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

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Polymers and High Performance Materials


Poly(methacrylic acid) (PMA) and poly(2-ethyl-2-oxazoline) (PEOZO) are a polyacid/polybase pair capable of forming reversible, pH-responsive, hydrogen-bonding complexes stabilized by hydrophobic effects in aqueous media. Linear PMA was modified with long-chain (number-average molecular weight: 10,000) PEOZO via statistical coupling reactions in organic media to prepare a series of PXIA-graft-PEOZO copolymers. Potentiometric titrations revealed that the presence of tethered PEOZO markedly increases the pK(a) values for PMA-g-PEOZO copolymers as compared with simple PMA/PEOZO mixtures at degrees of ionization, alpha, between 0.0 and 0.1. The dilute-solution PMA-PEOZO intramolecular association has been probed by monitoring the PEOZO NMR spin-spin (T-2) relaxation as a function of pH. Covalently attached PEOZO side chains participate in complexation at higher values of a than untethered PEOZO. Surprisingly, most PEOZO side chains did not take part in hydrogen bonding at low a, and the highest level of PEOZO incorporation induced a decrease in the number of PMA/PEOZO hydrogen bonds. The polymer self-diffusion as a function of a was measured with dynamic light scattering. At low pH, the copolymers had no charge and they were in a collapsed form. At high pH, the expected conformational expansion of the PMU units was enhanced at moderate levels of PEOZO incorporation. However, the highest PEOZO incorporation induced the onset of intramolecular associations between PEOZO units along the copolymer chains. Low shear rheometry and light scattering measurements were used in conjunction with the T-2 NMR measurements to propose a model consistent with the aforementioned behavior. (C) 2004 Wiley Periodicals, Inc.

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Journal of Polymer Science Part A-Polymer Chemistry





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