General Experimental Details 1 H and 11 B Nuclear Magnetic Resonance (NMR) was carried out on either a Bruker Avance III 400 and Bruker Avance Neo 700 respectively. Size exclusion chromatography (SEC) was measured on a Shimadzu LC-2030c system, run at 1 mL min -1 with chlorobenzene (80 °C) as the mobile phase and a mixed bead polystyrene gel (PLgel MIXED-B, supplied by Agilent) as the stationary phase. The sample was detected using an RID-40A detector and the molar masses were calibrated to known polystyrene standards (Agilent EASICAL PS-1). Fourier Transform Infra-red (FTIR) spectroscopy was carried on a Bruker Platinum ATR. Thermogravimetric analysis (TGA) was carried out on a TA Instruments TGA 5500 under a N2 atmosphere and a heating rate of 10 °C min -1 . DSC was carried out on a TA Instruments DSC2500 with a TA LN2P Pump attached. DSC measurements were carried out at a heating rate of 10 °C min -1 under a He atmosphere. Rheology was carried out at 25 °C using a Peltier heater on a Bholin Gemini Rheometer using a 20 mm parallel plate with a gap size between 100 and 400 μm. Solution UV-vis absorbance spectroscopy was carried out on a Shimadzu UV-3600i Plus in chlorobenzene with increasing concentrations of polyborosiloxane (0 -99.9 mg mL -1 ) and a constant concentration of P3HT (0.1 mg mL -1 ). A quartz cuvette of path length 1 mm was used.