Polyureas by interfacial polycondensation: Preparation and properties

An experimental study of polyurea membrane formation by interfacial polycondensation

“…Polyurea is a high melting thermoplastic [5], with a melting temperature of about 285 • C. Fig. 11(a) shows an exothermic peak at a temperature just below melting, at about 250 • C. As observed in our earlier work [5], this peak represents a cold crystalline transition, as the polymer chains arrange themselves into the maximally ordered structure under the conditions of increased mobility. Thus when this sample is allowed to cool and the DSC run again (Fig.…”

“…Samples of polyurea for various characterization studies were prepared as in previous work [5]. The microcapsules were first washed with distilled water and then with methanol several times (4-5 washes each) to eliminate traces of unreacted monomers.…”

“…A semi-crystalline nature is apparent, and all the samples showed prominent crystalline peaks in the region 10 • < 2Â < 30 • . A degree of crystallinity (X c ) can be calculated [5,[30][31][32] by drawing an amorphous halo and comparing the area under the crystalline peaks to the total area under the crystalline peaks and amorphous halo. Crystallinities of samples prepared under identical conditions (repeat runs, T14 and T15) along with that of other samples are shown in Table 4.…”

“…However, quantitative understanding of IP lags behind that of other established techniques, such as melt and solution polymerization. Experimental information on the influence of preparation conditions on polymer film properties, such as the molecular weight, crystallinity, permeability, etc., is scanty [4,5]. Other work, for example on membrane casting from polymer solutions, shows that the film microstructure, and consequent properties such as film density and permeability are affected significantly by the polymer precipitation mechanism [6].…”

“…With polyurea microcapsules, a variation in permeability by an order of magnitude could be achieved by varying the crystallinity of the polyurea [15]. The reaction kinetics seems to be important in controlling the crystallinity-there being a rough inverse correlation between rate and crystallinity [5,9,16]. The role of surfactants and interfacial tension in controlling particle structure has been sought to be explained based on thermodynamics [17].…”