Surface modifications of poly(3-alkylthiophene) films by graft copolymerization

Abstract

Films of alkyl-substituted polythiophenes (PTH), such as poly(3-hexylthiophene) (P6TH), poly(3-octylthiophene) (P8TH) and poly(3-dodecylthiophene) (P12TH) are susceptible to near-UV light induced graft copolymerization with acrylamide (AAm), acrylic acid (AAc), and the Na salt of styrenesulfonic acid (NaSS). In each case, the graft density is substantially enhanced if the PTH film has been pretreated with O3. Angle-dependent X-ray photoelectron spectroscopy (XPS) core-level spectra and surface water contact angle measurements reveal that for P8TH and P12TH films, but not the P6TH film, the grafted AAm and AAc polymers become submerged completely below the film surface to give rise to a hydrophobic surface and a hydrophilic interface. For aliphatic graft with a bulky substituent, such as NaSS, only partial penetration of the graft below the PTH surface was observed. The phenomena have been explained in terms of polymer chain mobility, substrate permeability and steric effect of the graft. Comparison is made with the similarly grafted polyaniline film, in which an abundance of graft has been found only at the film surface.