Hello, I think you can use solid state NMR. https://en.wikipedia.org/wiki/Solid-state_nuclear_magnetic_resonance In my experience of work with poor soluble polymers I used lower Mw fraction of polymer or oligomers for NMR study

Solid-state NMR is a powerful technique used to study the structure and dynamics of solid materials, including polymers. Swollen polymers refer to polymer samples that have absorbed or imbibed a solvent, causing the polymer chains to swell and become hydrated.

Solid-state NMR can provide valuable information about the local environment and interactions within the polymer matrix and the solvent molecules. It can reveal details about the molecular structure, chain packing, and interactions between the polymer and the solvent. The information obtained from solid-state NMR experiments can help in understanding the swelling behavior of polymers and their interactions with various solvents.

However, it's worth noting that running NMR experiments on swollen polymers may present certain challenges, such as sample preparation and handling to maintain the swollen state, as well as potential broadening of NMR signals due to the presence of solvent molecules. Proper care must be taken to ensure the NMR measurements are representative and accurately reflect the properties of the swollen polymer system. Additionally, the choice of NMR techniques and experimental conditions may need to be tailored to suit the specific characteristics of the swollen polymer under investigation.

In measuring NMR of polymer the polymer should be dissolved in a proper solvent

NMR analysis of polymers can be challenging and time-consuming due to the complexity of the spectra, particularly in cases of high molecular weight polymers or complex copolymers.

Instead of NMR, other analytical methods are commonly used to characterize polymers, including:

Balram Lohan thanks for this information