Title

Synthesis, Complex Formation, and Dilute-Solution Associative Behavior of Linear Poly(methacrylic acid) Incorporating Poly(ethylene glycol) and Poly(2-ethyl-2-oxazoline) Grafts

Date of Award

2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Charles L. McCormick

Advisor Department

Polymers and High Performance Materials

Abstract

The overall research objective is to develop polyacids containing polybase side chains capable of forming intrapolymer complexes, which provide large changes in macroscopic solution properties in response to changes in solution pH. The pH-responsive complexation and associative behavior of two copolymer series based on poly(methacrylic acid) (PMA) are investigated. The first series incorporates poly(ethylene glycol) (PEG) side chains capable of forming the well-known, reversible PEG/PMA complex into a PMA backbone. The PEG content was varied with a constant PMA chain length. The local interactions between PMA and PEG side chains were examined across the entire ionization range. The effect of these interactions on the final polymer conformation was evaluated. The second series utilized the more hydrophobic PEOZO as side chains on the PMA backbone. The incorporated PEOZO was varied, while the PMA chain length remained constant. The association between the PEOZO and PMA were probed as a function of pH, and the effect on the polymer conformation was determined. Linear PMA was modified with methoxy terminated, long-chain (5,000 MW), poly(ethylene glycol) (MPEG). The degree of ionization, α, was determined utilizing potentiometric titration. The presence of tethered MPEG markedly increased the pKa values over those of the PMA homopolymer or PMA/MPEG mixtures at α < 0.35. The dilute solution PMA-PEG intramolecular association was probed by monitoring the PEG nuclear magnetic resonance (NMR) spin-spin (T2 ) relaxation as a function of pH. Two populations of MPEG exist at appropriate ionizations; those participating in hydrogen bonding with the PMA backbone, and those not participating in hydrogen bonding. Polymer self-diffusion at varying degrees of ionization was measured using pulsed gradient spin-echo (PGSE) NMR and dynamic light scattering. Acidic conditions produced coil collapse, apparently arising from the formation of intramolecular hydrogen-bonded complexes along the polymer backbone. Under basic conditions, coil expansion was observed due to conformational changes (polyelecrolyte effect) and the added volume of the tethered MPEG, as well as the reduction of intramolecular complexation as the number of carboxylate anions increased. (Abstract shortened by UMI.)