Layered morphology of poly(phenylene)s in thin films induced by substitution of well-defined poly(epsilon-caprolactone) side chains

Abstract

Poly(c-caprolactone) (PCL)-based macromonomers and the corresponding substituted polyphenylene polymers have been synthesized in various chemical structures. The effect of chemical structure and the crystallization of PCL on the resulting morphology in thin films have been investigated. PCL macromonomers containing the central 2,5-dibromo-1,4-phenylene moiety were synthesized by ring-opening polymerization (ROP). Poly(phenylene) polymers were then synthesized by cross-coupling of the PCL macromonomers in Yamamato polycondensation reactions. Thin films of macromonomers and polymers were prepared by spin-coating on silicon substrates, and the resulting morphology in thin films was characterized by atomic force microscopy (AFM). Substitution of semicrystalline PCL side chains to the rigid poly(phenylene) backbone induced layered morphology in thin films. Our results indicate that increasing backbone rigidity causes grafted PCL side blocks to crystallize in better-defined layered structures parallel to the underlying substrate. Such layering was not observed when polystyrene (PSt) or poly(2-methyloxazoline) (POx) polymers were grafted to the rigid poly(phenylene) backbone. Hindering PCL crystallization by attaching PSt or POx to the end of PCL also prevented the formation of layered structures.