CHARACTERIZATION OF POROUS ORGANIC MATRICES IN THE SWOLLEN STATE BY NMR

VELASCO, MANUEL I.; SILLETTA, EMILIA V.; GOMEZ, CESAR G.; ACOSTA, RODOLFO H.; MONTI, GUSTAVO; STRUMIA, MIRIAM C.

Rosario

Taller; . Taller Fronteras en Resonancia Magnética: de los materiales a los sistemas biológicos; 2013

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Polymer matrices with well defined structure and pore sizes are widely used in several areas of chemistry such as catalysis, enzyme immobilization, HPLC, adsorbents or droug controled release. These polymers have pores in its structure both in the dry and swollen state. Although it is well known that the structures and properties greatly differ between these two states, only a few methods provide information about the swollen, even though most of the applications involve the matrices in this situation. Nuclear Magnetic Resonance (NMR) is a suitable tool for the study of the molecular dynamics of different liquids spatially confined in macro, meso and nanopores through changes in relaxation times. In transverse relaxation experiments, either diffusion inside the pore, or relaxation induced by mobility restriction of the liquid near the wall, are additional sources of relaxation, which are extremely useful in the determination of structural and functional properties. In particular the use of 1 H-CPMG allows the determination of the transverse relaxation time (T2) of the molecules of liquid, and this can be related to the pore size at which it has bound. Hence through relaxometry data it is not only possible to perform the characterization of the material in the swollen state, but also to monitor the behavior of the matrix during evaporation. For this work we synthesized polymers of 2-hydroxyethyl methacrylate (HEMA) cross-linked with ethylene glycol dimethacrylate (EGDMA), varying the proportion of crosslinking between 6 and 33%. The amount of crosslinking has a marked effect on the final properties of the material. Given the polar characteristics of the matrices, heptane was used to characterize the dry state, since the molecules enter in the pores but do not solvate the polymer chains, so the network morphology is not altered. On the other hand, water was used to study the properties of the matrix in the swollen state. Analizing the distribution of T 2 valuesis possible to determine parameters that are useful in the characterization of the material, such as pore size distribution, porosity and the contribution of each pore population to the total porosity. Furthermore, this technique allows the observation of the variation in the distribution of pore populations as the swelling liquid evaporates. This enables to infer specific properties of each organic matrices under studied. Sumarizing, NMR relaxometry provides information of the pore structure of different polymeric matrices. These parameters are useful for the characterization of porous materials and, unlike most conventional techniques, this information can be obtained in both the dry and the swollen state. The swollen state study also provides information on the structure of the mesh network. This technique represents a direct, simple, quick and non-destructive approach to determine the porperties and architecture of organic porous materials.