Regio regularity effects on chain mobility and entanglement for poly(3-hexylthiophene)

Poly(3-hexylthiophene-2,5-diyl) (P3HT) is a conjugated polymer that can serve as the active layer in a variety of electronic devices. However, its glass transition temperature (T$_{\alpha })$ and entanglement molecular weight (M$_{e})$ are still in dispute. These parameters are essential for estimating the density of tie chains, which are hypothesized to limit the bulk charge transport. A wide range of molecular weights of both regiorandom (RRa) and regioregular (RRe) P3HT were studied by oscillatory shear rheology. Coupled with the molecular weight distribution from GPC, M$_{e}$ was extracted by fitting the linear viscoelastic data of multiple MW samples using BoB software. Furthermore, two T$_{\alpha }$s were identified for both RRe and RRa P3HT. T$_{\alpha \, }$corresponds to the segmental motion and follows Flory-Fox equation well for various MWs with 2 C \textless T$_{\alpha }$ \textless 14 C, yielding high MW limit of T$_{\alpha \infty }$ $=$ 21 C. RRe has a larger M$_{e}$ than RRa, which might originate from their different T$_{\alpha PE}$ corresponding to the side chain packing. So, further investigation on their packing lengths via dilute solution light scattering will be crucial to understand entanglement in these semiflexible polymers.