Effect of the graft ratio on the properties of polythiophene‐g‐poly(ethylene glycol)

Graft copolymers formed by anchoring poly(ethylene glycol) (PEG) chains to conjugated polythiophene have been prepared by copolymerizing two compounds: unsubstituted α‐terthiophene (Th₃) and a thiophene‐derived macromonomer having an α‐terthiophene conjugated sequence and one Th₃ bearing a PEG chain with molecular weight of 2000 as substitute at the 3‐position of the central heterocycle (Th₃‐PEG₂₀₀₀). The grafting ratio of the resulting copolymers (PTh₃^*‐g‐PEG), which were obtained using 75:25 and 50:50 Th₃‐PEG₂₀₀₀:Th₃ weight ratios, is significantly smaller than that of copolymers derived from polymerization of macromonomers consisting of a α‐pentathiophene sequence in which the central ring bears a PEG chain of M_w = 2000 (PTh₅‐g‐PEG). The electroactivity and electrochemical stability of PTh₃^*‐g‐PEG is not only higher than that of PTh₅‐g‐PEG but also higher than that of PTh₃, the latter presenting a very compact structure that makes difficult the access and escape of dopant ions into the polymeric matrix during the redox processes. Furthermore, the optical π‐π^* lowest transition energy of PTh₃^*‐g‐PEG is lower than that of both PTh₅‐g‐PEG and PTh₃. These properties, combined with suitable wettability and roughness, result in an excellent behavior as bioactive platform of PTh₃^*‐g‐PEG copolymers, which are more biocompatible, in terms of cellular adhesion and proliferation, and electro‐compatible than PTh₅‐g‐PEG. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 239–252