Solution properties of hydrophobic derivatives of poly(ethylene-alt-maleic acid)

A library of hydrophobically modified polyelectrolytes was prepared by reacting linear alkyl amines with poly(ethylene-alt-maleic anhydride), followed by hydrolysis of the residual anhydride groups. Every reacted anhydride gives a pendent alkylamide plus a carboxylic acid group, and the result is a comb architecture. The lengths of the alkyl side chains were 3, 6, 8, or 10 carbons. The density of alkyl side chains was expressed as the fraction of anhydride groups reacted with alkyl amines (25 %, 50 %, and 75 %). The dominant factor influencing the aqueous solution properties is the alkyl chain length. C3 polymers had no pyrene receptive hydrophobic domains. C6 and C8 polymers bound pyrene at pH less than 6 and do not give reliable dynamic light scattering (DLS) results. C10 polymers displayed pyrene binding across the pH range and, based on DLS and AFM data, possibly appear as unimolecular nanogel dispersions from pH 7–9. At pH values > 9, our DLS measurements gave low-quality data, whereas at pH less than 7 both DLS and AFM results indicated nanogel aggregation. The C10 polymer properties were surprisingly insensitive to the degree of hydrophobic substitution over the range of 25–75 %. The nanogels with low alkyl contents were slightly more swollen and had high NaCl critical coagulation concentrations compared to the high alkyl content nanogels. These polymers are of particular interest because the non-derivatized maleic moieties in the polymers can form ester linkages to cellulose in an aqueous, catalyst-free process.