Rigid fluorinated polyimides with well-defined polystyrene/poly(pentafluoro styrene) side chains from atom transfer radical polymerization

Comb-shaped copolymers consisting of rigid fluorinated polyimide (FPI) backbone and well-defined polystyrene (PS) side chains (FPI-cb-PS), or poly(pentafluorostyrene) (PFS) side chains (FPI-cbPFS), were synthesized by atom transfer radical polymerization (ATRP) from the bromide-containing FPI macroinitiators (FPI-Br). The sizes of the FPI-Br macroinitiators (consisting of 14 repeat units in the rigid backbone) and cleaved PS and PFS brushes (consisting of 35-144 and 32-93 repeat units, respectively) were estimated from the gel permeation chromatography (GPC) results. The lengths of the PS and PFS side chains determined from H-1 NMR spectroscopy were comparable to those determined from GPC or theoretical analysis. X-ray photoelectron spectroscopy (XPS) results confirmed the presence of grafted PS and PFS side chains on the respective FPI-cb-PS and FPI-cb-PFS copolymers as well as the presence of one ATRP bromide initiator per FPI repeat unit in the FPI-Br macroinitiator. Orderly arrays of the comb-shaped macromolecules, consisting of rigid FPI rods (backbones) of 20-30 nm in length and flexible PS brushes (side chains) of 4-6 nm in width, were imaged by atomic force microscopy (AFM). In addition to having a dielectric constant (kappa) as low as 2.1, the resulting comb-shaped FPI-cb-PFS copolymer also exhibited good solution processability and good thermal stability (up to 470 degrees C).