Abstract
The intrinsic viscosity [η] of a poly(acrylic acid) (PAA) sample with a molecular weight of 4×106 in aqueous salt solution drastically increased by adding isopropyl amine (A-1). At the infinitely high concentration of the hydrochloric salt of A-1, where the electrostatic interaction is completely screened out, [η] was enlarged by 40 times as the degree of complexation fc increases from ca. zero to 0.6. Here fc was determined by potentiometric and NMR titrations. Furthermore, [η] at infinite ionic strength for PAA complexed with a bulkier and more hydrophobic amine, (R)-(+)-1-(phenyl)ethylamine (A-2), was higher than that for the complex of PAA and A-1 at the same fc. The drastic expansion of the PAA chain by the complexation with the amines A-1 and A-2 may arise from the chain stiffening and enhanced excluded volume effect.
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