We chose the widely studied poly (3-hexlythiophene) (P3HT) as the organic semiconducting polymer. Not only does P3HT allow charge transport through its conjugated polythiophene backbone, but the addition of hexyl side chains confers it with excellent solubility in organic solvents such as chloroform and chlorobenzene (Figure ). P3HT is a well-studied semiconducting polymer and as such perfectly suited for a fundamental blending study with PBS. To gain deeper insights into the effects of supramolecular entanglements and crosslinking density within PBS, two different PBS polymers were synthesised. By performing a condensation reaction between a low and high molar mass hydroxy terminated PDMS (PDMS-OH) and boric acid, the corresponding low (LPBS) and high molar mass (HPBS) polyborosiloxanes were obtained. The molar masses of the two different PDMS-OH polymers were chosen with respect to the critical molar mass (Mc) of linear PDMS (24.5 kg mol -1 ). LPBS was synthesised from a hydroxy-terminated PDMS with a molar mass lower than the Mc, whereas HPBS was synthesised from PDMS-OH with a molar mass exceeding Mc. The effect of this led to two different elastomeric networks which were studied using FTIR, differential scanning colorimetry (DSC), thermogravimetric analysis (TGA) and rheology. By obtaining the Hansen solubility parameters of P3HT and the PBS elastomers, the compatibility was theoretically deemed to be sufficient to produce a homogenous blend. Using a combination of optical, thermal, and mechanical characterisation tools, the effects of blending P3HT into the two different PBS systems at concentrations between 0.1 and 10 wt% are discussed.