  Exchanging hydrophobic alkyl-based side chains to hydrophilic glycol-based
side chains is a widely adopted method for improving mixed-transport device
performance, despite the impact on solid state packing and polymer-electrolyte
interactions being poorly understood. Presented here is a Molecular Dynamics
(MD) force field for modelling alkoxylated and glycolated polythiophenes. The
force field is validated against known packing motifs for their monomer
crystals. MD simulations, coupled with X-ray Diffraction (XRD), show that
alkoxylated polythiophenes will pack with a `tilted stack' and straight
interdigitating side chains, whilst their glycolated counterpart will pack with
a `deflected stack' and an s-bend side chain configuration. MD simulations
reveal water penetration pathways into the alkoxylated and glycolated crystals
- through the {\pi}-stack and through the lamellar stack respectively. Finally,
the two distinct ways tri-ethylene glycol polymers can bind to cations are
revealed, showing the formation of a meta-stable single bound state, or an
energetically deep double bound state, both with a strong side chain length
dependance. The minimum energy pathways for the formation of the chelates are
identified, showing the physical process through which cations can bind to one
or two side chains of a glycolated polythiophene, with consequences for ion
transport in bithiophene semiconductors.
