The solutions of random copolymers composed from butyl methacrylate
(BMA) and methacrylic acid (MAA) with variable molar ratio of BMA/MAA (between
100/0 and 60/40) in isopropanol (IPA) and IPA-water have been studied by the pulsed
field gradient (PFG) nuclear magnetic resonance (NMR) method. The self-diffusion
coefficients of isopropanol in BMA-MAA solutions were defined from the initial parts
of echo-attenuation curves whereas the polymer diffusivities (two orders of magnitude
lower than those for solvent) were separately measured applying solvent signal
suppression (maximum gradient of 10 T/m). The aim was to study an influence of
polymer concentration and BMA/MAA molar ratio on the diffusion constants of
solvent and polymer. The diffusion coefficients for IPA increased with increasing
BMA content in copolymer. The calculations based on Wang model to describe the
solvent diffusion showed that relative mass of bound solvent per mass of polymer
increased with increasing MAA content in the copolymer. The model of restricted
polymer diffusion have been applied to explain the data on diffusivity of polymer. The
macromolecules formed the transient aggregates with effective size that decreased with
decreasing MAA content. Some polymer aggregates composed network and resulted in
obstructive effect for diffusion of the rest nonconnected copolymer chains. At the study
of BMA-MAA copolymers in IPA-water solutions, the focus was on the effects of
molecular composition and neutralisation level of methacrylic acid.The results
obtained showed that the average diffusion coefficient of solvent in D-IPA/D2O
solutions of neutralised copolymer was larger than that in un-neutralised copolymer
IPA solutions. Polymer diffusion at infinite dilution in IPA-water allowed an estimate
for the effective hydrodynamic radius of unperturbed diffusive polymer as 2.6-4.8 nm.
Keywords: Apparent diffusion coefficient (Dapp), Bound solvent fraction (hb),
Butyl methacrylate (BMA), Deuterated isopropanol (D-IPA), Diffusion
coefficient for solvent (Dsolvent), Diffusion coefficient for polymer (Dpolymer),
Diffusion time Δ, Effective hydrodynamic radius of the polymers RH, Isopropanol
(IPA), Mass of bound solvent (mb), Mass of polymer (mp), Mean square
displacement , Methacrylic acid (MAA), Neutralised copolymer, Nuclear
Magnetic Resonance (NMR), Pulsed Field Gradient (PFG), “Solvation” parameter
(H=mb/mp), Triethanolamine (TEA), Weight fraction of polymer (wp).
