Silicones are well known as raw materials in the cosmetic industry. When we talk about silicones, most of us are thinking of various types of fluids. But, besides the broad spectrum of silicone fluids such as dimethicones, dimethiconols, phenyltrimethicones, amodimethicones and dimethicone copolyols, there does exist another major category of silicones which are of interest to the cosmetic industry — silicone resins and their derivatives.
Structure of Silicone Resins
What is the chemical difference between silicone fluids and silicone resins? If we look in our silicone materials toolbox, there are four basic units to experiment with: Munits, D-units, T-units and Q-units (Figure 1).
The difference between these building blocks is in the number of methyl groups directly attached to the silicon. M-units have three methyl groups and only one oxygen that can bond to another Si atom, thus M-units are used as stoppers or end groups. D-units have two methyl groups and two oxygen atoms and are used as chain extenders. Combinations of D-units and M-units with high D/M ratios yield linear molecules, known as dimethicones, having high viscosity.
With T-units and Q-units, we leave linear molecules that make up the world of silicone fluids and enter the threedimensional world of silicone resins. T-units have one methyl group and three oxygens. They build three-dimensional structures resembling cages, where the volume can be varied by adding D-units. M-units may be included to control molecular weight if desired, but are not required. Silicone resins built up from T-units are referred to as silsesquioxanes.
