In the terminal region G' and G'' linearly increase with frequency with a gradient of 2 and 1, respectively, for an ideal viscoelastic material according to the Maxwell model. For LPBS, the gradient for G' and G'' were 1.01 ± 0.02 and 2.03 ± 0.02, respectively signifying LPBS fits well with the Maxwell model. On the other hand, HPBS exhibited a gradient of 0.90 ± 0.01 and 1.83 ± 0.01 for G' and G'', revealing a deviation from the model. Increasing the frequency of oscillation led to a crossover point between G' and G'', signifying the change between its liquid state and solid state, and the reciprocal of this frequency is the terminal relaxation time of the material (τ). At the crossover point for LPBS and HPBS τ is calculated to be 1.1 s and 0.2 s. The stark difference in τ between the two elastomers clearly shows the influence of molar mass and/or crosslinking density on the relaxation dynamics of the resulting elastomer. This very phenomenon was explored by Seetapan et al., where they found that synthesising PBS from PDMS-OH with Mn above and below Mc of linear PDMS led to a stark difference in G' and τ. They theorised and calculated that synthesising PBS from PDMS-OH with Mn > Mc that trapped entanglements contributed to the relaxation, whereas using Mn < Mc it did not. Yet, when using PBS synthesised from PDMS-OH with Mn < Mc they observed a much larger G', which they attributed to a higher SiO-B crosslinking density. According to the FTIR spectroscopy results, LPBS contains a higher number of SiO-B stretches compared to HPBS and the Mn of LPDMS-OH and HPDMS-OH measured using SEC are below and above the respective Mc of linear PDMS. The data shown here fits well with the theory from Seetapan et al. indicating that the higher G' within the LVR and τ exhibited by LPBS compared to HPBS arises primarily from the higher crosslinking density, whereas both entanglement and crosslinking sites contribute to the G' of HPBS. The relaxation process at the crosslinking sites is assigned to a dynamic covalent bonding mechanism as discussed by Kurkin et al. At higher frequencies, a relaxation process is observed in LPBS with a maximum G'' at ~14 Hz, resulting in a secondary relaxation time (τ2) of 12 ms. The rather low relaxation time has been proposed to be the result of the formation of locally branched networks arising from the formation of dynamic dative bonds between oxygen and boron at the borate crosslinking sites or hydrogen bonding between unreacted OH groups. The concept is based on the dissociation and re-association of transient networks in addition to physical B-O-Si crosslinking according to the "sticky reptation" model. A linear fit of the LPDMS-OH SOAS results also show that G' and G'' also cross over at a similar time scale of ~11 ms suggesting that the transient network in LPDMS-OH is also present in LPBS. On the other hand, HPBS exhibits a lower number of crosslinking sites, but is synthesised from a PDMS-OH precursor above the Mc of linear PDMS. Therefore, the relaxation mechanism of HPBS can be assumed to arise due to polymer entanglements and dynamic covalent bonding. In summary, the different relaxation times obse rved between LPBS and HPBS are the result of a complex interplay between the number of dynamic and physical crosslinks, in addition to different entanglements caused by the different PDMS-OH precursor polymers employed for the synthesis of the respective PBS elastomers.