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NMR in study of intermolecular interactions and structure of polymer solutions and films

Victor Rodin

Victor Rodin (previous postdoc in the group, left in 2006)

The present work focuses on the intermolecular interactions and structure in polymer solutions and films made from random copolymer solutions.

The techniques we have used include 1H NMR relaxation times (T2, T1), PFG NMR (the diffusion constants of the polymer and the solvent), 13C CP/MAS NMR, high resolution 1H NMR in solution and NMR Imaging.

1H spectra of polyBMA
Figure 1: 1H-NMR spectra of partly dried polyBMA films

We consider the molecular mobility and self-diffusion of both solvent and polymer in different states (from solution to film formation). The films have been formed from isopropanol solutions using a range of compositions of n-butyl methacrylate (BMA) and methacrylic acid (MAA) random copolymers. The polymer diffusivity is two orders of magnitude slower than the diffusion constant values for the solvent. We have studied the influence of the concentration on the polymer aggregation in solution and the influence of the BMA/MAA molar ratio on the diffusion constants of both the polymer and the solvent.

Apparent self-diffusion coefficients (Dapp) for partly dried films decrease with increasing diffusion time showing that solvent is trapped in the film in a restricted environment. The fully dried films have also been re-swollen in H2O for different times and studied with NMR Imaging.

2D NMR image
Figure 2: 2D-NMR image of polyBMA film re-swollen in water

Significant progress has been made in imaging water ingress into the polymer films. Diffusion coefficients of the water in swollen films have been discussed in terms of restricted diffusion theory. NMR imaging showed how water penetrates into the polymer films giving information on the inner structure of the polymer films with different hydrophobic/hydrophylic ratios.

Sponsor: ICI