Microdomains in Hydrophobic Polyacids

Abstract

The alternating copolymers of maleic acid and n-alkyl vinyl ethers constitute a versatile group of polyacids which are ideally suited for studying the opposing effects of hydrophobic and ionic interactions in macromolecular behavior. The members with intermediate alkyl group size (n = 4–8) have been of special interest because they undergo conformational transitions from compact to random coil structures upon neutralization by base. The compact conformation is stabilized by the hydrophobic forces between the alkyl groups which form micelle—like microdomains inside the macromolecules. A number of selected studies which have been carried out in our laboratory to characterize the hydrophobic microdomains and the conformational transitions are reviewed here. These studies include fluorescence spectroscopy of dansylated copolymers, viscosity and phase separation investigations, and potentiometric titrations. Two recently developed methods for extracting novel information from the latter are included. One involves the resolution of appropriately chosen subunits into species differing in their states of deprotonation, which for the butyl copolymer leads to bimodal population distributions in the pH range where this copolymer undergoes its conformational transition. The other involves the determination of the micelle size for the case where the polyacid is large compared to the micelle and, therefore, may contain many micelles.