| Abstract: | Influence of Chemical Fine Structure of Vaselines on Physical and Technological Properties, 12: Influence of Chemical and Physical Data on the Practical Properties of Vaseline The influence of iso-fractions apart from normal and unsaturated hydrocarbons on the tack property of vaselines was studied. The tack is found to be the sum of tacks contributed by various molecular weight fractions obtained by gel permeation chromatography, which correlate with the observed chemical structures. Furthermore, other expected correlations between chemical structural groups and physical data, such as slip point and viscosity, were confirmed, which enable exact characterization of the vaselines studied. The results show that two different compositions yield vaselines having good practical properties: a) composition consisting of a large amount of long chain branched low melting tacky high molecular weight hydrocarbons (C-30 to C-200) and small proportions of n-paraffins and liquid hydrocarbons; b) compositions consisting of little high molecular weight solid iso-hydrocarbons (C-20 to C-100) together with n-paraffins and a large proportion of viscous tacky oil, which is composed of molecules having many short side chains. Since the vaselines of the type b) liberate the incorporated drugs more easily than those of the type a), to which also the so called natural vaselines belong, the type b) vaselines are considered to be optimum compositions. Practical properties of polymer-free bases could be compared with polymer-containing original vaselines by quantitative separation of the high polymers. Improvement of the practical properties of vaselines containing large proportions of oil can be accomplished by the addition of polyethylenes having molecular weights around 20 000, which can be dissolved in the vaseline base at elevated temperatures, and, on cooling, they improve the gel structure; however, these additives have disadvantages from technological viewpoint, since the processing has to be done at room temperature. Polyisobutylenes, that are frequently used, are unsuitable for improvement of the structure. |
