Amphiphilic maleic acid-containing alternating copolymers - 2. Dilute solution characterization by light scattering, intrinsic viscosity, and PGSE NMR spectroscopy

摘要

The dilute solution behavior of several alternating copolymers of maleic acid has been characterized by static and dynamic light scattering, intrinsic viscosity, and pulsed-gradient spin-echo NMR spectroscopy. The copolymer of maleic acid-sodium salt and isobutylene (IBMA-Na, M(w)similar to350 kg/mol) dissolves readily in concentrated aqueous salt solutions. Changes in chain dimensions with ionic strength and pH are similar to those of the lesser salt solution-soluble poly(acrylic acid-sodium salt). The hydrophobically modified (with n-butyl, n-hexyl, n-octyl, and phenethyl amines) copolymers of maleic acid-sodium salts and isobutylene (IBMA-NHR-Na) show no sign of large intermolecular aggregation in 0.1 N sodium acetate (NaAc). However, the sizes of the copolymers are relatively small compared to that of the ionized parent copolymer (IBMA-Na, M-w similar to350 kg/mol), suggesting intramolecular aggregation of the alkyl sidechain groups along the polymer backbone. The copolymer modified with the longer chain n-decyl, on the other hand, forms stable large intermolecular aggregates containing 33 chains/aggregate. The copolymers of maleic acid-sodium salt and styrene (SMA-Na) appear to have no signs of aggregation, despite being a hydrophobic polyelectrolyte. The copolymer of maleic acid-sodium salt and di-isobutylene (DIBAM-Na) has a similar salting-out concentration as SAM-Na. The radius of gyration measurements by static light scattering suggest that at least some fraction of the DIBAU-Na chains form large intermolecular aggregates. The copolymers of maleic acid-sodium salt with n-alkenes (n-C(m)AU-Na) in 0.1 N NaAc form small intermolecular aggregates (three to five chains/aggregate): In contrast to these static light scattering results, PGSE NMR diffusion measurements for the above aggregated systems indicate only one diffusion coefficient consistent with the motion of single isolated chains. A plausible explanation for this discrepancy is that the population of the aggregates is too small to be sufficiently detected in the PGSE NMR experiment. Furthermore, it is likely that the aggregate has a larger relaxation rate than the nonaggregate, and therefore has a comparatively reduced signal in the PGSE NMR experiment. (C) 2004 Wiley Periodicals, Inc.