Structural and physico-chemical properties of clathrate hydrates of tetraisoamylammonium polyacrylates

Abstract

Physico-chemical and structural characteristics have been studied of ionic clathrate hydrates of cross-linked (n = 1%) tetraisoamylammonium (TiAA) polyacrylates with different extent of substitution of proton-ions of the carboxylic groups for TiAA cations (x = 77%, 60%, 40%) in the polyacrylate. Powder X-ray diffraction studies have been carried out. All hydrates are isostructural to the earlier studied clathrate hydrate of cross-linked TiAA polyacrylate with x = 100%. The hexagonal structure with the space group P6/mmm and slightly different unit cell parameters (a ~ 12.24 Å, c ~ 12.70 Å) is related to the idealized Hexagonal Structure I of clathrate hydrates. Compositions, phase transition temperatures and decomposition enthalpies of the hydrates have been determined using differential thermal analysis and differential scanning calorimetry. The stability of the hydrates structure decreases with lessening of the content of TiAA cations in the polymeric molecule. The hydrates decomposition temperatures go down from + 14.6 to + 9.8 °C (for x = 100–40%) and the decomposition enthalpies—from 189.1 kJ/mol of hydrate to 84.0 kJ/mol of hydrate (for the same interval of x). The comparison has been made of physico-chemical characteristics of the ionic clathrate hydrates of cross-linked TiAA polyacrylates with those of the hydrates of tetrabutylammonium (TBA) polyacrylates and also of the ionic clathrate hydrates of TBA salts with monomeric anions.