influence of loose and semianchored siloxane polymer chains on the tack of crosslinked silicone rubber

The influence of addition of nonreactive silicone oil or semianchored silicone polymer on crosslinked poly(dimethylsiloxane) (PDMS) rubber-rubber adhesion was studied. The additives can be considered either a tackifier, or connector molecules, able to cross the interface and entangle. In both cases, it influences the tack of the elastomers. An additional variable is the molecular weight of the additive, which affects the reptation of the polymer chains. Polymer-polymer demixing, which is the result of thermodynamic incompatibility of mixed polymers is another factor that influences tack. It causes the free chains to appear at the surface forming a layer of oil, which actually destroys the tack of the PDMS samples. The resulting tack phenomena as a function of oil, respectively semianchored silicone polymer chains, are very much dependent on the transient nature of the polymer reptation: in many cases the polymers need very long time periods to obtain equilibrium in interphase crossing, or oil sweats out of the crosslinked polymers, forming a liquid layer between the two phases resulting in a low tack value, due to hydrodynamic wetting alone.