Characterization of porous polymer materials by time domain nmr

E. V. SILLETTA; M. I. VELASCO; C. G. GÓMEZ; S. STAPF; C. MATTEA; M. C. STRUMIA; R. H. ACOSTA; G. A. MONTI

Angra dos Reis

Congreso; 15th AUREMN meeting; 2015

Asociación de Usuarios de Resonancia Magnética de Brasil

Porous polymer matrices are widely used in several areas such as catalysis,enzyme immobilization, HPLC, adsorbents or drug controlled release. Thesepolymers have pores in their structures both in the dry and swollen state.Although it is well known that the structures and properties greatly differ betweenthese two states, only few analytical methods provide information about theswollen state, even though most of the applications involve swollen matrices and in nearly every case itsperformance is a sensitive function of the distribution of internal pore size. Nuclear MagneticResonance is a suitable tool for the study of the molecular dynamics ofdifferent liquids spatially confined in macro, meso and nanopores throughchanges in relaxation times. Inthis work, we describe the study of the pore structure of the macroporouspolymer of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate[poly(EGDMA-co- HEMA)] in the dry and in the swollen state by measuringrelaxation times of liquids contained in the polymer network [1, 2]. This information allows thecharacterization of the matrices in terms of pore distribution, water uptake,and swelling. The behaviour of polar liquids during evaporation and deswellingdynamics is monitored and described. An internal migration of water from theswollen polymer mesh into expanding pores takes place. With this procedure, itis possible to obtain information about the microscopic morphology behaviour ofthe matrix during evaporation and deswelling. Additionally, the pore diametercan be determined by measuring diffusion which is encoded though magnetic fielddistortions that arise due to heterogeneities in the magnetic field, which are producedby changes in magnetic susceptibilities in going from the pore wall to the porevoid (DDIF - Decay due to Diffusion in Internal Field) [3]. Comparison of the relaxation timespresent in different pore sizes provides information on surface interaction [4], in particular the influence ofhydrogen bond between water and hydroxyl groups as a function of the amount ofcrosslinker is determined. Results were obtained by combining measurementscarried out with a 1.4 T permanent magnet spectrometer, an NMR MOUSE and a FastField Cycling relaxometer. References 1.         Gomez, C.G., G. Pastrana,D. Serrano, E. Zuzek, M.A. Villar, and M.C. Strumia, Macroporous poly(EGDMA-co-HEMA) networks: Morphologicalcharacterization from their behaviour in the swelling process. Polymer,2012. 53 (14): p. 2949-2955.2.             Silletta, E.V., M.I. Velasco, C.G. Gomez, R.H. Acosta,M.C. Strumia, and G.A. Monti, Evaporationkinetics in swollen porous polymeric networks. Langmuir, 2014. 30(14): p. 4129-36.3.             Song, Y.Q., S. Ryu, and P.N. Sen, Determining multiple length scales in rocks. Nature, 2000. 406 (6792): p. 178-181.4.         Mitchell,J., L.M. Broche, T.C. Chandrasekera, D.J. Lurie, and L.F. Gladden, Exploring Surface Interactions in CatalystsUsing Low-Field Nuclear Magnetic Resonance. The Journal of PhysicalChemistry C, 2013. 117 (34): p.17699-17706.