PFG NMR in Studying Solutions of Carboxylated Acrylic Polymers

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).