Using the muon spectrometer HIFI, the ALC resonance will be measured to determine the electron spin relaxation of the polymer P3BT. This will complete the thiophene series, as P3HT and P3OT have already been measured. P3BT differs in structure to P3HT by having two less CH2 groups on the side chain. Thus the measurement will determine whether the reduced mass on the side chain affects the ALC amplitude and position as a function of temperature. Two different morphologies (as-purchased and recrystallined) of P3BT will be studied, to see if the quenching of the ALC resonance occurs, as observed in P3HT. If it does then the change in ALC amplitude with temperature can be compared for all three samples.