Synthesis and Characterization of Pyrene Labeled Poly(N-Isopropylacrylamide-Co-N-Acryloyl-L-Valine) Copolymers

Abstract

Pyrenebutylamide-labeled poly(N-isopropylacrylamide-co-N-acryloyl-L-valine) copolymers have been prepared by two different methods and their physicochemical properties have been compared. One sample was prepared via copolymerization of N-isopropylacrylamide (NIPAM), and N-acryloyl-valine (NAV) with N-[4-(1-pyrenyl)butylacrylamide], the other by post-modification of poly(N-isopropylacrylamide-co-N-acryloyl-L-valine-co-N-acryloxysuccinimide) copolymer with pyrenebutylamine hydrochloride. The polymers were characterized by 1H NMR and FTIR spectroscopy, Differential scanning calorimetry and light Scattering. Though the use of fluorescence spectroscopy several differences between the two types of copolymers were detected. By comparing the extent of pyrene excimer emission and pyrene monomer emission from solutions of the two polymers, it was concluded that the copolymer obtained by direct copolymerization (method 1) had an inherent ''blocky" microstructure, while the copolymers obtained by the post-modification route presented a more random microstructure. Intrapolymeric interaction exists in solutions of low copolymer concentrations. At higher concentrations both inter-and intrapolymeric interactions coexist. The presence of a number carboxylic groups in the PNIP AM chain significantly modifies the conformation properties of the copolymers, compared to poly(N-isopropylacrylamide). The copolymers contract and expand in response to external conditions such as pH and temperature. Their Lower critical solution temperature (LCST) changes with pH. The interactions between polymers and fluorescence quenchers were investigated. The quenching results reveal that hydrophilic cationic quenchers interact strongly with the randomly labeled-copolymer. Hydrophobic cationic species interact strongly with ''blocky" pyrene labeled copolymer. Anionic quencher interacts quite weakly with both copolymers owing to electrostatic repulsion.