Side-Chain Dynamics and Crystallization in a Series of Regiorandom Poly(3-alkylthiophenes)

A series of regiorandom poly(3-alkylthiophenes) [P3ATs] with 4 ≤ C ≤ 12 alkyl carbons per side chain are studied by shear, calorimetry, X-ray scattering techniques, and infrared spectroscopy. We show that the tendency of alkyl groups to segregate in small alkyl nanodomains is a common feature of semicrystalline and amorphous members of this series. Semicrystalline poly(3-dodecylthiophene) (C = 12) samples show a pronounced lamellar structure with a coherence length of about 150 A, corresponding to staples of main chain and alkyl nanodomains comparable to the findings for regioregular P3ATs, while the alkyl nanodomains in amorphous P3ATs have more irregular shape and boundaries. An additional relaxation process αPE, which is related to the dynamics of CH2 units in the alkyl nanodomains, appears in amorphous samples with C ≥ 6. Its frequency temperature dependence is very similar to that of the αPE process found in other side-chain polymers containing alkyl groups with identical length. This is a strong arg...