SAOS experiments on the PBS:P3HT blends were then carried out under the same conditions (10% strain) to assess the effects of increasing P3HT content on the mechanical dynamics (Figure , S12 and Table , S9). It should also be noted here that the batch of P3HT used is assumed to be above the Mc of P3HT according to experiments carried out by Koch et al. Upon adding 0.1 wt% P3HT to LPBS, τ does not significantly change from pure LPBS (τ = 1.2 s) and the gradient in the terminal region remains the same. The same effect is seen upon adding 0.1 wt% P3HT to HPBS, suggesting that the very small amount of P3HT does not disrupt the relaxation network. However, increasing the P3HT content in LPBS to 1 wt% almost doubles the relaxation time (τ = 1.9 and 1.6 s for 0.5 and 1.0 wt%, respectively) and the gradient in the terminal region deviates from the Maxwell model. Again a similar effect is observed in the HPBS:P3HT blends where increasing the P3HT content led to a maximum τ of 0.6 s at 0.5 wt%. The deviation from the maxwell model in the terminal region for both LPBS and HPBS blends with P3HT is ascribed to incorporation of a polymer that is not viscoelastic in the measured frequency range. The increase in τ with respect to P3HT in the PBS samples, suggests there is a critical point between 0.1 and 0.5 wt% of P3HT that causes a dramatic change in the dynamic network, preventing the relaxation processes discussed earlier for LPBS and HPBS. Similarly, the secondary relaxation τ2 for the LPBS samples increases from 12 to 24 ms upon adding 1 wt% P3HT. The effect is easier to recognise from the double log plot of tan δ vs frequency, where tan δ is G''/G' between 1-50 Hz (Figure ). Tan δ increases for all LPBS samples containing P3HT at the secondary relaxation point, however, in the terminal region (below ~1 Hz), tan δ decreases due to an increase in G'. This interesting rheological result shows that incorporation of P3HT into LPBS causes a dampening effect on the transient network, perhaps preventing hydrogen/dative bonding between LPBS chain ends. Conversely, tan δ decreases over the measured frequency range for HPBS:P3HT blends, indicating a harder material with increasing P3HT concentration. In summary, adding 1 wt% P3HT clearly disrupts the network for both LPBS and HPBS as seen by the increase in τ however the double log plot of tan δ vs frequency highlights the intricate mechanisms affecting the two viscoelastic networks and further work is needed to gain a deeper understanding of the disruptions caused by P3HT in the PBS networks.