Adsorption Of Poly(1-vinyl-2-pyrrolidone) On The Surface Of Highly Dispersed Amorphous Silica
ADSORPTION OF POLY(1-VINYL-2-PYRROLIDONE) ON THE SURFACE OF HIGHLY DISPERSED AMORPHOUS SILICA
L.A. Belyakova, D.Y. Lyashenko
Institute of Surface Chemistry of National Academy of Sciences, Kiev, Ukraine
Surface modification of highly dispersed amorphous silicas with various organic compounds is widely used for the preparation of new sorption materials possessing desired properties.
One of the promising investigations in this field is the study of possibility to prepare modified silicas for absorption of organic compounds from biologic liquids, and also for adsorption of biologically active and medicinal substances.
Therefore the interaction of poly(1-vinyl-2-pyrrolidone) (PVP) with highly dispersed silicas (hydroxylated Aerosil A-300 and Aerosil which is modified by Si‑H groups) has been investigated.
Poly(1-vinyl-2-pyrrolidone) has high hydrophilicity, pronounced tendency to complex formation, good adhesive properties. PVP is non-toxic. Poly(1-vinyl-2-pyrrolidone) is used for the medical purposes as a plasma-substituting solution, as a solution for the detoxication of human body and as prolonger of medicine action. It also used in textile, nutritive and pharmaceutical industries, in chromatographic analysis of medical compounds, for the separation of protein mixtures and for the synthesis of heterogeneous metal complex catalysts.
The adsorption of poly(1-vinyl-2-pyrrolidone) (Fluka, molecular weight10000) from water solutions (0.1-10.0%) at 25oC on the surface of hydroxylated silica or hydride silica has been studied. The hydride silica has been synthesized by interaction of Aerosil (preliminary evacuation at 400oC for 2h) with solution of methyldichlorosilane in toluene for 6h at the boiling. The silanol groups of silica surface interact with methylchlorosilane according to the reaction of electrophilic substitution with formation of=Si‑O‑Si(Cl)(CH3)H groups. The quantity of grafted Si‑H groups is0.526×10-3 mole×g-1.
Poly(1-vinyl-2-pyrrolidone) has characteristic absorption bands in IR spectrum at 3000 and 2970cm-1, which are assigned to asymmetric and
symmetric valence vibrations of the C‑H bonds in the methylene groups of aliphatic chain in polymer molecule. It also contains absorption band at 2925cm-1, which belongs to valence vibrations of the C-H bonds in the pentatomic ring of N-vinyl-2-pyrrolidone. The intensive absorption band of valence vibrations of the C=O bonds is observed at 1710cm-1. The 1530, 1500 and 1455cm-1absorption bands are assigned to the valence vibrations of the lactam ring, and the bands at 1420 and 1365 cm-1 are assigned to the straining vibrations of the C-H bonds. The IR spectrum of silica with adsorbed PVP contains the same absorption bands that the infrared spectrum of polymer, and it also has 3750cm-1 absorption band of isolated silanol groups.
It was established that hydride silica adsorbs PVP much better than hydroxylated silica under the same conditions. It was calculated (taking into the consideration the value of lading field of PVP molecule) that the maximum adsorption of PVP (in the studied concentration solution range) is not much higher than surface monolayer.
The process of PVP desorption from the silica surface was studied by means of infrared spectroscopy, weight thermal and gravimetric analysis. It was established that PVP desorption from the silica surface is observed at the contact with water at room temperature yet. The desorption process can be divided into two stages: quick desorption (90% of adsorbed polymer) and slow desorption. It was shown that after quick desorption of PVP the silica surface contains a small quantity of polymer - not more than 0.10-0.12 monolayer.
The thermal destruction of poly(1-vinyl-2-pyrrolidone) and PVP, which adsorbed on the silica surface, has been studied. The intensive thermal destruction of PVP is accompanied with three exoeffects on the DTA curve at 340, 400 and 515oC. The loss of polymer batch mass corresponds to these thermal effects on the TG and DTG curves. The thermal destruction of PVP, which adsorbed on the silica surface goes also through three stages, but also at much higher temperatures (365, 425-545 and 630-670oC). The nature of thermal destruction of PVP adsorbed on the silica surface depends on quantity of adsorbed polymer. The temperatures of thermal destruction of PVP adsorbed on the silica under the conditions of surface monolayer filling with poly(1-vinyl-2-pyrrolidone) are 25-60oC higher than the corresponding temperatures for the initial polymer. If the concentration of PVP on the silica surface decreases, the temperature of thermal effects relating to PVP thermal destruction increases.
Based on the study of silica interaction with PVP it was established that poly(1-vinyl-2-pyrrolidone) is reversible adsorbed on the surfaces of both hydroxylated silica and silica with methylhydride groups.
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