With intention to obtain a homogenous blend between a semiconducting polymer (P3HT) and an elastomer (PBS) exhibiting supramolecular interactions to exploit in flexible electronics, it was found that miscibility played a crucial role. The stark differences between using a polymer of molar mass above and below the Mc of linear PDMS to create a polyborosiloxane, led to elastomers with different thermal and mechanical properties. LPBS showed a complete loss in observed crystallisation and melting transitions in the precursor LPDMS-OH, and, according to the SAOS experiments in the low frequency terminal region, obeyed the Maxwell model well. This suggests that LPBS is a well-defined viscoelastomer whereby its relaxation mechanism is dominated by dynamic crosslinking. On the other hand, HPBS retained both crystallisation and melting transitions, with a similar χc to HPDMS-OH, indicating that the smaller number of SiO-B crosslinks observed by FTIR do not affect the polymers' crystalline structure. SAOS experiments on HPBS revealed a much quicker relaxation than for LPBS, which we assigned to polymer entanglements having a major contribution rather than the dynamic crosslinking mechanism observed in LBPS. Alongside this, HPBS does not fit the Maxwell model, indicating that the material deviates from a true viscoelastic response to stress.