNIPAAm-co-ANwas the lowest among PNIPAAm-co-MA, PNIPAAM-co-AH and PNIPAAm-co-ANfor hydrophobic and steric small fluorescent molecule. The fluorescence properties ofPNIPAAm-co-AN were characterized with the maximum excitation wavelength about350nm and maximum emission wavelength about400nm. The fluorescent emissionintensity of PNIPAAm-co-AN solution significantly grew along with the titration ofzinc acetate within the small range. The intensity of fluorescence was enhancedthrough the dynamic exchange of PNIPAAm-co-AN and formaldehyde solution withthe red shift. During the process PNIPAAm-co-AN fluorescence properties behaved agood responsiveness. The dynamic property of acylhydrazone can be proved by thechange of molecular weight of PNIPAAm-co-AN and glutaraldehyde hydrazone viaGPC traces. The results offered a model research for dynamic hydrazone bonds, and also a versatile method to functionalize ploymer.