Conformational Studies of Poly(2-(dimethylamino ethyl methacrylate) (PDMAEMA) and Poly(acrylic acid) (PAA) using Fluorescence Spectroscopy

This project aims to explore the aqueous solution dynamics of the poly(dimethyl aminoethyl methacrylate) (PDMAEMA) and poly(acrylic acid) (PAA) systems using fluorescence techniques. Both of these polymers were synthesised several times using free radical polymerisation techniques with two types of fluorophore labels included in synthesis. The resultant polymers were investigated using fluorescence techniques which include steady state fluorescence studies, fluorescence decay lifetimes and time resolved anisotropy measurements.
Initial solution dynamics of these polymer show that the PDMAEMA exhibits a coiled conformation at high pH values and adopts an expanded form at low pH values. PAA exhibits a partially coiled form at low pH values, but adopt a relatively expanded chain at a pH approximately more than their pKa. The study also shows that the pendant amine groups of the PDMAEMA polymer effect the fluorescence of the labels, and this is what is observed at high pH.
Addition of salts to PAA polymer promote coiling at low and high pH except salt of NaCl and CaBr2. When they added to the uncharged polymer, where it cause the polymer chain to flatten at low concentration of salt, and then to fold again under further addition of these salts. Effect of salts on PDMAEMA polymer conformation has been found to be efficient in growth of aggregation for the cationic polymer. However, salts like sodium chloride, sodium bromide and calcium bromide, has a different effect on the polymer conformation which exist in a coiled state, as they unfold the coiled polymer (at high pH) at low concentrations of them and refold it at high concentration.
The interactions between polyelectrolytes and the oppositely charged surfactant micelles have been investigated using fluorescence technique, in order to understand the conformation and the dynamics of these polyelectrolytes. Addition of cationic micelles (CTAC) to anionic PAA polymer (at high pH), and anionic micelles(SHS) to cationic PDMAEMA polymer(at low pH), change the conformation form of the polymers from an expanded chains to a collapsed structure, as the electrostatic forces assume to play the main role in such interactions. Whereas, the hydrophobic forces control the interactions in polymer/micelles system when the polymers adopt a coiled conformation.