Characterisation of silicone prepolymers and disparity in results

Liquid hydroxyfunctional polydimethylsiloxanes prepolymers (HOPDMS, Siloprens) with a range of relative molar masses, M(n) (25 500-88 000 g/mol) quoted by the supplier have been characterised by a number of techniques such as OH group titration, bulk viscometry, Gel Permeation Chromatography (GPC), and swelling measurements. The resulting molar masses of these prepolymer obtained through these techniques have been compared with one another and that of the values quoted by the manufacturer. Unexpected results of insensitivity of the properties of these prepolymer to the initial molar masses quoted by the suppliers have been observed. It has been found out that these results are dependent upon the type of technique used. The reason for these unexpected results has been discussed in detail and attributed to the multi functionality of the prepolymers, a characteristic not previously suspected or reported.