Reactive polydimethylsiloxanes, or RPDMS (Reactive Silicones), are a new class of silicone polymers with distinct characteristics that are gaining increasing fame in a wide range of industrial applications. PDMSs have interesting properties including low surface energy, biocompatibility, high thermal and oxidative stability as well as good water resistance. RPDMS are more versatile and functional than typical polydimethylsiloxanes (PDMS) since they go through multiple chemical reactions instead of just one.
Explaining the PDMS Functional Groups
Reactive Silicones are characterized by the presence of functional groups that enable chemical reactivity. Common reactive groups include vinyl, epoxy, amino, and hydrosilane functionalities. Other functional groups such a amino, hydroxy, and methacryloxy are also known for their properties as raw materials. These three functional groups, available through our Reactive Silicones portfolio, have specific compatibility with various materials (Figure 2).
The simultaneous presence of pendant organic groups attached to an inorganic backbone gives silicones their unique combination of physical, chemical, and mechanical properties. The low surface tension of liquid PDMS results from a combination of the properties of organic side groups (reactive) combined with the inorganic backbone (siloxane chains).
The methyl groups are able to closely pack at the surface due to their low intermolecular forces and the large Si-O-Si bond angle as seen in Figure 3A & 3B. The low critical surface tension of wetting of PDMS readily explains one of the most common features of silicone polymers: their excellent low adhesion which prevents most materials from strongly adhering to them. Conversely, their low surface tension means that they can wet almost all surfaces, thus fulfilling the first requirement of any adhesive system.
Another interesting consequence of the properties of the siloxane bond, is the value of n in the common linear trimethylsiloxy-endblocked-PDMS, (M-DIl-M) which can vary from zero to tens of thousands giving a range of viscosity from 0.65 to 2,500,000 centipoise to the polymeric material. This relationship between viscosity and polymer chain length allows PDMS polymers to vary in form from ‘water-like’ fluids to a flowable gum which helps with filler dispersion, while retaining the same chemical character. The length of the polymer chain is directly proportional to its molecular weight. The FM Bi & Mono terminal series of JNC’s Reactive Silicones offer a variety of polymer length chains, ranging from a molecular weight (MW) of 1000 up to 15000, to cater to the needs of any application that needs viscosity adjustment.
Chemically Reactive Functional Silicones
Silaplane FM-0815J is a monoterminal type reactive silicone with an Alkoxysilyl functional group. Unlike the other FM products, where filler dispersion properties only rely on the physical bond between the reactive group and fillers, FM 0815J’s siloxane chains and alkoxysilyl groups have the ability to chemically bond to the surface of the inorganic filler thus stabilizing the filler dispersion. They are also effective in reducing the viscosity of filler dispersion better than silane coupling agents.
Common Reactive Silicone properties
Another important property of silicones, and one that is particularly relevant to adhesion applications, is their high thermal stability compared to common organic polymers. This stability towards thermal energy opens a new window of opportunities for silicone adhesives.
Silicones are also able to build reactivity on the polymer. This allows the building of cured silicone networks of controlled molecular architectures with specific adhesion properties while maintaining the inherent physical properties of the PDMS chains. The combination of the unique bulk characteristics of the silicone networks, surface properties of the PDMS segments, and the specificity and controllability of the reactive groups, produces unique materials useful as adhesives, protective encapsulants, coatings and sealants.
Overall, reactive silicones are an essential ingredient in many products such as adhesives, sealants and Thermal interface materials, in which their chemical and physical properties contribute to the product’s performance. They are mainly used as a blending ingredient to improve the flowability, filler content and adhesion of specialty products. Aside from the adhesive industry application, reactive silicones’ properties are also starting to be recognized as a raw material at the cosmetic industry .
We support a wide product range of reactive silicones with multiple molecular weights and viscosities. We can also customize new grades of materials after consultation with our R&D department. Take the next step toward material excellence and development – reach out to our team today.
